Antenna Subreflector with Constant Phase Center and 3D Tracking

Abstract

A dual reflector earth station antenna (ESA) system for transmitting an uplink in a first frequency band and receiving a downlink in a second frequency band, the ESA system including: a reflector, a reflector tracking assembly coupled to the reflector and configured to control an orientation of the reflector, a feed horn coupled to the reflector and optimized for an approximately constant phase center for both the first frequency band and the second frequency band, a sub-reflector tracking assembly configured to track in X-, Y-, and Z-axes and supported near a focal point of the reflector, and a control system in communication with the sub-reflector tracking assembly and including at least one processor, the processor configured to adjust a sub-reflector of the sub-reflector tracking assembly along the X-, Y-, and Z-axes of the reflector until a signal gain of the reflector antenna is maximized for the second frequency band, whereby the optimization of the feed horn for an approximately constant phase center for both the first frequency band and the second frequency band simultaneously maximizes the signal gain of the reflector antenna for the first frequency band as well.

Description

[Technical field]

[0001] The embodiments described herein are directed generally to satellite communications, and more specifically to an antenna feed horn having a nearly constant phase center with a subreflector that tracks in the Z axis. [Background technology]

[0002] Electrically large reflector antennas enable RF communications links from satellites to earth stations with very narrow beamwidths. Typically, the earth station reflector antenna is aligned with the target satellite's orbit via a tracking mount that orients the entire antenna assembly to align the reflector antenna with the satellite. Due to the significant weight and wind forces of large reflector antennas, the use of a tracking mount with precise adjustment capability, e.g., within +0.05 degrees, would significantly increase the cost and complexity of the earth station.

[0003] No. 6,943,750 to Brooker et al. entitled "Self-Pointing Antenna Scanning," issued Sep. 13, 2005, and incorporated herein by reference in its entirety, discloses an antenna adjustment assembly for a reflector antenna that utilizes orthogonal adjustments made to the position of a subreflector relative to a main reflector. This subreflector tracking technique is particularly useful for small beam alignment adjustments between a reflector antenna and a satellite in geostationary orbit, for example, as the satellite wobble and / or drifts in orbit. Handling these small alignment adjustments via the subreflector tracking technique greatly simplifies the requirement for additional tracking mounts, if any.

[0004] The system and method described in U.S. Patent No. 8,199,061 (hereby incorporated by reference) includes an additional sub-reflector tracking in a third axis (the "Z" axis of the main reflector). Implementing this approach improves the stability of the downlink (20 GHz) signal. However, the uplink (30 GHz) stability is not improved as much as expected. Summary of the Invention

[0005] The present disclosure provides an improved communication system. The following summary is not intended to define all aspects of the present disclosure, and other features and advantages of the present disclosure will become apparent from the following detailed description, including the drawings. It should be understood that the present disclosure is intended to be linked as an integrated document, and that all combinations of features described herein are contemplated, even if the combinations of features are not found together in the same sentence or paragraph or section of the disclosure. Furthermore, the present disclosure includes, as an additional aspect, all embodiments of the present invention that are narrower in scope in any respect than the variations specifically mentioned herein.

[0006] As disclosed herein, in one embodiment, a dual reflector earth station antenna (ESA) system for transmitting an uplink in a first frequency band and receiving a downlink in a second frequency band includes a reflector, a reflector tracking assembly coupled to the reflector and configured to control an orientation of the reflector, a feed horn coupled to the reflector and optimized for an approximately constant phase center for both the first frequency band and the second frequency band, a sub-reflector tracking assembly including a sub-reflector configured to track in X-axis, Y-axis, and Z-axis and supported near a focal point of the reflector, and a control system in communication with the sub-reflector tracking assembly and including at least one processor, the processor configured to adjust a sub-reflector of the sub-reflector tracking assembly along the X-axis, Y-axis, and Z-axis of the reflector until a signal gain of the reflector antenna is maximized for the second frequency band, and the optimization of the feed horn for an approximately constant phase center for both the first frequency band and the second frequency band simultaneously maximizes the signal gain of the reflector antenna for the first frequency band as well.

[0007] In a further embodiment, the system further includes at least one feedback sensor configured to monitor a position of the sub-reflector tracking assembly in at least the X-axis and Y-axis, and the control system is further configured to adjust the sub-reflector tracking assembly via the reflector tracking assembly when the at least one feedback sensor indicates that an X-axis or Y-axis travel limit of the sub-reflector tracking assembly mount has been reached.

[0008] In a further embodiment, the feed horn has a variable flare angle optimized to provide a substantially constant phase center over a predetermined frequency range, the predetermined frequency being between 17.7 and 31 GHz.

[0009] In a further embodiment, the feed horn is a corrugated feed horn with a varying flare angle.

[0010] In a further embodiment, the feed horn has a linear taper and a very narrow flare angle of 6 degrees or less at the opening of the feed horn.

[0011] In a further embodiment, the feed horn has a half cosine taper to provide a narrow flare angle at the opening of the feed horn.

[0012] In a further embodiment, the control system is further configured to adjust the sub-reflector tracking assembly at periodic intervals.

[0013] As disclosed herein, in one embodiment, a method of reflector tracking with a dual reflector Earth Station Antenna (ESA) system for transmitting an uplink in a first frequency band and receiving a downlink in a second frequency band is disclosed, the ESA system including a feed horn optimized for a substantially constant phase center for both the first frequency band and the second frequency band, and a sub-reflector tracking assembly supported proximate a focal point of the reflector and trackable in X, Y and Z axes, the method including adjusting a sub-reflector of the sub-reflector tracking assembly along the X, Y and Z axes of the reflector until a signal gain of the reflector antenna is maximized for the second frequency band, where the optimization of the feed horn for a substantially constant phase center for both the first frequency band and the second frequency band simultaneously maximizes the signal gain of the reflector antenna for the first frequency band.

[0014] In a further embodiment, the adjustment of the sub-reflector tracking assembly is repeated at periodic intervals.

[0015] In a further embodiment, adjustments of the sub-reflector tracking assembly are initiated in response to changes in temperature.

[0016] In a further embodiment, adjustment of the sub-reflector tracking assembly is initiated in response to a preset time.

[0017] In a further embodiment, the range of adjustment along the z-axis is less than 0.5 inches.

[0018] In a further embodiment, the adjustment is provided by varying the signal gain.

[0019] In a further embodiment, the method further includes adjusting the sub-reflector tracking assembly to the recorded position of highest signal gain within a defined period of time, and resetting the recorded position if adjusting the sub-reflector tracking assembly results in a higher signal gain.

[0020] In a further embodiment, adjustment of the sub-mirror tracking assembly is performed via actuation of linear actuators for each of the X, Y and Z axes.

[0021] In a further embodiment, the method further includes adjusting the sub-mirror tracking assembly via the mirror tracking assembly when at least one feedback sensor indicates that an X-axis or Y-axis travel limit of the sub-mirror tracking assembly has been reached. [Brief description of the drawings]

[0022] The details of the present invention, both as to their structure and operation, can be gleaned in part from study of the accompanying drawings, in which like reference numerals refer to like parts and in which:

[0023] [Figure 1] FIG. 2 is a graph illustrating one embodiment of satellite communications between multiple ground stations. [Diagram 2] FIG. 1 is a graphical representation of a dual reflector earth station antenna system. [Diagram 3] FIG. 1 is a graph of a conventional feed horn with a 15 degree semi-flare angle that exhibits a large phase center shift with frequency. [Figure 4] FIG. 1 is a graphical representation of a feed horn with a variable flare angle optimized to achieve a nearly constant phase center over the frequency range of interest (i.e., 17.7-31 GHz). [Diagram 5] FIG. 1 is a graph of aperture efficiency for selected frequencies between 17.7 GHz and 31 GHz over a range of different subreflector heights (subheights) for a 15 degree semi-flared feed horn. [Figure 6] 1 is a graph of aperture efficiency for a range of subreflector heights (subheights) for a feed horn with near constant phase center for selected frequencies between 17.7 GHz and 31 GHz. [Figure 7] FIG. 1 is an isometric view of a subreflector tracking assembly. [Figure 8]FIG. 8 is an end view of the subreflector mount end of the assembly of FIG. [Figure 9] FIG. 9 is a cutaway side view taken along line AA in FIG. 8. [Figure 10] FIG. 9 is a cutaway side view taken along line BB in FIG. 8. [Figure 11] FIG. 8 is an isometric view of the assembly of FIG. 7 with the bellows coupled to the subreflector mount and base. [Figure 12] 2 is a functional block diagram of components of a communication device that may be used within the communication system of FIG. 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] 1 is a graphical illustration of one embodiment of satellite communications between multiple ground stations. A communications system ("system") 100 shows multiple ground stations 102, 104, 106 communicating with each other via a satellite 110. Each of the ground stations may include a dual reflector earth station antenna (ESA) system 102a, 104a, and 106a, respectively. Each ESA may include a sub-reflector tracking assembly and a dual reflector antenna tracking mount. In some embodiments, the communications system 100 may include more than three ground stations 102, 104, 106 and more than one satellite 110.

[0025] In a system such as the system 100 shown in FIG. 1, the sub-reflector tracker (SRT) technique can be used for dual reflector ESAs (e.g., antennas 102a, 104a and 106a in FIG. 1, 2 and 216 in FIG. 12) to scan the antenna beam by a small amount that is typically required to keep station on a geostationary orbit (GEO) satellite without the need to move the entire antenna structure. In a two-dimensional (2D) scan, the sub-reflector is shifted laterally in the XY plane perpendicular to the Z axis of the main reflector, which is the boresight direction of the antenna or the peak radiation direction without sub-reflector scanning. This sub-reflector shifting performs limited scanning of the antenna beam at azimuth (AZ) and / or elevation (EL) angles away from the normal non-scanning direction without moving the entire antenna structure that is typically required for ESAs.

[0026] The systems and methods described in U.S. Pat. No. 8,199,061 can be implemented in the ground stations 102, 103, and 106. These systems and methods allow the sub-reflector to be moved up and down, i.e., away from or closer to the surface of the main reflector, allowing the antenna to be adaptively refocused, for example, during normal tracking of a GEO satellite, as needed. In one example, this is used to provide adaptive refocusing of medium to large Ka-band antennas under thermal gradient conditions. These deformations may be due to solar or other reflector heating effects. Implementing this approach improves the stability of the downlink (e.g., 20 GHz) signal, but not the uplink (e.g., 30 GHz) stability as expected. This effect is due to the phase center of the feed horn shifting between the two different bands. The control software and algorithms can be modified to minimize this effect. Adding Z-axis tracking allows the antenna to be adaptively focused to maximize the downlink signal. For example, for Ka-band, the downlink signal is at or near 20 GHz.

[0027] FIG. 2 is a graphical illustration of a dual reflector ESA system that can be used in various embodiments of the invention, including the system shown in FIG. 1. The ESA includes a reflector 150 having a tracking assembly 152 for the reflector 150 and a sub-reflector tracking assembly 154 (including a sub-reflector), such as the sub-reflector tracking assembly 10 described in connection with FIGS. 8-11 below. The ESA further includes a feed horn 157 secured to the reflector 150 or a support structure via an outer support tube 159. The outer support tube 159 encloses an RF network that connects the feed horn to the input (transmit) and output (receive) ports (not shown) of the ESA. The feed horn 157, the outer support tube 159, and the RF network within the outer support tube 159 can be collectively referred to as a feed assembly. In the embodiment shown in FIG. 2, the sub-reflector tracking assembly 154 is supported by four columns at the 45 degree plane of the antenna (midway between the horizontal and vertical planes). The four struts are connected to the main reflector's mechanical support structure (either through holes in a panel or attached to supports on the reflector itself) and come together in an apex bracket on the subreflector tracking assembly 154. The tracking assembly on the reflector 152 controls the orientation of the large reflector 150. The subreflector tracking assembly 154 controls the position of the subreflector in the X, Y, and Z axes, typically scanning the antenna beam in small increments without having to move the entire antenna structure via the tracking assembly on the reflector 152.

[0028] One limitation of this approach is that the performance feedback that controls this optimization method is typically limited to the downlink signal. Therefore, if the optimal focus position (sub-height) of the sub-reflector is different for the uplink signal, this optimization of the downlink signal may actually degrade the uplink signal to an unacceptable level. Eliminating this issue allows this adaptive focus approach to be implemented more aggressively to better correct for even small focus errors.

[0029] The issue of different optimum sub-reflector heights for downlink and uplink signals is due to a shift in the phase center of the antenna feed horn. This is evident when comparing the optimum sub-reflector heights of two different feed horn designs shown in Figures 3 and 4 within the same antenna optical system. Figure 3 is a graphical representation of a conventional feed horn with a 15 degree semi-flare angle whose phase center moves significantly with frequency. Figure 4 is a graphical representation of a feed horn with a variable flare angle optimized to achieve a nearly constant phase center over the frequency range of interest (i.e., 17.7-31 GHz).

[0030] Figures 5 and 6 are plots of the calculated aperture efficiency for the two feed horns of Figures 3 and 4 operating in the same dual reflector antenna system. Note that for the conventional feed horn design (Figure 3) with a 15 degree semi-flare angle, the optimum sub-height differs significantly between the downlink (17.7-21.2 GHz) and uplink (27.5-31 GHz) bands, as shown in Figure 5. As the frequency increases from 17.7 GHz to 31 GHz, the optimum sub-height decreases by approximately 0.125 inches.

[0031] Looking at the optimized near-constant phase center feed horn (Figure 4), there is little difference in the optimal sub-height across the entire 17.7-31 GHz frequency range, as shown in Figure 6. Because the optimal sub-height is nearly constant for both uplink and downlink signals, using a near-constant phase center feed horn allows for more aggressive adaptive focusing by the SRT, including Z-axis sub-height adjustment, despite having performance feedback information for only the downlink signal.

[0032] Other implementations are possible. Shown above is a corrugated feed horn with various flare angles that have been computer optimized to produce a nearly constant phase center. However, this can also be achieved with other types of feed horns, including more conventionally designed feed horns with a linear taper at the feed horn opening and a very narrow flare angle (e.g., on the order of 6 degrees or less). These feed horns are typically very long and expensive to manufacture. Similarly, more conventional "compact taper" feed horns with half cosine tapers, well known to those skilled in the art, can also be used to provide a narrow flare angle at the opening with small variations in phase center versus frequency. These alternative approaches may be particularly preferable when the antenna optical system requires a more directional feed than can be achieved with the approach of varying the flare angle shown in FIG. 4 above.

[0033] In some embodiments, "substantially constant phase center" refers to a feed horn that is specifically designed to reduce phase center movement compared to more conventional feed horns. For example, a conventional horn with a linear taper (e.g., a 15 degree semi-flare angle) tends to have a significant inward phase center movement as the frequency increases across a wide frequency band (e.g., 17-31 GHz). More generally, "substantially constant phase center" refers to a feed horn that is specifically designed to reduce phase center movement compared to a more conventional feed horn with a 10 degree semi-flare angle or a more linear linear taper.

[0034] In another embodiment, a nearly constant phase center feed horn can be achieved by reducing the semi-flare angle of the horn to less than 10 degrees, which tends to minimize phase center movement over frequency. Further, the semi-flare angle of the horn can be reduced to the range of 5 to 6 degrees.

[0035] A further example of "nearly constant phase center" is shown in Figure 4. The phase center of a Ka-band feed horn with an "nearly constant" phase center moves within a 0.087 inch wide window along the rotational feed axis (Z-axis) over the frequency band of 17.7 to 31 GHz. From phase centers calculated at several frequencies across the band, the phase center varies from 5.514 inches to 5.601 inches within the horn opening.

[0036] The results above are for a conventional feed horn with a phase center defined as 15 degrees, where the phase center is taken to be a point inside the horn opening along the horn's axis of rotation, and if that point is taken as the horn's center of rotation (COR), then the far-field radiation phase will be equal to the far-field radiation phase at the boresight (0 degree) angle at an angle of 15 degrees. In this example, the horn radiation is circularly polarized in the principal planes. Other definitions of phase center can also be used.

[0037] Using the same 15 degree phase center definition as the conventional horn of Figure 3, the total variation in phase center depth relative to the aperture is 1.308 inches.

[0038] As shown in Figures 8-11, an exemplary embodiment of the sub-reflector tracking assembly 10 exhibits z-axis movement capability generally parallel to the boresight of the reflector antenna and can be used with a central feed horn of nearly constant phase to maximize performance. In one embodiment, the sub-reflector tracking assembly 10 is controlled by a control system, such as a processor 204 shown in Figure 12.

[0039] To minimize slop, drive windup, axis wobble or backlash, the sub-reflector tracking assembly 10 utilizes at least one linear actuator 12 for each of the X, Y and Z axes. Depending on the type of linear actuator 12 selected, one or more guides 14 may also be applied in parallel to each linear actuator 12 to reduce mechanical load on the linear actuator 12 and improve axial accuracy. The linear actuator 12 may be, for example, a stepper motor 16 with a lead screw 18 that drives a threaded nut 20 axially along the lead screw 18. The guide(s) 14 may be, for example, self-aligning, recirculating, ball bushing, or sliding linear bearings and / or rails.

[0040] In this embodiment, the X-axis and Y-axis linear actuator(s) 12 and guide(s) 14 are mounted between the subreflector mount 22 and the intermediate support 24, with the subreflector mount 22 positioned orthogonally relative to the intermediate support 24. The Z-axis linear actuator 12 may be disposed between the intermediate support 24 and a base 26. The base 26 may be provided with attachment point(s) 28 for interconnection with a mounting post supporting the subreflector tracking assembly 10. The subreflector is mounted to the subreflector mount 22 and positioned near the expected focal point of the associated primary reflector. In an embodiment in which the Z-axis linear actuator 12 primarily corrects thermal defocus, the range of the Z-axis linear actuator 12 may be significantly smaller than the X-axis and Y-axis linear actuator(s) 12. For example, an 8.1 m reflector antenna may utilize a Z-axis linear actuator 12 with a travel range of 0.5 inches or less.

[0041] The arrangement of the Z-axis linear actuator 12 and the X-axis and Y-axis linear actuator(s) 12 on either side of the intermediate support 24 is independent of which end of the subreflector tracking assembly 10 the subreflector is mounted on, which likewise are coupled to a mounting post. For example, in an alternative reverse configuration, the subreflector mount 22 could be coupled to a post of the reflector antenna, and the subreflector could be coupled to the base 26.

[0042] The spatial calculations for driving the various linear actuator(s) 12 along each axis can be simplified by arranging each of the base 26, intermediate support 24, and subreflector mount 22 parallel to one another. Feedback sensors 30 along each axis can be used to monitor the position along the range of travel of each linear actuator 12. The feedback sensors 30 can be implemented, for example, as linear potentiometers 32, resolvers, encoders, or limit switch(es).

[0043] Control, power, and / or feedback wiring may be routed through one or more sleeve(s) 34 that penetrate the intermediate support 24 to minimize the possibility of the wiring being damaged over time by movement between the base 26 and the intermediate support 24 driven by the Z-axis linear actuator 12. A bellows 36 coupled to the periphery of the base 26 and the subreflector mount 22 may be applied to isolate and environmentally protect the interior 38 of the subreflector tracking assembly 10 from the exterior 40. One or more drainage hole(s) 42 may be provided in the bellows 36 and / or the subreflector mount to minimize the possibility of condensation or the like building up within the assembly over time.

[0044] In use, a three-point peaking algorithm can be applied which monitors the signal level seen by the receiver, the signal gain to determine the beam peak. As the linear actuator(s) 12 move the subreflector mount 22 and thereby the subreflector, the change in signal gain is monitored to drive further scanning movements of the subreflector tracking assembly 10, always with respect to the X, Y, Z coordinate position of the subreflector at the last recorded beam peak. The peaking algorithm does not need to distinguish between optimal beam alignment and scanning focus, since the beam peak occurs when both alignment and focus are optimal. If a nearly constant phase centre feed horn is used, the optimal sub height is nearly constant for both uplink and downlink signals, so more aggressive adaptive focusing can be used, despite having performance feedback information for only the downlink signal.

[0045] Periodic intervals can be applied between scans to obtain additional beam peaks. Similarly, scans in the Z-axis can be further initiated in response to preset times, signal gain changes, time intervals, and / or temperature changes sensed, for example, by a temperature sensor local to the reflector antenna.

[0046] If the peaking algorithm directs the assembly out of range on either the X or Y axis, a signal and / or alarm may be generated to initiate an adjustment of the antenna tracking mount to re-center the assembly.

[0047] Parts list for Figs. 7 to 11. 10 Sub-reflector tracking assembly 12 Linear Actuators 14 Guide 16 Stepping motor 18 Lead screw 20 Threaded Nuts 22 Sub-reflector mount 24 Intermediate support 26 Base 28 mounting points 30 Feedback Sensor 32 Linear Potentiometer 34 Sleeve 36 Bellows 38 Interior 40 Exterior 42 Drainage hole

[0048] One embodiment includes a method for reflector tracking in a dual reflector ESA, such as the dual reflector ESA described in connection with FIG. 2, transmitting an uplink in a first frequency band and receiving a downlink in a second frequency band. The ESA includes a feed horn optimized for a nearly constant phase center for both the first and second frequency bands, and capable of subreflector tracking in the X, Y and Z axes (e.g., using the subreflector tracking assembly 10 described above). The X and Y axes are used to move the subreflector laterally in a plane perpendicular to the reflector's axis of symmetry (rotation) to steer the beam. This is used, for example, to keep the satellite pointing at a satellite that typically moves slightly over time. This corresponds to a very small azimuth correction in both azimuth and elevation of the entire antenna. That is, how such tracking is achieved in an antenna system without a subreflector tracking assembly for the X and Y axis subreflector movement.

[0049] The X and Y axis movements of the sub-mirror tracker assembly are used for beam steering, while the Z axis movement of the sub-mirror tracker assembly is used primarily for signal peaking.

[0050] The method may be performed under the control of a control system such as, for example, processor 204 shown in Figure 12. The method includes adjusting a subreflector mount (e.g., mount 22) of a subreflector tracking assembly supported proximate a focal point of the reflector antenna along the X-, Y- and Z-axes of the reflector antenna until a signal gain in a second frequency band received by the reflector antenna is maximized, and adjusting the subreflector mount via the reflector tracking assembly (e.g., 152 in Figure 2) of the reflector antenna when a feedback sensor indicates that an X- or Y-axis travel limit of the subreflector mount has been reached.

[0051] The method may further include adjusting the sub-reflector tracking assembly at periodic intervals.

[0052] Additionally or alternatively, adjustment of the sub-reflector tracking assembly may be initiated in response to a change in temperature, and / or adjustment of the sub-reflector tracking assembly may be initiated in response to a preset time, and / or adjustment of the sub-reflector tracking assembly may be initiated by a change in signal gain.

[0053] The method may further include adjusting the sub-reflector tracking assembly to a recorded position of highest signal gain within a predefined period of time, and resetting the recorded position if a higher signal gain is obtained by adjusting the sub-reflector tracking assembly.

[0054] Figure 12 is a functional block diagram of components of a communications device that may be used within the communications system of Figure 1. As shown, a communications device 200 may be implemented as a ground station of Figure 1. For example, each of the ground stations 102, 104, and 106 may be implemented as an example of a communications device 200.

[0055] The communication device ("device") 200 may include one or more processors 204 that control the operation of the communication device 200. The processor 204 may also be referred to as a central processing unit (CPU). The communication device 200 further includes a memory 206 operatively connected to the processor 204, the memory 206 including both read-only memory (ROM) and random access memory (RAM) to provide instructions and data to the processor 204. A portion of the memory 206 may also include non-volatile random access memory (NVRAM). The processor 204 typically performs logical and arithmetic operations based on program instructions stored in the memory 206. The instructions in the memory 206 are executable to implement the methods described herein.

[0056] When the communications device 200 is implemented or used as a receiving node or ground station, the processor 204 can be configured to process information from a number of different signal types. In such an embodiment, the communications device 200 is implemented as a ground station 106 and configured to receive the composite signal 136 and parse or separate it into its constituent signals (e.g., signal 122 and signal 124). For example, the processor 204 can be configured to determine the frequency, bandwidth, modulation type, shaping coefficients, and symbol trajectories, among other transmission characteristics, to recreate or regenerate the signals 122, 124. The processor 204 can implement various processes or methods in a particular signal separation and interference reduction module ("module") 202 to affect such decisions.

[0057] Processor 204 may comprise or be a component of a processing system implemented with one or more processors 204. Processor 204 may be implemented by any combination of one or more of a general purpose microprocessor, a microcontroller, a digital signal processor (DSP)(s), a field programmable gate array (FPGA)(s), a programmable logic device (PLD)(s), a controller, a state machine, gate logic, discrete hardware components, a dedicated hardware finite state machine, or any other suitable entity capable of performing calculations or other manipulations of information.

[0058] The processor 204 may also include a machine-readable medium for storing software. Software shall be construed broadly to mean any type of instructions, whether referred to as software, firmware, middleware, microcode, hardware description language, or the like. The instructions may include code (e.g., code in source code format, binary code format, executable code format, or any other suitable code format). The instructions, when executed by the one or more processors 204, cause the processing system to perform and control various functions described herein.

[0059] The communications device 200 may also include a housing 208 that includes a transmitter 210 and a receiver 212 to enable transmission and reception of data between the communications device 200 and a remote location. For example, such communications may occur between the ground stations 102, 104, and 106. The transmitter 210 and receiver 212 may be combined into a transceiver 214. An antenna 216 may be mounted to the housing 208 and electrically coupled to the transceiver 214 or to the transmitter 210 and receiver 212 independently. Alternatively, the antenna may be located remotely from the communications device 200 and connected by a cable. The communications device 200 may also include multiple transmitters, multiple receivers, multiple transceivers, and / or multiple antennas (not shown).

[0060] The communications device 200 may also include a signal detector 218 that may be used to detect and quantify the level of signals received by the transceiver 214. The signal detector 218 may detect signal characteristics such as frequency, bandwidth, symbol rate, total energy, energy per symbol, power spectral density, and other signal characteristics. The signal detector 218 may be further configured to process input data (e.g., one or more signals 122, 124) to ensure that the processor 204 is receiving the correct bandwidth-limited portion of the wireless communications spectrum in use.

[0061] The communications device 200 may also include a digital signal processor (DSP) 220 for use in processing signals. The DSP 220 may be configured to generate data units for transmission. The DSP 220 may further cooperate with the signal detector 218 and the processor 204 to determine certain characteristics of the composite signal 136.

[0062] The communication device 200, in some aspects, may further comprise a user interface 222. The user interface 222 may include a keypad, a microphone, a speaker, and / or a display. The user interface 222 may include any element or component that conveys information to and / or receives input from a user of the device 200.

[0063] The various components of device 200 described herein may be coupled together by a bus system 226. The bus system 226 may include, for example, a power bus, a control signal bus, and a status signal bus in addition to a data bus. In one embodiment, the bus 226 provides communication to the various elements of an EAS system controlled by the processor 204. Those skilled in the art will appreciate that the components of device 200 may be coupled together or may use some other mechanism to accept or provide input to one another.

[0064] Although a number of separate components are shown in Figure 12, one or more of the components may be combined or commonly implemented. For example, the processor 204 may be used to implement the functionality described above with respect to the processor 204 as well as the functionality described above with respect to the signal detector 218 and / or the DSP 220. Also, each component shown in Figure 12 may be implemented using multiple separate elements. Additionally, the processor 204 may be used to implement any of the components, modules, circuits, etc. described below, or each may be implemented using multiple separate elements.

[0065] Various exemplary steps or processes described in connection with the embodiments disclosed herein may be implemented or performed by one or more processors, such as a general purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof intended to perform the functions described herein. A general purpose processor may be a microprocessor, but in the alternative, the processor may be any processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices, such as, for example, a combination of a DSP and a microprocessor, multiple microprocessors, one or more microprocessors in combination with a DSP core, or other such configurations.

[0066] The functions of the steps and modules of a method or algorithm described in connection with the embodiments disclosed herein may be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. The software module may reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, a hard disk, a removable disk, a CD-ROM, or any other form of storage medium. An exemplary storage medium may be coupled to the processor such that the processor can read information from, and write information to, the storage medium. Alternatively, the storage medium may be integral to the processor. The processor and the storage medium may reside in an ASIC.

[0067] The above description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles described herein may be applied to other embodiments without departing from the spirit or scope of the present disclosure. It should therefore be understood that the description and drawings presented herein represent presently preferred embodiments of the present invention, and thus represent the subject matter broadly contemplated by the present disclosure. It is further understood that the scope of the present disclosure fully encompasses other embodiments that will become apparent to those skilled in the art, and thus the scope of the present disclosure is not limited by anything other than the appended claims.

Claims

1. 1. A dual reflector Earth Station Antenna (ESA) system for transmitting an uplink in a first frequency band and receiving a downlink in a second frequency band, the ESA system comprising: A reflector; a reflector tracking assembly coupled to the reflector and configured to control an orientation of the reflector; a feed horn coupled to the reflector and optimized for a substantially constant phase center for both the first frequency band and the second frequency band; a sub-reflector tracking assembly configured for tracking in the X-axis, Y-axis, and Z-axis and including a sub-reflector supported near a focal point of the reflector; in communication with the sub-reflector tracking assembly; a control system including at least one processor configured to adjust the subreflector of the subreflector tracking assembly along X, Y and Z axes of the reflector until a signal gain of the reflector antenna is maximized for the second frequency band; The system, wherein the optimization of the feed horn to a substantially constant phase center for both the first frequency band and the second frequency band simultaneously maximizes signal gain of the reflector antenna for the first frequency band.

2. The system of claim 1 , further comprising at least one feedback sensor configured to monitor the position of the subreflector tracking assembly in at least the X and Y axes.

3. 3. The system of claim 2, wherein the control system is further configured to adjust the sub-reflector tracking assembly via the reflector tracking assembly when the at least one feedback sensor indicates that an X-axis or Y-axis travel limit of the sub-reflector tracking assembly mount has been reached.

4. 10. The system of claim 1, wherein the feed horn has a variable flare angle optimized for a nearly constant phase center over a range of frequencies.

5. The system of claim 4, wherein the predetermined frequency is between 17.7 and 31 GHz.

6. The system of claim 1 , wherein the feed horn is a corrugated feed horn with a varying flare angle.

7. 10. The system of claim 9, wherein the feed horn has a linear taper at an opening of the feed horn and has a very narrow flare angle of 6 degrees or less.

8. 10. The system of claim 1, wherein the feed horn has a half cosine taper to provide a narrow flare angle at an opening of the feed horn.

9. The system of claim 1 , wherein the control system is further configured to adjust the subreflector tracking assembly at periodic intervals.

10. 1. A method of reflector tracking with a dual reflector Earth Station Antenna (ESA) system for transmitting an uplink in a first frequency band and receiving a downlink in a second frequency band, the ESA system including a feed horn optimized for a substantially constant phase center for both the first frequency band and the second frequency band, and a sub-reflector tracking assembly supported proximate a reflector focal point and trackable in an X-axis, a Y-axis, and a Z-axis, the method comprising: adjusting the sub-reflector tracking assembly along the X, Y and Z axes of the reflector until a signal gain of the reflector is maximized in the second frequency band; The method of claim 1, wherein the optimization of the feed horn for a substantially constant phase center for both the first frequency band and the second frequency band simultaneously maximizes signal gain of the reflector for the first frequency band.

11. The method of claim 10 , wherein the adjustment of the subreflector tracking assembly is repeated at periodic intervals.

12. The method of claim 10 , wherein the adjustment of the subreflector tracking assembly is initiated in response to a change in temperature.

13. The method of claim 10 , wherein the adjustment of the subreflector tracking assembly is initiated in response to a preset time.

14. The method of claim 10, wherein the range of adjustment along the Z axis is less than 0.5 inches.

15. The method of claim 10 , wherein the adjustment is enabled by a change in the signal gain.

16. 11. The method of claim 10, further comprising the steps of: adjusting the sub-reflector tracking assembly to a recorded position of the highest signal gain within a defined period of time; and resetting the recorded position if the adjustment of the sub-reflector tracking assembly results in a higher signal gain.

17. The method of claim 10 , wherein the adjustment of the sub-mirror tracking assembly is performed by actuating linear actuators for each of the X, Y, and Z axes.

18. 11. The method of claim 10, further comprising adjusting the sub-reflector tracking assembly via a reflector tracking assembly when at least one feedback sensor indicates that an X-axis or Y-axis travel limit of the sub-reflector tracking assembly has been reached.

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