Communications: directive radio wave systems and devices (e.g. – Directive – Including a steerable array
Reexamination Certificate
1992-09-11
2004-07-27
Issing, Gregory C. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Directive
Including a steerable array
C342S374000
Reexamination Certificate
active
06768456
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to antenna systems and, in particular, to an antenna system that uses a multi-element antenna array to receive an electromagnetic signal and generate a plurality of electrical signals that are representative of the received electromagnetic signal and a multi-beam beamformer to produce at least two spatially independent, overlapping beams from the electrical signals provided by the array.
2. Description of the Related Art
Presently, antenna systems are used in many aeronautical applications. One application for an antenna system is as part of a radar on an aircraft where the antenna system is used to obtain positional information on the objects in the space surrounding the aircraft. This positional information is then typically used to either avoid an object, such as another aircraft, or to home in on an object, such as a navigational beacon.
Present radar antenna system technology is becoming increasingly hard-pressed to provide sufficient information on the space around an aircraft as the speed of the aircraft on which the radar antenna system is mounted and of the other aircraft in the surrounding airspace increases. Specifically, present radar antenna systems are generally proving inadequate with respect to their detection range, field of view, resolution, or combinations thereof in situations that involve high-speed aircraft. For example, if the radar antenna system in one of two high-speed aircraft that are approaching one another has a short range, the radar antenna system may not be able to provide information on the other aircraft in time to avoid a collision. If, on the other hand, the radar antenna system in an aircraft has a limited area of coverage, and the aircraft is attempting to join up with a high-speed aircraft, the high-speed aircraft may not be detected with such a radar antenna system. Further, if the antenna system in an aircraft has a limited resolution, the ability of the aircraft to make the appropriate course corrections may be compromised.
Further, high-speed aircraft also exhibit high skin temperatures that are on the order of 3000° F. and higher. These temperatures present severe radiation problems to any radar antenna system mounted on the aircraft. Conventional approaches to this problem ordinarily involve the design of a radome, which protects the radar antenna system and forms part of the skin of the aircraft, that employs exotic materials and/or active cooling systems that are generally complex and expensive.
Further, to realize higher velocities and/or improved maneuvering characteristics, the aerodynamics of aircraft are being constantly improved. However, the ability to realize the improved performance is becoming increasing sensitive to anything that may affect the aerodynamics of the aircraft. Consequently, the design of a radar antenna system that is to be deployed on aircraft must consider the effects of the radar antenna system on the aerodynamics of the aircraft.
The ability of aircraft-based radar antenna systems to provide adequate information on objects in the surrounding space is also becoming increasingly difficult due to the reductions in the radar cross-sections of many of these objects. For example, as aircraft become more aerodynamic, their radar cross-section typically decreases, thereby making it more difficult for a radar antenna system to detect the aircraft. As a result, other types of sensors or detectors that operate on different principles, such as electro-optic sensors, are being used in conjunction with, or to supplement the radar. At least with respect to aircraft-based radar, the space to accommodate additional sensors, and especially those sensors that are to be used in high-speed aircraft environments, is limited. Consequently, the impact of a radar antenna system must be considered in such situations.
Another application in which the performance of present antenna systems is becoming increasingly less reliable is when there is a need for a very focused or narrow beam (transmitted or received) with low side lobes and/or high gain. A narrow beam with low side lobes is, for example, desirable in situations in which the goal is to reduce the possibility of the signals produced by either the antenna system or an object in the antenna system's scanning area from being intercepted. High gain is also desirable in such a situation because it allows the antenna system to detect objects that produce low-power signals, or, stated another way, to operate in environments where there is a low signal-to-noise ratio (SNR). Present antenna systems that use partially overlapping beams in such situations have become increasingly less reliable as the need to operate in lower SNR environments increases.
Yet a further concern with respect to antenna systems is that as the performance requirements of the various applications has increased, the antenna systems that are designed to meet these requirements have tended to become more complex. This is of concern because increasing complexity generally results in a reduced reliability that is unacceptable in many applications.
SUMMARY OF THE INVENTION
Based on the foregoing, an object of the present invention is to provide an antenna system that addresses the high range, resolution, and field of view requirements of high-speed aircraft environments.
A further object of the present invention is to provide an antenna system that can be used in high-speed, high-temperature environments which substantially reduces the need for a radome formed of exotic material and/or the use of a complex cooling system.
Yet another object of the present invention is to provide an antenna system that is sensitive to the aerodynamics of the aircraft on which it is mounted.
Another object of the present invention is to provide an antenna system that addresses the concern for space on an aircraft and especially the space associated with the frontal surface or nose portion of an aircraft.
A further object of the present invention is to provide an antenna system that addresses applications in which the interception of an antenna system signal is undesirable.
Yet a further object of the present invention is to provide an antenna system that is relatively simple and reliable.
One embodiment of the antenna system of the present invention that is suitable for aircraft or ground-based applications includes an antenna array for receiving an electromagnetic signal and providing a plurality of signals that are representative of the electromagnetic signal. The antenna array is comprised of a plurality of antenna elements, each of which is capable of providing one signal of the plurality of signals. The antenna system further includes a beamformer for processing a first subset and a second subset of the plurality of signals provided by the antenna array to produce two “beams”. The beams are electrical signals that are representative of the electromagnetic signal received from a particular area. To be able to change the characteristics of the beams, the beamformer includes a switching network that permits selection of which antenna elements will provide the signals comprising the first and second subsets. For example, by changing the number of antenna elements whose signals comprise the beams, the beamwidths of the beams can be changed. Similarly, by changing the identity of the antenna elements whose signals make up the first and second subsets, the baseline between the two beams can be altered. This can be useful in resolving positional ambiguities. The antenna system further includes a device for cooperatively using the first and second beams produced by the beamformer to determine information on the surrounding environment, such as the location of an object. Specifically, the device can perform an amplitude comparison of the two beams to attain coarse positional information and a phase comparison of the two beams to realize an interferometer that provides fine or high resolution positional information.
In another embodiment of the ant
Boone Theresa Cronin
Lalezari Farzin
Ball Aerospace & Technologies Corp.
Issing Gregory C.
Sheridan & Ross P.C.
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