Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01Q—ANTENNAS, i.e. RADIO AERIALS
  • H01Q19/00—Combinations of primary active antenna elements and units with secondary devices, e.g. with quasi-optical devices, for giving the antenna a desired directional characteristic
  • H01Q19/10—Combinations of primary active antenna elements and units with secondary devices, e.g. with quasi-optical devices, for giving the antenna a desired directional characteristic using reflecting surfaces
  • H01Q19/18—Combinations of primary active antenna elements and units with secondary devices, e.g. with quasi-optical devices, for giving the antenna a desired directional characteristic using reflecting surfaces having two or more spaced reflecting surfaces
  • H01Q19/19—Combinations of primary active antenna elements and units with secondary devices, e.g. with quasi-optical devices, for giving the antenna a desired directional characteristic using reflecting surfaces having two or more spaced reflecting surfaces comprising one main concave reflecting surface associated with an auxiliary reflecting surface
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01Q—ANTENNAS, i.e. RADIO AERIALS
  • H01Q1/00—Details of, or arrangements associated with, antennas
  • H01Q1/27—Adaptation for use in or on movable bodies
  • H01Q1/28—Adaptation for use in or on aircraft, missiles, satellites, or balloons
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01Q—ANTENNAS, i.e. RADIO AERIALS
  • H01Q3/00—Arrangements for changing or varying the orientation or the shape of the directional pattern of the waves radiated from an antenna or antenna system
  • H01Q3/02—Arrangements for changing or varying the orientation or the shape of the directional pattern of the waves radiated from an antenna or antenna system using mechanical movement of antenna or antenna system as a whole
  • H01Q3/04—Arrangements for changing or varying the orientation or the shape of the directional pattern of the waves radiated from an antenna or antenna system using mechanical movement of antenna or antenna system as a whole for varying one co-ordinate of the orientation

Definitions

• the present system relates to antenna systems, and more particularly to a method and apparatus for mounting a reflector antenna in such a manner as to minimize the swept arc of the antenna when the antenna is rotated about its azimuth axis.
• BACKGROUND OF THE INVENTION [0003]
• the frontal surface area of an antenna mounted on an aircraft, under a radome, is of critical importance with respect to the aerodynamics of the aircraft. This is because of the drag created by the radome and the resulting effects on aircraft performance and fuel consumption. With reflector antennas that must be rotated about their azimuth axes, the "swept arc" of the antenna is larger than the overall width of the main reflector of the antenna.
• the diameter of the swept arc produced by the main reflector is considerably larger than the diameter of the main reflector itself when the azimuth axis of rotation is located at, or rearward of, the center of the main reflector. [0005] It is therefore extremely important that the height and width of a reflector antenna be held to the minimum dimensions consistent with the required electromagnetic performance of the antenna. More particularly, it is important for the main reflector of an antenna intended to be mounted on an outer surface of an aircraft, to be mounted in such a manner that the swept arc of the antenna is minimized when the antenna is rotated about its azimuth axis. Minimizing the swept arc of the antenna would thus minimize the dimensions of the radome required to cover the antenna, and thereby minimize the corresponding drag created by the radome while an aircraft on which the radome is mounted is in flight.
• the antenna system generally comprises a main reflector which is mounted on a mounting platform.
• the mounting platform is rotatable about an azimuth axis to allow the azimuth scanning angle of the antenna to be adjusted as needed.
• An azimuth motor is used for rotating the platform as needed to aim the main reflector in accordance with the desired azimuth scanning angle.
• a principal feature is that the azimuth axis about which the main reflector is rotated is disposed forward of the vertex of the main reflector, rather than at, or rearward of, the vertex of the main reflector.
• the azimuth axis is located at a point within a plane bisecting the outermost edges of the main reflector. In another preferred embodiment, the azimuth axis is located forward of the outermost edges of the main reflector. With either arrangement, the swept arc of the main reflector is reduced from that which would otherwise be produced if the azimuth axis was located in a plane coincident with the vertex of the main reflector, or rearward of the vertex of the main reflector. The maximum reduction in swept arc is provided by locating the azimuth axis within the plane bisecting between the outermost ends of the main reflector.
• the antenna system has the azimuth axis of rotation placed between the feed horn and the subreflector.
• the antenna system has the azimuth axis of rotation placed between the vertex of the main reflector and the subreflector.
• Each of these embodiments reduce the swept arc of the main reflector over that which would be produced with the azimuth axis of rotation positioned rearward of the main reflector, while still providing extremely compact arrangements that are well suited for use on a high speed mobile platform, where the antenna system needs to be housed within a radome.
• Figure 1 is a simplified diagram of the swept arc produced by a prior art mounting arrangement wherein the azimuth axis of rotation of the main reflector is disposed slightly rearward of the center of the main reflector;
• Figure 2 is a plan view of a prior art reflector antenna;
• Figure 3 is a side view of an antenna system in accordance with a preferred embodiment of the present system illustrating the azimuth axis located within a plane extending between the outermost edges of the main reflector of the antenna;
• Figure 4 is a diagram illustrating the reduced diameter of a swept arc produced by locating the azimuth axis of rotation as shown in Figure 3;
• Figure 5 is a side view of the antenna system of the present invention located with the azimuth axis disposed in a plane located forward of the outermost edges of
• the following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the system, its application, or uses.
• the antenna system 10 includes a main reflector 12 having a center (i.e., vertex) 12a and outermost edge portions 12b.
• a subreflector 14 is positioned forward of a feedhom 16 located at the center 12a of the main reflector 12.
• a pair of low noise amplifiers (LNA) 18 and 20 are used, as are a pair of diplexers 22 and 24, for performing signal conditioning operations on the received and transmitted signals.
• An elevation motor 26 is used to position the main reflector 12 at a desired elevation angle, while an azimuth motor 28 is used to rotate the main reflector 12 about an azimuth axis to position the main reflector at a desired azimuth angle.
• An encoder 30 is used to track the azimuth angle of the main reflector 12 and to provide feedback to the azimuth motor 28.
• the antenna system 100 is similar to antenna system 10 by the use of a main reflector 102 having an axial center (i.e., vertex) 102a and outermost lateral edge portions 102b.
• a feedhorn 104 is disposed at the center 102a of the main reflector 102.
• the main reflector 102 is supported on a platform 106 which places the azimuth axis of rotation 108 of the main reflector 102 in a plane which extends through the outermost edges 102b of the main reflector.
• the platform 106 is rotated about the azimuth axis of rotation 108 by an azimuth motor 110 to thus position the main reflector 102 at a desired azimuth angle.
• a two channel coaxial rotary joint 112 is preferably employed to enable the necessary electrical connections between the feedhom 104 and a transmission line 112a which extends through an outer surface 114 of an aircraft.
• the radome which would ordinarily enclose the entire antenna system 100 has not been shown.
• a swept arc 116 is shown which is produced by rotational movement of the main reflector 102, shown in highly simplified form, of the antenna system 100.
• the azimuth axis of rotation 108 is located such that it extends through the outermost lateral edges 102b of the main reflector 102, as described in connection with Figure 3, the radius of the swept arc 116 is minimized to the maximum extent.
• the swept arc 116 is approximately one-half that of the overall length 118 of the reflector 102.
• locating the azimuth axis of rotation 108 forward of the center (i.e., vertex) 102a of the main reflector 102 i.e., to the right of center point 102a in Figure 3 dramatically reduces the swept arc produced by the main reflector.
• This reduction in the overall area, and volume, of the swept arc is also visible from a comparison of Figures 1 arid 4.
• the location of the azimuth axis of rotation of the antenna system 100 shown in Figure 3, however, in some applications, may result in an unacceptable degree of blockage of the signal being transmitted and/or received by the antenna system 100.
• FIG. 5 Antenna system 200 shown in Figure 5 is identical with antenna system 100 shown in Figure 3 with the exception that mounting platform 206 has a longer overall length to allow the azimuth axis of rotation 108 to be located forward (i.e., to the right in Figure 5) of the outermost edges 202b of the main reflector 202. It will also be appreciated that components of the antenna system 200 in common with those of antenna system 100 have been designated by reference numerals increased by a factor of 100 over those used to denote the components of the antenna system 100.
• the swept arc produced by the antenna system 200 is shown in Figure 6.
• the swept arc is designated by dashed circle 220.
• the maximum, effective frontal width of the main reflector 202 is thus represented by arrow 222, which is only slightly larger than a diameter 226 of the main reflector.
• the radius of rotation of the reflector 202 is represented by line 224.
• Antenna 300 is identical in construction to the antennas 100 and 200 and forms a Cassegrain antenna having a main reflector 302 in the shape of a dish, a feedhorn 304, a subreflector 305, and a platform 306 supporting the main reflector.
• the subreflector 305 is supported in front of the feedhorn 304, and from the main reflector 302, by a support structure 307.
• the subreflector 305 is disposed within a plane residing in between the feedhorn 304 and outermost edge 302b of the main reflector 302.
• the platform is supported for rotation in the azimuth plane about an azimuth axis of rotation 308 by a suitable motor 310.
• a coaxial rotary joint 312 is coupled to a transmission line 312a.
• Transmission line 312a may comprise a coaxial cable or any other suitable electrical conductor(s).
• the antenna 300 differs from antennas 100 and 200 in that the azimuth axis of rotation is disposed forward of a vertex 302a of the main reflector 302, but rearward of outermost edge 302b of the main reflector.
• the azimuth axis of rotation is disposed in between the subreflector 305 and the feedhorn 304.
• This placement of the azimuth axis 308 provides a degree of reduction in the diameter of the swept arc of the main reflector 302 over that which would be produced by locating the azimuth axis at the vertex 302a, but not to the same degree as locating the azimuth axis 302a at the outermost edge 302b.
• Figure 8 shows another embodiment of the antenna system 300'. The components corresponding to those of Figure 7 are denoted with common reference numerals that also have a prime symbol .
• the antenna system 300' is identical in construction to the antenna system 300 with the only difference being that the azimuth axis of rotation 308' is located in a plane residing in between the outermost edge 302b' of the main reflector 302' and the subreflector 305'. Both of the antennas 300 and 300' reduce the swept arc beyond that of the prior art antenna shown in Figure 1. [0027]
• the preferred embodiments of the present system thus provide a means for supporting a reflector antenna in a manner which minimizes the effective frontal area of the reflector antenna, and thus allows a radome having a smaller frontal area to be employed in covering the antenna when the antenna is located on an outer surface of an aircraft.

Landscapes

• Physics & Mathematics (AREA)
• Engineering & Computer Science (AREA)
• Astronomy & Astrophysics (AREA)
• Aviation & Aerospace Engineering (AREA)
• General Physics & Mathematics (AREA)
• Remote Sensing (AREA)
• Aerials With Secondary Devices (AREA)
• Variable-Direction Aerials And Aerial Arrays (AREA)

Priority Applications (4)

Applications Claiming Priority (2)

Publications (3)

Family

ID=35503593

Family Applications (1)

Country Status (6)

Families Citing this family (9)

Family Cites Families (16)

• 2004
  • 2004-06-02 US US10/859,486 patent/US7042409B2/en not_active Expired - Lifetime
• 2005
  • 2005-05-05 WO PCT/US2005/015609 patent/WO2005120189A2/en not_active Ceased
  • 2005-05-05 JP JP2007515117A patent/JP2008502207A/ja active Pending
  • 2005-05-05 CA CA2584977A patent/CA2584977C/en not_active Expired - Lifetime
  • 2005-05-05 EP EP05746820A patent/EP1761970A2/en not_active Ceased
  • 2005-05-05 CN CN2005800262728A patent/CN101160691B/zh not_active Expired - Lifetime

Also Published As

Similar Documents

Legal Events