Patent Grant
10749252
Not applicable
The present invention generally relates to antennas, and more particularly, to a global positioning system (GPS) antenna payload configuration for enhanced positioning, navigation and timing (PNT) accuracy and reduced high power risk.
Future global positioning system (GPS) spacecraft employ three different L-band antennas including earth coverage (EC), military earth coverage (MEC) and regional military protection (RMP) antennas to broadcast the full set of GPS L-band signals. Each antenna may have a separate phase and group delay center, which can produce PNT errors if not suitably compensated. For example, during regular spacecraft yaw orbital maneuvers, required to reduce peak-to-peak thermal variations, MEC and RMP phase and group delay centers can rotate about the EC phase center creating an additional source of PNT errors for MEC and RMP users.
The existing GPS helix antenna arrays used for EC, MEC, and RMP transmit substantially high average continuous wave (CW) powers that are typically greater than 300 W CW per antenna. Thus, these tapered helix antennas are susceptible to high-power multipaction creating single-point failure risks. The EC antenna is particularly vulnerable to multipaction due to higher powers. The existing GPS EC antenna elements are interleaved with Ultra High Frequency (UHF) crosslink antennas and the MEC antenna elements are in close proximity to the UHF antenna. These close proximities increase the risk for passive intermodulation (PIM) in and near the antennas due to high signal strength from both UHF and L-band signals. Further, the existing GPS EC antenna L1 and/or L2 patterns have angular suck-outs (nulls) toward the space service volume (SSV) at about ±23.5° and/or ±26°, which diminishes transmitted signal power to geosynchronous satellite SSV users.
According to various aspects of the subject technology, systems and configurations are disclosed for providing a global positioning system (GPS) antenna payload configuration for enhanced positioning, navigation and timing (PNT) accuracy and reduced high power risk. In one or more aspects, the GPS antenna payload configuration of the subject technology can reduce the PNT error and the risk for multipaction and passive intermodulation (PIM).
In one or more aspects, an antenna array for a global positioning system (GPS) includes a first antenna element and a number of second antenna elements. The antenna array is placed at a location on the spacecraft nadir antenna deck that is above the center of gravity of the spacecraft. The first antenna element is located at the center of the antenna array and is surrounded by the second antenna elements. The first antenna element can produce a beam with a predefined null-to-null beamwidth, and the second antenna elements can form a multi-beam phased array. In some implementations, the first antenna element can be an antenna element of the second antenna elements.
In yet other aspects, a communication satellite system includes an antenna array comprising a central antenna and a number of surrounding antennas, two or more groups of amplifiers and two or more frequency multiplexers. Each group of amplifiers includes a number of amplifiers operable at a frequency band. Each frequency multiplexer can combine amplified signals from a group of amplifiers. The antenna array is placed at a location on the spacecraft nadir antenna deck that is above the center of gravity of the spacecraft. The central antenna can produce a beam with a predefined null-to-null beamwidth, and the surrounding antennas are configured to form a multi-beam phased array.
In yet other aspects, a method of configuring a GPS antenna payload includes forming an antenna array having a central antenna and a number of surrounding antennas. The method further includes configuring the central antenna to produce a beam with a predefined null-to-null beamwidth, and configuring the surrounding antennas to form a multi-beam phased array. The antenna array is mounted at a location on the spacecraft nadir deck that is above the center of gravity of the spacecraft.
The foregoing has outlined rather broadly the features of the present disclosure in order that the detailed description that follows can be better understood. Additional features and advantages of the disclosure will be described hereinafter, which form the subject of the claims.
For a more complete understanding of the present disclosure, and the advantages thereof, reference is now made to the following descriptions to be taken in conjunction with the accompanying drawings describing specific aspects of the disclosure, wherein:
The detailed description set forth below is intended as a description of various configurations of the subject technology and is not intended to represent the only configurations in which the subject technology can be practiced. The appended drawings are incorporated herein and constitute a part of the detailed description. The detailed description includes specific details for the purpose of providing a thorough understanding of the subject technology. However, it will be clear and apparent to those skilled in the art that the subject technology is not limited to the specific details set forth herein and can be practiced using one or more implementations. In one or more instances, well-known structures and components are shown in block diagram form in order to avoid obscuring the concepts of the subject technology.
According to some aspects of the subject technology, methods and configuration are disclosed for providing a global positioning system (GPS) antenna payload configuration for enhanced positioning, navigation and timing (PNT) accuracy and reduced high power risk. The GPS antenna payload configuration of the subject technology can reduce the PNT error and the risk for multipaction and passive intermodulation (PIM). Multipaction is an electron resonance effect that can occur when Radio Frequency (RF) fields accelerate electrons in a vacuum and cause them to impact with a surface, which depending on its energy, release one or more electrons into the vacuum. PIM can occur in passive devices (e.g., cables, antennas etc.) subjected to two or more high-power tones. The high-power tones can mix at device nonlinearities such as junctions of dissimilar metals or metal-oxide junctions, such as loose corroded connectors.
A GPS navigation array is based on advanced short backfire antennas (A-SBFAs), as described in the U.S. patent application Ser. No. 14/715,500, entitled “High Efficiency Short Backfire Antenna Using Anisotropic Impedance Walls,” filed May 18, 2015, incorporated by reference herein. The GPS navigation array is oriented above the center of gravity (CG), combined with a UHF crosslink antenna, which has an offset on the bus (e.g. deployed) or alternatively a Ka-band crosslink array (as described in U.S. patent application Ser. No. 15/993,407, entitled “Combined Crosslink and Comm Link Phased Array for Satellite Applications,” filed May 30, 2018, incorporated by reference herein. Orienting all of the three L-band antennas above the CG results in the best possible PNT accuracy by minimizing L-band phase center movement of the EC and RMP signals during a yaw turn and relative movement caused by the satellite traversing a user on the surface of the earth as opposed to an L-band antenna that is offset from the CG and of separate apertures. This not only improves accuracy by minimizing the uncorrelated error between signals (e.g., variation of group delay and inter-signal variation) on the same and different frequencies, but also negates the need to broadcast messages to users to account for the offset. Implementing the RMP antenna as an array spreads the power over many elements and greatly reduces multipaction and PIM risks. An array also offers multiple beams covering multiple areas of operations (AOs) to meet future customer needs. Replacing helix antennas with A-SBFAs having high power capability can significantly reduce the high power risk for the EC and MEC antennas, even though the power through the antenna is increased. Also, in contrast to helix antennas where the phase and group delay center moves along the helix with frequency, the A-SBFA has a nearly constant phase and group delay center with frequency which further reduces PNT error over the earth field of view. And finally, generating EC beams from a single A-SBFA or small array can avoid the suck-outs (nulls) toward the SSV.
The EC, MEC and RMP antennas can use GPS helix antenna arrays to transmit substantially high average CW powers, which make them susceptible to high-power multipaction creating single-point failure risks. The EC antenna can be particularly vulnerable to multipaction due to higher powers. The subject technology mitigates this problem by replacing the EC helix array by either an A-SBFA which can handle high power or a small array, for example, a 7-element patch array, where the power from each element are combined spatially. The subject technology also implements the RMP antenna as an array to spread the power over many elements to greatly reduce multipaction and PIM risks. The close proximity of the EC and MEC antennas to the UHF antennas can increase the risk for PIM in the antennas and surrounding structure due to high signal strength from both UHF and L-band signals. The subject technology mitigates this problem by either deploying the UHF antenna away from the L-band antennas or by using a crosslink antenna at a much higher frequency, e.g., Ka-band. Further, transmitted signal power to geosynchronous satellites can be diminished by the angular suck-outs (nulls) toward the SSV of the L1 and/or L2 patterns of the GPS EC antenna (e.g., about ±23.5° and/or) ±26°. The subject technology mitigates this problem by using a small EC antenna with null width out to about ±35° which improves SSV signal availability. And finally, in the prior art L-band antennas the EC, MEC and RMP antennas have different phase and group delay centers, resulting in PNT error. The subject technology mitigates this problem by orienting all of the three L-band antennas above the CG of the spacecraft to achieve the highest possible PNT accuracy, which eliminates, for example, L-band phase center movement of the EC, MEC and RMP signals during a yaw turn of the GPS spacecraft 100. This can improve accuracy by minimizing the uncorrelated error between signals (e.g., variation of group delay and inter-signal variation) on the same and different frequencies. The subject technology further improves uncorrelated error between signals by implementing EC and RMP antenna elements with constant phase and group delay center over frequency.
In the example configuration 500A, the encoded signals include civil and military codes (L1-band) signal 502 (hereinafter “signal 502”), civil and military codes (L2-band) signal 504 (hereinafter “signal 504”) and civil codes (L5-band) signal 506 (hereinafter “signal 506”). The signals 502, 504 and 506 are amplified by the two groups 510-1 and 510-2 of TWTAs. Each of the groups 510-1 and 510-2 of TWTAs include an L1-, an L2- and an L5-band TWTA. The output of each of the groups 510-1 and 510-2 of TWTAs is at a specific frequency band and are transmitted, via cables 525, to the frequency triplexers 520-1 and 520-2 for combining the three frequencies (L1-, L2- and L5-band). The output of the triplexers 520-1 and 520-2 are transmitted, via cables 525, to the power splitters 530-1 and 530-2. The power splitter 530-1 splits the power of the first combined signal from the triplexer 520-1 into three components for delivery, via cables 525, to three EC antenna elements of the first group of EC antenna elements 550-1. The power splitter 530-2 splits the power of the second combined signal from the triplexer 520-2 into four components for delivery, via cables 525, to four EC antenna elements of the second group of EC antenna elements 550-2. The relative power between the two groups 510-1 and 510-2 of TWTAs is selected such that the 7 individual antenna elements are the same.
In the example configuration 500B, the signal 502, 504 and 506 are amplified by the three groups 510-1, 510-2 and 510-3 of TWTAs. Each of the groups 510-1, 510-2 and 510-3 of TWTAs include an L1-, an L2- and an L5-band TWTAs. The output of each of the groups 510-1, 510-2 and 510-3 of TWTAs is at a specific frequency band and are transmitted, via cables 525, to the frequency triplexers 520-1, 520-2 and 520-3 for combining the three frequencies (L1-, L2- and L5-band). The output of the triplexers 520-1, 520-2 and 520-3 are transmitted, via cables 525, to the power splitters 530-1, 532-1 and 532-2. The power splitter 530-1 splits the power of the first combined signal from the triplexer 520-1 into three components for delivery, via cables 525, to three EC antennas of the first group of EC antenna elements 552-1. The power splitter 532-1 splits the power of the second combined signal from the triplexer 520-2 into two components for delivery, via cables 525, to two EC antennas of the second group of EC antenna elements 552-2. The power splitter 532-2 splits the power of the third combined signal from the triplexer 520-3 into two components for delivery, via cables 525, to two EC antennas of the third group of EC antenna elements 552-3. The relative power between the three groups 510-1, 510-2 and 510-3 of TWTAs is selected such that the 7 individual antenna elements are the same.
In the example configuration 500C, the signal 502, 504 and 506 are amplified by the seven groups 510-1 . . . 510-7 of SSPAs. Each of the groups 510-1, 510-2 and 510-3 of SSPAs include an L1-, an L2- and an L5-band SSPAs. The output of each of the groups 510-1 . . . 510-7 of SSPAs is at a specific frequency band and are transmitted, via cables 525, to the frequency triplexers 520-1 . . . 520-7 for combining the three frequencies (L1-, L2- and L5-band). The outputs of each of the triplexers 520-1 . . . 520-7 are transmitted, via cables 525, to each of the corresponding seven EC antenna elements 550-1 . . . 550-7. The relative power between the seven groups 510-1 to 510-7 of TWTAs is uniform such that the 7 individual antenna elements are the same.
The examples of EC payload configurations 500A through 500C enable combining multiple encoded signals onboard the spacecraft (e.g., satellite) to achieve a reduced PNT error, reduced power density along each RF path and lower power per amplifier. The EC payload configurations of the subject technology are not limited to the payload configurations 500A through 500C discussed herein and can include other ways of combining the encoded signals.
In some aspects, the subject technology is related to antennas, and more particularly, to a GPS antenna payload configuration for enhanced PNT accuracy and reduced high power risk. In some aspects, the subject technology may be used in various markets, including for example and without limitation, space technology, communications systems, navigation, GPS, and advanced short backfire antenna markets.
Those of skill in the art would appreciate that the various illustrative blocks, modules, elements, components, methods, and algorithms described herein may be implemented as electronic hardware, computer software, or combinations of both. To illustrate this interchangeability of hardware and software, various illustrative blocks, modules, elements, components, methods, and algorithms have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. Skilled artisans may implement the described functionality in varying ways for each particular application. Various components and blocks may be arranged differently (e.g., arranged in a different order, or partitioned in a different way) all without departing from the scope of the subject technology.
It is understood that any specific order or hierarchy of blocks in the processes disclosed is an illustration of example approaches. Based upon design preferences, it is understood that the specific order or hierarchy of blocks in the processes may be rearranged, or that all illustrated blocks be performed. Any of the blocks may be performed simultaneously. In one or more implementations, multitasking and parallel processing may be advantageous. Moreover, the separation of various system components in the embodiments described above should not be understood as requiring such separation in all embodiments, and it should be understood that the described program components and systems can generally be integrated together in a single hardware and software product or packaged into multiple hardware and software products.
As used in this specification and any claims of this application, the terms “base station”, “receiver”, “computer”, “server”, “processor”, and “memory” all refer to electronic or other technological devices. These terms exclude people or groups of people. For the purposes of the specification, the terms “display” or “displaying” means displaying on an electronic device.
The description of the subject technology is provided to enable any person skilled in the art to practice the various aspects described herein. While the subject technology has been particularly described with reference to the various figures and aspects, it should be understood that these are for illustration purposes only and should not be taken as limiting the scope of the subject technology.
A reference to an element in the singular is not intended to mean “one and only one” unless specifically stated, but rather “one or more.” The term “some” refers to one or more. Underlined and/or italicized headings and subheadings are used for convenience only, do not limit the subject technology, and are not referred to in connection with the interpretation of the description of the subject technology. All structural and functional equivalents to the elements of the various aspects described throughout this disclosure that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference and intended to be encompassed by the subject technology. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the above description.
Although the invention has been described with reference to the disclosed aspects, one having ordinary skill in the art will readily appreciate that these aspects are only illustrative of the invention. It should be understood that various modifications can be made without departing from the spirit of the invention. The particular aspects disclosed above are illustrative only, as the present invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular illustrative aspects disclosed above may be altered, combined, or modified and all such variations are considered within the scope and spirit of the present invention. While compositions and methods are described in terms of “comprising,” “containing,” or “including” various components or steps, the compositions and methods can also “consist essentially of” or “consist of” the various components and operations. All numbers and ranges disclosed above can vary by some amount. Whenever a numerical range with a lower limit and an upper limit is disclosed, any number and any subrange falling within the broader range are specifically disclosed. Also, the terms in the claims have their plain, ordinary meaning unless otherwise explicitly and clearly defined by the patentee. If there is any conflict in the usages of a word or term in this specification and one or more patent or other documents that may be incorporated herein by reference, the definitions that are consistent with this specification should be adopted.
