Communications: radio wave antennas – Antennas – Combined with diverse-type art device
Reexamination Certificate
1995-06-30
2001-05-01
Wimer, Michael C. (Department: 2821)
Communications: radio wave antennas
Antennas
Combined with diverse-type art device
C343S725000, C343S779000
Reexamination Certificate
active
06225955
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates in general to the field of antennas. More particularly, the invention relates to dual-mode, common-aperture antenna systems that transmit and/or receive electromagnetic radiation in at least two frequency bands.
2. Description of the Prior Art
Radar is an active system which has been used extensively for detecting and determining the range and direction of distant objects such as ships and aircraft. Radar does this by illuminating the object with radiation and then receiving, analyzing and displaying the reflections. Many modern radar systems have sufficient resolving power to permit the identification of an object by analyzing its characteristic reflected pattern, or signature, as displayed by detection and classification equipment. In general, the resolution of a radar system and, therefore, its ability to identify objects from its signature increases as the operating frequency increases.
The ability of radar systems to effectively illuminate an object and receive a useful reflection can also vary with its operating frequency. For example, radar operation is often impacted by adverse weather conditions that can significantly alter the electromagnetic transmittance of the atmosphere. Specifically, while dense fog can have little effect on a microwave radar beam, it can quickly attenuate the short-wavelength beam of, for example, a laser radar. Those skilled in the art have therefore recognized that while most high-resolution radar systems produce good object-identification signatures, they can have limited ability at finding and/or illuminating objects under, for example, adverse weather conditions. Conversely, while many low-resolution radar systems may produce poor object-identification signatures, they have superior capacity at quickly finding objects under most operating conditions.
Consequently, in the field of object detection and identification, it has been found desirable to employ multi-mode radar systems that transmit and/or receive radiation in a number of frequency bands. These multi-mode radar systems have important applications in various apparatus such as aircraft landing systems, target acquisition and guidance equipment in smart bombs, obstacle detection radar for high-speed trains, marine navigation equipment, vehicle collision avoidance systems, and the like. In many of these applications, the radar system must be mounted in an apparatus having limited room and/or be capable of tolerating high acceleration forces. As such, one of the most critical problems confronting designers of multi-mode radar systems has been the low-cost fabrication of efficient, dual-mode antennas that are simple, compact and sturdy. The present invention fulfills this need.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to provide an efficient multi-mode, common-aperture antenna system capable of simultaneously transmitting and/or receiving electromagnetic radiation in a number of frequency bands.
Another object of the invention is the provision of a common-aperture antenna system that may be used as a front-end of various millimeter-wave/or microwave/optical transceivers.
A further object of the present invention is to provide a dual-mode, common-aperture antenna system that is efficient, compact, sturdy, easy to align and inexpensive to fabricate.
The general purpose of this invention is to provide an improved low-cost, efficient and reliable, multi-mode antenna capable of simultaneously transmitting and/or receiving radiation in at least two frequency bands. To attain this, the present invention contemplates a unique common-aperture antenna system having first and second beam antennas. The first beam antenna has a first antenna feed and a first beam-forming device, defining a first antenna aperture, for forming a first radiation pattern along a first beam axis. The second beam antenna has a second antenna feed and a second beam-forming device, defining a second antenna aperture, for forming a second radiation beam pattern along a second beam axis. The second antenna aperture is less than half the size of and located within the boundary of the first antenna aperture. A radiation energy device connects to the first antenna feed for feeding radiation in a first frequency band and to the second antenna feed for feeding radiation in a second frequency band different from the first frequency band.
More specifically, the present invention is directed to a multi-mode, common-aperture antenna system capable of simultaneously transmitting and/or receiving electromagnetic radiation in at least two frequency bands. The antenna system includes a first beam antenna comprised of a parabolic reflector and four open-ended waveguides that act as an antenna feed. The parabolic reflector focuses radiation along a first beam axis that may be scanned electronically or mechanically. The four waveguides extend from the focus of the parabolic reflector to transceivers that transmit and/or receive radiation in a first mode. The transceivers mount at the rear of the reflector. The antenna system also includes a second beam antenna which operates in a second mode, e.g. optical or infrared (IR) mode. The second beam antenna includes a small opening in the parabolic reflector that acts as an optical aperture for a focusing lens mounted at the rear of the reflector and positioned coaxially with the small opening. An optical apparatus occupies the focal plane of the focusing lens. The optical apparatus generates and/or senses optical radiation incident with the beam axis of the second beam antenna.
REFERENCES:
patent: 4284991 (1981-08-01), Dupressoir
patent: 4010242 (1991-02-01), None
Chang Yu-Wen
Freibergs Elmer
Wandinger Lothar
O'Meara John M.
The United States of America as represented by the Secretary of
Wimer Michael C.
Zelenka Michael
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