Reconfigurable payload using non-focused reflector antenna for HIEO and GEO satellites

An antenna system for generating and configuring at least one defocused beam is provided. The antenna system includes a reflector having a focal plane and a non-parabolic curvature for forming the at least one defocused beam, and a plurality of feed antennas that illuminate the reflector. Each feed antenna is disposed in the focal plane of the reflector. The antenna system further includes at least one incoming signal dividing network that divides at least one incoming signal into a plurality of sub-signals, each corresponding to one of the feed antennas, a plurality of variable phase shifters, each receiving one of the sub-signals from the incoming signal dividing network and phase shifting the sub-signal to generate a corresponding phase-shifted sub-signal, and a plurality of fixed-amplitude amplifiers, at least one corresponding to each of the feed antennas. The at least one amplifier for each feed antenna amplifies the corresponding phase-shifted sub-signal to generate an amplified phase-shifted sub-signal which is provided to the corresponding feed antenna.

Not applicable.

FIELD OF THE INVENTION

The present invention generally relates to spacecraft payloads and, in particular, relates to reconfigurable payloads for highly inclined elliptical orbit (HIEO) and geostationary orbit (GEO) communication satellites.

BACKGROUND OF THE INVENTION

Satellites with reconfigurable payloads provide desirable on-orbit mission flexibility. A reconfigurable payload allows a satellite to change the shape and location of its beams in order to change earth coverage regions. These changes may be necessary in order to compensate for spacecraft yaw steering, to back up or replace another satellite in-orbit, or as a result of changing market demands or customer requirements.

One approach to providing a reconfigurable payload involves using a Gregorian reflector antenna with an elliptical sub-reflector in order to produce a very broad elliptical beam. By rotating the elliptical sub-reflector, the far-field beam can be rotated to compensate for the yaw rotation of the satellite. This approach suffers from reliability problems because the reconfiguration is mechanical. Moreover, the gain of such an antenna is insufficient for many applications.

Another approach to providing a reconfigurable payload uses phased array optics to illuminate a reflector. In this approach, several hundred optical elements are used to provide the required phase delay between elements. Because of the large number of elements, this approach suffers from increased mass and expense. Moreover, this approach is unsuitable for handling large power loads due to the fact that the large number of amplifiers required can not be accommodated on a spacecraft. Other limitations include the difficulty of power dissipation and very high cost.

Yet another approach uses a system in which a feed array is located out of the focal plane of a parabolic reflector to de-focus the beam. This approach provides limited or no beam reconfiguration. Further, because the basic reflector geometry is de-optimized, the system suffers from increased scan losses, inferior cross-polar performance, mutual coupling effects and the like. Moreover, the number of optical and other elements required is still undesirably large, and the system requires complex input and output hybrid matrices.

Accordingly, there is a need for a flexible, reconfigurable payload with less complexity, more beam configurability, better reliability, and higher performance. The present invention satisfies these needs, and provides other benefits as well.

SUMMARY OF THE INVENTION

In accordance with the present invention, an antenna system having improved on-orbit beam configurability is provided. The antenna system includes a plurality of feed antennas located in the focal plane of a non-parabolic reflector that illuminate the reflector to form one or more defocused beams. The configurability is provided by changing the relative phase distribution among the feed antennas, which is accomplished at a low-level (i.e., prior to amplification). One or more incoming signals are divided in one or more corresponding dividing networks and are provided to a plurality of variable phase shifters, each of which corresponds to one of the feed antennas. After phase shifting, the signals are amplified by a plurality of fixed-amplitude amplifiers and provided to the feed antennas.

According to one embodiment, the present invention is an antenna system for generating and configuring at least one defocused beam. The antenna system includes a reflector having a focal plane and a non-parabolic curvature that forms the at least one defocused beam and a plurality of feed antennas that illuminate the reflector. Each feed antenna is disposed in the focal plane of the reflector. The antenna system further includes at least one incoming signal dividing network that divides at least one incoming signal into a plurality of sub-signals. Each sub-signal corresponds to one of the plurality of feed antennas. The antenna system further includes a plurality of variable phase shifters, each variable phase shifter receiving one of the plurality of sub-signals from the at least one incoming signal dividing network and phase shifting the one of the plurality of sub-signals to generate a corresponding phase-shifted sub-signal. The antenna system further includes a plurality of fixed-amplitude amplifiers, at least one amplifier corresponding to each of the plurality of feed antennas. The at least one amplifier for each feed antenna amplifies the corresponding phase-shifted sub-signal to generate an amplified phase-shifted sub-signal which is provided to the corresponding feed antenna.

According to another embodiment, the present invention is a method for generating and configuring at least one defocused beam using an antenna system including a reflector having a non-parabolic curvature and a plurality of feed antennas disposed in a focal plane of the reflector. The method includes the step of dividing at least one incoming signal with at least one incoming signal dividing network into a plurality of sub-signals, each sub-signal corresponding to one of the plurality of feed antennas. The method further includes the step of phase shifting the plurality of sub-signals with a plurality of variable phase shifters, each variable phase shifter receiving one of the plurality of sub-signals from the at least one incoming signal dividing network and phase shifting the one of the plurality of sub-signals to generate a corresponding phase-shifted sub-signal. The method further includes the step of amplifying the plurality of phase-shifted sub-signals with a plurality of fixed-amplitude amplifiers, at least one amplifier corresponding to each of the plurality of feed antennas. The at least one amplifier for each feed antenna amplifies a corresponding phase-shifted sub-signal to generate an amplified phase-shifted sub-signal which is provided to the corresponding feed antenna. The method further includes the step of illuminating the reflector with the plurality of feed antennas to generate the at least one defocused beam.

According to yet another embodiment, the present invention is a method for generating and configuring at least one defocused beam using an antenna system including a reflector having non-parabolic curvature and a plurality of feed antennas disposed in a focal plane of the reflector, the reflector including a single-axis gimbal mechanism. The method includes the step of dividing at least one incoming signal with at least one incoming signal dividing network into a plurality of sub-signals, each sub-signal corresponding to one of the plurality of feed antennas. The method further includes the step of phase shifting the plurality of sub-signals with a plurality of variable phase shifters, each variable phase shifter receiving one of the plurality of sub-signals from the at least one incoming signal dividing network and phase shifting the one of the plurality of sub-signals to generate a corresponding phase-shifted sub-signal. The method further includes the step of amplifying the plurality of phase-shifted sub-signals with a plurality of fixed-amplitude amplifiers, at least one amplifier corresponding to each of the plurality of feed antennas. The at least one amplifier for each feed antenna amplifies a corresponding phase-shifted sub-signal to generate an amplified phase-shifted sub-signal which is provided to the corresponding feed antenna. The method further includes the step of illuminating the reflector with the plurality of feed antennas to generate the at least one defocused beam. The plurality of variable phase shifters phase shift the plurality of sub-signals to compensate for a yawing motion of the antenna system. The single-axis gimbal mechanism of the reflector gimbals the reflector to compensate for a rolling motion of the antenna system.

It is to be understood that both the foregoing summary of the invention and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.

DETAILED DESCRIPTION OF THE INVENTION

In the following detailed description, numerous specific details are set forth to provide a full understanding of the present invention. It will be apparent, however, to one ordinarily skilled in the art that the present invention may be practiced without some of these specific details. In other instances, well-known structures and techniques have not been shown in detail to avoid unnecessarily obscuring the present invention.

FIG. 1illustrates an antenna system for generating and configuring at least one defocused beam according to one embodiment of the present invention. Antenna system100includes a reflector110having a non-parabolic curvature for forming one or more defocused beams. A plurality of feed antennas120are disposed in the focal plane111of reflector110. The feed antennas120illuminate reflector110to generate the one or more defocused beams in the following manner.

An incoming signal130is divided by an incoming signal dividing network140into a plurality of sub-signals145. Each sub signal145corresponds to one of the feed antennas120. Each sub-signal145is received from incoming signal dividing network140by a variable phase shifter150which phase shifts sub-signal145to generate a corresponding phase-shifted sub-signal155. A corresponding fixed-amplitude amplifier160amplifies each phase-shifted sub-signal155to generate an amplified phase-shifted sub-signal165which is provided to the corresponding feed antenna120. Feed antennas120together illuminate reflector110with amplified phase-shifted sub-signals165to generate the one or more defocused beams.

Amplifiers160are fixed-amplitude amplifiers. Accordingly, the configuration of the one or more beams is accomplished with phase-only synthesis, as is discussed in greater detail below. The use of fixed-amplitude amplifiers allows antenna system100to operate close to saturation with maximum DC-to-RF conversion efficiency (e.g., about 60% efficiency). According to one embodiment, amplifiers160are traveling wave tube amplifiers (“TWTAs”). According to an alternate embodiment, amplifiers160may be solid state power amplifiers (“SSPAs”) or any other fixed-amplitude amplifiers.

Reflector110has a non-parabolic curvature to form one or more defocused beams. According to one embodiment of the present invention, the curvature of reflector110is optimized to minimize the number of elements (e.g., amplifiers, feed antennas, etc.) in the feed array and to efficiently combine the individual beamlets (i.e., the signals from each feed antenna120). For example, according to one embodiment, the curvature of reflector110is selected so that the resultant beam has a quadratic phase distribution in the aperture plane of reflector110. This curvature broadens the one or more defocused beams to about 2 to 3 times the breadth that would be generated by a parabolic reflector, thereby reducing the required number of feed array elements by a factor of 4, as is discussed in greater detail below with respect toFIG. 4.

According to one embodiment, reflector110is a 12 meter mesh reflector. According to other embodiments, reflector110may be any other size, and may be any other kind of reflector known to those of skill in the art. According to one embodiment, reflector110may include a single-axis gimbal mechanism105to provide ground track compensation for the rolling motion of a satellite vehicle on which antenna system100is deployed.

According to one embodiment, variable phase shifters150are 8-bit phase shifters with the ability to adjust the phase of a signal in increments of 1.4°. According to other embodiments, variable phase shifters150may be any kind of phase shifter known to those of skill in the art. Post-amplification signal losses are kept low by phase shifting the sub-signals145with variable phase shifters150prior to amplification.

While in the exemplary embodiment illustrated inFIG. 1, incoming signal dividing network140is illustrated as a 1:3 network (i.e., dividing incoming signal130into three sub-signals145), the scope of the present invention is not limited to such an arrangement. Rather, an incoming signal dividing network of the present invention may divide an incoming signal into any number of sub-signals, corresponding to the number of feed antennas, as will be apparent to one of skill in the art. For example, in an embodiment in which the antenna system has 37 feed antennas, an incoming signal dividing network of the present invention will divide an incoming signal into 37 sub-signals.

The amplification in antenna system100is distributed by providing feed antennas120with corresponding amplifiers160. This distributed amplification mitigates the risk of multipaction. While in the present exemplary embodiment illustrated inFIG. 1, one amplifier160corresponds to each feed antenna120, the scope of the present invention is not limited to such an arrangement. Rather, as will be apparent to one of skill in the art, an antenna system of the present invention may have more than one amplifier corresponding to each feed antenna, as is illustrated in greater detail with respect toFIG. 2.

Turning toFIG. 2, an antenna system according to another embodiment of the present invention is illustrated. Antenna system200includes a reflector210having a non-parabolic curvature for forming one or more defocused beams. A plurality of feed antennas220are disposed in the focal plane211of reflector210. The feed antennas220illuminate reflector210to generate the one or more defocused beams in the following manner.

An incoming signal230is divided by an incoming signal dividing network240into a plurality of sub-signals245. Each sub signal245corresponds to one of the feed antennas220. Each sub-signal245is received from incoming signal dividing network240by a variable phase shifter250which phase shifts sub-signal245to generate a corresponding phase-shifted sub-signal255. A corresponding pre-amp dividing network270divides each phase-shifted sub-signal255to generate a plurality of divided phase-shifted sub-signals275. Each divided phase-shifted sub-signal275is provided to a corresponding fixed-amplitude amplifier260. Each amplifier260amplifies the corresponding divided phase-shifted sub-signal275to generate an amplified divided phase-shifted sub-signal265. Corresponding to each pre-amp dividing network270is a combining network280, which receives the amplified divided phase-shifted sub-signals265from each amplifier in a group of amplifiers corresponding to one feed antenna220and combines them to generate a corresponding amplified phase-shifted sub-signal285, which is provided to the corresponding feed antenna220. Feed antennas220together illuminate reflector210with amplified phase-shifted sub-signals285to the generate the one or more defocused beams.

According to one aspect of the present invention, the RF power of an antenna system of the present invention depends upon the number of feed antennas provided and the number of amplifiers associated with each feed antenna. Accordingly, Table 1, below, illustrates various arrangements in which the number of feed antennas and the number of amplifiers associated with each feed antenna are varied to provide a different levels of RF power. For the purposes of the present exemplary embodiment of Table 1, each amplifier is assumed to be a 230 W TWTA.

In the exemplary embodiment illustrated inFIG. 2, each feed antenna220has two corresponding fixed-amplitude amplifiers260. The scope of the present invention, however, is not limited to such an arrangement. Rather, as will be apparent to one of skill in the art, the present invention has application to antenna systems in which any number of amplifiers corresponds to each feed antenna, including arrangements in which different numbers of amplifiers correspond to different feed antennas.

For example,FIG. 3Aillustrates a feed array310according to one aspect of the present invention in which one feed antenna316corresponds to two fixed-amplitude amplifiers306and307, while other feed antennas315and317each correspond to one fixed-amplitude amplifier305and308, respectively. If each amplifier305,306,307and308have the same amplitude, feed antenna316will provide a beamlet with twice the amplitude of feed antennas315and317.

FIG. 3Billustrates a feed array320according to another aspect of the present invention, in which fixed-amplitude amplifiers do not correspond to particular feed antennas. An incoming signal321is divided by an incoming signal dividing network322into a plurality of sub-signals323. Each sub signal323corresponds to one of the feed antennas349and350. Each sub-signal323is received from incoming signal dividing network322by a variable phase shifter324which phase shifts sub-signal323to generate a corresponding phase-shifted sub-signal325. A redundancy ring with a plurality of fixed-amplitude amplifiers326amplifies phase-shifted sub-signals325and passes the amplified phase-shifted sub-signals327to couplers328and329. In the present exemplary embodiment, each coupler328is a 2:1 coupler, while coupler329is a 32:1 coupler. Accordingly, feed antenna350will provide a beamlet with 16 times the amplitude of any of feed antennas349.

FIG. 3Cillustrates a feed array360according to another aspect of the present invention, in which multiple incoming signals are provided to generate multiple beams. Each incoming signal361is divided by a corresponding incoming signal dividing network362to generate a corresponding plurality of sub-signals363. Each sub signal363generated by a single incoming signal dividing network corresponds to one of the feed antennas377. Each sub signal363is received from one of the incoming signal dividing networks362by a variable attenuator364and a variable phase shifter365which adjust the amplitude of sub-signal363, and phase shift sub-signal363, respectively, to generate a corresponding phase-shifted sub-signal366. Corresponding to each incoming signal dividing network362is a combining network367which combines one phase-shifted sub-signal366corresponding to each incoming signal dividing network362to generate a combined phase-shifted sub-signal368corresponding to one of the feed antennas377. The combined phase-shifted sub-signals368are received from combining networks367by an input hybrid matrix369, which generates hybrid phase-shifted sub-signals370. Each hybrid phase-shifted sub-signal370corresponds to one of the feed antennas377. Each hybrid phase-shifted sub-signal370passes through redundancy input switch matrix371and is provided to a corresponding fixed-amplitude amplifier372which amplifies the corresponding hybrid phase-shifted sub-signal370to generate an amplified hybrid phase-shifted sub-signal373. Amplified hybrid phase-shifted sub-signals373then pass through redundancy output switch matrix374and are received by an output hybrid matrix375, which generates amplified phase-shifted sub-signals376, which are provided to corresponding feed antennas377. Feed antennas377together illuminate a non-focused reflector (not illustrated) to generate a plurality of defocused beams.

Turning toFIG. 4, the curvature of a reflector of an antenna system according to various embodiments of the present invention is illustrated in greater detail.FIG. 4illustrates a feed array430illuminating three different reflectors410,411and412. Feed array430is disposed in the focal plane (not shown) of all three reflectors410,411and412, although the angles inFIG. 4have been exaggerated for clarity. Reflector411is a parabolic reflector. Accordingly, the corresponding wavefront421in the aperture plane of reflector411has a uniform phase. Reflector410has been “opened up” with respect to parabolic reflector411(i.e., the curvature of reflector410is less than that of reflector411) such that the corresponding wavefront420in the aperture plane of reflector410has a quadratic phase distribution. A quadratic phase distribution significantly broadens the one or more beams formed by reflector410, reducing the number of feed elements required to perform the necessary beam configurations by a factor of 4. Similarly, reflector412has been “closed in” with respect to parabolic reflector411(i.e., the curvature of reflector411is greater than that of reflector411) such that the corresponding wavefront422in the aperture plane of reflector412has a quadratic phase distribution.

While the non-parabolic reflectors410and412inFIG. 4have been illustrated as possessing a curvature for generating a quadratic phase distribution in a wavefront at their respective aperture planes, the scope of the present invention is not limited to such an arrangement. Rather, the present invention has application to reflectors with any non-parabolic curvature to generate one or more de-focused beams.

While due to the constraints imposed by schematic diagrams the feed arrays in the foregoing exemplary embodiments have been illustrated as including feed antennas arranged in a linear fashion, the scope of the present invention is not limited to such an arrangement. Rather, as will be apparent to one of skill in the art, the present invention has application to antenna systems in which the feed arrays include feed antennas in any arrangement. For example, as illustrated in greater detail with respect toFIGS. 5A and 5B, below, a feed array of the present invention may be arranged as a two-dimensional array.

FIG. 5Aillustrates the arrangement of a feed array500suitable for use in a HIEO satellite according to one aspect of the present invention. Feed array500includes 37 feed antennas501, each of which has the same amplitude of 238 W. The uniform distribution of amplitude between the large number of feed antennas501provides the extensive on-orbit configurability need to compensate for the continual yawing of a HIEO satellite.FIG. 5B, by way of contrast, illustrates a feed array510including 7 feed antennas511and512. Inner feed antenna512has a much larger amplitude (i.e., 5,328 W) than the outer feed antennas511(i.e., 380 W). The amplitudes of feed antennas511and512are, as inFIG. 5A, fixed amplitudes. This distribution of power among the feed antennas, in which the outer feed antennas512have about a −11.5 dB taper relative to central feed antenna511, is suitable for use in a GEO satellite, in which the required on-orbit configurability is not as extensive as in a HIEO satellite.

Turning toFIG. 6, the geometry of an antenna system according to one embodiment of the present invention is illustrated. Antenna system600includes non-parabolic reflector610and feed array620disposed in the focal plane630of reflector610. Reflector610has a diameter D. Focal plane630is located a focal distance F from reflector610. Feed array620is offset a height h from the edge of reflector610. According to one embodiment, to minimize scan loss, reflector610has a diameter D of 12.0 m and a focal distance F of 8.4 m, providing a moderate F/D ratio of about 0.7.

An antenna system of the present invention utilizes phase-only synthesis to configure (e.g., steer, shape, rotate, etc.) the one or more beams that it generates. For example, according to one experimental embodiment of the present invention, an antenna system of the present invention was mathematically modeled to illustrate the capability of phase-only synthesis to provide yaw compensation for a HIEO satellite with 50° of inclination and 12 hours of coverage over the continental United States (“CONUS”). The antenna system of the present exemplary embodiment included 37 feed antennas with 0.24 m apertures and equal amplitudes of 238 W illuminating a 12.0 m non-parabolic reflector with a left-handed circularly polarized (“LHCP”) signal in the S-Band (i.e. 2320.0 to 2332.5 MHz).

FIGS. 7 to 9illustrate the Effective isotropically-radiated power (“EIRP”) contour plots for this exemplary embodiment at each of 0°, 90° and 180° of yaw when the satellite is at apogee (i.e., 08:00 hr). As can be seen with reference toFIG. 7, the antenna system is able to generate a beam providing an EIRP of well over 60 dB for the CONUS 700 at 0° yaw. When the satellite on which the antenna system is yawed by 90°, the antenna system is able to compensate by reshaping the beam using phase-only synthesis, as can be seen with reference toFIG. 8, in which the CONUS 800 at 90° yaw is still provided with an EIRP of well over 60 dB. Even as the satellite yaws to 180°, the antenna system is able to compensate using phase-only synthesis, as can be seen with reference toFIG. 9, in which the CONUS 900 at 180° yaw is still provided with an EIRP of well over 60 dB. The phase-only synthesis allows the beam to cover the CONUS more efficiently, since less spill-over energy is expended outside of the desired coverage area.

Table 2, below, illustrates the phase delays introduced by the variable phase shifters (i.e., phase-only synthesis) at apogee for each of the 37 feed antennas in the antenna of the present exemplary embodiment at each of 0°, 45°, 90°, 135° and 180° of yaw.

As can be seen with reference to Table 2, the amplitude of each feed antenna was a constant −15.682 dB (supplied by a single 238 W fixed-amplitude amplifier per feed antenna). The beam configuration was accordingly provided solely by the phase shift introduced in each beamlet by the variable phase shifters.

Turning toFIGS. 10A and 10B, an additional performance advantage of an antenna system according to one embodiment of the present invention is illustrated.FIG. 10Billustrates the phase distribution of the primary pattern of an antenna system according to one embodiment of the present invention, at each of 0° (1030), 45° yaw (1031),90° yaw (1032) and 135° yaw (1033).FIG. 10Ais a graph illustrating the cross-polar isolation of the primary pattern of the same antenna system. Over the angle subtended by the feed array (i.e., from about −25° to about 25°), the difference between cross-polar directivity (1020at 0° yaw,1021at 45° yaw,1022at 90° yaw, and1023at 135° yaw) and the co-polar directivity (1010at 0° yaw,1011at 45° yaw,1012at 90° yaw, and1013at 135° yaw) in the primary pattern is greater than 33 dB. This cross-polar isolation of greater than 33 dB in the primary pattern permits an antenna system of the present invention to enjoy high gain and directivity, regardless of the phase distribution of the feed array.

Turning toFIG. 11, a cross-polar isolation contour plot for this exemplary embodiment at 0° of yaw when the satellite is at apogee (i.e., 08:00 hr) is illustrated. As can be seen with reference toFIG. 11, the antenna system is able to generate a beam providing better than 30 dB cross-polar isolation for the CONUS 1100.

According to another experimental embodiment of the present invention, an antenna system of the present invention was mathematically modeled to illustrate the capability of phase-only synthesis to provide on-orbit beam reconfiguration for a GEO satellite with an orbital arc of 94° to 98° west. The antenna system of the present exemplary embodiment included 7 feed antennas with 0.37 m apertures and a fixed power distribution (i.e., a central feed of 24×222 W and 6 outer feeds of 2×190 W) illuminating a 12.0 m non-parabolic shaped reflector with a left-handed circularly polarized (“LHCP”) signal in the S-Band (i.e., 2320.0 to 2332.5 MHz). The primary pattern cross-polar isolation was shown to be better than 40 dB, with a feed efficiency of greater than 85% and a multipaction margin for 9 KW peak power of 6.5 dB.

FIGS. 12 and 13illustrate the EIRP contour plots for this exemplary embodiment at 96° W for a baseline configuration and for a configuration in which an additional 1 dB more EIRP is provided to Canada. As can be seen with reference toFIG. 12, the antenna system is able to generate a beam providing an EIRP of well over 64 dB for the CONUS 1200. Turning toFIG. 13, through phase-only synthesis, the antenna system is able to reconfigure the beam to provide an additional 1 dB of EIRP to Canada 1310 while still providing over 64 dB for the CONUS 1300.

FIG. 14illustrates a cross-polar isolation contour plot for the baseline configuration of this exemplary embodiment at 96° W. As can be seen with reference toFIG. 14, the antenna system is able to generate a beam providing a cross-polar isolation of better than 36 dB for substantially all of the CONUS 1400. Turning toFIG. 15, when the antenna system is reconfigured through phase-only synthesis to provide an additional 1 dB of EIRP to Canada 1510, the cross-polar isolation over the CONUS 1500 and substantially all of Canada 1510 remains better than 36 dB.

Table 3, below, illustrates the phase delays introduced by the variable phase shifters (i.e., phase-only synthesis) for each of the 7 feed antennas in the antenna system of the present exemplary embodiment in the baseline configuration and to provide an additional 1° of EIRP TO Canada.

As can be seen with reference to Table 3, the amplitude of each feed antenna was kept constant, and the beam configuration was provided solely by the phase shift introduced in each beamlet by the variable phase shifters.

FIG. 16is a flowchart illustrating a method for generating and configuring at least one defocused beam using an antenna system with a non-parabolic reflector and an array of feed antennas according to one embodiment of the present invention. As is discussed in greater detail above, the array of feed antennas is disposed in the focal plane of the non-parabolic reflector. In step1610, an incoming signal is divided into a plurality of sub signals using an incoming signal dividing network. Each sub-signal corresponds to one of the feed antennas in the feed array. In step1620, each of the sub-signals is phase-shifted, using a variable phase shifter, to generate a corresponding phase-shifted sub-signal. In step1630, each of the phase-shifted sub-signals is amplified by one or more amplifiers to generate an amplified phase-shifted sub-signal. As discussed in greater detail with respect toFIG. 2, above, in an embodiment in which more than one amplifier corresponds to each feed antenna, each phase-shifted sub-signal will first be divided by a corresponding pre-amp dividing network to generate a plurality of divided phase-shifted sub-signals, which, after amplification, will be combined in a combining network. In step1640, each amplified phase-shifted sub-signal generated in step1630is provided to the corresponding feed antenna which, in step1650, illuminates the non-parabolic reflector to generate at least one defocused beam.

While the present invention has been particularly described with reference to the various figures and embodiments, it should be understood that these are for illustration purposes only and should not be taken as limiting the scope of the invention. There may be many other ways to implement the invention. Many changes and modifications may be made to the invention, by one having ordinary skill in the art, without departing from the spirit and scope the invention.