WO2015040500A2

WO2015040500A2 - Feed system for beam steerable circular antenna arrays

Info

Publication number: WO2015040500A2
Application number: PCT/IB2014/002934
Authority: WO
Inventors: Jean-Jacques Laurin; Ramin Deban; Ali MIRKAMALI; Francis SIAKA
Original assignee: Polyvalor, Limited Partnership
Priority date: 2013-09-09
Filing date: 2014-09-09
Publication date: 2015-03-26
Also published as: WO2015040500A3

Abstract

There is provided a feed system for at least one antenna array, the at least one antenna array comprising a plurality of fixed antenna elements arranged in at least one substantially circular array about an axis, the feed system comprising a substantially planar rotating member rotatable about the axis, the rotating member having a circular edge and comprising a radiating unit adapted to radiate power towards the edge, the radiated power escaping the rotating member at the edge; and a connecting member interconnecting the rotating member to the plurality of antenna elements, the connecting member having a circular shape and positioned about the edge of the rotating member in spaced relationship therewith, the at least one antenna array positioned adjacent the connecting member with the at least one antenna array, the rotating member, and the connecting member concentric about the axis, the connecting member adapted to guide the radiated power escaping the rotating member towards the plurality of antenna elements.

Description

FEED SYSTEM FOR BEAM STEERABLE CIRCULAR ANTENNA ARRAYS

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This patent application claims priority of US provisional Application Serial No. 61/875,458, filed on September 9, 2013, the contents of which are hereby incorporated.

TECHNICAL FIELD

[0002] The present invention relates to the field of feed systems for circular antenna arrays.

BACKGROUND OF THE ART

[0003] Beam steering is required in many wireless systems, such as radars and satellite systems. Generally, the beam can be steered using mechanical or electronic systems. Weather radars are one of the applications that require beam steering for predicting meteorological phenomena. In particular, weather radars can be used by atmosphere scientists to locate precipitation and estimate the type and motion thereof. Conventional weather radars use a mechanical rotating parabolic reflector antenna to scan the beam in the azimuth and elevation planes. In order to quickly predict various meteorological phenomena, it is desirable for the antenna systems to be agile. However, due to the size and high weight of conventional antenna systems, their rotation is typically costly and slow. As a result, the amount of data available for weather models is reduced, therefore degrading the quality of predictions

[0004] There is therefore a need for an improved antenna system.

SUMMARY

[0005] In accordance with a first broad aspect, there is provided a feed system for at least one antenna array, the at least one antenna array comprising a plurality of fixed antenna elements arranged in at least one substantially circular array about an axis, the feed system comprising a substantially planar rotating member rotatable about the axis, the rotating member having a circular edge and comprising a radiating unit adapted to radiate power towards the edge, the radiated power escaping the rotating member at the edge; and a connecting member interconnecting the rotating member to the plurality of antenna elements, the connecting member having a circular shape and positioned about the edge of the rotating member in spaced relationship therewith, the at least one antenna array positioned adjacent the connecting member with the at least one antenna array, the rotating member, and the connecting member concentric about the axis, the connecting member adapted to guide the radiated power escaping the rotating member towards the plurality of antenna elements.

[0006] In some embodiments, the rotating member is arranged for one of continuous rotation about the axis and rotation about the axis by a plurality of fixed angular steps.

[0007] In some embodiments, the rotating member comprises a first plate and at least one second plate parallel to the first plate, each pair of adjacent ones of the first plate and the at least one second plate forming a first radial parallel plate waveguide.

[0008] In some embodiments, the radiating unit comprises a reflector and a feed source provided within the first waveguide, the feed source positioned at a focal point of the reflector, the power radiated upon the feed source radiating microwave energy towards the reflector and the reflector reflecting the microwave energy towards the edge.

[0009] In some embodiments, the connecting member comprises a body having a circular inner wall, a first surface and at least one second surface extending away from the body, the first surface positioned adjacent the first plate and defining therewith a first cut-off region, and each of the at least one second surface positioned adjacent a corresponding one of the at least one second plate and defining therewith a second cutoff region, each first and second cut-off region preventing propagation of the microwave energy therein.

[0010] In some embodiments, the at least one second surface is substantially parallel and opposite to the first surface, the first and the at least one second plate positioned within a space formed between the first surface and the at least one second surface. [0011] In some embodiments, the connecting member further comprises at least one third surface connected to the first surface and the at least one second surface, the at least one third surface forming a second radial waveguide with the at least one second plate.

[0012] In some embodiments, the first plate, the second plate, and the at least one third surface are each made of an electrically conductive material and the first surface and the at least one second surface are made of an artificial magnetically conductive material.

[0013] In some embodiments, a height of the first waveguide is set to less than a half wavelength for only allowing TEM mode propagation within the first waveguide and a distance between the at least one first surface and the first plate and a distance between the at least one second surface and the corresponding one of the at least one second plate are set to less than a quarter wavelength for preventing the power escaping the rotating member from leaking out of the first waveguide and into first and the second cut-off region, thereby creating at least one channel for independently guiding the power from each first waveguide towards the plurality of antenna elements of each one of the at least one antenna array.

[0014] In some embodiments, the first surface and the at least one second surface each comprise a plurality of concentric cylindrical grooves.

[0015] In some embodiments, a height of the second waveguide is set to less than a half wavelength for cutting propagation of high order modes within the second waveguide, thereby creating the at least one channel within the second waveguide.

[0016] In some embodiments, the connecting member comprises a plurality of transitions distributed around the axis, each one of the plurality of transitions provided adjacent the first waveguide and coupled to at least a selected one of the plurality of antenna elements of the at least one antenna array, the transition configured for directing the power guided through the first waveguide towards the at least one selected antenna element. [0017] In some embodiments, the radiated power escapes the rotating member through successive angular sections of the edge as the rotating member is rotated, the connecting member adapted to guide the power for exciting selected ones of the plurality of antenna elements provided adjacent each angular section, thereby causing the azimuth plane to be swept as the rotating member completes a 360 degree rotation, at least one of a direction and a speed of rotation of the rotating member being selected for causing at least one area of interest of the azimuth plane to be swept.

[0018] In accordance with a second broad aspect, there is provided a method for feeding at least one antenna array, the at least one antenna array comprising a plurality of fixed antenna elements arranged in at least one substantially circular array about an axis, the method comprising providing a substantially planar rotating member rotatable about the axis, the rotating member having a circular edge and comprising a radiating unit adapted to radiate power towards the edge, the radiated power escaping the rotating member at the edge; providing a connecting member for interconnecting the rotating member to the plurality of antenna elements, the connecting member having a circular shape and positioned about the edge of the rotating member in spaced relationship therewith, the at least one antenna array positioned adjacent the connecting member with the at least one antenna array, the rotating member, and the connecting member concentric about the axis; and guiding the radiated power escaping the rotating member towards the plurality of antenna elements using the connecting member.

[0019] In some embodiments, providing the rotating member comprises providing a first plate and at least one second plate parallel to the first plate, each pair of adjacent ones of the first plate and the at least one second plate forming a first radial parallel plate waveguide.

[0020] In some embodiments, providing the rotating member comprises providing the radiating unit comprising a reflector and a feed source within the first waveguide, the feed source positioned at a focal point of the reflector, the power radiated upon the feed source radiating microwave energy towards the reflector and the reflector reflecting the microwave energy towards the edge. [0021] In some embodiments, providing the connecting member comprises providing a body having a circular inner wall and a first surface and at least one second surface extending away from the body, the first surface positioned adjacent the first plate and defining therewith a first cut-off region, and each of the at least one second surface positioned adjacent a corresponding one of the at least one second plate and defining therewith a second cut-off region, each first and second cut-off region preventing propagation of the microwave energy therein.

[0022] In some embodiments, the at least one second surface is substantially parallel and opposite to the first surface, the first and the at least one second plate positioned within a space formed between the first surface and the at least one second surface.

[0023] In some embodiments, providing the connecting member further comprises providing at least one third surface connected to the first surface and the at least one second surface, the at least one third surface forming a second radial waveguide with the at least one second plate.

[0024] In some embodiments, providing the rotating member and the connecting member comprises providing the first plate, the second plate, and the at least one third surface each made of an electrically conductive material and providing the first surface and the at least one second surface each made of an artificial magnetically conductive material.

[0025] In some embodiments, the method further comprises setting a height of the first waveguide to less than a half wavelength for only allowing TEM mode propagation within the first waveguide and setting a distance between the at least one first surface and the first plate and a distance between the at least one second surface and the corresponding one of the at least one second plate to less than a quarter wavelength for preventing the power escaping the rotating member from leaking out of the first waveguide and into the first and the second cut-off region, thereby creating at least one channel for independently guiding the power from each first waveguide towards the plurality of antenna elements of each one of the at least one antenna array. [0026] In some embodiments, the method further comprises setting a height of the second waveguide to less than a half wavelength for cutting propagation of high order modes within the second waveguide, thereby creating the at least one channel within the second waveguide.

[0027] In some embodiments, the method further comprises providing the connecting member with a plurality of transitions distributed around the axis, each one of the plurality of transitions provided adjacent the first waveguide and coupled to at least a selected one of the plurality of antenna elements of the at least one antenna array, and directing the power guided through the first waveguide towards the at least one selected antenna element.

[0028] In some embodiments, the method further comprises guiding the power during rotation of the rotating member towards successive ones of the plurality of antenna elements for sweeping the azimuth plane as the rotating member completes a 360 degree rotation, at least one of a direction and a speed of rotation of the rotating member selected for causing at least one area of interest of the azimuth plane to be swept.

[0029] In accordance with a third broad aspect, there is provided an antenna system comprising at least one antenna array comprising a plurality of fixed antenna elements arranged in at least one substantially circular array about an axis; and a feed system for feeding the at least one antenna array, the feed system comprising a substantially planar rotating member rotatable about the axis, the rotating member having a circular edge and comprising a radiating unit adapted to radiate power towards the edge, the radiated power escaping the rotating member at the edge, and a connecting member interconnecting the rotating member to the plurality of antenna elements, the connecting member having a circular shape and positioned about the edge of the rotating member in spaced relationship therewith, the at least one antenna array positioned adjacent the connecting member with the at least one antenna array, the rotating member, and the connecting member concentric about the axis, the connecting member adapted to guide the radiated power escaping the rotating member towards the plurality of antenna elements. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Further features and advantages of the present invention will become apparent from the following detailed description, taken in combination with the appended drawings, in which:

[0031] Figure 1 is a schematic diagram of a feed system for exciting a circular array of static antenna elements, in accordance with an illustrative embodiment of the present invention;

[0032] Figure 2 shows a top view of the feed system of Figure 1 and a close-up view of an angular sector of the feed system;

[0033] Figure 3 is a schematic diagram of the feed system of Figure 2;

[0034] Figure 4 is a front schematic view of the feed system of Figure 3;

[0035] Figure 5 is a top schematic view of the rotating member of Figure

2;

[0036] Figure 6 is a perspective view of the horn antenna of Figure 5;

[0037] Figure 7 shows a top and a bottom view of two pieces forming the coupling member of Figure 2, in an unassembled configuration;

[0038] Figure 8 is a bottom perspective view of a selected one of the pieces of Figure 7;

[0039] Figure 9 is a perspective view of the assembled feed system showing a quarter of the coupling member, in accordance with an illustrative embodiment of the present invention;

[0040] Figure 10 is a front schematic view of a multichannel implementation of the system of Figure 1 in accordance with a first illustrative embodiment; [0041] Figure 11a is a front schematic view of a multichannel implementation of the system of Figure 1 in accordance with a second illustrative embodiment; and

[0042] Figure l ib is a front schematic view of the multichannel implementation of Figure 1 la for seven rotating plates.

[0043] It will be noted that throughout the appended drawings, like features are identified by like reference numerals.

DETAILED DESCRIPTION OF THE INVENTION

[0044] Referring now to Figure 1, a feed system 100 for exciting a circular array of static (or fixed) antenna elements as in 102 will now be described. The feed system 100 illustratively uses a space feeding technique to feed the circular array. For this purpose, the antenna elements 102 are illustratively vertical scanning antennas and may comprise any suitable radiating elements configured for scanning electronically by varying frequency or phase, or for scanning mechanically with appropriate means. This may include, but is not limited to, microstrip patch antennas, dipoles, monopoles, horns, leaky wave antennas, slot antennas, reflectarray antennas, or the like. Still, it is desirable for all antenna elements 102 in the array to be of the same type. In one embodiment, the antenna elements 102 are positioned symmetrically (i.e. spaced uniformly) on an essentially circular circumference so as to achieve a uniform circular antenna array. Although the antenna array is described herein as being circular, it should be understood that the antenna elements 102 may also be arranged in a quasi-circular array that does not form a perfect circle. The antenna array can therefore be referred to as substantially circular. The feed system 100 may be used for weather radar applications although it should be understood that other applications, such as navigation radar or surveillance applications, may apply.

[0045] The feed system 100 comprises a stationary coupling (or connecting) member 104 and a rotating member 106 adapted to rotate relative to the coupling member 104 about an axis A. In the illustrated embodiment, the rotating member 106 rotates about axis A counterclockwise in the direction of arrows B, with the rotating member 106 extending along a plane transverse to the axis A. It should however be understood that the rotating member 106 may rotate clockwise about axis A. The coupling member 104 and the rotating member 106 are illustratively circular and concentric about the axis A with the rotating member 106 constituting an inner moving section and the coupling member 104 constituting an outer static (or stationary) section. For this purpose, the coupling member 104 may comprise a body positioned about an edge (not shown) of the rotating member 106 in spaced relationship therewith. In this manner, and as will be discussed further below, the rotating member 106 can freely rotate within the fixed coupling member 104. Although not illustrated, it should be understood that the coupling member 104 and the rotating member 106 may be attached to and held in place relative to one another by a suitable support structure.

[0046] As will be also discussed further below, the coupling member 104 in turn couples (or interconnects) the rotating member 106 to the antenna elements 102 for transferring thereto power guided by the rotating member 106. For this purpose, the antenna elements 102 are illustratively positioned along a perimeter of the coupling member 104. As the rotating member 106 revolves about axis A, the feed system 100 then excites through the coupling member 104 a specific angular sector, i.e. a given number of antenna elements as in 102, of the circular array at any given time. The azimuth plane is then swept as the rotating member 106 completes a full 360 degrees turn. As such, the main beam of the generated radiation pattern can be steered as the rotating member 106 rotates about the axis A and azimuth beam steering can be controlled by the rotating member 106.

[0047] Referring to Figure 2 and Figure 3, the feed system 100 may be implemented with a radial parallel plate waveguide. In one embodiment, the rotating member 106 comprises a first electrical conductor plate 108a and a second electrical conductor plate 108b that together form the radial waveguide. The plates 108a, 108b have a circular shape and are opposite and substantially parallel to one another. The plates 108a, 108b are illustratively perfect electrical conductor (PEC) plates, as shown in Figure 3. It should however be understood that the plates 108a, 108b may be made of any electrically conductive material, such as metals (e.g. aluminum, copper, or the like) or metallized insulators. The coupling member 104 illustratively comprises a body 110 and substantially parallel and opposite surfaces 112a, 112b positioned adjacent an outer edge 114 (e.g. about a perimeter) of the rotating member 106. Each surface 112a, 112b is illustratively positioned adjacent a respective surface 108a, 108b. The surfaces 112a, 112b illustratively implement an artificial magnetic conductor or other high impedance surface so that the region comprised between surfaces 112a and 108a (and equivalently surfaces 112b and 108b) is cut-off for all possible electromagnetic wave modes within the frequency band of operation.

[0048] The body 110 may be a perfect electric conductor (PEC) that can be approximated by electrically conductive metals, such as aluminum, copper, or the like, or metallized insulators. The body 110 illustratively comprises apertures (not shown) each adapted to receive therein a transition or port 116 configured to extract microwave power emanating from the edge 114 of the rotating member 106 (e.g. a given angular section of the edge) and to direct the extracted microwave power towards a given one of the antenna elements (reference 102 in Figure 1). It should therefore be understood that a plurality of transitions may be arranged along a perimeter of the coupling member 104 (e.g. equally distributed around the axis A in Figure 1) for allowing the power to be directed towards the plurality of antenna elements forming the circular array. Coaxial ports (as illustrated) may be used to feed the antenna elements 102. It should be understood that transitions having any other suitable configuration, e.g. coupling elements, such as slots or wires, or waveguide ports other than coaxial ports, may be used to feed the antenna elements 102.

[0049] The surfaces 112a, 112b each extend away from an end as in 118 of the body 110 and may be connected thereto through any suitable means, such as fasteners, fixations, screws, bolts, or the like (not shown). The surfaces 112a, 112b and the body 110 may also be formed as a single member. In particular, the surfaces 112a, 112b extend away from the body 110 and towards the center (not shown) of the rotating member 106 so as to be substantially parallel to the plates 108a, 108b. End portions of the plates 108a, 108b are then disposed within a space (not shown) formed between the surfaces 112a, 112b, with the edge 114 of the rotating member 106 (and accordingly the edge portions of the plates 108a, 108b) being positioned adjacent an inner vertical wall (not shown) of the body 110. It is desirable for the inner wall of the body 110 to be illustratively circular so as to have rotation symmetry about the rotation axis A of the feed system 100. Still, the outer wall (not shown) of the body 110 may have any suitable shape.

[0050] It is desirable for the antenna elements 102 to receive the whole of the power guided by the rotating member 106. Indeed, the power, upon exiting the rotating member at the edge 114 thereof, may either flow upward or downward inside the coupling member 104. In one embodiment, the antenna elements 102, and accordingly the transitions (e.g. the ports 116), are provided at the top of the feed system 100 and it is therefore desirable for the power exiting the rotating member 106 to be directed upwards. It should however be understood that other configurations may apply and that the power may also be directed downwards or both upwards and downwards by accordingly providing transitions (e.g. the ports 116) at the top and/or the bottom of the feed system 100. In order to prevent leakage of microwave power from the edge 114 and towards the bottom of the coupling member 104, a cut-off region delimited by a bottom plate (e.g. surface 112b), which is an artificial implementation of a perfect magnetic conductor (PMC), may be provided at the bottom of the structure. In particular, in one embodiment, in order to prevent any undesired power leakage into the regions comprised between surfaces 112a and 108a and surfaces 112b and 108b, both the surfaces 112a, 112b are implemented as artificial magnetic conductor (AMC) surfaces having any suitable configuration or structure, such as printed electromagnetic band gap structures, corrugated surfaces, or any other type of high impedance surface.

[0051] In the configuration shown in Figure 2 and Figure 3, the surfaces

112a, 112b each correspond to an inner surface (not shown) of a respective cylindrical corrugated member 120, which implements the artificial magnetic conductor. As discussed above, the corrugated member 120 may be formed so as to be integral to the body 110 of the coupling member 104 or may be attached thereto using any suitable means. Each corrugated member 120 comprises a plurality of concentric cylindrical grooves 122 (see Figure 3) between two (2) adjacent rings as in 123, the grooves connected by a metallic plate (not shown). The surfaces 112a, 112b are thus each corrugated, with each corrugated surface 112a, 112b being formed by alternating grooves 122 and rings 123. This allows to handle higher microwave power than when printed electromagnetic band gap structures are used. In addition, corrugated surfaces exhibit higher mechanical robustness than electromagnetic band gap structures. Also, cylindrical corrugated surfaces may be used to achieve a cylindrical symmetry in the coupling member 104. As discussed above, although corrugated surfaces are illustrated and described herein, it should be understood that the artificial magnetic conductor AMC surfaces as in 112a, 112b, which create the cut-off regions, may be implemented using any suitable technique. For example, other types of AMC implemented with single or multilayer metallized printed circuit boards, which includes but is not limited to patch elements, mushroom elements, and the like, may apply.

[0052] Each surface 112a, 112b then forms with an adjacent plate 108a,

108b a cut-off region in which waves do not propagate. By setting the height (not shown) of each one of such cut-off regions to less than a quarter of the free-space wavelength, assuming an air dielectric, it becomes possible to prevent any of the modes of the waveguide structure, which forms the rotating member 106), from propagating into the region comprised between surfaces 112a and 108a (and equivalently surfaces 112b and 108b). This allows to effectively avoid leakage at the top and bottom of the feed system 100. Moreover, the body 110 may comprise a first (or top) outer PEC surface 124a and a second (or bottom) outer PEC surface 124b opposite to the first surface 124a (see Figure 3). In one embodiment, the surfaces 124a and 124b are substantially parallel. The PEC surfaces 124a, 124b are illustratively connected to (e.g. integral with or attached to using suitable means) corrugated surfaces 112a, 112b, respectively. In one embodiment, the PEC surfaces 124a, 124b are substantially parallel to the plates 108a, 108b, respectively. In one embodiment, the surfaces 112b and 124b extend along the same plane. In this embodiment, the top surface 124a may then form a second waveguide (e.g. a parallel plate waveguide) with the top plate 108a of the rotating member 106 and power radiated from the rotating member 106 may be directed upwards through this waveguide. In order to allow only the transverse electromagnetic (TEM) mode to propagate and therefore guide power radiated by the rotating member 104 through the waveguide created at the top of the structure, the height of the waveguide (formed by surface 124a and plate 108a) may be set to less than half the wavelength in the waveguide. In the illustrated embodiment, the dimensions and positioning of the surfaces 112a, 112b, 124a, 124b is further selected such that the power escaping the rotating member 106 is only directed upwards. For this purpose, the surfaces 112a, 112b, 124a, and 124b extend away from the body 110 with both surfaces 112a and 124a being positioned over the top plate 108a while only surface 112b is positioned below the lower plate 108b. Therefore, in this embodiment, only one waveguide is formed at the top of the structure (by plate 108a and surface 124a) to direct the power upwards.

[0053] Power radiated by the rotating member 106 (e.g. emanating from the edge 114) can then be prevented from leaking using the cut-off regions (formed by surfaces 112a, 112b and respective plates 108a, 108b) and can be guided through the second waveguide (formed by surface 124a and plate 108a) along the direction of arrows C of Figure 3 for subsequent transmission to the antenna elements (reference 102 in Figure 1). A probe 126 may then be used to achieve a transition between the second waveguide and the coaxial port 116 (or, as discussed above, coupling slots, coupling wires, or any other type of waveguide port) provided in the body 110 of the coupling member 104. For this purpose, the probe 126 illustratively extends into the second waveguide. Microwave power emanating from the edge 114 of the rotating member 106 (e.g. from the first waveguide formed by the rotating plates 108a, 108b) can therefore be directed, e.g. via the cut-off regions, the second waveguide, the coaxial port 116, and the probe 126, towards the antenna elements 102. For this purpose, each port 116 and probe 126 combination is illustratively connected to a selected one of the antenna elements 102 for transmitting microwave power thereto. In some embodiments, each port 116 and probe 126 combination may be connected to a subset of the antenna elements 102. As power may only escape the rotating member 106 at a portion of the edge 114, a selected number of the ports 116 and probes 126 (e.g. provided adjacent the edge) may receive power and accordingly power is transmitted to a selected number of the antenna elements 102 the ports 116 and probes 126 are connected to. All antenna elements 102 are therefore successively excited as a complete 360 degree rotation is achieved by the rotating member 106.

[0054] Although the feed system 100 is illustrated as being configured such that the microwave power is directed via probes as in 126 and ports as in 116 towards a top of the structure, it should be understood that the power may similarly be directed towards a bottom (or both bottom and top) of the structure using suitable means. For this purpose, the probes as in 126 and ports as in 116 may be provided on the bottom surface 124b of the body 110 and the configuration of the structure adapted accordingly to prevent leakage of power at the top of the coupling member 104. [0055] It can be seen from Figure 3 that the feed system 100 is designed such that the coupling member 104 comprising the body 110 and the surfaces 112a, 112b is spaced from the rotating member 106 and therefore makes no electrical contact therewith. In this manner, the rotating member 106, and more particularly the plates 108a, 108b, make no electrical contact with any other component of the feed system 100 and is configured to rotate freely. The configuration of the rotating member 106 and coupling member 104 results in a lightweight feed system 100, thereby increasing the agility thereof. In particular, only one rotary joint (not shown) may be provided at the center of the rotating member 106 and prove sufficient to enable movement in the feed system 100. Continuous rotation of the rotating member 106, and accordingly continuous steering of the beam in the azimuth plane, can then be achieved. Indeed, the rotating member 106 may either rotate by fixed angular steps or have a continuous rotation.

[0056] Referring now to Figure 4, there is illustrated a design of the feed system 100 in accordance with one embodiment. It should be understood that the dimensions discussed herein with reference to Figure 4 are exemplary only and that other configurations may apply. In the illustrated embodiment, the feed system 100 is designed assuming that the radial rotating parallel plate waveguide formed by the plates 108a, 108b is excited at the center of the waveguide. Therefore, it is assumed that the structure of the feed system 100 has N-fold rotation symmetry, with N being the number of elements in the circular array of antenna elements (reference 102 in Figure 1). In particular, it is assumed that the radius (not shown) of the rotating member 106 is 10λ, where λ is the wavelength in free space, and that the distance (not shown) between the antenna elements 102 is 0.65λ. It should be understood that the feed system 100 may also be designed assuming the rotating member 106 is not symmetrical, although this may result in degradation in the performance of the feed system 100. As such, other dimensions may apply.

[0057] As discussed above, the coupling member (reference 104 in Figure

1) may be designed such that the distance h3 between the PEC plates 108a and 124a is less than half wavelength, thereby cutting off the propagation of high order modes. In one embodiment optimized for operation at a frequency of 10 GHz, the distance h3 is set to 9mm. The length Lprobe of the probe 126 (e.g. of the section of the probe 126 extending away from the plate 124a and towards the plate 108a) may then be set to a quarter wavelength in order to cancel the reactance of the probe 126. The end (not shown) of the probe 126 may further be terminated with a tip having one of a variety of shapes suitable to increase the frequency bandwidth of the system. For example, the tip of the probe's end may have a conical shape, a spherical shape, a multi-radius cylinder shape, or the like. The length Lprobe and the diameter (not shown) of the probe can be further adjusted to provide impedance matching, in order to ensure adequate coupling to the rotating member 106. In addition, the distance L0 between the probe 126 and the upper corrugated surface 112a may be selected to compensate for the reactive part of the input impedance of the probe 126. The distance L0 may be about a quarter wavelength. In one embodiment, the length Lprobe and the distance L0 may be set to 6.5mm and 7.5mm, respectively, in order to achieve the desired matching. It should be understood that other dimensions may apply for different operating frequencies.

[0058] Still referring to Figure 4, the distance hi between the upper corrugated surface 112a and the corresponding upper PEC plate 108a as well as the distance h2 between the bottom corrugated surface 112b and the corresponding bottom PEC plate 108b may be selected so as to be less than a quarter wavelength. In this manner, it is possible to prevent propagation of microwave power inside each cut-off region formed by the PEC plate 108a or 108b and the corresponding AMC surface 112a or 112b (i.e. prevent microwave power leakage outside the coupling member 104). In one embodiment, the distances hi and h2 are chosen to be equal to 3mm. In another embodiment, the distances hi and h2 may be progressively modified so as to increase the frequency bandwidth of the overall system. At an operating frequency in the X-band, e.g. lOGhz, as suitable for weather radar applications, the height h4 of each groove 122 of the corrugation members 120 may further be chosen to be approximately equal to a quarter of the wavelength λ, e.g. 7.5mm, at the operating frequency. Moreover, as the microwave power is illustratively small after the first period of each corrugated surface 112a, 112b, the length LI of each corrugated surface 112a, 112b may be set to one wavelength, e.g. 30mm, at the operating frequency of 10GHz. Also, it is desirable for the period of each corrugated surface 112a, 112b to be smaller than the operating wavelength λ so that the corrugated surfaces 112a, 112b behave as AMC surfaces. For a corrugated surface as in 112b comprising five (5) grooves 122 per operating wavelength (as illustrated), the width w of the rings 123 may be equal to 2mm and the width g of the grooves 122 to 3mm. It should be understood that other numbers of grooves as in 122, and accordingly other thicknesses as in w and spacings as in g, may apply. It should also be understood that operating frequencies other than the X-band may apply and that the above-mentioned dimensions may be varied accordingly.

[0059] In the illustrated embodiment, in which the inner surface of the body 110 is substantially flat, the radial distance D between the rotating member 106 (e.g. the edge 114 in Figure 3) and the coupling member 104 (e.g. the body 110 in Figure 3) may be determined by performing a parametric study. In particular, the variation of the system's S-parameters versus the radial distance D when the distance h3 between the PEC plates 108a and 124a is set to 9mm may be determined. In one embodiment, the parametric study shows that a suitable value for the radial distance D is equal to 19mm. It should be understood that the radial distance D may be determined using any suitable means other than a parametric study and that other values for the radial distance D may apply. It should also be understood that, although the area (not shown) delimited by the first PEC surface 124a, the second PEC surface 124b, and the body 110 appears rectangular in cross section (see Figure 3 and Figure 4), the area may have any other suitable shape (e.g. wedge, conical, or the like) so as to favor power transfer to the ports as in 116 and eventually to the antenna elements 102.

[0060] Referring now to Figure 5, the rotating member 106 illustratively determines the exciting vector of the circular array elements (reference 102 in Figure 1). As discussed above, as the rotating member 106 rotates about axis A, only a given number of antenna elements 102 are excited through the coupling member 104 at any given time. For this purpose, the rotating member 106 comprises a radiating unit having a feed source 202 and a reflector 204. The rotating member 106 can thus be seen as a circular planar lens. In one embodiment, the feed source 202 is an H-plane horn antenna and the reflector 204 is a two-dimensional (2D) offset-fed parabolic reflector. It should be understood that other suitable feed sources as in 202 and reflectors as in 204 may apply. For instance, the reflector 204 may comprise a reflectarray or a directly radiating array fed with a beam forming network (not shown). A feed-horn and a lens implemented with shaped dielectric or transmitarray elements may also apply. The feed source 202 and reflector 204 are illustratively positioned within the radial parallel plate waveguide (not shown) formed by the PEC plates (references 108a, 108b of Figure 4) of the rotating member 106. In this manner, it becomes possible to reduce the side lobe level of the antenna array's radiation pattern. The reflector 204 is illustratively illuminated by the feed source 202, which is positioned at the focal point 206 of the reflector 204. As a result, the reflector 204 reflects towards the edge 114 of the rotating member 106, as illustrated by arrows E, the microwave energy radiated by the feed source 202. The geometry of the reflector 204 may be designed such that a desired radiation pattern, and more particularly beamforming, is obtained for changing the radiation characteristics of the system in the azimuth plane. As such, by varying the geometry (e.g. size) of the reflector 204, the number of transitions (e.g. ports 116 and probes 126) that receive the radiated microwave energy, and accordingly the number of antenna elements 102 to which the energy is transmitted, can be varied.

[0061] In one embodiment, the rotating member 106 is designed such that the focal length f of the reflector 204 is equal to 10λ and the radius (not shown) of the parallel plate waveguide is also set to 10λ for a diameter d of 20λ. Accordingly, the aperture length Laperture of the reflector 204 may be set to 11.9λ, as determined using suitable computation techniques. The value of Laperture is illustratively based on several factors to reduce losses and scattering in the structure and may be optimized through computer simulations. In order to only allow the TEM mode to propagate, it may be desirable for the separation (reference hO in Figure 4) between the plates 108a, 108b to be set to less than half the wavelength λ. In one embodiment, the distance hO is set to 5mm. Also, the thickness (reference t in Figure 4) of each one of the plates 108a, 108b may be set to 2mm. It should be understood that the above-mentioned dimensions may be varied as desired depending on the applications and mechanical requirements.

[0062] Referring now to Figure 6, the feed source 202 is illustratively implemented as a planar horn, which comprises a body 208, and is fed by a feeding probe 210 positioned within the body 208. In one embodiment illustrated in Figure 5, the feed source 202 has an aperture width Waperture of 2.4λ or 71.4mm, a first dimension DO of 2λ or 60mm and a second dimension Dl of 0.397λ or 11.9mm. The distance D2 between the feeding probe 210 and the antenna taper may further be set to 0.52λ or 15.6mm with the feeding probe 210 further having a height (not shown) of 4mm and a diameter (not shown) of 2mm. It should be understood that the dimensions of the feed source 202, and more particularly the opening Waperture thereof, may be varied in order to adjust the width of the main beam emitted by the feed source 202.

[0063] The components (e.g. feed source 202, reflector 204) of the rotating member 106 may be manufactured by machining aluminum plates (not shown), or plates made of any other suitable metal or a metallized insulator, using any suitable process, such as cutting, Computer Numerical Control (CNC) milling machining, laser machining, water-jet machining, or the like, and using any suitable machine, such as a laser, water-jet machine, CNC machine, or the like. Although not illustrated, absorbers may also be provided at the edge (reference 114 in Figure 5) of the rotating member 106 in the areas not illuminated by the reflector 204 in order to reduce spillover and diffraction effects. As shown in Figure 7 and Figure 8, the coupling member 104 may be manufactured in two separate pieces, namely a first or upper member 302a and a second or lower member 302b, which are then assembled together using suitable means. As shown in Figure 9, the manufactured rotating member 106 may then be placed at the desired position with respect to the coupling member 104, within the spacing formed between the corrugated surfaces (references 112a and 112b in Figure 4).

[0064] In this manner, it is possible to achieve a light and low-volume feed system (reference 100 in Figure 1) having a low moment of inertia, therefore leading to better agility. Indeed, as the coupling member 104 is spaced from the rotating member 106, the rotating member 106 can be rotated at a high speed relative to the coupling member 104. In addition, the design of the feed system 100 allows to change the direction of rotation of the rotating member 106 relative to the coupling member 104. Also, during rotation, the feed system 100 can quickly return (e.g. by changing the direction and/or speed of rotation) to an area of interest of the azimuth plane in order to obtain high resolution scanning over a particular area. Moreover, by providing the coupling member 104 separate from the rotating member 106, it becomes possible to change the radiating elements (reference 102 in Figure 1) on the circular antenna array without having to change the entire feed system 100. As such, a wide variety of radiating elements, including vertical beam steering antennas, can be used as the antenna elements 102. [0065] Referring now to Figure 10, there is illustrated an alternative embodiment 400 of the feed system of Figure 1. In this embodiment, a multichannel implementation is shown, which allows to simultaneously and independently feed more than one circular array of antenna elements (reference 102 in Figure 1). Therefore, arrays of antenna elements with different polarizations or radiation patterns may be fed using the same feed system 400 and synchronized scanning of the arrays' radiation patterns in the azimuth plane can be achieved. For this purpose, the feed system 400 illustratively comprises a plurality (e.g. three (3)) rotating plates as in 402a, 402b, 402c, which are parallel to one another and form the rotating member (reference 106 in Figure 1). It should be understood that any number of rotating plates other than three (3) may apply. A parallel plate waveguide is then formed between each pair of adjacent rotating plates, e.g. a first waveguide is formed by plate 402a and plate 402b and another waveguide is formed by plate 402b and plate 402c. An independent beamforming system or radiating unit (not shown), including for instance a feed source (e.g. a horn antenna) and a reflector (e.g. a parabolic reflector), as discussed with reference to Figure 5 and Figure 6, may then be implemented within the waveguide formed by each pair of adjacent rotating plates as in 402a, 402b, 402c. The rotating plates as in 402a, 402b, 402c are then illustratively positioned in a space formed between corrugated surfaces 404a and 404b of the coupling member (reference 104 in Figure 1). In particular, the upper corrugated surface 404a is positioned adjacent the upper rotating plate 402a while the lower corrugated surface 404b is positioned adjacent the lower rotating plate 402c. In this manner, a cut-off region, in which wave propagation is prevented, is formed by each corrugated surface and the corresponding plate adjacent thereto. For instance, a cut-off region is formed by the space between the upper corrugated surface 404a and the upper rotating plate 402a while another cut-off region is formed by the space between the lower corrugated surface 404b and the lower rotating plate 402c.

[0066] In the illustrated embodiment, the feed system 400 further comprises a corrugated surface arrangement 406 adjacent the edge (not shown) of the rotating member, and more particularly adjacent the end (not shown) of rotating surface 402b. The corrugated surface arrangement 406 illustratively comprises a body (not shown) having inner corrugated surfaces 408a, 408b, and 408c. The surfaces 408a and 408c are opposite and substantially parallel to one another and connected through surface 408b, which is substantially perpendicular to both surfaces 408a and 408c. It should be understood that other configurations (e.g. wedge, conical, etc.) may apply. The middle rotating plate 404b illustratively has a greater diameter than the plates 404a, 404c so as to extend in between surfaces 408a and 408b and adjacent surface 408c. In this manner, waves are prevented from propagating in the region of the corrugated surface arrangement 406 and decoupling between the waveguides is achieved. In particular, providing the arrangement 406 allows to create separate channels for the waveguides formed by each pair of adjacent rotating plates, namely a first channel for the first waveguide formed by plate 402a and plate 402b and a second channel for the second waveguide formed by plate 402b and plate 402c. In addition, cross-talk between the channels is prevented. The arrangement 406 therefore allows decoupling between the waveguides such that power guided by the first waveguide is decoupled from power guided by the second waveguide and the power can be guided through the separate channels.

[0067] Circular arrays of probes as in 410a and 410b are illustratively provided, with each probe array directing the power radiated by a given waveguide towards the antenna elements (not shown) of a given antenna array, each waveguide coupling to only one of the two probes 410a, 410b. In the illustrated embodiment, the probes as in 410a are provided at a top of the feed system 400 for directing power guided through the first waveguide, and accordingly through the first channel, to a first circular array of antenna elements (not shown) provided at a top of the structure. The probes as in 410b are in turn provided at a bottom of the feed system 400 for directing power guided through the second waveguide, and accordingly through the second channel, to a second circular array of antenna elements (not shown) provided at a bottom of the structure.

[0068] Still referring to Figure 10, in some embodiments, PEC surfaces as in 412a and 412b may be provided adjacent the probes 410a, 410b to further guide the power escaping from each waveguide (formed by a pair of rotating plates 402a, 402b, 402c) towards the corresponding probe 410a, 410b through the creation of suitable channel(s) (e.g. within the waveguide(s)). For this purpose, each surface 412a, 412b is illustratively connected between the corrugated arrangement 406 and the probe 410a, 410b provided at the corrugated surface 404a, 404b, as illustrated. Each surface 412a, 412b may further extend beyond the corresponding probe 410a, 410b (e.g. to the left in Figure 10) to connect to the corresponding corrugated surface 404a, 404b. Again, the surfaces 404a, 404b, 408a, 408b, 408c, 412a, and 412b may be attached to one another using suitable attachment means or may form an integral member. It should be understood that the length of each surface 412a, 412b may be adjusted to guide the power as desired. It should also be understood that, depending on the embodiment, the feed structure may comprise at least one of the PEC plate arrangement and the corrugated arrangement to guide power emanating from the rotating member. In one embodiment, when the rotating member comprises two rotating plates, the PEC plate arrangement (as in PEC plate 124a) may be provided. Still, when the rotating member comprises more than two rotating plates, it is desirable to use the corrugated member to prevent crosstalk between the waveguides created by each pair of rotating plates. A PEC plate arrangement may then be used in addition to the corrugated arrangement, as shown in Figure 10.

[0069] The possibilities of the system 400 could be extended to augment its diversity by either:

- Using antenna arrays with orthogonal polarizations in each channel;

- Using antennas with different radiation patterns, e.g. elevation coverages on each channel;

- Allowing different azimuth coverages in each channel;

- Etc.

[0070] Referring now to Figure 11a, there is illustrated a second alternative embodiment 500 of the feed system of Figure 1. As shown in Figure 11a, the concept described above with reference to Figure 10 can be extended by using N+l parallel rotating plates as in 502 to create N independent feeding systems (not shown) for N corresponding antenna arrays (not shown), with each feeding system comprising an array of probes as in 504 for directing towards a corresponding antenna array the power radiated by a given waveguide formed by a pair of adjacent rotating plates. In this embodiment, the N antenna arrays are illustratively arranged be concentric about the axis A of Figure 1. In the azimuth plane, the beams of these N arrays would be scanned simultaneously with the rotation of the parallel plates as in 502.

[0071] Although the feed system 500 is shown as comprising probes 504 at a top of the structure, it should be understood that the probes may alternatively be provided at a bottom of the structure. Also, probes 504 may be provided at both the top and the bottom, as illustrated in Figure l ib. A corrugated arrangement 506 may also be provided, similarly to the arrangement 406 shown in Figure 10b, to allow decoupling between the waveguides formed by pairs of rotating plates.

[0072] The above description is meant to be exemplary only, and one skilled in the art will recognize that changes may be made to the embodiments described without departing from the scope of the invention disclosed. Modifications which fall within the scope of the present invention will be apparent to those skilled in the art, in light of a review of this disclosure, and such modifications are intended to fall within the appended claims.

Claims

CLAIMS What is claimed is:

1. A feed system for at least one antenna array, the at least one antenna array comprising a plurality of fixed antenna elements arranged in at least one substantially circular array about an axis, the feed system comprising: a substantially planar rotating member rotatable about the axis, the rotating member having a circular edge and comprising a radiating unit adapted to radiate power towards the edge, the radiated power escaping the rotating member at the edge; and a connecting member interconnecting the rotating member to the plurality of antenna elements, the connecting member having a circular shape and positioned about the edge of the rotating member in spaced relationship therewith, the at least one antenna array positioned adjacent the connecting member with the at least one antenna array, the rotating member, and the connecting member concentric about the axis, the connecting member adapted to guide the radiated power escaping the rotating member towards the plurality of antenna elements.

2. The system of claim 1, wherein the rotating member is arranged for one of continuous rotation about the axis and rotation about the axis by a plurality of fixed angular steps.

3. The system of claim 1 or 2, wherein the rotating member comprises a first plate and at least one second plate parallel to the first plate, each pair of adjacent ones of the first plate and the at least one second plate forming a first radial parallel plate waveguide.

4. The system of any one of claims 1 to 3, wherein the radiating unit comprises a reflector and a feed source provided within the first waveguide, the feed source positioned at a focal point of the reflector, the power radiated upon the feed source radiating microwave energy towards the reflector and the reflector reflecting the microwave energy towards the edge.

5. The system of claim 4, wherein the connecting member comprises a body having a circular inner wall, a first surface and at least one second surface extending away from the body, the first surface positioned adjacent the first plate and defining therewith a first cut-off region, and each of the at least one second surface positioned adjacent a corresponding one of the at least one second plate and defining therewith a second cut-off region, each first and second cut-off region preventing propagation of the microwave energy therein.

6. The system of claim 5, wherein the at least one second surface is substantially parallel and opposite to the first surface, the first and the at least one second plate positioned within a space formed between the first surface and the at least one second surface.

7. The system of claim 6, wherein the connecting member further comprises at least one third surface connected to the first surface and the at least one second surface, the at least one third surface forming a second radial waveguide with the at least one second plate.

8. The system of claim 7, wherein the first plate, the second plate, and the at least one third surface are each made of an electrically conductive material and the first surface and the at least one second surface are made of an artificial magnetically conductive material.

9. The system of claim 8, wherein the at least one first surface and the at least one second surface each comprise a plurality of concentric cylindrical grooves.

10. The system of any one of claims 7 to 9, wherein a height of the first waveguide is set to less than a half wavelength for only allowing TEM mode propagation within the first waveguide and a distance between the at least one first surface and the first plate and a distance between the at least one second surface and the corresponding one of the at least one second plate are set to less than a quarter wavelength for preventing the power escaping the rotating member from leaking out of the first waveguide and into the first and the second cut-off region, thereby creating at least one channel for independently guiding the power from each first waveguide towards the plurality of antenna elements of each one of the at least one antenna array.

11. The system of claim 10, wherein a height of the second waveguide is set to less than a half wavelength for cutting propagation of high order modes within the second waveguide, thereby creating the at least one channel within the second waveguide.

12. The system of any one of claims 3 to 11, wherein the connecting member comprises a plurality of transitions distributed around the axis, each one of the plurality of transitions provided adjacent the first waveguide and coupled to at least a selected one of the plurality of antenna elements of the at least one antenna array, the transition configured for directing the power guided through the first waveguide towards the at least one selected antenna element.

13. The system of any one claim 1 to 12, wherein the radiated power escapes the rotating member through successive angular sections of the edge as the rotating member is rotated, the connecting member adapted to guide the power for exciting selected ones of the plurality of antenna elements provided adjacent each angular section, thereby causing the azimuth plane to be swept as the rotating member completes a 360 degree rotation, at least one of a direction and a speed of rotation of the rotating member being selected for causing at least one area of interest of the azimuth plane to be swept.

14. A method for feeding at least one antenna array, the at least one antenna array comprising a plurality of fixed antenna elements arranged in at least one substantially circular array about an axis, the method comprising: providing a substantially planar rotating member rotatable about the axis, the rotating member having a circular edge and comprising a radiating unit adapted to radiate power towards the edge, the radiated power escaping the rotating member at the edge; providing a connecting member for interconnecting the rotating member to the plurality of antenna elements, the connecting member having a circular shape and positioned about the edge of the rotating member in spaced relationship therewith, the at least one antenna array positioned adjacent the connecting member with the at least one antenna array, the rotating member, and the connecting member concentric about the axis; and guiding the radiated power escaping the rotating member towards the plurality of antenna elements using the connecting member.

15. The method of claim 14, wherein providing the rotating member comprises providing a first plate and at least one second plate parallel to the first plate, each pair of adjacent ones of the first plate and the at least one second plate forming a first radial parallel plate waveguide.

16. The method of any one of claims 14 to 15, wherein providing the rotating member comprises providing the radiating unit comprising a reflector and a feed source within the first waveguide, the feed source positioned at a focal point of the reflector, the power radiated upon the feed source radiating microwave energy towards the reflector and the reflector reflecting the microwave energy towards the edge.

17. The method of claim 16, wherein providing the connecting member comprises providing a body having a circular inner wall and a first surface and at least one second surface extending away from the body, the first surface positioned adjacent the first plate and defining therewith a first cut-off region, and each of the at least one second surface positioned adjacent a corresponding one of the at least one second plate and defining therewith a second cut-off region, each first and second cut-off region preventing propagation of the microwave energy therein.

18. The method of claim 17, wherein the at least one second surface is substantially parallel and opposite to the first surface, the first and the at least one second plate positioned within a space formed between the first surface and the at least one second surface.

19. The method of claim 18, wherein providing the connecting member further comprises providing at least one third surface connected to the first surface and the at least one second surface, the at least one third surface forming a second radial waveguide with the at least one second plate.

20. The method of claim 19, wherein providing the rotating member and the connecting member comprises providing the first plate, the second plate, and the at least one third surface each made of an electrically conductive material and providing the first surface and the at least one second surface each made of an artificial magnetically conductive material.

21. The method of claim 20, further comprising setting a height of the first waveguide to less than a half wavelength for only allowing TEM mode propagation within the first waveguide and setting a distance between the at least one first surface and the first plate and a distance between the at least one second surface and the corresponding one of the at least one second plate to less than a quarter wavelength for preventing the power escaping the rotating member from leaking out of the first waveguide and into the first and the second cut-off region, thereby creating at least one channel for independently guiding the power from each first waveguide towards the plurality of antenna elements of each one of the at least one antenna array.

22. The method of claim 21, further comprising setting a height of the second waveguide to less than a half wavelength for cutting propagation of high order modes within the second waveguide, thereby creating the at least one channel within the second waveguide.

23. The method of claim 22, further comprising providing the connecting member with a plurality of transitions distributed around the axis, each one of the plurality of transitions provided adjacent the first waveguide and coupled to at least a selected one of the plurality of antenna elements of the at least one antenna array, and directing the power guided through the first waveguide towards the at least one selected antenna element.

24. The method of any one claim 1 to 23, further comprising guiding the power during rotation of the rotating member towards successive ones of the plurality of antenna elements for sweeping the azimuth plane as the rotating member completes a 360 degree rotation, at least one of a direction and a speed of rotation of the rotating member selected for causing at least one area of interest of the azimuth plane to be swept.

25. An antenna system comprising: at least one antenna array comprising a plurality of fixed antenna elements arranged in at least one substantially circular array about an axis; and a feed system for feeding the at least one antenna array, the feed system comprising a substantially planar rotating member rotatable about the axis, the rotating member having a circular edge and comprising a radiating unit adapted to radiate power towards the edge, the radiated power escaping the rotating member at the edge, and a connecting member interconnecting the rotating member to the plurality of antenna elements, the connecting member having a circular shape and positioned about the edge of the rotating member in spaced relationship therewith, the at least one antenna array positioned adjacent the connecting member with the at least one antenna array, the rotating member, and the connecting member concentric about the axis, the connecting member adapted to guide the radiated power escaping the rotating member towards the plurality of antenna elements.