WO2009036305A1

WO2009036305A1 - Communication system with broadband antenna

Info

Publication number: WO2009036305A1
Application number: PCT/US2008/076216
Authority: WO
Inventors: Frank J. Blanda; Michael J. Barrett; Matthew N. Landel; Matthew A. Flannery; Michael J. Choiniere; William Mcnary; Richard B. Anderson
Original assignee: Aerosat Corporation
Priority date: 2007-09-13
Filing date: 2008-09-12
Publication date: 2009-03-19
Also published as: JP5453269B2; CN101842938A; CN101842938B; JP2014082786A; CN104505594A; EP2188870A1; CN104505594B; JP2010539812A; JP5735144B2; HK1206871A1

Abstract

A Communications system including an antenna array and electronics assembly that may be mounted on and in a vehicle. The communication system may generally comprise an external subassembly that is mounted on an exterior surface of the vehicle, and an internal subassembly that is located within the vehicle, the external and internal subassemblies being communicatively coupled to one another. The external subassembly may comprise the antenna array as well as mounting equipment and steering actuators to move the antenna array in azimuth, elevation and polarization (for example, to track a satellite or other signal source). The internal subassembly may comprise most of the electronics associated with the communication system.

Description

COMMUNICATION SYSTEM WITH BROADBAND ANTENNA

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent Application No. 60/971,958 entitled "Communication System with Broadband Antenna" filed September 13, 2007, and to U.S. Provisional Patent Application No. 60/973,112 entitled "Communication System with Broadband Antenna" filed September 17, 2007, and to U.S. Provisional Patent Application No. 61/095,167 entitled "Communication System with Broadband Antenna" filed September 8, 2008, each of which is incorporated herein by reference in its entirety.

BACKGROUND

Field of the Invention

The present invention relates to wireless communication systems, in particular, to an antenna and communications subsystem that may be used on passenger vehicles.

Discussion of Related Art

Many communication systems involve reception of an information signal from a satellite. Conventional systems have used many types of antennas to receive the signal from the satellite, such as Rotman lenses, Luneberg lenses, dish antennas or phased arrays. However, these systems may suffer from limited field of view or low efficiency that limit their ability to receive satellite signals. In particular, these conventional systems may lack the performance required to receive satellite signals where either the signal strength is low or noise is high, for example, signals from low elevation satellites. In addition, many conventional systems do not include any or sufficient polarization correction and therefore cross-polarized signal noise may interfere with the desired signal, preventing the system from properly receiving the desired signal. Further, locating such systems on a fuselage of an aircraft for transmission or reception of signals poses a number of issues that can be addressed for such systems. There is therefore a need for an improved communication system, including an improved antenna system, which may be able to receive weak signals or communication signals in adverse environments, and which can be located at least partly on a fuselage of an aircraft.

SUMMARY OF THE INVENTION Aspects and embodiments are directed to a communications system including an antenna array and electronics assembly that may be mounted on and in a vehicle. The communication system may generally comprise an external subassembly that is mounted on an exterior surface of the vehicle, and an internal subassembly that is located within the vehicle, the external and internal subassemblies being communicatively coupled to one another. As discussed below, the external subassembly may comprise the antenna array as well as mounting equipment and steering actuators to move the antenna array in azimuth, elevation and polarization (for example, to track a satellite or other signal source). The internal subassembly may comprise most of the electronics associated with the communication system. Locating the internal subassembly within the vehicle may facilitate access to the electronics, and may protect the electronics from the environment exterior to the vehicle, as discussed in further detail below. Embodiments of the communication system provide numerous advantages over prior art systems, including being of relatively small size and weight (which may be particularly advantageous for a system mounted on an aircraft), and having excellent, broadband RF performance, as discussed further below.

According to one embodiment, an antenna array comprises a plurality of horn antenna elements, a corresponding plurality of dielectric lenses, each dielectric lens of the plurality of dielectric lenses being coupled to a respective horn antenna element of the plurality of horn antenna elements, and a waveguide feed network coupling the plurality of horn antenna elements to a common feed point, wherein the plurality of horn antenna elements and corresponding plurality of dielectric lenses are shaped and sized such that the antenna array is tapered at either end of the antenna array.

In one example, the plurality of horn antenna elements are arranged in two parallel rows, and wherein the two parallel rows are offset from one another along the length of the antenna array by one half the width of one of the plurality of horn antenna elements. In another example, the plurality of horn antenna elements includes an interior horn antenna element, a third horn antenna element, a second horn antenna element, and an end horn antenna element, wherein the third horn antenna element is smaller than the interior horn antenna element and is located closer to an end of the antenna array than the interior horn antenna element, wherein the second horn antenna element is smaller than the third horn antenna element and is located closer to the end of the antenna array than the third horn antenna element, and wherein the end horn antenna element is smaller than the second horn antenna element and is located at the end of the antenna array. In another example, the plurality of dielectric lenses elements includes an interior dielectric lens, a third dielectric lens, a second dielectric lens, and an end dielectric lens, wherein the interior dielectric lens is coupled to the interior horn antenna element, wherein the third dielectric lens is smaller than the interior dielectric lens and is coupled to the third horn antenna element, wherein the second dielectric lens is smaller than the third dielectric lens and is coupled to the second horn antenna element, and wherein the end dielectric lens is smaller than the second dielectric lens and is coupled to the end horn antenna element. The antenn array may further comprise a plurality of horn inserts, each one of the plurality of horn inserts being located within a respective one of the plurality of horn antenna elements. In one example, the horn inserts located within the end horn antenna element and the second horn antenna elements are made of a radar absorbent material. In another example, each dielectric lens is fastened to the respective horn antenna element with a fiberglass pin. Another aspect is directed to a method of calibrating a vehicle-mounted antenna array. In one embodiment, the method comprises determining an RF center of a beam pattern of the antenna relative to a location of a position encoder mounted on the antenna array, calculating a first pitch offset and a first roll offset of the antenna array relative to the location of the position encoder, and storing the calculated first pitch and roll offsets in a local memory device. In another embodiment, the method further comprises receiving data representative of a vehicle pitch and vehicle roll of a host vehicle upon which the antenna array is mounted, sensing with the position encoder, an antenna pitch and antenna roll, calculating an second pitch offset between the vehicle pitch and the antenna pitch, calculating a second roll offset between the vehicle roll and the antenna roll, and storing the calculated second pitch and roll offsets in the local memory device. In one example, method further comprises storing the calculated second pitch and roll offsets in a remote memory device. In another example, the method further comprises correcting the second pitch and roll offsets based on the first pitch and roll offsets, and storing the corrected second pitch and roll offsets in the local memory device. The method may further comprise storing the corrected second pitch and roll offsets in the remote memory device. In one example, the method further comprises receiving data representative of a vehicle heading of the host vehicle, pointing the antenna array at a selected satellite signal source, determining an antenna heading based on a signal lock with the selected satellite signal source, calculating a heading offset between the vehicle heading and the antenna heading, and storing the heading offset in the local memory device. The method may further comprise storing the heading offset in the remote memory device. In one example, receiving data representative of the vehicle pitch and vehicle roll of the host vehicle includes receiving the date from a navigation system in the host vehicle.

According to another embodiment, a communications system comprises a first subsystem comprising an antenna array configured to receive and transmit signals, a gimbal assembly configured to mount the antenna array a host platform and to move the antenna array in azimuth and elevation, a first memory device, and at least one position encoder mounted to the antenna array, and a second sub-system communicatively coupled to the first sub-system and comprising a second memory device, and a control unit configured to control movement of the antenna array in azimuth and elevation, wherein the at least one position encoder is configured to detect a pitch and roll of the antenna array relative to a factory-calibrated level position of the antenna array and to provide a first antenna data signal representative of the detected pitch and roll of the antenna array, wherein the first and second memory devices are communicatively coupled together and are configured to receive and store the antenna data signal. In one example, the first and second memory devices are further configured to store identifying information about the first and second sub-systems.

According to another embodiment, a vehicle-mounted communications system comprises an external sub-system mounted to an exterior surface of the vehicle, the external sub-system comprising an antenna array configured to receive and transmit signals, a gimbal assembly configured to mount the antenna array to the vehicle and to move the antenna array in azimuth and elevation, a local memory device, and at least one position encoder mounted to the antenna array, and an internal sub-system communicatively coupled to the first sub-system and comprising a control memory device, and a control unit configured to control movement of the antenna array in azimuth and elevation, wherein the control unit is configured to receive data representative of a pitch and roll of the vehicle upon which the antenna array is mounted, wherein the position encoder is configured to sense a pitch and roll of the antenna array, wherein the control unit is configured to calculate a pitch offset between the pitch of the vehicle and the pitch of the antenna and a roll offset between the roll of the vehicle and the roll of the antenna, and wherein the control memory device is configured to store the calculated pitch and roll offsets.

In one example, the local memory device is configured to store the calculated pitch and roll offsets. In another example, the local and control memory devices are further configured to store identifying information about the internal and external sub-systems. Another aspect is directed to a communications system comprising an antenna array including a plurality of antenna elements each adapted to receive an information signal from a signal source, and a feed network coupling the plurality of antenna elements to a common feed point, and a polarization converter unit coupled to the common feed point, the polarization converter unit configured to compensate for polarization skew between the antenna array and the signal source. In one embodiment, the polarization converter unit comprises a rotary orthomode transducer configured to receive two orthogonally polarized component signals making up the information signal and to provide a polarization-corrected output signal, a drive system coupled to the rotary orthomode transducer configured to receive a control signal representative of a desired degree of rotation of the rotary orthomode transducer, and a motor configured to provide power to the drive system to rotate the rotary orthomode transducer to the desired degree of rotation.

In one example, the polarization converted unit is mounted to the antenna array. In another example, the plurality of antenna elements and the feed network are arranged to provide a cavity between the feed network and the plurality of antenna elements, wherein the polarization converter unit is mounted at least partially within the cavity. In another example, the plurality of antenna elements are horn antenna elements, and the feed network is a waveguide feed network.

According to one embodiment, an antenna array comprises a plurality of horn antenna elements, a corresponding plurality of dielectric lenses, each dielectric lens of the plurality of dielectric lenses being coupled to a respective horn antenna element of the plurality of horn antenna elements, and a waveguide feed network coupling the plurality of horn antenna elements to a common feed point, wherein each dielectric lens is a planoconvex lens having a planar side and an opposing convex side, wherein each dielectric lens comprises a plurality of impedance matching features formed proximate an interior surface of the convex side, and wherein an exterior surface of the convex side is smooth.

In one example, the plurality of impedance matching features includes a plurality of hollow tubes. In another example, each dielectric lens further comprises a plurality of impedance matching grooves extending from a surface of the planar side into an interior of the dielectric lens. The plurality of dielectric lenses may comprise, for example, a cross- linked polystyrene material or, for example, Rexolite™.

In another embodiment, an antenna array comprises a plurality of horn antenna elements configured to receive an information signal, a corresponding plurality of orthomode transducers, each respective orthomode transducer coupled to a respective horn antenna element and configured to split the information signal into a first component signal and second component signal, the first and second component signals being orthogonally polarized, and a waveguide feed network coupling the plurality of orthomode transducers to a common feed point, the waveguide feed network configured to sum the component signals from each orthomode transducer in both the E-plane and the H-plane. In one example, the waveguide feed network comprises a first path to guide the first component signal and a second path to guide the second component signal, wherein the first path sums in the E-plane the first component signals received from each orthomode transducer, wherein the second path sums in the H-plane the second component signals received from each orthomode transducer, and wherein the waveguide feed network is configured to provide at the common feed point a first summed component signal and a second summed component signal. In another example, the plurality of orthomode transducers comprises a first orthomode transducer coupled to a first horn antenna element and a orthomode transducer coupled to a second horn antenna element, wherein the waveguide feed network includes a waveguide T-junction having a first input configured to receive the first component signal from the first orthomode transducer and a second input configured to receive the first component signal from the second orthomode transducer, and an output configured to provide an output signal corresponding to a weighted sum of the two first component signals, and wherein the waveguide T-junction comprises a tuning element configured to bias the waveguide T-junction to produce the weighted sum of the two first component signals.

Another aspect is directed to a communications system mountable on a vehicle. In one embodiment, the communications system comprises an external sub-system, mountable on an exterior surface of the vehicle, comprising an antenna array configured to receive and transmit information signals, and a gimbal assembly configured to mount the antenna array to the exterior surface of the vehicle and to move the antenna array in azimuth and elevation, and an internal sub-system, mountable within the vehicle, comprising a control unit and a transceiver, the internal sub-system communicatively coupled to the external sub-system and configured to provide power and control signals to the external sub-system, wherein the control unit is configured to provide the control signals to the gimbal assembly to control the movement of the antenna array in azimuth and elevation, wherein gimbal assembly comprises a mounting bracket configured to mount the external sub- system to the exterior surface of the vehicle, an antenna mounting bracket configured to mount the antenna array to the gimbal assembly.

In one example of the communications system the mounting bracket comprises a central portion and four feet connected to the central portion by four corresponding arm portions; and wherein each of the four feet is positioned outside of a rotational sweep of the antenna array. In another example, the external sub-system further comprises a rotary joint positioned inside the central portion of the mounting bracket, the rotary joint coupling the external sub-system to the internal sub-system. In another example, the antenna mounting bracket grips the antenna array at two locations along the length of the antenna array, neither point being at an end of the antenna array. In another example, the gimbal assembly comprises an elevation drive assembly configured to receive a control signal from the control unit and to rotate the antenna array in elevation responsive to the control signal. The elevation drive assembly may include a push-pull pulley system. In another example, the gimbal assembly further comprises a polarization converter unit mounted to the antenna array and configured to move the antenna array in polarization responsive to a polarization Still other aspects, embodiments, and advantages of these exemplary aspects and embodiments, are discussed in detail below. Moreover, it is to be understood that both the foregoing information and the following detailed description are merely illustrative examples of various aspects and embodiments, and are intended to provide an overview or framework for understanding the nature and character of the claimed aspects and embodiments. Any embodiment disclosed herein may be combined with any other embodiment in any manner consistent with the objects, aims, and needs disclosed herein, and references to "an embodiment," "some embodiments," "an alternate embodiment," "various embodiments," "one embodiment" or the like are not necessarily mutually exclusive and are intended to indicate that a particular feature, structure, or characteristic described in connection with the embodiment may be included in at least one embodiment. The appearances of such terms herein are not necessarily all referring to the same embodiment. The accompanying drawings are included to provide illustration and a further understanding of the various aspects and embodiments, and are incorporated in and constitute a part of this specification. The drawings, together with the remainder of the specification, serve to explain principles and operations of the described and claimed aspects and embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

Various aspects of at least one embodiment are discussed below with reference to the accompanying figures, which are not intended to be drawn to scale. Where technical features in the figures, detailed description or any claim are followed by references signs, the reference signs have been included for the sole purpose of increasing the intelligibility of the figures, detailed description, and claims. Accordingly, neither the reference signs nor their absence are intended to have any limiting effect on the scope of any claim elements. In the figures, each identical or nearly identical component that is illustrated in various figures is represented by a like numeral. For purposes of clarity, not every component may be labeled in every figure. The figures are provided for the purposes of illustration and explanation and are not intended as a definition of the limits of the invention. In the figures:

FIG. 1 is a functional block diagram of one example of a communications system according to aspects of the invention;

FIG. 2 is a functional block diagram illustrating one example of an external subsystem according to aspects of the invention;

FIG. 3 is an illustration of an aircraft showing a portion of a communications system mounted in and on the aircraft in accordance with aspects of the invention; FIG. 4 is a perspective view of one example of an external sub-system according to aspects of the invention;

FIG. 5 is a plan view of one example of a radome according to aspects of the invention;

FIG. 6 is a perspective view of one example of an external sub-system without a cover, according to aspects of the invention;

FIG. 7 is an exploded view of the external sub-system of FIG. 6;

FIG. 8 is a plan view of one example of a mounting bracket for securing the external sub-system to a host platform, according to aspects of the invention;

FIG. 9 is a partial exploded view of one example of an elevation drive according to aspects of the invention;

FIG. 10 is a functional diagram of one example of a pulley system that may be used to move the antenna array in elevation, according to aspects of the invention;

FIG. 11 is a schematic diagram illustrating the use of spring loaded cams to tune antenna array vibrations according to aspects of the invention; FIG. 12 is a front view of one example of an antenna array according to aspects of the invention;

FIG. 13 is a partial exploded view of the antenna array of FIG. 12;

FIG. 14 is a cross-sectional diagram of one example of a horn antenna;

FIG. 15 is a side view of one example of an interior horn antenna element, according to aspects of the invention; FIG. 16 is a side view of one example of a third horn antenna element, according to aspects of the invention;

FIG. 17 is a side view of one example of a second horn antenna element, according to aspects of the invention; FIG. 18 is a side view of one example of an end horn antenna element, according to aspects of the invention;

FIG. 19 is a side view of one example of an interior dielectric lens according to aspects of the invention;

FIG. 20 is a perspective view of the interior dielectric lens of FIG. 19; FIG. 21 is a plan view of the planar surface of the dielectric lens of FIG. 19;

FIG. 22A is a side view of one example of a third dielectric lens according to aspects of the invention;

FIG. 22B is a plan view of the planar surface of the third dielectric lens of FIG. 22A; FIG. 23 A is a side view of one example of a second dielectric lens according to aspects of the invention;

FIG. 23B is a plan view of the planar surface of the second dielectric lens of FIG. 23A;

FIG. 24A is a side view of one example of an end dielectric lens according to aspects of the invention;

FIG. 24B is a plan view of the planar surface of the end dielectric lens of FIG. 24A;

FIG. 25 is a side view of another example of a dielectric lens according to aspects of the invention; FIG. 26 is a side view of another example of a dielectric lens according to aspects of the invention;

FIG. 27A is a side view of one example of a pin that can be used to fasten the dielectric lens to the antenna element in accordance with aspects of the invention;

FIG. 27B is a radial cross-sectional view of the pin of FIG. 27A; FIGS. 28 A-C are perspective views of retaining clips that can be used to fasten the dielectric lenses to the antenna elements in accordance with aspects of the invention; FIG. 29 is a perspective view of one example of a dielectric lens showing a slot for receiving a retaining clip in accordance with aspects of the invention;

FIG. 30 is a side view of another example of a retaining clip used to secure at least some of the dielectric lenses in the antenna array in accordance with aspects of the invention;

FIG. 3 IA is an isometric view of one example of a horn insert according to aspects of the invention;

FIG. 3 IB is an end view of the horn insert of FIG. 3 IA;

FIGS. 32 A-C are isometric views of further examples of horn inserts according to aspects of the invention;

FIG. 33 A is an illustration of a beam pattern, for zero degree roll, of one embodiment of the antenna array according to aspects of the invention, the array having an element spacing of about ¹A wavelength;

FIG. 33B is an illustration of a beam pattern, for 15 degree roll, of the same embodiment of the antenna array;

FIG. 34 is a diagram illustrating another example of an antenna array according to aspects of the invention;

FIG. 35 is an illustration of one example of a horn antenna element with an integrated orthomode transducer according to aspects of the invention; FIG. 36 is a perspective view of one example of an orthomode transducer according to aspects of the invention;

FIG. 37 is a perspective view of another example of an orthomode transducer according to aspects of the invention;

FIG. 38 is another view of the orthomode transducer of FIG. 37; FIG. 39 is a perspective view of one example of a waveguide feed network according to aspects of the invention;

FIG. 4OA is an illustration of a portion of one example of a feed network according to aspects of the invention;

FIG. 4OB is a cross-sectional view of the portion of the feed network of FIG. 4OA taken along line A-A in FIG. 4OA; FIG. 41 is a diagram of another example of a portion of a feed network according to aspects of the invention;

FIG. 42 is a perspective view of one example of a waveguide T-junction according to aspects of the invention; FIG. 43 is a diagram of a portion of another example of a feed network according to aspects of the invention;

FIG. 44 is partial exploded view of one example of an antenna array including a polarization converter unit according to aspects of the invention;

FIG. 45 is a partial exploded view of one example of a polarization converter unit according to aspects of the invention;

FIG. 46 is a perspective view of one example of a low noise amplifier according to aspects of the invention;

FIG. 47 is a functional block diagram of one example of an internal sub-system according to aspects of the invention; FIG. 48 is a functional block diagram of one example of a down-converter unit according to aspects of the invention;

FIG. 49 is a perspective view of one example of a housing for the internal subsystem according to aspects of the invention; and

FIG. 50 is a flow diagram illustrating one example of a calibration process according to aspects of the invention.

DETAILED DESCRIPTION

At least some aspects and embodiments are directed to a communication system including an antenna array and electronics subassembly that may be mounted on and in a vehicle. The communication system may generally comprise an external subassembly that is mounted on an exterior surface of the vehicle, and an internal subassembly that is located within the vehicle, the external and internal subassemblies being communicatively coupled to one another. As discussed below, the external subassembly may comprise the antenna array as well as mounting equipment and steering actuators to move the antenna array in azimuth, elevation and polarization (for example, to track a satellite or other signal source). The internal subassembly may comprise most of the electronics associated with the communication system. Locating the internal subassembly within the vehicle may facilitate access to the electronics, and may protect the electronics from the environment exterior to the vehicle, as discussed in further detail below. Embodiments of the communication system provide numerous advantages over prior art systems, including being of relatively small size and weight (which may be particularly advantageous for a system mounted on an aircraft), and having excellent, broadband RF performance, as discussed further below.

It is to be appreciated that embodiments of the methods and apparatuses discussed herein are not limited in application to the details of construction and the arrangement of components set forth in the following description or illustrated in the accompanying drawings. The methods and apparatuses are capable of implementation in other embodiments and of being practiced or of being carried out in various ways. Examples of specific implementations are provided herein for illustrative purposes only and are not intended to be limiting. In particular, acts, elements and features discussed in connection with any one or more embodiments are not intended to be excluded from a similar role in any other embodiments. Also, the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. Any references to embodiments or elements or acts of the systems and methods herein referred to in the singular may also embrace embodiments including a plurality of these elements, and any references in plural to any embodiment or element or act herein may also embrace embodiments including only a single element. References in the singular or plural form are not intended to limit the presently disclosed systems or methods, their components, acts, or elements. The use herein of "including," "comprising," "having," "containing," "involving," and variations thereof is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. References to "or" may be construed as inclusive so that any terms described using "or" may indicate any of a single, more than one, and all of the described terms. Any references to front and back, left and right, top and bottom, and upper and lower are intended for convenience of description, not to limit the present systems and methods or their components to any one positional or spatial orientation. Referring to FIG. 1, there is illustrated a block diagram of one example of a communications system including an external sub-system 102 and an internal sub-system 104. The external sub-system 102 comprises an antenna array 106 and a gimbal assembly 108, each of which is discussed in detail below. The antenna array 106 receives communications signals from a signal source 110 and also transmits signals to one or more destinations, as discussed further below. The internal sub-system 102 may be coupled to the external sub-system 104 via cables and other transmission media (such as waveguide) that carry power, data and control signals. The internal sub-system 104 may comprise a majority of the electronics of the communications system to process the signals to be transmitted and received by the antenna array 106. In one example, the internal subsystem 104 includes an antenna control unit 112 that communicates with the gimbal assembly 108 to control the antenna array 106. For example, the antenna control unit 112 may provide control signals to the gimbal assembly 108 to point the antenna array correctly in azimuth and elevation to receive a desired signal from the signal source 110. The antenna control unit 112 may also communicate with various other components of the internal sub-system 104, as discussed further below. A high power transceiver 114 receives and processes signals received by the antenna array 106 and may output these signals via a modem 116. Modem 116 may operate in a manner known to those skilled in the art. The high power transceiver 114 also processes signals to be transmitted by the antenna array 106.

According to one embodiment, the internal sub-system 104 also comprises a power supply 118 that provides power to the various components of the internal sub-system 104 as well as to the external sub-system 102. It is to be appreciated that the power supply 118 may include a dedicated power supply that is part of the internal sub-system, or may include any necessary components to convert and supply power from the host vehicle's power supply to the components of the internal sub-system that require power. The internal sub-system may further comprise a network management server 120. A navigation reference system 122, which may be part of the internal sub-system 104 or separate therefrom and in communication therewith, may provide navigation data from the vehicle in which the communication system is installed, as discussed further below. Referring to FIG. 2, in one embodiment, the gimbal assembly 108 includes a low noise amplifier 124 which, for signal-to-noise considerations, should be placed as close to the antenna array as possible and therefore is included in the external sub-system 102 rather than in the internal sub-system 104. In one example, the gimbal assembly 108 further comprises a mechanical and antenna pointing assembly 126 which may include a tilt sensor used to sense angular position of the external subassembly (not illustrated), and a polarization converter unit 128 used to adjust for polarization skew between the antenna array 106 and a signal source 110, as discussed further below. The gimbal assembly 108 may further include a memory device 130 that can include data specific to the external sub-system 102, as discussed further below.

According to one embodiment, the communication system can be mounted on and in a vehicle, such as an aircraft or automobile. Referring to FIG. 3, there is illustrated an example of an aircraft 132 equipped with a communications system according to aspects of the invention. It is to be appreciated that although the following discussion of aspects and embodiments of the communications system may refer primarily to a system installed on an aircraft, the invention is not so limited and embodiments of the communications system may be installed on a variety of different vehicles, including ships, trains, automobiles and aircraft, as well as on stationary platforms, such as commercial or residential buildings. The external sub-system 102 may be mounted to the aircraft 132 at any suitable location. The location of mounting of the external subassembly on the aircraft (or other vehicle) may be selected by considering various factors, such as, for example, aerodynamic considerations, weight balance, ease of installation and/or maintenance of the system, FAA requirements, interference with other components, and field of view of the antenna array. As discussed above, the external sub-system 102 includes an antenna array 106 (See FIG. 1) that receives an information signal of interest 134 from a signal source 110. The signal source 110 may be another vehicle, a satellite, a fixed or stationary platform, such as a base station, tower or broadcasting station, or any other type of information signal source. The information signal 134 may be any communication signal, including but not limited to, TV signals, signals encoded (digitally or otherwise) with maintenance, positional or other information, voice or audio transmissions, etc. In one example, the system forms parts of a communications network that can be used to send information about the system itself or about components of the aircraft 132 (e.g., operating information, required maintenance information, etc.) to a remote server or control/maintenance facility to provide remote monitoring of the system and/or the aircraft.

As known to those familiar with the operation of satellites in many regions of the world, there exists a variety of satellites operating frequencies resulting in broad bands of frequency operations. Direct Broadcast satellites, for example, may receive signals at frequencies of approximately 14.0 GHz- 14.5 GHz, while the satellite may send down signals in a range of frequencies from approximately 10.7 GHz- 12.75 GHz. Table 1 below illustrates some of the variables, in addition to frequency, that exist for reception of direct broadcast signals, which are accommodated by the antenna assembly and system of the present invention. The signal source 110 may include any of these, or other, types of satellites.

TABLE 1

Still referring to FIG. 3, the communication system may include or may be coupled to a plurality of passenger interfaces, such as seatback display units 136, associated headphones and a selection panel to provide individual channel selection, internet access & capability, and the like to each passenger. Alternatively, for example live video may also be distributed to all passengers for shared viewing through a plurality of screens placed periodically in the passenger area of the aircraft. Signals may be provided between the internal sub-system 104 and the passenger interfaces either wirelessly or using cables. Further, the communications system may also include a system control/display station 138 that may be located, for example, in the cabin area for use by, for example, a flight attendant on a commercial airline to control the overall system and such that no direct human interaction with the external subassembly is needed except for servicing and repair. In one example, the communication system may be used as a front end of a satellite video reception system on a moving vehicle such as the aircraft of FIG. 3. The satellite video reception system can be used to provide to any number of passengers within the vehicle with live programming such as, for example, news, weather, sports, network programming, movies and the like.

Referring to FIG. 4, there is illustrated in perspective view one embodiment of an external sub-system 102. As discussed above, the external sub-system 102 comprises the antenna array 106 that is adapted to receive signals from an information source (110 in FIG. 1) and to transmit signals. As discussed further below, the antenna array 106 may include a plurality of antenna elements (not shown) coupled to a feed network 202. In one example, these antenna elements are horn antennas and the feed network 202 is a waveguide feed network. Each of the antenna elements may be coupled to a respective lens 204 configured to improve the gain of the respective antenna element, as discussed further below. Retaining clips 206a, 206b and 206c may be used to fasten the lenses 204 to the respective antenna elements, as also discussed below. According to one embodiment, the antenna array 106, by virtue of the construction and arrangement of the feed network 202 and antenna elements and lenses 204, forms a substantially rigid structure with only a base mode structural natural frequency. From a structural oscillation point of view, the antenna array 106 may therefore act as a single unit, rather than an array of multiple individual units. An advantage of such a substantially rigid structure for the antenna array 106 may include minimal oscillation of the antenna array which could otherwise adversely affect the performance and pointing accuracy of the antenna array. In one example, the base mode structure natural frequency of the antenna array 106 is about 20 Hertz (Hz). The antenna array 106 may be mounted to the gimbal assembly 108 using an antenna mounting bracket 208. As illustrated in FIG. 4, in one embodiment, the antenna mounting bracket 208 grips the antenna array 106 not at the ends of the antenna array, but rather at points closer to the center of the antenna array. These grip points of the antenna mounting bracket may be substantially symmetrically spaced from the length-wise center of the antenna array 106. Gripping the antenna array 106 at interior points along its length, rather than at the ends, may further facilitate reducing unwanted structural oscillation of the antenna array.

Still referring to FIG. 4, in at least some embodiments, a substantial portion of the external sub-system 102 may be covered by a cover 210. The cover 210 may provide environmental protection for at least some of the components of the external subassembly 102. Cables 212a, 212b and 212c may be used to carry data, power and control signals between the internal sub-system 104 and the external sub-system 102. It is to be appreciated that the communications system is not limited to the use of three sets of cables 212a, 212b and 212c as illustrated in FIG. 4, and any suitable number of cables may be used. The external sub-system 102 may be mounted to the vehicle using a mounting bracket 214 that can be fastened to the body of the vehicle (e.g., to the fuselage of aircraft 132).

According to one embodiment, the external sub-system may be covered by a radome that may serve to reduce drag force generated by the external subassembly as the vehicle 132 moves. An example of a radome 270 is illustrated in FIG. 5. In one example, the radome has a maximum height of about 9.5 inches and a length 272 of about 64.4 inches; however, it is to be appreciated that the size of the radome 270 in any given embodiment may depend on the size of the antenna array 106 and other components of the external sub-system 106. According to one example, the radome 270 is transmissive to radio frequency (RF) signals transmitted and/or received by the antenna array 106. The radome 270 may be made of materials known to those of skill in the art including, but not limited to, laminated plies of fibers such as quartz or glass, and resins such as epoxy, polyester, cyanate ester or bismaleamide. These or other materials may be used in combination with honeycomb or foam to form a highly transmissive, light-weight radome construction. Referring to FIG. 6, there is illustrated an example of the external sub-system 102 shown without the cover 210. Various components of the external sub-system are discussed in more detail below with continuing reference to FIG. 6.

Referring to FIG. 7, there is illustrated a partial exploded view of the example of the external sub-system 102 shown in FIG. 6. In one example, the cover 210 comprises several parts, such as an upper portion 210a, a rear portion 210b, and two side portions 210c and 21Od that may be fastened together to form the cover 210. However, it is to be appreciated that the invention is not so limited and the cover 210 may comprise more or fewer than four parts and that the cover parts may be configured differently than illustrated in FIG. 7. In one example, the cover parts are fastened together using only fasteners such as screws or bolts. The number of fasteners may be a minimum needed to secure the cover so as to avoid unnecessary delay and complications in removing the cover when necessary to access the external sub-system 102 (e.g., to upgrade or repair components). In another example, an adhesive may be used, alone or in conjunction with fasteners, to secure the cover parts 210a-d together. However, in some applications, for example, where the external sub-system 102 is mounted on an aircraft 132, the use of adhesive may be undesirable as it may further complicate removal of the cover 210.

As discussed above, the external sub-system 102 may be mounted to the vehicle (or other platform) using the mounting bracket 214. An example of the mounting bracket 214 is illustrated in FIG. 8. In the illustrated example, the mounting bracket includes a central portion 216 and four feet 218 at the ends of portions 220 that extend outward from the central portion 216. The mounting bracket 214 may be fastened to the vehicle by fasteners, such as screws or bolts, through the feet 218. The use of a mounting bracket 214 having a configuration similar to that illustrated in FIG. 8 may be advantageous in some applications because only four fasteners may required to securely mount the mounting bracket, and therefore the external sub-system 102, to the vehicle, facilitating easy installation of the external sub-system on the vehicle. In one example, the feet 218 may be positioned outside of the rotation sweep of the antenna array 106 such that the fasteners may be accessed regardless of the position of the antenna array. This configuration may facilitate installation, and particularly removal, of the mounting bracket 214, and thus of the external sub-system 102 under a variety of conditions and orientations of the antenna array 106. Cables that carry power, data and/or control signals between the external sub-system 102 and internal sub-system 104 may pass through the central portion 216. A gasket or other sealing device may be used to seal the connection between the central portion 216 of the mounting bracket 214 (or a cable carrier extending therethrough) and the vehicle body, as a hole must be provided in the vehicle body to allow the cables to pass through to the internal sub-system 104.

According to one embodiment, at least portions of the external sub-system 102 (e.g., the antenna array 106 and at least some parts of the gimbal assembly 108) are moveable in any or all of elevation, azimuth and polarization to facilitate communication with the signal source 110 from a plurality of locations and orientations of the vehicle. Accordingly, the gimbal assembly 108 may be designed to accommodate such movement. In one embodiment, the central portion 216 of the mounting bracket 214 may accommodate an azimuth assembly 222 that defines the center of azimuth rotation. The azimuth assembly 222 may include, for example, a rotary joint that may penetrate the vehicle shell (e.g., the shell of aircraft 132) to allow cables to pass through the vehicle shell between the internal sub-system 104 and the external sub-system 102. The one example, the azimuth assembly may include the rotary joint and a slip ring, as discrete parts or as an integrated assembly, to allow radio frequency (RF) communication, power and control signals to travel, via the cables 212a-c, between the movable parts of the external sub-system 102 and a stationary host platform of the aircraft 132. The rotary joint and slip ring combination, or other device known to those of skill in the art, may enable the antenna array 106 to rotate continuously in azimuth in either direction with respect to the host aircraft 132, thereby enabling the mountable subsystem to provide continuous hemispherical, or greater, coverage when used in combination with an azimuth motor. Without the rotary joint, or a similar device, the antenna array 106 would have to travel until it reached a stop then travel back again to keep cables from wrapping around each other. Referring again to FIGS. 6 and 7, in one embodiment, the gimbal assembly 108 includes motors and drive assemblies to move the antenna array 106 in both azimuth and elevation. To move the antenna array 106 in azimuth, the gimbal assembly 108 may include an azimuth drive assembly 224 coupled to an azimuth hub 226. In one example, the azimuth hub 226 is coupled, via a wire 228, to an azimuth pulley 230 that encircles the central portion 216 of the mounting bracket 214. The azimuth drive assembly 224 may include control circuitry as well as an azimuth motor housed within azimuth motor enclosure 232. The azimuth drive assembly may receive control signals from the antenna control unit 112 (see FIG. 1) and actuate the azimuth motor to rotate the antenna array 106 in azimuth.

According to one embodiment, the gimbal assembly 108 includes an elevation drive assembly 234 that is coupled via a flexible coupling 236 to an elevation motor 238. The elevation motor 238 is mounted to an elevation motor support 240 and may be housed within housing 242. In the illustrated example, elevation drives 244a and 244b are coupled to the antenna mounting bracket 208 and are mounted to the azimuth hub 226, thereby mechanically coupling the antenna array 106 to the azimuth drive system. As shown in FIG. 7, in one embodiment, the antenna mounting bracket 208 has a partial cylindrical shape, and the elevation drives 244a, 244b include arc-shaped side supports that support the curved antenna mounting bracket 208. Referring to FIG. 9, there is illustrated a partial exploded view of the right-side elevation drive 244a. It is to be appreciated that the left-side elevation drive 244b may be a substantial mirror image of the right-side elevation drive 244a. As shown in FIG. 9, the elevation drive 244a includes an arc-shaped side support 246 with rollers 248 that allow the antenna mounting bracket 208, and thus the antenna array 106 to move along the curved track, thereby allowing the antenna array 106 to rotate in elevation.

In one example, using flexible couplings, such as flexible coupling 236, to interconnect various components may add to the ease of manufacture of the external subsystem 102 by absorbing tilt and/or angle tolerances in connections and removing or reducing strain on the connections. According to one embodiment, the elevation drive system may use a pulley system to move the antenna array 106 in elevation. An example of a push and pull pulley system is illustrated schematically in FIG. 10. The push and pull pulley system includes a drive sprocket 250 and an idler 252 coupled via a wire 254 in a continuous loop to the antenna array 106. Referring to FIGS. 6 and 8, there is illustrated an example the push and pull pulley system including the drive sprockets 250 in the elevation drive assembly 234 (see FIG. 7) and the idler 252 coupled to the elevation drive 244a. As shown in FIG. 9, the idler 252 may include a shaft 256, roller 258 and bracket 260. The elevation motor in housing 232 may provide power to drive the pulley system to cause the antenna mounting bracket 208 to rotate on rollers 248 along the arc-shaped track formed by the side supports 246. The push and pull pulley system may thus effect movement of the antenna array 106 in elevation responsive to a control signal, as discussed further below. In one example, the antenna array may be moveable over an elevation angle range of approximately -10° to 90° (zenith). An advantage of configuring the pulley system as a push and pull system is that it may allow the use of a low-torque elevation motor. In addition, the antenna mounting bracket 208 may comprise relatively wide bands to provide a broad support for the antenna array 106 and distribute the load of the array over a large portion of the antenna mounting bracket. This feature may further facilitate use of a relatively small, low-torque elevation motor.

According to one embodiment, the antenna mounting bracket 208 may include spring-loaded cams 262, as illustrated schematically in FIG. 11. These spring loaded cams 262 may be used to tune out high frequency vibrations of the antenna array 106. In one example, the spring loaded cams 262 are spring loaded wedge cams. In another example, registration of the antenna array on the arc of the antenna mounting bracket 208 may be maintained by wedge and standard cams 264. In addition, snubber wheels (not shown) may be provided on the antenna mounting bracket 208 to prevent rocking of the antenna array 106. The antenna array 106 may tend to rock back and forth as a result of its structural natural frequency. The snubber wheels may prevent this rocking, changing the rocking motion into a purely translational movement (i.e., up and down movement), which does not affect the pointing angle of the antenna array.

Referring again to FIGS. 6 and 7, in one embodiment, the gimbal assembly 108 includes a gimbal connection card 266 that provides connections between the various cables and components in the external sub-system 102 as well as to the antenna control unit 112 and/or other components of the internal sub-system 104. This gimbal connection card 266 may receive connectorized cables and may replace the traditional cable harness used in many wiring situations, thereby greatly simplifying connecting components of the external sub-system 102 together and/or to the internal sub-system 104. With the gimbal connection card 266, each component of the external sub-system 102 may include a connectorized cable such that it can be easily plugged into the gimbal connection card. Thus, each component may be connected to, or disconnected from, the gimbal connection card 266, and thus to other components of the system, without any need to change or interfere with the wiring of other components. As discussed above, according to one embodiment, the antenna array 106 comprises a plurality of antenna elements, such as horn antennas 268 (see FIG. 6), coupled to a feed network 202, which in at least some embodiments is a waveguide network. Additionally, each antenna element 268 may be coupled to a corresponding dielectric lens 204. The dielectric lenses 204 may serve to focus incoming or transmitted radiation to and from the antenna elements 268 and to enhance the gain of the antenna elements, as will be discussed in more detail below. The feed network 202 may be adapted based on the type and configuration of the antenna elements 268 used in the antenna array 106. In the example illustrated in FIGS. 4, 6 and 7, the feed network 202 is a custom sized and shaped waveguide feed network. An advantage of waveguide is that it is generally less lossy than other transmission media such as cable or microstrip. It may therefore be advantageous to use waveguide for the feed network 202 in applications where it may be desirable to reduce or minimize loss associated with the antenna array 106. However, it is to be appreciated that the feed network 202 may be constructed wholly or in part using transmission media other than waveguide. The feed network 202 will be described in more detail below.

Referring to FIGS. 12 and 13, there are illustrated a front view (FIG. 12) and a partial exploded view (FIG. 13) of one example of the antenna array 106. In the illustrated example, the antenna array 106 comprises an array of 64 rectangular horn antennas 268 disposed in two parallel rows (i.e., in a 2x32 configuration). However, it is to be appreciated that antenna array 106 may include any number of antenna elements each of which may be any type of suitable antenna. For example, an alternative antenna array may include eight circular or rectangular horn antennas in 2x4 or 1x8 configurations. Although in some applications it may be advantageous for the antenna elements to be antennas having a wide bandwidth, such as, for example, horn antennas, the invention is not limited to horn antennas and any suitable antenna may be used. Thus, although the following discussion will refer primarily to the illustrated example of a 2x32 array of rectangular horn antennas, it is to be understood that the discussion applies equally to other types and sizes of arrays, with modifications that may be apparent to those of skill in the art.

In general, each horn antenna element 268 may receive incoming electromagnetic radiation though an aperture 302 defined by the sides 304 of the antenna element, as shown in FIG. 14. The antenna element 268 may focus the received radiation to a feed point 306 at which the antenna element is coupled to the feed network 202 (not shown in FIG. 14). It is to be appreciated that while the antenna array 106 will be further discussed herein primarily in terms of receiving incoming radiation from an information source, the antenna array may also operate in a transmitting mode wherein the feed network 202 provides a signal to each antenna element 268, via the corresponding feed point 306, and the antenna array transmits the signal.

As discussed above, according to one embodiment, the external sub-system 102 may be mounted on a vehicle, such as an aircraft 132 as illustrated in FIG. 3. In this and similar applications, it may be desirable to reduce the height of the antenna array 106 (and that of the entire external sub-system 102) to minimize drag as the aircraft moves. Accordingly, low-profile antenna elements 268 may be presently preferred for such applications. Therefore, in one example, the horn antenna elements 268 are constructed to have a relatively wide internal angle 308, resulting in a relatively wide aperture width 310, to provide a large aperture area while keeping the height 312 of the horn antenna element 268 relatively small. In one example, the horn antenna elements 288 are sized such that the horn-to-horn azimuthal spacing on the same row is about 1 wavelength at the highest transmit frequency. This sizing may help to keep the first grating lobe outside of visible space across the frequency band of operation, as discussed further below.

One result of the use of low-height, wide aperture horn antennas as the antenna elements 268 is that the antenna elements may have a lower gain than might be preferable. This lower gain results because, as shown in FIG. 14, there may be a significant path length difference between a first signal 314 vertically incident on the horn aperture 302, and a second signal 316 incident along the side 304 of the antenna element 268. This path length difference may result in significant phase difference between the first and second signals 314, 316, resulting in signal interference and lower overall gain. Therefore, according to one embodiment, a dielectric lens 204 is coupled to each horn antenna element 268 to improve the gain of the horn antenna element. The dielectric lens 204 may be mounted at the aperture 310 of the horn antenna element 268 to focus the RF energy at the feed point 306 of the horn antenna element. The dielectric lens 204 may serve to match the phase and path length of the signals incident at different angles on the horn antenna element 268, thereby increasing the gain of the antenna array 106.

According to one embodiment, the antenna array 106 is tapered to further facilitate sidelobe reduction in the beam pattern of the antenna array. In one example, the outer three horn antenna elements 268 at each end of each row of antenna elements are smaller than the remaining antenna elements, which may be substantially identical in size and shape. The dielectric lenses 204 associated with these tapered antenna elements 268 may be correspondingly smaller than the lenses associated with the remaining antenna elements. This tapering of the antenna array 106 can be seen with reference to FIGS. 12 and 13. As shown in FIGS. 12 and 13, in one example the third dielectric lens 318 from each end of each row of the antenna array 106 is slightly smaller than the interior 26 dielectric lenses 320 of each row. In one example, all of the interior dielectric lenses 320, and corresponding interior horn antenna elements 322 are substantially identical in size. An example of an interior horn antenna element 322 is illustrated in FIG. 15. The third horn antenna elements 324 associated with the third dielectric lenses 318 may be slightly smaller than the interior horn antenna elements 322. An example of a third horn antenna element 324 is illustrated in FIG. 16. Similarly, the second horn antenna element 326 from each end of each row, and its associated second dielectric lens 328, may be slightly smaller than the third horn antenna element 324 and third dielectric lens 318, respectively. One example of a second horn antenna element 326 is illustrated in FIG. 17. Similarly, the end horn antenna element 330 on each end of each row, and its associated end dielectric lens 332, may be slightly smaller than the second horn antenna element 326 and second dielectric lens 328, respectively. An example of an end horn antenna element 330 is illustrated in FIG. 18. In this manner, by decreasing the sizes of the horn antenna elements 268, and associated dielectric lenses 204, at and towards the edges of the antenna array 106, the antenna array is tapered. Careful design of the taper may facilitate sidelobe reduction in the beam pattern of the antenna array 106, as discussed further below. According to one embodiment, the dielectric lenses 204 are plano-convex lenses that may be mounted above and/or partially within the horn antenna aperture 302. For the purposes of this specification, a plano-convex lens is defined as a lens having one substantially flat surface and an opposing convex surface. The dielectric lens 204 may be shaped in accordance with known optic principals including, for example, diffraction in accordance with Snell's Law, so that the lens may focus incoming radiation to the feed point 306 of the horn antenna element 268.

Referring to FIG. 19, there is illustrated in side view of one example of an interior dielectric lens 320. In the illustrated example, the dielectric lens 320 is a plano-convex lens having a planar surface 336 and an opposing convex surface 338. It may be seen that the convex shape of the dielectric lens 302 results in a greater vertical depth of dielectric material being present in the center 334 (which may be positioned above a center of the corresponding horn aperture 302) compared with the edges of the lens. Thus, a vertically incident signal, such as the first signal 314 (see FIG. 14) may pass through a greater amount of dielectric material than does the second signal 316 incident along the edge 304 of the horn antenna element 268. Because electromagnetic signals travel more slowly through dielectric than through air, the shape of the dielectric lens 320 may thus be used to equalize the electrical path length of the first and second incident signals 314, 316. By reducing phase mismatch between signals incident on the horn antenna element 268 from different angles, the dielectric lens 320 may serve to increase the gain of the horn antenna element.

Reflections of the signal incident on the convex surface 338 of the dielectric lens 320 may typically result from an impedance mismatch between the air medium and the lens medium. The characteristic impedance of free space (or dry air) is known to be approximately 377 Ohms. For the dielectric lens 204, the characteristic impedance is inversely proportional to the square root of the dielectric constant of the lens material. Thus, the higher the dielectric constant of the lens material, the greater, in general, the impedance mismatch between the lens and the air. The dielectric constant of the lens material is a characteristic quantity of a given dielectric substance, sometimes called the relative permittivity. In general, the dielectric constant is a complex number, containing a real part that represents the material's reflective surface properties, also referred to as Fresnel reflection coefficients, and an imaginary part that represents the material's radio absorption properties. The closer the permittivity of the lens material is relative to air, the lower the percentage of a received communication signal that is reflected.

The dielectric material of the lenses 204 may be selected based, at least in part, on a known dielectric constant and loss tangent value of the material. For example, in many applications it may be desirable to reduce or minimize loss in the antenna array 106 and therefore it may be desirable to select a material for the lens having a low loss tangent. Size and weight restrictions on the antenna array 106, at least in part, determine a range for the dielectric constant of the material because, in general, the lower the dielectric constant of the material, the larger the lens may be. In some applications, it may be desirable to manufacture the dielectric lenses 204 from a material having a relatively high dielectric constant in order to reduce the size and weight of the lens. However, reflections resulting from the impedance mismatch between the lens and the air may be undesirable.

Accordingly, in one embodiment, the dielectric lenses 204 have impedance matching features formed in either or both of the convex surface 338 and the planar surface 336. Referring again to FIG. 19, the dielectric lens 320 includes impedance matching holes 340 formed just below the interior surface of the convex surface 338. These holes 340 may extend as "tubes" along the depth of the dielectric lens 320, as illustrated in FIG. 20. The holes 340 may improve the impedance match of the dielectric lens 320 to the surrounding air by lowering the effective dielectric constant of the lens at and near the convex surface 338. Improving the impedance match between the dielectric lens 320 and the surrounding air may reduce RF energy reflection at the lens/air interface, thereby maximizing, or at least improving, antenna efficiency. Similarly, impedance matching grooves 342 may be provided in the planar surface 336 of the dielectric lens 320 to reduce the impedance mismatch between the lens and the air in the horn antenna element 268. An example of a pattern of grooves 342 that may be provided in the planar surface 336 of the dielectric lens 320 is illustrated in FIG. 21. Adding impedance matching holes 240 and/or grooves 342 may have the added advantage of reducing the weight of the dielectric lens 320 because less material is used (material is removed to form the holes and/or grooves).

The magnitude of the reflected signal may be significantly reduced by the presence of impedance matching features at the lens surfaces. With the impedance matching holes 340, the reflected signal at the convex surface 338 may be decreased as a function of η_n, the refractive indices at each boundary, according to equation 1 below:

A further reduction in the reflected signal may be obtained by optimizing the diameter of the holes 340 such that direct and internally reflected signals add constructively. In one example, the holes 340 are substantially similarly sized and have a diameter of about 0.129 inches.

It is to be appreciated that although the above discussion of the impedance matching features of the dielectric lens referred primarily to the interior dielectric lenses 320, the discussion applies equally to the tapered dielectric lenses 318, 328 and 330. The number of impedance matching holes 340 and/or impedance matching grooves 342 formed in each of the tapered lenses 318, 328 and 332 may vary with respect to the interior lenses 320 due to the smaller size and altered shape of the tapered lenses 318, 328 and 332. In addition, the "groove pocket" or area of the planar surface 336 in which the impedance matching grooves 342 are formed may be smaller for the smaller lenses, as discussed further below. Referring to FIG. 19, in one example, the dielectric lens 320 has a groove pocket length 350 of about 3.000 inches and a groove pocket width 352 of about 0.650 inches.

Referring to FIG. 22A, there is illustrated a side view of one example of a third dielectric lens 318. FIG. 22B illustrates an example of the planar surface 336 of the third dielectric lens 318, showing the impedance matching grooves 342, Because the third dielectric lens 318 is slightly smaller than the interior dielectric lens 320, the groove pocket length 350 may be about 2.750 inches, slightly smaller than that of the interior dielectric lens 320. In one example, the width of the various different horn antenna elements 268 may remain constant although their lengths vary to achieve the tapering. Accordingly, the groove pocket width 352 may remain approximately the same for all the dielectric lenses 318, 320, 328 and 332. FIGS. 23 A and 23B illustrate a side view of one example of a second dielectric lens 328 and a corresponding plan view of the planar surface 336 of the second dielectric lens, respectively. In one example, the second dielectric lens 328 may have a groove pocket length 350 of about 2.200 inches. Similarly, FIGS. 24A and 24B respectively illustrate a side view of one example of an end dielectric lens 332 and a corresponding plan view of the planar surface 336 of the end dielectric lens 332. In one example, the end dielectric lens 332 has a groove pocket length 350 of about 1.650 inches. Referring again to FIG. 21, in one example, the grooves 342 on the planar surface

336 have a "horizontal" center-to-center spacing 344 of about 0.750 inches and a "vertical" center-to-center spacing 346 of about 0.325 inches. The grooves 342 may have a "horizontal" width 348 of about 0.125 inches and a "vertical" width 354 of about 0.135 inches. In one example, the grooves 342 have a depth of about 0.087 inches. These dimensions may be approximately the same for the grooves 342 formed in each of the varying lenses 318, 320, 328 and 332. However, it is to be appreciated that the size and spacing of the grooves 342 may vary with the size of the dielectric lens 204 and the dielectric constant of the material used to make the lenses.

The lenses may be created by, for example, milling a solid block of lens material and thereby forming the convex-piano lenses. The impedance matching holes 340 and/or grooves 342 may be formed by milling, etching, or other processes known to those skilled in the art. It is to be appreciated that the terms "holes" and "grooves" are merely exemplary and are not intended to be limiting in terms of the shape or size of the features. It is to be appreciated that there are numerous variations for the size, shape and structural features of the dielectric lenses 204 and the invention is not limited to the use of dielectric lenses having the sizes, shapes and structural features of the above-discussed examples. For example, referring to FIG. 25, there is illustrated a side view of an alternate embodiment of a dielectric lens 356 that may be used for some or all of dielectric lenses 204. The dielectric lens 356 is a plano-convex lens having a convex surface 338 and a planar surface 336, as discussed above. In one example, the dielectric lens 356 has impedance matching grooves 358 formed in the external convex surface 338. The grooves 358 may reduce the percentage of dielectric material at the surface of the lens, which effectively reduces the dielectric constant, bringing it closer to that of air. In one example, the dielectric constant may be reduced from about 2.53 to 1.59. The groove walls, being approximately one quarter wavelength thick in one example, act to reduce signal reflection at the lens/air boundary and optimize efficiency. The grooved region thus provides a smaller "step" change in dielectric constant between the air and the remaining lens material, facilitating impedance matching.

The grooves 358 may be formed in many different configurations including, but not limited to, parallel (horizontal or vertical) lines, an array of discrete indentations, a continuous, back and forth line, a series of regularly spaced holes or indentations spaced, for example, every one half wavelength, etc. There may be either an even or odd number of grooves, and the grooves may be regularly or irregularly spaced. In one example, the grooves 358 are evenly spaced, and may be easily machined into the lens material using standard milling techniques and practices. In one example, the grooves may be machines so that they have a substantially identical width, for ease of machining. In another example, each of the grooves 358 has a concave surface feature at a greatest depth of the groove where the groove may taper to a dull point on the inside of the lens structure. As discussed above, in embodiments where the lens 356 is a plano-convex lens, the lens has a greater depth of lens material near the center of the lens as compared with the edges of the lens. Accordingly, in at least one embodiment, the depth of the grooves 358 varies with location on the lens surface. For example, the depth to which each of the grooves is milled may increase the farther a groove is located from the apex, or center 360, of the convex lens surface. In one example, the grooves may penetrate the surface by approximately one quarter- wavelength in depth near the center axis and may be regularly spaced to maintain the coherent summing of the direct and internally reflected signals, becoming successively deeper as the grooves approach the periphery of the lens.

The width of the grooves 358 may be constant or may also vary with location on the lens surface. In one example, the grooves 358 may typically have a width 368 of approximately one tenth of a wavelength (at the center of the operating frequency range) or less. The size of the lens 356 and of the grooves 358 formed in the lens surface may be dependent on the desired operating frequency of the antenna array 106. In one specific example, the dielectric lenses 204 are designed for use in the Ku frequency band (10.70 - 12.75 GHz), having an appropriate height and length for this frequency band.

Still referring to FIG. 25, in one embodiment, the dielectric lens 356 has impedance matching grooves 358 and 362 formed on both the convex lens surface 338 and the planar surface 336, respectively. In one example, the grooves 362 are milled into the planar surface 336 as a series of parallel lines or array of indentations, similar to the grooves 358 which are milled into the convex surface 338 of the lens 356. In one example, the grooves 362 are uniform with a constant width 364. However, it is to be understood that the grooves need not be uniform and may have varying widths and depths depending on desired characteristics of the lens 356. Unlike the exterior grooves 358 on the convex surface 338, the grooves 362 on the planar surface 336 may not vary in depth the farther each groove is from the center 360 of the lens 356, but instead all the grooves 362 may have a substantially similar depth 366 and width 364.

In the example illustrated in FIG. 25, the grooves 358 on the convex surface 338 of the dielectric lens 356 are not perfectly aligned with the grooves 362 on the planar surface 336 of the lens, but instead may be offset. For example, every peak on the exterior, convex surface 338 of the lens 356 may be aligned to a trough or valley on the planar surface 336. Conversely, every peak on the planar surface 336 of the lens 356 may be offset by a trough that is milled into the exterior convex surface 338 of the lens. In one example, the grooves 362 may have a width 364 of approximately 0.090 inches. The illustrated example, having grooves 362 on the planar surface 336 and grooves 358 on the convex surface 338 of the lens 356 may reduce the reflected RF energy by approximately 0.23 dB, roughly half of the 0.46 dB reflected by a similarly- sized non-grooved lens made of the same material. In the example illustrated in FIG. 25, each of the grooves 358 is introduced normal

(perpendicular) to the convex surface 338 of the dielectric lens 356. FIG. 26 illustrates an alternate example in which the grooves 358 are formed parallel to each other, and thus at least some of the grooves 358 are introduced at an angle other than perpendicular into the convex surface 338 of the dielectric lens 356. It is to be appreciated that an advantage of the embodiment illustrated in FIG. 26 is that it is easier to provide the grooves 358 in parallel because all of the grooves are cut in parallel planes. In particular, it is easier to manufacture the dielectric lens 356 with parallel grooves 358 because all of the machining is vertical and rotation of the part being machined is not needed.

In many applications, the external sub-system 102, including the antenna array 106, is exposed to environmental conditions such as precipitation and varying humidity. In such environments, it is possible for moisture to collect within the grooves 358 on the convex surface 338 of the dielectric lenses 204 in those embodiments of the lenses in which the grooves are milled (or otherwise fabricated) on the external surface of the lens. Such collection of moisture in the grooves 358 may be highly undesirable as it may degrade the RF performance of the lens, for example, by changing the effective dielectric constant of the lens and adversely affecting the impedance match between the lens and the surrounding air. For example, build-up of water from condensation inside the grooves 358 of the dielectric lens may cause a reduction in signal power of about 2 dB. In addition, particularly in situations where the antenna array 106 is subject to wide temperature variations, any water collected in the grooves 358 can freeze and cause structural problems, such as cracking of the lens, due to expansion of the water when it turns to ice. It may be possible to reduce moisture collection in the external grooves 358 by covering the antenna array 106 with a radome and, in some examples, coating the interior surface of the radome with a material adapted to shed water. One example of a coating material that may be used is fluorothane. However, it is to be appreciated that the invention is not limited to the use of fluorothane and other water- shedding materials may be used instead. However, even when the antenna array is covered with a radome coated with a moisture- shedding material, it may not be possible to completely prevent moisture from collecting in the grooves 358. In addition, dust particles and other material may also collect in the grooves 358, further affecting the RF performance of the lens and adding to environmental wear and tear on the lens. Accordingly, it at least some embodiments, it is presently preferable to provide the impedance matching features on the interior, rather than exterior, surface of the dielectric lens 204. For example, as discussed and illustrated above, the impedance matching holes 340 are provided on the interior of the dielectric lenses 204, such that the exterior convex surface 338 may remain smooth. According to another embodiment, impedance matching between the dielectric lens 204 and the surrounding air can be achieved by forming the dielectric lens out of two or more dielectric materials having different dielectric constants. For example, the interior portion of the dielectric lens 204 can be made from one material, and another material with a lower dielectric constant can be used in bands along the convex surface 338 and planar surface 336. In this manner, the change in effective dielectric constant from the air to the outer portion of the lens and then to the inner portion of the lens, and back again, may be made more gradual, thereby reducing unwanted reflections. With the use of several materials with gradually decreasing dielectric constants, a dielectric lens 204 with a gradually changing effective dielectric constant can be created. In one example, an adhesive can be used to adhere together the various layers of different materials. In this example, care should be taken to ensure good adhesion between the different layers so as to avoid reflections that may occur as a result of pockets of poor adhesion, or minute spaces, between the different layers. In addition, particularly for applications in which the dielectric lenses 204 are likely to encounter a wide range of temperatures, it may be important to carefully select the different dielectric materials to have similar coefficients of thermal expansion, so as to avoid or minimize stresses on the boundaries between the different materials which could shorten the life of the dielectric lenses 204 and cause degradation in the structural integrity and/or RF performance of the lenses.

As discussed above, the dielectric lenses 204 may be designed to have an optimal combination of weight, dielectric constant, loss tangent, and a refractive index that is stable across a large temperature range. It may also be desirable that the dielectric lenses 204 do not deform or warp as a result of exposure to large temperature ranges or during fabrication. It may also be preferable for the dielectric lenses 204 to absorb only very small amounts, e.g., less than 0.1 %, of moisture or water when exposed to humid conditions, such that any absorbed moisture will not adversely affect the combination of dielectric constant, loss tangent, and refractive index of the lens. Furthermore, for affordability, it may be desirable that the dielectric lenses 204 be easily fabricated. In addition, it may be desirable that the lens should be able to maintain its dielectric constant, loss tangent, and a refractive index and chemically resist alkalis, alcohols, aliphatic hydrocarbons and mineral acids. According to one embodiment, the dielectric lenses 204 are constructed using a certain form of polystyrene that is affordable to make, resistant to physical shock, and can operate across the wide range of the thermal conditions likely to be experienced when the antenna array 106 is mounted on an aircraft. In one example, this material is a rigid form of polystyrene known as crossed-linked polystyrene. Polystyrene formed with high cross linking, for example, 20% or more cross-linking, may be formed into a highly rigid structure whose shape may not be affected by solvents and which also may have a low dielectric constant, low loss tangent, and low index of refraction. In one example, a cross- linked polymer polystyrene may have the following characteristics: a dielectric constant of approximately 2.5, a loss tangent of less than 0.0007, a moisture absorption of less than 0.1 %, and low plastic deformation property. Polymers such as polystyrene can be formed with low dielectric loss and may have non-polar or substantially non-polar constituents, and thermoplastic elastomers with thermoplastic and elastomeric polymeric components. The term "non-polar" refers to monomeric units that are free from dipoles or in which the dipoles are substantially vectorially balanced. In these polymeric materials, the dielectric properties are principally a result of electronic polarization effects. For example, a 1 % or 2% divinylbenzene and styrene mixture may be polymerized through radical reaction to give a crossed linked polymer that may provide a low-loss dielectric material to form the thermoplastic polymeric component. Polystyrene may be comprised of, for example, the following polar or non-polar monomeric units: styrene, alpha- methylstyrene, olefins, halogenated olefins, sulfones, urethanes, esters, amides, carbonates, imides, acrylonitrile, and co-polymers and mixtures thereof. Non-polar monomeric units such as, for example, styrene and alpha-methylstyrene, and olefins such as propylene and ethylene, and copolymers and mixtures thereof, may also be used. The thermoplastic polymeric component may be selected from polystyrene, poly(alpha-methylstyrene), and polyolefins. A dielectric lens 204 constructed from a cross-linked polymer polystyrene, such as that described above, may be easily formed using conventional machining operations, and may be grinded to surface accuracies of less than approximately 0.0002 inches. The cross- linked polymer polystyrene may maintain its dielectric constant within 2% down to temperatures exceeding the - 7OF, and may also have a chemically resistant material property that is resistant to alkalis, alcohols, aliphatic hydrocarbons and mineral acids. In one example, the dielectric lens 204 so formed includes an example of the impedance matching features discussed above. In these examples, the dielectric lens 204 may be formed of a combination of a low loss lens material, which may be cross-linked polystyrene and thermosetting resins, for example, cast from monomer sheets & rods. One example of such a material is known as Rexolite®. Rexolite® is a unique cross- linked polystyrene microwave plastic made by C-Lec Plastics, Inc. Rexolite® maintains a dielectric constant of about 2.53 through 500 GHz with extremely low dissipation factors. Rexolite® exhibits no permanent deformation or plastic flow under normal loads. All casting may be stress-free, and may not require stress relieving prior to, during or after machining. During one test, Rexolite® was found to absorb less than .08% of moisture after having been immersed in boiling water for 1000 hours, and without significant change in dielectric constant. The tool configurations used to machine Rexolite® may be similar to those used on Acrylic. Rexolite® may thus be machined using standard technology. Due to high resistance to cold flow and inherent freedom from stress, Rexolite® may be easily machined or laser beam cut to very close tolerances, for example, accuracies of approximately 0.0001 can be obtained by grinding. Crazing may be avoided by using sharp tools and avoiding excessive heat during polishing. Rexolite® is chemically resistant to alkalis, alcohols, aliphatic hydrocarbons and mineral acids. In addition, Rexolite® is about 5% lighter than Acrylic and less than half the weight of TFE (Teflon) by volume.

As discussed above, the dielectric lenses 204 may be mounted to the horn antenna elements 268 and designed to fit over and at least partially inside the respective horn antenna element. Referring again to FIG. 19, in one embodiment, the dielectric lens 320 has tapered sides 370 to facilitate secure mounting of the lens to the corresponding horn antenna element 322. In one example, the slope of the tapered sides 370 of the dielectric lens 320 is approximately the same as the slope of the sides 304 of the horn antenna element 322. Such tapered sides 370 may facilitate self-centering of the dielectric lens 320 with respect to the horn antenna element 322. A pin 372 may be used to fasten the dielectric lens 320 to the horn antenna element 322. An example of a pin 372 that may be used to fasten the dielectric lenses 204 to their respective antenna elements 268 is illustrated in FIGS. 27A and 27B. Referring to FIG. 27A, in one example, the pin 372 has a length 374 of about 0.320 inches, with a tolerance of about 0.030 inches. Referring to FIG. 27B, in one example, the pin 372 has a diameter 376 of about 0.098 inches with a tolerance of about 0.001 inches. In one example, the pin 372 is made of fiberglass. However, it is to be appreciated that a variety of other materials may be suitable.

Referring again to FIGS. 22 A, 23 A and 24A, in one embodiment, to facilitate mounting of the tapered lenses 318, 328 and 332 to their respective horn antenna elements 324, 326 and 330, the length 350 of the planar surface 336, i.e., the length of the groove pocket discussed above, may be reduced relative to the overall length the lenses by, for example, milling. The reduced footprint of planar surface 336 may allow the lenses 318, 328 and 332 to be partially inserted into the respective horn antenna elements 324, 326 and 330. Pins 372 may be used to fasten the dielectric lenses 318, 328 and 332 to the respective horn antenna elements 324, 326 and 330.

According to one embodiment, retaining clips 206a, 206b and 206c (see FIGS. 4 and 13) are used to fasten the tapered dielectric lenses 318, 328 and 332 to their respective horn antenna elements 324, 326 and 330. In one example, these retaining clips are used in conjunction with the pins 372 to more securely fasten the dielectric lenses 318, 328 and 332 to the horn antenna elements 324, 326 and 330. Alternatively, the retaining clips 206a, 206b and 206c may be used instead of the pins 372. This arrangement may be preferable where the lenses 318, 328 and 332 are small and there may be insufficient room to use a pin 372 without comprising either the structural integrity of the lens or the RF performance of the lens. In addition, it is to be appreciated that various other fastening mechanisms may be suitable to mount the dielectric lenses 204 to the horn antenna elements 268. FIGS. 28A-C respectively illustrate examples of retaining clips 206a, 206b and 206c that can be used to fasten the dielectric lenses 318, 328 and 332 to the respective horn antenna elements 324, 326 and 330. Referring to FIG. 29, in one example, the dielectric lenses 328 includes a slot 378 to receive the retaining clip 206b. Similar slots may be provided on dielectric lenses 318 and 332. Referring again to FIG. 13, in one embodiment, an additional retaining clip 380 is used to further secure the tapered lenses 318, 328 and 332. In the illustrated example, four such retaining clips 380 are used, one at each end of each of the two rows of antenna elements in the antenna array 106. An example of the retaining clip 380 is illustrated in FIG. 30. In another example, the dielectric lenses 204 are glued into the respective horn antenna elements using an adhesive. Adhesive fastening may be used alone or in combination with any or all of the pins 372 and retaining clips 206a, 206b, 206c and 380 discussed above. In one example, the pins 372 and/or retaining clips 206a, 206b, 206c and 380 are used as secondary attachment means in conjunction with an adhesive to more securely fasten the dielectric lenses 204 to the respective antenna elements 268. This arrangement may be preferable, for example, where the antenna array 106 is mounted to an aircraft and must meet applicable safety standards.

Still referring to FIG. 13, in one embodiment, horn inserts 382 are placed inside at least some of the horn antenna elements 268, beneath the dielectric lenses 204. As discussed above, in some applications, such as where the communication system is mounted on an aircraft 132, the antenna array 106 may experience large variations in environmental conditions such as temperature, humidity and pressure. These changing conditions can cause moisture to collect on and in the various components of the antenna array 106, which can have an adverse effect the performance of the antenna array. Accordingly, in one embodiment, horn inserts 382 are placed inside the horn antenna elements 268 to prevent moisture from collecting inside the horn antenna elements. In one embodiment, the horn inserts 382 are made from an extruded polystyrene insulation. In another example, the horn inserts are made of Styrofoam. However, it will be appreciated by those skilled in the art that a variety of other materials may be suitable.

Referring to FIG. 3 IA, there is illustrated one example of a horn insert 382a sized for insertion into an interior horn antenna element 322. In one example, the horn insert 382a has a length 384 of approximately 2.899 inches. As illustrated in FIGS. 3 IA and 3 IB, in one example, the horn insert 382a has a slightly tapered edge, such that the width 386a of the horn insert 382a is approximately 0.745 inches, with a tolerance of approximately 0.005 inches, whereas the width 386b including the tapered edge is approximately 0.790 inches. In one example, the tapered edge of the horn insert 382a has an angle of about 45 degrees. It is to be appreciated that the horn inserts 382 for the smaller horn antenna elements 324, 326 and 330 may be appropriately smaller than the horn insert 382a for the interior horn antenna element 322, and may also have modified shapes to better fit to the shapes of the corresponding horn antenna elements. For example, referring to FIG. 32A, there is illustrated an example of a horn insert 382b sized and shaped to be placed within the third horn antenna element 324. In one example, the horn insert 382b has a length 384 of approximately 2.850 inches. FIG. 32B illustrates an example of a horn insert 382c sized and shaped to be accommodated by the second horn antenna element 326. In one example, the horn insert 382c has a length 384 of approximately 2.300 inches. FIG. 32C illustrates an example of a horn insert 382d sized and shaped to be accommodated by the end horn antenna element 330. In one example, the horn insert 382d has a length 384 of approximately 1.750 inches. In the examples illustrated in FIGS. 32B and 32C, the horn inserts 382c and 382d have partial straight edges 388, rather than having a continuously curved surface as do the illustrated examples of horn inserts 382a and 392b. However, it is to be appreciated that numerous variations on the shapes and sizes of the horn inserts 382 are possible and the invention is not limited to the illustrated examples. In addition, the shapes and sizes of the horn inserts 382 may vary depending on the shapes and sizes of the various antenna elements 268 used in the antenna array 106.

As discussed above, in one embodiment, the antenna array 106 is tapered, having smaller antenna elements 268 near the edges of the array, to reduce sidelobes in the beam pattern of the array. The smaller antenna elements 324, 326 and 330 have a lower signal amplitude and contribute less than do the interior antenna elements 322 to the overall signal received or transmitted by the array. By appropriately sizing these antenna elements 324, 326 and 330, and their associated dielectric lenses 318, 328 and 332, the signal contribution from these elements, and therefore the beam pattern of the antenna array can be adjusted to reduce sidelobes. In addition, as discussed further below, the feed network 202 can be designed to weight the signal contribution from different antenna elements 268 differently, thereby further controlling the beam pattern of the antenna array 106 and reducing sidelobes. In one example, the horn inserts 382 may also be constructed to facilitate sidelobe suppression. For example, the horn inserts 382 for some or all of the outer horn antenna elements 324, 326 and 330 may be made from a radar absorbent material (RAM) to further attenuate the signal contribution of these antenna elements. Selected ones of the horn inserts 382 in the interior horn antenna elements 322 may also be made of RAM to further control the beam pattern. Sidelobe reduction may be advantageous for several reasons including, for example, to improve the gain of the antenna array (having lower sidelobes means that more energy is captured in the main, useful, lobe of the antenna radiation pattern), and to meet certain performance goals and/or regulations (e.g., the FAA may set specifications for sidelobe suppression for applications such as satellite television or radio). For applications in which the antenna array 106 is mounted on a vehicle, such as an aircraft, the effect of the vehicle's movement on the antenna beam pattern may also be taken into account. For example, when the antenna array 106 is mounted on an aircraft 132, the beam pattern should be such that it meets sidelobe specifications (set, for example, by the FAA or other international authorities or regulations) not only when directly aligned with the signal source 110, but also when there is a polarization offset between the antenna array and the signal source due to movement of the aircraft. Thus, any or all of the size, shape, and arrangement (including taper and spacing) of the antenna elements 268 and associated dielectric lenses 204 and horn inserts 382, and the arrangement of the feed network (discussed below), may be controlled to facilitate producing a beam pattern that meets sidelobe suppression standards for various orientations (polarization offsets) of the antenna array relative to the signal source or destination.

Referring again to FIG. 12, in another embodiment, the two rows of antenna elements 268 making up the antenna array 106 are slightly offset from one another along the length of the array, rather than being perfectly aligned. In the illustrated example, it can be seen that the top row of antenna elements 268 is positioned slightly to the left (from the viewpoint of one looking at the face of the antenna array) of the bottom row of antenna elements 268. This positional offset may also facilitate sidelobe reduction in the radiation pattern of the antenna array 106. In one example, the offset is equal to about one half the width of one antenna element 268 in the antenna array 106, as shown in FIG. 12, so as to minimize sidelobes in visible space for the zero degree elevation angle plane. Referring to FIG. 33A, there is illustrated a beam pattern as a plot of simulated antenna gain as a function of azimuth angle for an embodiment of an antenna array, with an approximate half-wavelength antenna element spacing and including the tapering, row offset, RAM horn inserts and feed network biasing discussed above and below. The beam pattern illustrated in FIG. 33 A is for an operating frequency of 14.3 GHz and a zero degree "roll" or polarization offset between the signal source 110 and the antenna array 106. Line 390 represents an example of the sidelobe suppression requirement for the antenna array, and line 392 represents a co-polarization requirement. FIG. 33B illustrates the simulated beam pattern for the same antenna array as for FIG. 33 A, but with a 15 degree polarization offset. It can be seen that the beam pattern in FIG. 33B still meets the sidelobe suppression and co-polarization requirements. In one example, by suitably designing the feed network, the antenna element spacing, antenna array row offset and taper, and using RAM horn inserts in the antenna elements towards the edges of the array, the antenna array can be made to have a beam pattern that meets applicable sidelobe suppression requirements for up to about a 25 degree polarization offset.

As discussed above, the antenna array 106 includes a feed network 202 coupled to each of the antenna elements 268, and in one embodiment, the feed network 202 is a waveguide feed network, as illustrated in FIGS. 4, 6, 7 and 13. The feed network 202 operates, when the antenna array 106 is in receive mode, to receive signals from each of the horn antenna elements 268 and to provide one or more output signals at a feed port that is coupled to the communication system electronics. Similarly, when the antenna array 106 operates in transmit mode, the feed network 202 guides signals provided at the feed port to each of the antenna elements 268 for transmission. Accordingly, it is to be appreciated that although the following discussion will refer primarily to operation in the receiving mode, the components may operate in a similar manner, with signal flow reversed, when the antenna array 106 is operating in the transmit mode. It is also to be appreciated that although the feed network 202 is illustrated as a waveguide feed network, and may be a waveguide feed network in presently preferred embodiments, the feed network may be implemented using any suitable technology, such as printed circuit, coaxial cable, etc., as will be recognized by those skilled in the art.

According to one embodiment, the waveguide feed network 202 is a compressed, non-conforming (i.e., custom sized and shaped) waveguide feed that has a low profile and is designed to fit within a constrained volume. As discussed above, in some applications, the antenna array 106 will be mounted on a moving vehicle, such as an automobile or aircraft, and it may therefore be desirable for the antenna array to occupy as small a volume as possible, so as to have minimal impact on the aerodynamics of the vehicle and to be easily mountable on the vehicle. Accordingly, the feed network 202 may be shaped and arranged to occupy a reduced volume. In one embodiment, the feed network 202 perfoπns signal summing/splitting in both the E-plane and the H-plane, a feature which contributes to the ability to provide a compressed, low-profile feed network, as discussed further below. In one embodiment, the feed network 202 may be designed to fit behind the two rows of antenna elements 268, as illustrated in FIG. 13, such that a polarization converter unit, discussed below, may fit "inside" the antenna array 106. Alternatively, the feed network 202 may be designed to fit between the two rows of antenna elements 268, as illustrated in FIG. 34. In either arrangement, or in various other arrangements that may be apparent to those skilled in the art, the feed network 202 may have a compressed, low- profile design. Referring to FIG. 35, in one embodiment, each antenna element 268 is coupled, at its feed point 306 to an orthomode transducer (OMT) 402. The OMT 402 may provide a coupling interface between the antenna element 268 and the feed network 202, and may also isolate two orthogonal linearly polarized RF signals, as discussed further below. When the antenna array 106 receives a signal, the OMT 402 receives the input signal from the antenna element 268 at a first port and splits the signal into two orthogonal component signals which are provided at second and third ports 404, 406. When the antenna array transmits a signal, the OMT 402 receives the two orthogonally polarized component signals at the second and third ports 404, 406 and combines them to provide at the first port and to the antenna element 268, a signal for transmission. In the illustrated example, the OMT 402 is integrally formed with the antenna element 268. However, it is to be appreciated that the OMT 402 may be formed as a separate component from the antenna element 268 and coupled to the antenna element.

As discussed above, in one embodiment, the OMT 402 splits an RF signal received at the first port into two orthogonal RF component signals. One RF component signal has its E- field parallel to the long axis of the horn (designated here as vertical, V) and the other RF component signal has its E- field parallel to the short axis of the horn (designated here as horizontal, H). These RF component signals are referred to herein as the vertically polarized RF component signal, or vertical component signal (V), and the horizontally polarized RF component signal, or horizontal component signal (H). From these two orthogonal component signals, any transmitted input signal may be reconstructed by vector combining the two component signals. Referring to FIG. 36, there is illustrated an isometric view of one example of a compact, broadband orthomode transducer (OMT) 402. In one example, the OMT 402 is a multi-faceted waveguide OMT that provides for the transmission of orthogonal electromagnetic waves. As discussed above, the OMT 402 includes two rectangular waveguide ports 404, 406 in planes perpendicular to each other, as well as a first rectangular waveguide port 408. Embodied within the waveguide OMT 402 are multi- faceted surfaces that form a plurality of inclined, horizontal, and vertical surfaces that are described in more detail below. For the antenna array 106 operating in the receive mode, port 408 can be considered an input terminal of the OMT 402, and ports 404 and 406 can be considered the output terminals of the OMT 402. In one embodiment, the combination of the multi-faceted surfaces of the OMT 402 are positioned and oriented to propagate simultaneously the horizontally-polarized electric waves, H, and the vertically-polarized waves, V, in the region of port 408, while generating very little reflection of the signals. Another example of an OMT 402 is illustrated in FIG. 37. In the example illustrated in FIG. 37, the multi-faceted surfaces include, and are not limited to, the inclines 410 and 412 which are symmetrically positioned on the left and right sides of the vertical centerline of the OMT 402, and inclines 414 and 416 which are each symmetrical to each other and depicted near the square cross-sectional end of the waveguide OMT 402. The incline planes 410 and 414 are each offset 45 degrees from each other forming a ninety degree included angle at their mutual intersection. Likewise, inclines 412 and 416 are each offset 45 degrees from each other forming a ninety degree included angle at their mutual intersection. Inclines 410 and 412 are coplanar, as are inclines 414 and 416, and positioned symmetrically within the OMT 402. In one example, the mutual intersection of the inclines also forms an effective low-loss transition for electromagnetic waves generated from the corresponding antenna element 268. The mutual intersection may also coincide with the feed point 306 of the antenna element 268.

Referring to FIGS. 37 and 38, in one example, horizontal and vertical electromagnetic waves may enter the terminal 408 of the waveguide OMT 81. The vertically polarized electromagnetic wave, V, propagates through port 408, through a space bounded by the left and right sidewalls of the waveguide OMT 402 and the horizontal surfaces 418, 420, 422, 424, 426 and 428 of the waveguide OMT 402, which form a space designed for the frequency band of use, and are transmitted to port 404. In one example, little or none of the vertically polarized electric wave V is transmitted to port 406 of the OMT 402 due to frequency cut-off effects caused by the metal walls depicted as 430, 432, 434, and 436. The multi-faceted features of the OMT 402 may form an effective waveguide. In one example, the effective waveguide dimensions are approximately 0.600 inches in width and 0.270 inches in height and provide a very low loss transmission for frequencies in the 10.7 GHz to 14.5 GHz band.

Still referring to FIG. 37, in one example, the horizontally polarized electric waves H enter the waveguide OMT 402 through the terminal 408, which is bounded by upper and lower inner walls of the OMT 402 and forms a space bounded between surfaces 430, 432, 434, 436, 438, and 440 of the waveguide OMT 81. Little or none of the horizontally polarized electric wave H may be transmitted to port 404 of the OMT 402 due to frequency cut-off effects caused by the space formed between the walls depicted as 418, 420, 422, 424, 426 and 428. It is to be appreciated that the waveguide type OMT 402 may provide several advantages, including a miniature form factor, and a broadband propagation with low loss. It will further be appreciated by those skilled in the art that variations on the OMT 402 are possible, and the invention is not limited to the illustrated examples.

In one example, the vertically polarized electromagnetic wave V of a basic mode such as TEOl is propagated from the port 408 of the OMT 402, through the waveguide

OMT, bypasses the rectangular branching waveguides of 406, and is propagated in a basic mode such as TEOl to the port 404. During the transit of the vertically polarized electromagnetic wave V, each of spaces defined between upper and lower sidewalls of the rectangular branching waveguides in the OMT 402 may be designed so as to be equal to or smaller than a half of the free-space wavelength of the frequency band in use. Thus, the vertically polarized electromagnetic wave V may not propagate into port 406 due to the cut-off effect of those spaces with very low reflection characteristics. Thus, the vertically polarized electromagnetic wave V provided to port 408 may be efficiently transmitted to port 404 and provided at that port as the vertical component signal, while the OMT 402 suppresses the reflection to the port 408 and eliminates propagation to port 406. Similarly, the horizontally-polarized electromagnetic wave H in a basic mode TElO propagates from port 408 through the OMT 402, bypassing the waveguide branch for port 404, and is provided at port 406 as the horizontal component signal.

It is to be appreciated, as has been discussed above that although the operation of the OMT 402 has been described with respect to the case where the signal flow is such that port 408 is an input terminal, and the ports 404 and 406 are output terminals, the OMT 402 can also be operated such that the ports 404 and 406 are input terminals for orthogonal component signals which are combined and provided at the output terminal, port 408. Further, it is to be appreciated that the OMT 402 may also contain substantially circular or elliptical waveguides and terminations. According to one embodiment, the feed network 202 includes a first path coupled to the second port 404 of the OMT 402 that guides the vertically polarized component signal, and a second path coupled to the third port 406 of the OMT 402 that guides the horizontally polarized component signal. Each path is coupled to all of the antenna elements 268 in the antenna array 106. Thus, each of the two orthogonally polarized component signals may travel a separate, isolated path from the respective ports 404, 406 of the OMT 402 to a feed port where the signals are fed to the system electronics, as discussed below. For receive mode of the antenna array 106, the feed network 202 receives the vertically and horizontally polarized component signals from each antenna element and sums them along the two feed paths to provide at the feed port one vertically polarized signal and one horizontally polarized signal. For transmit mode of the antenna array 106, the feed network 202 receives a vertically polarized signal at the feed port and splits that signal into the vertical component signals provided at port 404 of each OMT 402. Similarly, the feed network 202 receives a horizontally polarized signal at the feed port and splits it into the horizontal component signals provided at port 406 of each OMT 402. In one example, the two paths are substantially symmetrical, including the same number of bends, T-junctions and other waveguide path elements such that the feed network 202 does not impart a phase imbalance to the vertical and horizontal component signals.

As discussed above, in one embodiment, the feed network 202 includes both a path in which signal summing is done in the E-plane, and a path in which signal summing is done in the H-plane. Summing in both the E-plane and the H-plane allows the feed network to be substantially more compact than a similar feed network in which summing is done only in one plane. In particular, using both the E-plane and H-plane allows the two paths 440, 442 of the feed network to interweave, as shown in FIG. 39, due to the different size and shape of the two paths. Accordingly, the entire feed network 202 may fit within a smaller volume than if the summing for both paths were done in the same plane. In one example, the vertical component signals are fed to and guided by the E- plane path and the horizontal component signals are fed to and guided by the H-plane path. However, it is to be appreciated that the opposite arrangement, namely that the horizontal component signals are guided by the E-plane path and the vertical component signals are guided by the H-plane path, can be implemented. Both the vertical component signal and the horizontal component signal are made up of both E-plane and H-plane fields; therefore, either component signal may be summed in either plane. Accordingly, the two feed paths of the feed network 202 will be referred to herein as the horizontal feed path and the vertical feed path, and it is to be understood that either path may sum/split the signals in either the H-plane or the E-plane.

According to one embodiment, the feed network 202 includes a plurality of E- plane T-junctions and bends to couple all of the antenna elements 268 together in the E- plane path, and a plurality of H-plane T-junctions and bends to couple all of the antenna elements 268 together in the H-plane path. When the antenna array 106 is operating in receive mode, the T-junctions operate to add the component signals (vertical or horizontal) received from each antenna element 268 to provide a single output signal (in each orthogonal polarization) at the feed port. When the antenna array 106 is operating in transmit mode, the T-junctions serve as power-dividers, to split a signal from the single feed port (for each orthogonal component signal) to feed each antenna element 268 in the antenna array 106.

Referring to FIG. 4OA, there is illustrated one example of a portion of the horizontal feed path showing several waveguide T-junctions and bends. FIG. 4OB is a cross-sectional view of the portion of the horizontal feed path taken along line A-A in FIG. 4OA. Referring to FIGS. 4OA and 4OB, in one example, the waveguide T-junctions 444 include narrowed sections 446 (as compared to the width of the remaining sections) that perform a function of impedance matching. The narrowed sections may have higher impedance than the wider sections and may typically be approximately one-quarter wavelength in length. In another example, the waveguide feed network 202 has rounded bends 448, rather than sharp 90 degree bends, which may further allow the feed network 202 to take up less space than if right-angled bends were used, and also may serve to decrease phase distortion of the signal as it passes through the bends. In one example, vertical component signals are summed after going through waveguide step transformers and 90 degree chamfered bends 448 that are all designed for minimal VSWR. Similarly, the horizontal component signals may be summed after going through waveguide step transformers and 90 degree chamfered bends 448 that are all designed for minimal VSWR. As discussed above, in one embodiment, each of the horizontal and vertical feed paths in the feed network 202 has the same number of bends in each direction so that the two component signals receive an equal phase delay from propagation through the feed network 202.

According to one embodiment, the waveguide T-junctions include a notch 450 at the cross-point of the T that may serve to decrease phase distortion of the signal as it passes through the T-junction 444. In another embodiment, there is a stepped septum at the center of the H-plane waveguide T-junctions 444. In another embodiment, there is a "V" shaped septum at the center of the E-plane waveguide T-junction 444. For impedance matching, the waveguide short wall dimension on the two inputs to the E-plane T-junction may be approximately ¹A the short wall dimension of the output waveguide section. In another example, a short conductive tuning cylinder 452 is provided at the tip of the septum, as illustrated in FIG. 41. The tuning cylinder 452 protrudes into the waveguide, perpendicular to one of the broad walls of the waveguide and, in the illustrated example, terminates in a small "ball" 454. In one example, the tuning cylinder 452 has a length 456 of about 0.214 inches and the "ball" 454 has a diameter 458 of about 0.082 inches. However, it is to be appreciated that these dimensions are exemplary only as the dimensions of all features of the waveguide feed network 202, including those of the tuning cylinder 452 and "ball" 454, may vary depending on the desired operating frequency band of the antenna array 106. Some example angles of curvature of the sections of the waveguide are also illustrated in FIG. 41 and are also exemplary only and not intended to be limiting. In one embodiment, the position of the E and H-plane waveguide T-junction septums are located such that they are biased toward either one of the two input ports of the T-junction, so as to create an amplitude balance or imbalance. Referring to FIG. 42, from a summing perspective, the T-junction receives signals at two inputs 460 and 462 and provides a summed signal at output 464. by biasing the T-junction in favor of one input, for example, input 460, the contribution of the signal received at that input 460 may be greater in the summed signal at the output 464 than is the contribution from the signal at the other input 462. This relationship may be give by the following equation:

S₀₁₁₁ = AS_{1 +} BS₂ (2) where S₁ and S₂ are the signals received at inputs 460 and 462, and A and B are scaling factors determined by the biasing of the T-junction. Biasing of the T-junction 444 may also be achieved using the tuning element 466. If the tuning element 466 is centered in the T-junction 444, as shown in FIG. 42, the scaling factors A and B may be equal, such that the signals at the two inputs 460 and 462 are summed equally. However, by altering the shape and/or location of the tuning element 466, one scaling factor can be made larger than the other, such that the summed output signal S_out includes a larger contribution of the signal from the input with the larger scaling factor.

For example, referring to FIG. 43, there is illustrated a portion of the feed network 202 showing several T-junctions 444 with biasing tuning elements 466. In the illustrated example, the tuning cylinder 452 is offset to the right of the center of the T-junction, and the "ball" 454 offset from the tuning cylinder 452, such that it has a larger portion to the left side of the tuning cylinder 452 than to the right side. Thus, the scaling factors of the two arms 468a, 468b of the T-junction 444 are different. By controlling the offset of the tuning cylinder 452 and the shape and offset of the "ball" 454, the contribution of the signal travelling through each arm 468a, 468b to the summed signal at output 464 can be controlled. In this manner, the contribution of the component signals from each antenna element 268 in the antenna array 106 can be controlled, thereby creating a signal amplitude taper in addition to the physical tapering (i.e., smaller horn antenna elements and associated dielectric lenses) of the array discussed above. This signal amplitude tapering can be controlled to facilitate achieving a desired level of sidelobe suppression, as discussed above. It is to be appreciated that in the transmit mode, when signal flow is reversed, the offset and shape of the tuning elements 466 control the amplitude of the component signals provided to each antenna element 268 in the antenna array 106, and thereby facilitate sidelobe suppression in the transmit beam pattern of the array. Thus, the beam patterns illustrated in FIGS. 33A and 33B, with high sidelobe suppression/reduction, may be achieved by a combination of the size, number and spacing of the antenna elements, the physical tapering of the antenna array, and the design of the feed network 202 to include signal amplitude tapering. An advantage of designing the feed network 202 to contribute to sidelobe suppression includes the fact that further ones of the horn antenna elements 268 need not be made smaller and therefore, there greater sidelobe suppression may be achieved at a small cost to antenna efficiency.

According to one embodiment, dielectric inserts may be positioned within the feed network 202 at various locations, for example, within the E-plane and/or H-plane T- j unctions. The size of the dielectric insert and the dielectric constant of the material used to form the dielectric insert may be selected to improve the RF impedance match and transmission characteristics between the input(s) and output(s) of the waveguide T- junctions. In one example, the dielectric insert may be constructed from Rexolite®. The length and width of the dielectric insert(s) may be selected so that the dielectric insert fits snugly within the waveguide at the desired location. In one example, the dielectric insert may have a plurality of holes formed therein. The holes may serve to lower the effective dielectric constant of the dielectric insert such that a good impedance match may be achieved.

As discussed above, in one embodiment, the feed network 202, in receive mode, sums the vertical and horizontal component signals from each antenna element 268 in the antenna array 106 and provides at the feed port a summed vertically polarized signal and a summed horizontally polarized signal. In one embodiment, the two summed signals are recombined by the system electronics. Alternatively, in another embodiment, the feed network 202 includes a feed orthomode transducer (not shown) at the feed port that combines the two orthogonal summed signals in the same manner discussed above with respect to the OMT 402. In one example, the antenna OMT 402 and feed OMT may be orthogonally fed. Thus, the vertical component signal may receive a first phase delay φi from the antenna OMT 402, a path delay φ_p, and a second phase delay Φ₂ from the feed OMT. Similarly, the horizontal component signal may receive a first phase delay φ₂ from the antenna OMT 402, a path delay φ_p, and a second phase delay φi from the feed OMT. Thus, the combination of the two OMTs, orthogonally fed, may cause each of the vertical and horizontal component signals to receive a substantially equal total phase delay, as shown below in equation 3,

Φ[(fiϊ + φ₁) + φ_p + φ₂] = Φ[(fiϊ + φ₂) + φ_p + φ_r]

(3) where (cot + φi) and (cot + φ₂) are the vertically and horizontally polarized component signals and which are phase matched at the output port of the feed OMT. It is to be appreciated that although the operation of the OMTs and feed network 202 have been discussed in terms of two orthogonal linearly polarized component signals, the invention is not so limited and the OMTs may alternatively be designed to split an incoming signal into two orthogonal circularly polarized (e.g., left-hand polarized and right-hand polarized) signals (and to recombine these component signals). In this case, the feed network 202 may be designed to guide the two orthogonal circularly polarized signals.

According to another embodiment, the two orthogonally polarized summed component signals from the feed network (V and H) are fed to a first feed OMT having a circular dual mode port. A circular rotary waveguide section may be connected to the circular dual mode port of the first feed OMT. A second feed OMT, also having a circular dual mode port, may be connected to the circular rotary waveguide, such that the second feed OMT may rotate on the axis of the circular dual mode port. Thus, in at least one example, the phase lengths of the V signal and the H signal from the feed network 202 through the circular dual mode port of the first feed OMT are effectively equal. Rotating the second feed OMT effectively creates two linear, orthogonally polarized signals for any slant angle at the output of the second feed OMT. In one example, the feed OMTs and circular rotary waveguide may be located off the antenna array. In this example, a flexible waveguide may be used to connect the final T-junction of the feed network 202 to the first feed OMT so as to accommodate movement of the antenna array. According to one embodiment, the feed network 202 may be manufactured in component pieces that are then mechanically coupled together. As discussed above, the feed network 202 may comprise a plurality of symmetrical sections, forming a "tree-like" structure to couple each of the antenna elements 268 in the antenna array 106 to a single feed point. Thus, the structure of the feed network 202 may be conducive to separation into elements that can be individually manufactured and then coupled together. In one example, the feed network 202 is manufactured by casting metal into the required sections and then brazing the metal to finish it. The casting and brazing steps may be performed on sections of the feed network at a time, for example, sections that include four antenna elements. These finished pieces may then be coupled together to create the entire feed network 202. In another example, the antenna array, including the feed network 202 and the horn antenna elements 268, is arranged such that it is symmetrical along a center line taken along its length. Accordingly, in this example, the antenna array can be divided along this center line into two symmetrical sections, each of which can individually manufactured (e.g., by casting and brazing) and then coupled together. Dividing the antenna array 106 "longitudinally" may greatly shorten the manufacturing time, even though each of the two sections may be significantly more complex than the smaller four- element or similar sections that arise when the array is split as discussed above.

Satellite (or other communication) signals may be transmitted on two orthogonal wave fronts. This allows the satellite (or other information source) to transmit more information on the same frequencies and rely on polarization diversity to keep the signals from interfering. If the antenna array 106 is directly underneath or on a same meridian as the transmit antenna on the satellite (or other signal source 110), the receive antenna array and the transmit source antenna polarizations may be aligned. However, as discussed above, in some instances there may be a polarization skew between the antenna array 106 and the signal source 110 caused by the relative positions of the signal source 110 and the host platform of the antenna array 106. For example, for applications in which the antenna array 106 is mounted on an aircraft 132, the pitch, roll, yaw and spatial location (e.g., meridian or longitude) of the aircraft may result in a polarization skew β between the signal source 110 and the antenna array 106. Accordingly, in one embodiment, the external sub- system 102 includes a polarization converter unit that is adapted to compensate for polarization skew between the information source and the antenna array. Referring to FIG. 44, there is illustrated one example of the antenna array 106 including a polarization converter unit (PCU) 502 coupled thereto. As discussed above, in the illustrated example, the antenna array 106 is arranged such that PCU 502 fits "inside" the array. This arrangement may be advantageous in terms of maintaining a relatively small footprint and volume of the external sub-system 102; however, it is to be appreciated that the invention is not limited to the arrangement illustrated in FIG. 44, and the PCU 502 may be located in any suitable location on the external sub-system 102. In addition, in other embodiments, polarization skew compensation may be done purely electronically. Accordingly, the internal sub-system 104 may include electronics (circuitry and/or software) adapted to compensate for polarization skew β between the antenna array 106 and the signal source 110, and optionally also for any polarization skew between the vertical and horizontal component signals. In one example, the polarization converter unit 502, or other signal processing electronics, may be adapted to accommodate either or both of linearly polarized signals and circularly polarized signals. According to one embodiment, the PCU 502 may provide the polarization- corrected signal to a low noise amplifier 504 which amplifies the signal and feeds it to the internal sub-system 104. As discussed above, the bulk of the signal processing and control electronics of the communications system may be included in the internal sub-system 104 and housed within the host platform so as to protect it from environmental conditions. However, as known to those skilled in the art, in many applications it is desirable to have the low noise amplifier 504 as close to the antenna feed as possible for signal-to-noise considerations. Accordingly, in one embodiment, the low noise amplifier 504 is part of the external sub-system 102. In the example illustrated in the FIG. 44, the low noise amplifier is mounted to the PCU 502 such that it may receive the polarization-corrected signal from the PCU 502 directly, or over a very short path. The amplified signal from the low noise amplifier 504 may then be fed to the internal sub-system 104, as discussed further below.

Referring to FIG. 45, there is illustrated an exploded view of one example of a polarization converter unit (PCU) 502. As discussed above, the low noise amplifier (LNA) 504 may be mounted to the PCU 502. Accordingly, the PCU 502 may include a mount 506 for the low noise amplifier 504. In the illustrated example, the LNA 504 is a waveguide -based LNA, and the LNA mount 506 is a waveguide section that receives the polarization-corrected signal from the PCU 502 and feeds it to the waveguide-based LNA.

According to one embodiment, the PCU 502 includes a rotary orthomode transducer (OMT) 508 that is responsible for the polarization skew correction, as discussed further below. The rotary OMT 508 is mounted to a spine 510 along which runs a cable 512 for the PCU drive. On end 514 of the cable 512 is coupled to the rotary OMT 508, and the other end 516 is coupled to a master pulley 518. A motor 520 supplies the power to drive the master pulley 518 and pulley 522 to rotate the rotary OMT 508 using the cable 512. The motor 520 may be supported by a motor mount 524. In one embodiment, the two summed component signals, vertical and horizontal, from the feed point of the antenna array 106 are fed to first and second waveguide ports 526, 528 of the rotary OMT 508. The two waveguide ports 526, 538 are coupled to rotatable section 530 of the rotary OMT 508. The rotatable section 530 rotates the received electromagnetic fields to compensate for polarization skew β between the signal source 110 and the antenna array 106. A polarization encoder 532 may be used to determine a degree of rotation of the rotary OMT 508, corresponding to a desired polarization correction factor. In one example, the PCU 502 receives control signals from the antenna control unit 112 (see FIG. 1) that determine the required degree of rotation needed to correct for a measured/detected polarization skew. The resultant, polarization-corrected signal is fed via a waveguide section 534 to the low noise amplifier 504. In one example, the PCU 502 is rotatable up to approximately 270 degrees in either direction (clockwise or anticlockwise).

As discussed above, in one example, polarization skew compensation can be performed electronically. However, compensating for polarization skew β mechanically, using an embodiment of the PCU 502 discussed above, may have several advantages. For example, mechanical polarization skew compensation does not suffer from efficiency losses associated with converting an RF signal into an electronic signal (to be processed to compensate for the polarization skew) and back into an RF signal. In addition, the mechanical PCU 502 may be capable of handling very high power signals, particularly useful for compensating for polarization skew when the antenna array 106 is transmitting, whereas the electronics that may perform electronic polarization skew may require that the signals be relatively low power.

Still referring to FIG. 45, in one embodiment, for receive operation of the antenna array 106, the output of the rotary OMT 508 is coupled to the low noise amplifier 504. The amplified signal from the low noise amplifier 508 may be fed via cable 536 to a rotary joint 538 that couples the external sub-system 102 to the internal sub-system 104. For transmit operation of the antenna array 106, a signal to be transmitted by the antenna array may be fed via another rotary joint 538 and cable 540 directly to the rotary OMT 508. In one example, the rotary joints 538 are single channel rotary joints. The rotary joints 538 may be coupled to RF coaxial cables and/or flexible waveguide on the internal sub-system 104 side. The rotary joints 538 may accommodate rotation of the antenna array 106 in azimuth.

Referring to FIG. 46, there is illustrated an example of a low noise amplifier 504. The low noise amplifier 504 includes a waveguide port 542 that may be coupled to the rotary OMT 508. An output port 544 may be coupled to the cable 536 to take the amplified signal to the internal sub-system 104, as discussed above. In one example, the output port 544 is a coaxial port designed to mate with a coaxial cable. Power may be supplied to the low noise amplifier 504 (e.g., via the internal sub-system 104) through a power connector 546. Referring again to FIG. 1, in receive mode, the signal received and processed

(e.g., passed through the waveguide feed network 202, adjusted by the PCU 502 to compensate for polarization skew β, and amplified by the low noise amplifier 504) by the external sub-system 102 is fed to the internal sub-system 104. The following discussion of the operation of the internal sub-system 104 may refer primarily to the antenna array 106 receiving a signal from the signal source 110; however, those skilled in the art will recognize that any component may operate for reverse signal flow when the antenna array 106 is transmitting a signal.

Referring to FIG. 47, there is illustrated a block diagram of one example of an internal sub-system 104. As discussed above, the internal sub-system may include an antenna control unit 112 that provides control signals to some or all of the components of the internal and external sub-systems 104, 102, respectively. A high power transceiver 114 may receive the amplified signal from the low noise amplifier 504; that signal being referred to herein as the "received signal," and process the received signal as discussed further below. The high power transceiver may also receive a signal to be transmitted by the antenna array 106 from the modem 116, process that signal, and output a "transmit signal." The received signal and the transmit signal pass between the internal sub-system 104 and the external sub-system 104 via a connector 140. It is to be appreciated that the connector 140 may include the rotary joint(s) 538 as well as any intervening cables and other components between the rotary joint(s) 538 and the internal sub-system electronics. As illustrated in FIG. 47, in addition to the received and transmit signals on lines 142a and 142b, respectively, the connector 140 may also pass power (on line 144) from the power supply 118 and control signals (on line 146) from the antenna control unit 112 to components of the external sub-system 102.

According to one embodiment, the internal sub-system 104 comprises a down- converter unit (DCU) 148 that may receive input signals, e.g. the linearly or circularly polarized signals via the connector 140 and may provide output signals, e.g. linearly or circularly polarized signals, on lines 150, at a lower frequency than the frequency of the input signals received. The DCU 148 will be described in more detail below. The signals on line 150 may be processed by signal processing electronics 152. Similarly, in the transmit path, the internal sub-system 104 may include an up-converter unit 154. The transmit signal may be received by the internal sub-system 104 via connector 156 from a signal source, such as, for example, a passenger or user interface, processed by the signal processing electronics 152 and up-converted to the transmit frequency by the up-converter unit 154. As will be recognized by those skilled in the art, the up-converter unit 154 may operate in a similar manner to the down-converter unit 148, for example, by mixing the transmit signal with a local oscillator signal to change the frequency of the data signal, as discussed further below.

As discussed above, signals may be transmitted and/or received by the antenna array 106 over a wide range of frequencies extending up to several Gigahertz. For example, the vertical and horizontal component signals may be in a frequency range of approximately 10.7 GHz - 12.75 GHz. Therefore, in some applications, particularly where the antenna array 106 may be receiving and/or transmitting at very high frequencies, it may be preferable to perform the down-conversion or up-conversion using two local oscillators. Accordingly, in at least one embodiment, the internal sub-system 104 may optionally include a second local oscillator to converts the signal of interest to a frequency useable by the modem 116. It is to be appreciated that the signal processing may occur before any down or up conversion, in between different down/up conversion stages, or after all down/up conversion has been performed. In receive mode, the down- converted and processed signals may be supplied via modem 116 and connector 156 to the passenger interfaces (e.g., seatback displays) for access by passengers associated with the host vehicle. Similarly, in transmit mode, the signals to be processed, up-converted and transmitted may be received from the passenger interface(s) via connector 156.

Referring to FIG. 48, there is illustrated a functional block diagram of one embodiment of a down-converter unit (DCU) 148. It is to be appreciated that FIG. 48 is only intended to represent the functional implementation of the DCU 148, and not necessarily the physical implementation. Furthermore, the up-converter unit 154 and down-converter unit 158 may be implemented with a similar structure, as would be appreciated by those skilled in the art. In one example, the DCU 148 is constructed to take an RF signal, for example, in a frequency range of 10.7 GHz to 12.75 GHz and down- convert the 10.7 GHz to 11.7 GHz portion of the band to an intermediate frequency (IF) signal, for example, in a frequency range of 0.95 GHz to 1.95 GHz. A second local oscillator 158 is used to convert the 11.7 GHz to 12.75 GHz portion of the band to an IF of 1.1 GHz to 2.15 GHz.

Still referring to FIG. 48, according to one embodiment, the DCU 148 receives power from the power supply 118 (see FTG. 1) via line 162. According to one embodiment, DCU 148 receives an RF signal on line(s) 142a and may provide output IF signals on line(s) 166. As discussed above, the RF signal may supplied from the external sub-system 102 (e.g., from the low noise amplifier) via connector 140. In one example, directional couplers 168 are used to inject a built-in-test signal from local oscillator 170. A switch 172 that may be controlled, via a control interface 174, by the antenna control unit 112 (which provides control signals on line(s) 176 to the control interface 174) is used to control when the built-in-test signal is injected. A power divider 178 may be used to split a single signal from the local oscillator 70 and provide it to both paths. The through ports of the directional couplers 168 may be coupled to bandpass filters 180 that may be used to filter the received signals to remove any unwanted signal harmonics. As discussed above, the received signal may be split into two bands that are down-converted using the two local oscillators; therefore, as shown in FIG. 48, the DCU 148 may include two bandpass filters 180 to split the received signal into the two bands. The filtered signals may then be fed to mixers 182a, 182b. The mixer 182a may mix the signal with a local oscillator tone received on line 183 from local oscillator 184 to down-convert the first portion of the band to IF frequencies. Similarly, the second mixer 182b may mix the signal with a local oscillator tone received on line 160 from the second local oscillator 158 to down-convert the second portion of the band to IF frequencies. In one example, the second local oscillator 184 may be able to tune in frequency from 7 GHz to 8 GHz, thus allowing a wide range of operating and IF frequencies. Amplifiers 188 and/or attenuators 189 may be used to balance the IF signals. Filters 190 may be used to minimize undesired mixer products that may be present in the IF signals before the IF signals are provided on output lines 166.

Thus, the internal sub-system 104 may receive data, communication or other signals to be transmitted by the antenna array 106 from, for example, passenger interfaces within the host vehicle, may process these signals, and provide the transmit signal via connector 140 to the external subs-system 102. In the external sub-system 102, the polarization converter unit 502 may compensate for polarization skew β between the antenna array 106 and the desired destination of the transmit signal. The feed network 202 of the antenna array 106 may split the transmit signal into two orthogonally polarized component signals that are each split among all antenna elements 268 in the antenna array 106. Each antenna element 268 may include an OMT 402 that recombines the two orthogonal component signals into a signal that is transmitted by the antenna element 268. Similarly, the antenna array 106 may receive an information signal from a signal source via each antenna element 268 in the array. The feed network 202 may split the signal received at each antenna element 268 into two orthogonal component signals and sum the component signals, in each polarization, from all antenna elements to produce two orthogonal summed signals. These summed signals may be corrected for polarization skew β between the signal source 110 and the antenna array 106 and recombined into a received signal that is amplified by a low noise amplifier and passed, via connector 140 to the internal sub-system 104. In the internal sub-system 104, the received signal may be processed (e.g., down-converted) and supplied via connector 156 to passenger interfaces in the host vehicle. According to one embodiment, the internal sub-system is contained within a housing that is mounted in the interior of the host vehicle. An example of such a housing 192 is illustrated in FIG. 49. As discussed above, in some applications, particularly where the communication system is used on an aircraft, the exterior of the vehicle may be subjected to wide variations in temperature, pressure and humidity. Subjecting electronic components to such varying conditions may significantly shorten the life of the electronic components. By placing the electronic components within the vehicle, the components are protected from the potentially harsh environment outside of the vehicle. In addition, it may be easier to implement more effective thermal control of the components. Furthermore, locating the electronics inside the vehicle may allow easy access to the electronics for maintenance, repair and replacement. In one embodiment, the mounting bracket 214 may allow for ease of installation and removal of the external sub-system 102. The connector 140, which may include a rotary joint 538 as discussed above, may penetrate the surface of the host vehicle to allow cables to travel between the external subsystem 102 and the interior of the host vehicle. Thus, signals such as the information, control and power signals, may be provided to and from the external sub-system 102 and the internal sub-system 104.

Referring to FIG. 49, in one example, the housing 192 is a small, thin box that may be designed to fit between the airframe and insulation of the aircraft. The housing may include a fan 194 to cool the electronic components inside the housing. To facilitate thermal control of the electronics, airflow may be directed over the housing 192 to cool the housing and electronics therein. The housing may include connectors 196a and 196b to receive power from the host vehicle's power supply, and connector 196c (e.g., an Ethernet connector) to receive communications signals, for example, from passenger interfaces in the host vehicle. In one example, the internal sub-system includes a fault indicator to indicate when there is a malfunction in the internal sub-system 104. For example, the fault indicator may include a bi-color (e.g., white and black) flag, with one color being visible through the housing 192 at any given time. A first color (e.g., white) may indicate that the internal sub-system 104 is functioning within normal parameters, whereas the second color (e.g., black) may indicate a fault. In one example, the fault indicator is mechanically (e.g., magnetically) actuated such that it may operate even when power is not supplied to the internal sub- system 104.

As illustrated in FIGS. 1 and 47, in one embodiment, the high power transceiver 114, which may include a power amplifier (not shown) used in the transmit chain, is within the internal sub-system 104. It has been found that when the power amplifier is connected to the antenna array 106 via a cable, such as coaxial cable, significant loss can occur when the power amplifier is relatively far from the antenna array (i.e., the cable connecting them is long). However, as discussed above, in many applications it may be highly preferable to have the system electronics, including the power amplifier, inside the host vehicle (i.e., as part of the internal sub-system 104), which may result in a significant distance between the power amplifier and the antenna array 106. To address the issue of loss in the connection between the power amplifier and the antenna array 106, in one embodiment, the connector 140 includes a flexible waveguide that carries the transmit signal from the internal sub-system 104 (e.g., from the power amplifier) to the rotary joint 538. Flexible waveguide may be used to absorb connection tolerances and allow more flexibility in the placement of the waveguide and/or the internal sub-system housing 192. Waveguide is a low loss transmission medium. It has been found that by using a flexible waveguide connection, there is negligible degradation in the system performance resulting from the power amplifier being relatively far from the antenna array 106. In one example, a filter, such as a bandpass filter, is incorporated into the flexible waveguide connection element to filter out unwanted frequency components from the transmit signal. Thus, a single, easily replaceable element that includes both filtering components and transmission line for connecting the high power transceiver 114 to the antenna array 106 may be provided. Accordingly, replacing this single element may allow changing the bandpass filter, and thus making changes to the frequency band of operation of the system, without a need to change the internal sub-system 104. In addition, because the waveguide is a lower loss transmission medium than coaxial cable, the transmit signal may be lower power (because it experiences less loss on the path to the antenna array), thereby reducing the power consumption of the communications system. In addition, it is to be appreciated that a similar flexible waveguide connection element, optionally including filtering components, may be used in the receive chain to couple the transceiver 114 to the rotary joint 538 connecting to the low noise amplifier 504.

The pointing accuracy of the antenna array 106 (i.e., how accurately the antenna array can be aimed at the signal source 110 or signal destination) may be a critical performance metric for the communications system. However, particularly where the communications system is mounted on a vehicle, such as aircraft 132, there are numerous conditions (e.g., shape and available mounting locations, environmental factors and mechanical tolerances) that can adversely affect the pointing accuracy if not accounted for. Accordingly, in one embodiment, a calibration procedure is used to correct for mechanical tolerances in the antenna array and structural tolerances in the host vehicle, and to automatically detect and adjust for replacement of components, as discussed further below. In one example, the calibration procedure may account for positional offsets and biases in the external sub-system relative to the vehicle's navigational system. The following discussion will assume that the vehicle is an aircraft, and refer to the aircraft's inertial navigation system 122; however, it is to be appreciated that the calibration procedure may be applied regardless of the type of vehicle on which the system is installed.

Referring to FIG. 50, there is illustrated a flow diagram of one example of a calibration procedure. A first stage in the calibration procedure may include a factory calibration stage 602. This stage 602 may be performed before the communication system is installed on a vehicle. In one example, the antenna array 106 includes with one or more position encoders (also referred to as "tilt sensors"), mounted directly on the antenna array, that sense a pointing position of the antenna array in azimuth and elevation. In one example, the position encoders provide data representative of the pitch and roll of the antenna array 106. During operation of the system, information from the position encoders may be fed back to the antenna control unit 112 (See FIG. 1) to assist the antenna control unit 112 in providing control signals to the motors (and associated motor drives) to point the antenna array 106 at a desired angle in azimuth and elevation. Therefore, in one embodiment, the factory calibration stage 602 includes a procedure to locate the RF center of the antenna array 106 relative to the locations of the position encoders (step 604). This procedure may account for any offset in position between the RF center of the antenna array 106 and the location of the encoders, allowing the encoders to be located at any convenient location on the array. In addition, variations in the position encoder data over temperature may also be calibrated. The calculated offsets may be stored (step 606) in the memory device 130 (See FIG. 1) that may be accessed by the antenna control unit 112 during further calibration and/or operation of the communication system. In one example, the information stored in the memory device 130 includes the position encoder calibration data (e.g., temperature variations etc.), mechanical calibration and correction data (e.g., offset between antenna array and position encoders), as discussed above, as well as normal operating parameters and limits, and (optionally) serial number and/or part number data for the external sub-system 102 as a whole or for individual components thereof (e.g., for the antenna array 106 or PCU 502). Mechanical calibration data may accounts for all geometric variables between the RF center of the antenna array 106 and the mounting and gimbal assemblies. The serial number and/or part number information may be used for automatic detection of (and correction for) part replacement, as discussed further below. Data storage in the memory device 130 allows individual characteristics of each external sub-system 102 to be determined and stored during factory manufacture and calibration 602.

In one embodiment, the communication system includes two memory devices, one memory device 130 located in the external sub-system 102 and the other in the internal sub-system 104. The memory device 130 in the external sub-system 102 is referred to herein as the antenna memory 130, and the memory device in the internal sub-system is referred to herein as the antenna control memory. It is to be appreciated that the antenna control memory may be incorporated as part of the antenna control unit 112 or may be a separate device (not shown in FIG. 1) communicatively coupled to the antenna control unit 112. The memories may be any type of suitable electronic memory including, but not limited to, random access memory or flash memory, as known to those skilled in the art. The antenna memory 130 and the antenna control memory may be communicatively coupled to one another to allow data transfer between the two memories. This data sharing between the antenna memory 130 and the antenna control memory may provide a complete data set for the communication system which may be used, for example, to detect and execute initial installation calibration procedures (discussed below), to detect replacement of various components of the communication system or of external components (such as the aircraft's inertial navigation system), and to recalculate system data set items as required by part replacements, as discussed further below.

In one embodiment, the calibration data, such as the offsets calculated above, may be stored in both the antenna memory 130 and the antenna control memory. Any changes or updates to the calibration memory may similarly be stored in both memories. This dual-memory structure may provide several advantages, including redundancy of the data (i.e., if one memory is damaged, the data will not be lost as it is also stored in the second memory) and the ability to "swap out" either the external or internal sub-systems (or components thereof) and replace them with new/updated components without having to redo the factory calibration. For example, if the internal sub-system were to be replaced, the new antenna control memory may download the calibration data stored in the antenna memory 130, thereby avoiding the need to recalibrate the system.

Referring again to FIG. 50, after factory calibration 602, the communications system may be installed on the host vehicle. Thus, a second stage of calibration may include an installation calibration 608. As discussed further below, the installation calibration procedure 608 may account for offsets and tolerances between the mounted antenna array 106 and the aircraft's inertial navigation system 122 and make installation of the external sub-system far simpler than conventional procedures.

Generally vehicles, including aircraft, do not have large flat surfaces upon which the external sub-system 102 can be mounted, but rather the surfaces may have some slant or curvature. Accordingly, when the external sub-system is mounted on such a surface, there will be some offset of the antenna array from level. Furthermore, given that it may be unlikely that the antenna array will be mounted very close to the aircraft' s inertial navigation system sensors, there may also be an offset between the antenna array 106 and the inertial navigation system 122. The installation calibration procedure 608 may account for these offsets, as discussed further below. Conventional installation procedures may allow the external sub-system 102 may be accurately placed to within a few tenths of a degree to the know biases of the aircraft's inertial navigation system 122. However, if not compensated for, even this few tenths of a degree can cause the antenna array to not point at the satellite accurately enough for the onboard receivers to lock on the signal using only a pointing calculation, and thus may result in loss of signal for the passenger. Furthermore, accurate placement of the external sub-system 102 on the vehicle may be difficult and time-consuming. It may therefore be preferable to use an installation calibration procedure 608 that obviates the need for accurate placement of the external sub-system on the vehicle.

As discussed above, the external sub-system 102 may include one or more position encoders that may sense a pitch and roll of the antenna array 106 once it is installed on the vehicle. In one example, the pitch and roll of the antenna array may be calculated relative to the pitch and roll of the on-board inertial navigational system 122 (step 610). In one example, step 610 includes using on-board parameters to measure offsets between the antenna array frame-of-reference (measured by the position encoders and corrected using the stored factory calibration data) and the aircraft frame-of reference (measured using the inertial navigation system 122). This allows determination of pitch and roll offsets without time-consuming manual calibration and removes aircraft manufacturing tolerances. In addition, because all pitch and roll offsets can be accounted for by the calibration, there is no need to accurately place the external sub-system 102 on the aircraft. Rather, the error between the antenna array alignment and inertial navigational system alignment is simply stored in memory devices and compensated for by the antenna control unit 112 when it supplies pointing control signals to the antenna array 106. Thus, the installation calibration 608 may greatly improve the ease of installation of the system. Conventional antenna alignment processes are typically only performed during initial antenna system installation and are done by manual processes. Conventional manual processes usually do not have the ability to input delta roll, delta pitch and delta yaw numbers, so the manual process requires the use of shims. These shims are small sheets of filler material, for example aluminum shims, that are positioned between the attachment base of the antenna and the aircraft, for example, to force the antenna system coordinates to agree with the navigation system coordinates. However, the use of shims requires the removal of the radome, the placement of shims and the reinstallation of the radome. This is a very time consuming and dangerous approach. Only limited people are authorized to work on top of the aircraft and it requires a significant amount of staging. Once the alignment is completed the radome has to be reattached and the radome seal cured for several hours. This manual alignment process can be very time-consuming and difficult. By contrast, the automatic installation calibration procedure 608 may be performed quickly and easily without the need to move the antenna array.

Referring again to FTG. 50, after the pitch and roll offsets have been calculated by comparing the (corrected) data from the position encoders and data from the inertial navigation system 122, and stored (step 610), the heading offset may be calculated using a satellite signal lock (step 612). In one example, step 610 may include instructing the antenna control unit 112 to point the antenna array 106 at a known satellite to check heading alignment of the antenna array 106 with the navigational system 112. When this alignment check is requested, the antenna control unit 112 may initially use the inertial navigation data to point at the chosen satellite. Initially, i.e., when the antenna array 106 has not been aligned or calibrated for heading offsets, the system may start scanning the area to look for a peak received signal. The peak may be determined when the system has located the highest signal strength. The error between the antenna's pointing heading (determined using the position encoders, for example) and the heading indicated by the navigational system may be calculated and recorded in the memory devices, as discussed above. Because the pitch and roll offsets may already have been determined (step 610) and compensated for, the heading offset may be calculated using a single satellite. Thus, the installation calibration procedure 608 may be used to easily and automatically account for any bias or offset between the antenna array 106 and the aircraft's inertial navigational system 122. This allows the antenna control unit 112 (See FIG. 1) to receive navigational information from the inertial navigational system 122 of the vehicle and use the navigational information to accurately point the antenna array 106, without errors resulting from offset between the inertial navigational system 122 and the antenna array 106. According to one embodiment, installation calibration procedure 608 may be implemented with software running on or under control of the antenna control unit 112. The installation calibration data may also be stored in both the antenna memory 130 and the antenna control memory. As discussed above, in one embodiment, the communication system is capable of automatically detecting replacement of various system components and adjusting for this replacement through the communication between the antenna memory 130 and the antenna control memory. In one example, at power-up, each of the antenna memory 130 and the antenna control memory may query the other to determine whether either memory device is new, using the shared and locally stored data. By comparing the existing data with any new data provided by the new memory device, the system can automatically calculate compensations for the potentially different tolerances and parameters of the new component identified by the new memory device. At each power-up, the system may determine whether conditions exist to re-evaluate the current calibration offsets. If such conditions exist, then the system may evaluate whether the current offsets remain valid. This provides for detection and correction of any airframe changes including replacement of the inertial navigation system 122. In addition, tracking updates during flight may address any slow drift from the inertial navigation system 122 and/or airframe mechanical changes as might be caused by hull pressurization and temperature effects.

In some applications, even after precise calibration, navigational data alone may be insufficient to keep the antenna array locked to a desired source within acceptable tolerance levels. Therefore, according to one embodiment, the antenna control unit 112 may implement a tracking algorithm that may use both navigational data and signal feedback data to track a signal source. The tracking algorithm may always be looking for the strongest satellite signal, thus if the inertial navigation data is slow, the tracking algorithm may take over to find the optimum pointing angle. When the inertial navigation data is accurate and up to date, the system may use the inertial data to compute its azimuth and elevation angles since this data will coincide with the peak of the beam. This is because the inertial navigation system coordinates may accurately point the antenna, without measurable error, at the intended satellite; that is, predicted look angles and optimum look angles will be identical. When the inertial navigation data is not accurate the tracking software may be used to maintain the pointing as it inherently can "correct" differences between the calculated look angles and optimum look angles up to about 5 degrees. In one embodiment, the antenna array may be controlled to locate a peak of a desired signal from the information source. The antenna array may then be "dithered" about the signal peak to determine the beam width of the source signal (relative to the beam width of the antenna array). In one example, the antenna control unit 112 may monitor the amplitude of the received signal may use the amplitude of the received signal to determine the optimum azimuth and elevation pointing angle by discretely repositioning the antenna from its calculated position to slight offset positions and determining if the signal received strength is optimized, and if not repositioning the antenna orientation in the optimized direction, and so forth. As known to those experienced in the art, geometric calculations can be easily used to determine look angles to geostationary satellites from known coordinates, including those from aircraft. By locating and tracking three satellites, triangulation data can be used to further refine any biases between the antenna array look directions and the navigational system data. The refined error may then be stored in the antenna control memory and antenna memory 130 and used to facilitate accurate tracking of a desired signal source 110 during operation of the system.

Referring again to FTG. 48, in one example to implement the tracking algorithm, the antenna control unit 112 may sample the received signal from, for example, the DCU 148 (on line 166), although it is to be appreciated that the antenna control unit 112 may alternatively sample the signal from the signal processing electronics 152 or second DCU 158. Thus, although the following discussion will refer to the signal from the DCU 148 being sampled, it is to be appreciated that the invention is not so limited. According to one embodiment, the control interface 174 of the DCU 148 may sample the signal on line 166 and may provide a signal to the antenna control unit 112 via line 176. It is to be appreciated that the sampling may require components such as, for example, directional couplers, an RF detector and analog-to-digital converter (not shown) to take the IF signal from lines 166 and convert it to information to be supplied to the antenna control unit 112. The antenna control unit 112 may use the amplitude of the sampled signal to adjust the pointing angle of the antenna array, similar to the dithering discussed above as part of a continuing calibration procedure. The tracking/in-flight calibration procedure may also be used to update offsets in-flight to address in-flight changes and slow drift of aircraft components. Having thus described several aspects of at least one embodiment, it is to be appreciated various alterations, modifications, and improvements will readily occur to those skilled in the art. Such alterations, modifications, and improvements are intended to be part of this disclosure and are intended to be within the scope of the invention. Accordingly, the foregoing description and drawings are by way of example only.

Claims

1. An antenna array comprising: a plurality of horn antenna elements; a corresponding plurality of dielectric lenses, each dielectric lens of the plurality of dielectric lenses being coupled to a respective horn antenna element of the plurality of horn antenna elements; and a waveguide feed network coupling the plurality of horn antenna elements to a common feed point; wherein the plurality of horn antenna elements and corresponding plurality of dielectric lenses are shaped and sized such that the antenna array is tapered at either end of the antenna array.

2. The antenna array as claimed in claim 100, wherein the plurality of horn antenna elements are arranged in two parallel rows, and wherein the two parallel rows are offset from one another along the length of the antenna array by one half the width of one of the plurality of horn antenna elements.

3. The antenna array as claimed in one of claims 1 and 2, wherein the plurality of horn antenna elements includes an interior horn antenna element, a third horn antenna element, a second horn antenna element, and an end horn antenna element; wherein the third horn antenna element is smaller than the interior horn antenna element and is located closer to an end of the antenna array than the interior horn antenna element; wherein the second horn antenna element is smaller than the third horn antenna element and is located closer to the end of the antenna array than the third horn antenna element; and wherein the end horn antenna element is smaller than the second horn antenna element and is located at the end of the antenna array.

4. The antenna array as claimed in claim 3, wherein the plurality of dielectric lenses elements includes an interior dielectric lens, a third dielectric lens, a second dielectric lens, and an end dielectric lens; wherein the interior dielectric lens is coupled to the interior horn antenna element; wherein the third dielectric lens is smaller than the interior dielectric lens and is coupled to the third horn antenna element; wherein the second dielectric lens is smaller than the third dielectric lens and is coupled to the second horn antenna element; and wherein the end dielectric lens is smaller than the second dielectric lens and is coupled to the end horn antenna element.

5. The antenna array as claimed in one of claims 3 and 4, further comprising a plurality of horn inserts, each one of the plurality of horn inserts being located within a respective one of the plurality of horn antenna elements.

6. The antenna array as claimed in claim 5, wherein the horn inserts located within the end horn antenna element and the second horn antenna elements are made of a radar absorbent material.

7. The antenna array as claimed in any one of claims 1-5, wherein each dielectric lens is fastened to the respective horn antenna element with a fiberglass pin.

8. A method of calibrating a vehicle-mounted antenna array; the method comprising: determining an RF center of a beam pattern of the antenna relative to a location of a position encoder mounted on the antenna array; calculating a first pitch offset and a first roll offset of the antenna array relative to the location of the position encoder; and storing the calculated first pitch and roll offsets in a local memory device.

9. The method as claimed in claim 8, further comprising: receiving data representative of a vehicle pitch and vehicle roll of a host vehicle upon which the antenna array is mounted; sensing with the position encoder, an antenna pitch and antenna roll; calculating an second pitch offset between the vehicle pitch and the antenna pitch; calculating a second roll offset between the vehicle roll and the antenna roll; and storing the calculated second pitch and roll offsets in the local memory device.

10. The method as claimed in claim 9, further comprising storing the calculated second pitch and roll offsets in a remote memory device.

11. The method as claimed in one of claims 9 and 10, further comprising: correcting the second pitch and roll offsets based on the first pitch and roll offsets; and storing the corrected second pitch and roll offsets in the local memory device.

12. The method as claimed in claim 11, further comprising storing the corrected second pitch and roll offsets in the remote memory device.

13. The method as claimed in one of claims 10-12, further comprising: receiving data representative of a vehicle heading of the host vehicle; pointing the antenna array at a selected satellite signal source; determining an antenna heading based on a signal lock with the selected satellite signal source; calculating a heading offset between the vehicle heading and the antenna heading; and storing the heading offset in the local memory device.

14. The method as claimed in claim 13, further comprising storing the heading offset in the remote memory device.

15. The method as claimed in any one of claims 9-14, wherein receiving data representative of the vehicle pitch and vehicle roll of the host vehicle includes receiving the date from a navigation system in the host vehicle.

16. A communications system comprising: an first sub-system comprising an antenna array configured to receive and transmit signals, a gimbal assembly configured to mount the antenna array a host platform and to move the antenna array in azimuth and elevation, a first memory device, and at least one position encoder mounted to the antenna array; a second sub-system communicatively coupled to the first sub-system and comprising a second memory device, and a control unit configured to control movement of the antenna array in azimuth and elevation; wherein the at least one position encoder is configured to detect a pitch and roll of the antenna array relative to a factory-calibrated level position of the antenna array and to provide a first antenna data signal representative of the detected pitch and roll of the antenna array; wherein the first and second memory devices are communicatively coupled together and are configured to receive and store the antenna data signal.

17. The communications system as claimed in claim 16, wherein the first and second memory devices are further configured to store identifying information about the first and second sub-systems.

18. A vehicle-mounted communications system comprising: an external sub-system mounted to an exterior surface of the vehicle, the external sub-system comprising an antenna array configured to receive and transmit signals, a gimbal assembly configured to mount the antenna array to the vehicle and to move the antenna array in azimuth and elevation, a local memory device, and at least one position encoder mounted to the antenna array; and an internal sub-system communicatively coupled to the first sub-system and comprising a control memory device, and a control unit configured to control movement of the antenna array in azimuth and elevation; wherein the control unit is configured to receive data representative of a pitch and roll of the vehicle upon which the antenna array is mounted; wherein the position encoder is configured to sense a pitch and roll of the antenna array; wherein the control unit is configured to calculate a pitch offset between the pitch of the vehicle and the pitch of the antenna and a roll offset between the roll of the vehicle and the roll of the antenna; and wherein the control memory device is configured to store the calculated pitch and roll offsets.

19. The vehicle-mounted communications system as claimed in claim 18, wherein the local memory device is configured to store the calculated pitch and roll offsets.

20. The vehicle-mounted communications system as claimed in claim 19, wherein the local and control memory devices are further configured to store identifying information about the internal and external sub-systems.

21. A communications system comprising: an antenna array including a plurality of antenna elements each adapted to receive an information signal from a signal source, and a feed network coupling the plurality of antenna elements to a common feed point; and a polarization converter unit coupled to the common feed point, the polarization converter unit configured to compensate for polarization skew between the antenna array and the signal source; wherein the polarization converter unit comprises: a rotary orthomode transducer configured to receive two orthogonally polarized component signals making up the information signal and to provide a polarization-corrected output signal; a drive system coupled to the rotary orthomode transducer configured to receive a control signal representative of a desired degree of rotation of the rotary orthomode transducer; and a motor configured to provide power to the drive system to rotate the rotary orthomode transducer to the desired degree of rotation.

22. The communications system as claimed in claim 21, wherein the polarization converted unit is mounted to the antenna array.

23. The communications system as claimed in claim 22, wherein the plurality of antenna elements and the feed network are arranged to provide a cavity between the feed network and the plurality of antenna elements; and wherein the polarization converter unit is mounted at least partially within the cavity.

24. The communications system as claimed in any one of claims 21-23, wherein the plurality of antenna elements are horn antenna elements; and wherein the feed network is a waveguide feed network.

25. An antenna array comprising: a plurality of horn antenna elements; a corresponding plurality of dielectric lenses, each dielectric lens of the plurality of dielectric lenses being coupled to a respective horn antenna element of the plurality of horn antenna elements; and a waveguide feed network coupling the plurality of horn antenna elements to a common feed point; wherein each dielectric lens is a plano-convex lens having a planar side and an opposing convex side; wherein each dielectric lens comprises a plurality of impedance matching features formed proximate an interior surface of the convex side; and wherein an exterior surface of the convex side is smooth.

26. The antenna array as claimed in claim 25, wherein the plurality of impedance matching features includes a plurality of hollow tubes.

27. The antenna array as claimed in one of claims 25 and 26, wherein each dielectric lens further comprises a plurality of impedance matching grooves extending from a surface of the planar side into an interior of the dielectric lens.

28. The antenna array as claimed in any one of claims 25-27, wherein the plurality of dielectric lenses comprise a cross-linked polystyrene material.

29. The antenna array as claimed in any one of claims 25-27, wherein the plurality of dielectric lenses comprise Rexolite™.

30. An antenna array comprising: a plurality of horn antenna elements configured to receive an information signal; a corresponding plurality of orthomode transducers, each respective orthomode transducer coupled to a respective horn antenna element and configured to split the information signal into a first component signal and second component signal, the first and second component signals being orthogonally polarized; a waveguide feed network coupling the plurality of orthomode transducers to a common feed point, the waveguide feed network configured to sum the component signals from each orthomode transducer in both the E-plane and the H-plane.

31. The antenna array as claimed in claim 30, wherein the waveguide feed network comprises a first path to guide the first component signal and a second path to guide the second component signal; wherein the first path sums in the E-plane the first component signals received from each orthomode transducer; wherein the second path sums in the H-plane the second component signals received from each orthomode transducer; and wherein the waveguide feed network is configured to provide at the common feed point a first summed component signal and a second summed component signal.

32. The antenna array as claimed in one of claims 30 and 31, wherein the plurality of orthomode transducers comprises a first orthomode transducer coupled to a first horn antenna element and a orthomode transducer coupled to a second horn antenna element; wherein the waveguide feed network includes a waveguide T-junction having a first input configured to receive the first component signal from the first orthomode transducer and a second input configured to receive the first component signal from the second orthomode transducer, and an output configured to provide an output signal corresponding to a weighted sum of the two first component signals; and wherein the waveguide T-junction comprises a tuning element configured to bias the waveguide T-junction to produce the weighted sum of the two first component signals.

33. A communications system mountable on a vehicle, the communications system comprising: an external sub-system, mountable on an exterior surface of the vehicle, comprising an antenna array configured to receive and transmit information signals, and a gimbal assembly configured to mount the antenna array to the exterior surface of the vehicle and to move the antenna array in azimuth and elevation; an internal sub-system, mountable within the vehicle, comprising a control unit and a transceiver, the internal sub-system communicatively coupled to the external sub-system and configured to provide power and control signals to the external sub-system; wherein the control unit is configured to provide the control signals to the gimbal assembly to control the movement of the antenna array in azimuth and elevation; wherein gimbal assembly comprises a mounting bracket configured to mount the external sub- system to the exterior surface of the vehicle, and an antenna mounting bracket configured to mount the antenna array to the gimbal assembly.

34. The communications system as claimed in claim 33, wherein the mounting bracket comprises a central portion and four feet connected to the central portion by four corresponding arm portions; and wherein each of the four feet is positioned outside of a rotational sweep of the antenna array.

35. The communications system as claimed in claim 34, further comprising a rotary joint positioned inside the central portion of the mounting bracket, the rotary joint coupling the external sub-system to the internal sub-system.

36. The communications system as claimed in any one of claims 33-35, wherein the antenna mounting bracket grips the antenna array at two locations along the length of the antenna array, neither point being at an end of the antenna array.

36. The communications system as claimed in any one of claims 33-36, wherein the gimbal assembly further comprises an elevation drive assembly configured to receive a control signal from the control unit and to rotate the antenna array in elevation responsive to the control signal.

37. The communications system as claimed in claim 36, wherein the elevation drive assembly includes a push-pull pulley system.

38. The communications system as claimed in any one of claims 33-37, wherein the gimbal assembly further comprises a polarization converter unit mounted to the antenna array and configured to move the antenna array in polarization responsive to a polarization control signal received from the control unit.