Communications: radio wave antennas – Antennas – Wave guide type
Reexamination Certificate
2000-02-10
2001-10-23
Wong, Don (Department: 2821)
Communications: radio wave antennas
Antennas
Wave guide type
C343S755000, C343S756000, C343S757000
Reexamination Certificate
active
06307522
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates generally to compact solid state radar antenna structures, and more particularly, to microwave or millimeter wave radar antenna structures employing a folded optics path, a front transreflector, and a rear polarizing reflector.
2. Discussion of the Background Art
Solid state electronic microwave and millimeter wave radars generally contain three main components, a transceiver for generating and receiving electromagnetic radiation, an antenna for collimating and focusing the radiation, and a feed assembly for coupling the radiation from the transceiver to the antenna. In addition to collimating and focusing the emitted radiation, the antenna also receives and focuses the radiation reflected from detected objects, and provides it to the transceiver. To provide a compact structure, it is known to utilize a folded optics path, such that the longitudinal dimension of the antenna is less than the focal length of the lens alone. See, for example, U.S. Pat. No. 5,455,589 issued on Oct. 3, 1995 to Huguenin et al. and entitled “Compact Microwave and Millimeter Wave Radar”. In the arrangement disclosed by Huguenin et al., a planoconvex lens is used to obtain radiation collimation.
In U.S. Pat. No. 4,599,623, issued to Havkin et al. on Jul. 8, 1986 and entitled “Polarizer Reflector and Reflecting Plate Scanning Antenna Including Same”, there is disclosed an antenna which includes a front transreflector and a rear polarizer reflector, also known as a twist reflector. The transreflector is a polarizer, also known as an analyzer, that transmits radiation having a particular polarization, and that reflects radiation having a polarization orthogonal to the particular polarization. The front transreflector is a paraboloid, which transmits linear polarized, collimated electromagnetic (EM) radiation. In a receive mode, the paraboloid transreflector focuses linear polarized EM radiation. The twist reflector taught by Havkin et al. is flat and orthogonal to the axis of the paraboloid transreflector. As a consequence, the flat twist reflector arrangement reflects incident, linearly polarized EM radiation, and imparts a ninety degree twist such that the incident radiation is reflected with a polarization having an orthogonal ninety degree twist.
The antenna structure disclosed by Havkin et al. is a component of a microwave or millimeter wave EM radar in which the front transreflector is in front of an EM feed, at a focus of the antenna. The axis of the paraboloid transreflector and the axis of the orthogonal twist reflector must align to define properly the directions in which the antenna transmits and receives radiation. The need for this alignment gives rise to a problem in manufacturing. Specifically, alignment of the parabolic transreflector axis is made difficult because the orientation of the paraboloid changes as the transreflector undergoes thermal expansion and contraction with variations in temperature. Moreover, another disadvantage of the Havkin et al. arrangement resides in its required length. That is, the Havkin et al. structure requires that the EM feed be positioned at the actual focal length of the paraboloid, which limits any reduction of the actual length of the antenna.
Accordingly, there exists a need for a compact solid state radar antenna structure in which the possibility of improper or inefficient performance as a result of variations in temperature during manufacture and/or operation is reduced.
SUMMARY OF THE INVENTION
The aforementioned need is addressed, and an advance is made in the art, by an antenna which may be readily manufactured without substantial axial misalignment attributable to variations in temperature. To this end, the invention provides a base foundation to which is mounted both, an aligned EM feed, and an aligned and stationary twist reflector. The axis of the EM feed and the axis of the twist reflector are aligned, and remain substantially aligned, relative to the axis of the antenna despite variations in temperature.
In accordance with another aspect of the invention, a folded optics path is realized to provide radiation collimation to thereby advantageously reduce the length of the antenna. In contrast to Havkin et al., in which the antenna feed is positioned at the actual focal point of a collimating parabolic transreflector, the twist reflector of the inventive antenna disclosed herein is parabolic so that the transreflector is located substantially closer to the parabolic twist reflector than the focal point of the parabolic twist reflector. Accordingly, an antenna of substantially shorter length is realized. Moreover, the use of a parabolic twist reflector—as opposed to the planoconvex lens employed in other known arrangements—provides an additional benefit in that collimation is obtained without a lens to simplify both the mathematical optics and the structure of the antenna.
In accordance with yet another aspect of the invention, the aforementioned base foundation upon which the parabolic twist reflector is constructed is realized as non-paraboloid structure having a parabolic surface. The non-paraboloid base provides a foundation that preserves the alignment of the axis of the parabolic surface and the parabolic twist reflector relative to an axis of an antenna despite variations in temperature.
REFERENCES:
patent: 3771160 (1973-11-01), Laverick
patent: 4504835 (1985-03-01), Howard et al.
patent: 4509055 (1985-04-01), Fassett
patent: 4574287 (1986-03-01), Waters
patent: 4599623 (1986-07-01), Havkin et al.
patent: 4743907 (1988-05-01), Gellekink
patent: 5434587 (1995-07-01), Hannan
patent: 5455589 (1995-10-01), Huguenin et al.
patent: 5680139 (1997-10-01), Huguenin et al.
patent: 6150991 (2000-11-01), Hulderman
Chen Shih-Chao
Tyco Electronics Corporation
Wong Don
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