Patent Grant
9337535
Not applicable.
The present invention generally relates to satellite antennas, and more particularly to a low cost, high-performance, switched multi-feed steerable antenna system.
Many satellite communication systems may use devices known as single reflector antennas as the means of sending electromagnetic signals. Such antennas may include a reflector surface, either paraboloid or otherwise shaped, and a feed placed at or near the reflector focus. The antenna may operate in a receiving mode, transmitting mode, or both simultaneously. The electromagnetic energy received or transmitted by the antenna may be collimated into a narrow beam and directed from the satellite towards a specified location on the earth surface. This location may be fixed for the duration of the mission, except for minor adjustments, in which case the antenna structure and the mounting method is static and relatively simple. However, very often the antenna direction of radiation may vary, either because the requirements of the mission have changed, or because the intended target travels as a function of time. The antenna needs to be steered to direct the beam towards a specified location. Such steerable antennas have to incorporate special features in their mechanical and electrical design in order to perform their function.
Current implementation options for steerable beam antennas are principally governed by tradeoffs of performance/functionality vs. cost/mass/volume. The antenna designer may be faced first with two main choices. One is a fully steerable system, where the reflector and the feed form a single mechanical assembly, are placed together on a gimbal steering mechanism, and controlled as a unit. This type of system offers the best performance, virtually invariable with the scan angle. However, it may have two main drawbacks. First, it may require an RF rotary joint or a flexible waveguide connection at the interface between the steerable antenna and the RF transponder circuitry. Solutions to this RF interface issue have been addressed by installing the RF transponder circuitry onto the antenna eliminating the need for a flexible interface, but this may limit the utility and may result in significant increases in deployed/gimbaled mass. Second, such a solution may be unacceptably costly to implement, and may require large volume, mass, and sturdy gimbal mechanisms. Third, stowage of multiple full steered antennas can be problematic, driving spacecraft launch vehicle faring size and cost. Achieving sufficiently high rates of motion, meeting acceleration/deceleration limits, and ensuring cycle lifetimes may all be very difficult. For these reasons, with the exception of small steerable antennas, fully steerable systems are rarely practical.
The second choice is a system with an independently steerable reflector and a fixed feed. In this type of steerable antenna, only the reflector is placed on a gimbal steering mechanism. The feed is mounted on the satellite body and may not require a rotary joint for its connection to the transponder. Since the reflector mass is relatively small, it is possible to use economic light-weight gimbals, achieve high rates of motion, and long cycle lifetimes. However, a steerable antenna with a rotating reflector and a fixed feed may suffer from a loss of performance (e.g., decrease in peak gain and changes in the beam shape) as the steering angle increases. This loss of performance is usually referred to as the scan loss. When the reflector rotates in order to steer the beam towards the desired direction, the focal point of the reflector may move away from the fixed feed, and the ray relationship between the feed and the reflector may gradually become less optimal. For large diameter antennas that need to steer over a wide range of scan angles, the scan loss may be high (2-5 dB as an example) and therefore prohibitive. Nevertheless, the systems with an independently steered reflector and a fixed feed are often the only practical option.
For the steerable antenna systems using a steerable reflector and a fixed feed, there are in turn two main design options, again trading off performance vs. cost/mass/volume. The first design option is a reflector rotated about center, where the gimbal mechanism is placed behind the reflector surface, with the center of rotation near or in the vicinity of the aperture center. Since the reflector center is then approximately stationary, and the movement of the reflector rim relative to the feed is minimized, the scan loss may be minimized. However, placing the gimbal at the aperture center, which usually means away from the spacecraft body, is often difficult to implement, requires additional mass and volume, and may be impossible to accommodate for multiple reflectors systems stowed in an overlapped configuration.
The second design option is a reflector rotated about vertex, where the gimbal mechanism is placed in the vicinity of the reflector vertex. This is the most convenient location from the viewpoint of mechanical implementation, with the gimbal located close to the spacecraft body, allowing a compact, low mass, low cost solution. This approach allows for more compact stowage, and enables stowage of multiple nested reflectors along a single side of the spacecraft. However, because the reflector displacement relative to the feed is larger than for the reflector rotated about the center, the scan loss for this method is unfortunately much higher. In spite of the advantages of its mechanical implementation, the scan performance of a reflector steered about its vertex, for the same range of scan angles, is usually inferior.
In some aspects, an apparatus for satellite communication is described. The apparatus may include a reflector configured to redirect electromagnetic energy. Each of the multiple feeds may be positioned at a predetermined location with respect to the reflector. A feed-switching mechanism may be configured to selectively activate for use at least one of the multiple feeds. A steering mechanism may be configured to steer the reflector such that a focal point of the reflector approximately coincides with a position of an activated feed of the multiple feeds. The reflector may be mechanically independent of the plurality of feeds and the feed-switching mechanism.
In other aspects, a method for providing a satellite communication antenna may include providing a reflector that redirects electromagnetic energy. Multiple feeds may be positioned at a predetermined location with respect to the reflector. A feed-switching mechanism may be configured to selectively activate for use at least one of the multiple feeds. A steering mechanism may be configured to steer the reflector such that a focal point of the reflector approximately coincides with a position of an activated feed of the plurality of feeds. The reflector may be mechanically independent of the plurality of feeds and the feed-switching mechanism.
In yet other aspects, a low-cost, low scan-loss satellite antenna may include a reflector coupled to a steering mechanism and configured to redirect electromagnetic energy. The steering mechanism may be configured to steer the reflector to a position that focuses a spot beam of the antenna on a target. A feed-switching mechanism may be configured to selectively activate for use at least one of multiple feeds of a network of feeds. A focal point of the reflector may approximately coincide with a position of an activated feed of the plurality of feeds, and the reflector may be mechanically independent of the plurality of feeds and the feed-switching mechanism.
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 present disclosure is directed, in part, to methods and configurations for providing low cost, high performance, switched multi-feed steerable antennas. The subject technology is generally directed to satellite antennas, and in particular to multi-feed (e.g., more than one, for example, five feeds or more) antenna solutions that can provide scan performance approaching that of a fully steered system while at the same time maintaining the cost advantages of a vertex steered system. In some aspects, using additional feeds along with a switch selection network, the scanned beam performance of the vertex-steered antenna system can be made to closely approximate the performance of the fully-steered antenna. The subject technology may improve upon the existing solutions by enhancing the performance, for example, by 4 dB, and providing a worst case scan loss of ˜2 dB (e.g., at limb of earth) and areas of less than ˜1 dB, in significant portions of a characteristic scan loss versus scan-angle plot, as discussed in greater detail herein.
The fully steered antenna system 100C may provide essentially a desired scan-loss performance, but at a high cost. The high cost of the fully-steered system 100C may be due to the required launch packaging components (e.g., launch locks, deployment hinges, etc.) and the systems required to pass radio frequency (RF) signals across a moving interface (e.g., RF rotary joints or flexible waveguide).
A desirable antenna solution for satellite designers should provide scan performance approaching that of the fully steered system (e.g., 100C), while at the same time maintaining the cost advantages of a vertex-steered antenna system (e.g., 100C) that is modified to closely approximate the performance of the fully-steered antenna system 100C. The antenna systems 100A-C, are either high-cost systems with excellent scanned beam performance (e.g., system 100C), medium-cost and medium performance systems (e.g., system 100B), or relatively low-cost systems with compromised scanned beam performance (e.g., system 100A). The subject technology may drastically improve in performance, cost, and compactness upon these solutions by using a switch network to allow selection of one or more feeds, based on the application, as described herein.
The subject disclosure describes a steerable antenna system that overcomes the performance problems of a system with a reflector rotated about its vertex (e.g., 100A), while retaining the simplicity and low cost advantages of its mechanical realization. The resulting performance levels may be comparable or superior to the scan performance achievable with a reflector system rotated about its center (e.g., 100B). Stowage of nested reflectors is readily achievable. More importantly, the subject technology may use multiple switchable feeds, placed in fixed positions corresponding to the positions of the reflector focal point as a function of the steering angle. The feeds may be fixed to the spacecraft body, eliminating the need for flexible RF interfaces when changing the beam pointing. The subject technique is not limited to the vertex system, but is also applicable and can be equally well employed in the context of the center rotated reflector system, enhancing its scan performance even further.
For each position of the reflector 210, one of the multiple feeds may be selected by a switch network described herein. The location of the feeds 230, 232, and 234 may be configured such that each feed is positioned at a focal point (e.g., antenna focal point) of the reflector 210 at one of the positions (e.g., P1, P2, or P3). For example, as shown in
Each of the groups of feeds (e.g., groups 520, 530, 540, and 560) may include a number of feeds of different sizes. For example, the group 560 may include three or more large feeds 562 and one or more smaller feeds such as 564 and 566. The smaller feeds 564 and 566 can operate at higher frequencies than the large feeds 562. In some aspects, a feed-switching mechanism may selectively activate two or more low-frequency feeds 562 at the same time, so that the two or more low-frequency feeds 562 can collectively operate as an equivalent larger feed. A steering mechanism (e.g., 220 of
In some aspects, the antenna system 500 may cover more or less than three distinct frequency bands. In some aspects, the two higher frequency bands may use one of feeds 564 and 566 per focal point location and the third lower frequency band may be implemented using a three element array formed by feeds 562. Beam scanning may be performed, for example, by rotating reflector 510 with a steering mechanism by first selecting one of the feed-reflector switchable configurations, as a scan departure state, and minimizing scan-angle and scan-loss. For example, as the scan-loss deviates from the departure state, the scan-loss increases, and at some point a new feed-reflector configuration can be selected to decrease the scan-loss.
In some aspects, the subject technology is related to multi-feed antennas (e.g., more than one, for example, five feeds or more), and in particular to antenna solutions that can provide scan performance approaching that of a fully steered system, while at the same time maintaining the cost advantages of a vertex steered system. In some aspects, the subject technology may be used in various markets, including for example and without limitation, advanced sensors, data transmission and communications, and radar and active phased array markets.
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 is 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.
This application claims the benefit of priority under 35 U.S.C. §119 from U.S. Provisional Patent Application 61/677,446 filed Jul. 30, 2012, which is incorporated herein by reference in its entirety.
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