Communications: radio wave antennas – Antennas – Wave guide type
Reexamination Certificate
1999-08-23
2001-10-23
Wong, Don (Department: 2821)
Communications: radio wave antennas
Antennas
Wave guide type
C343S755000, C343S753000, C342S053000
Reexamination Certificate
active
06307521
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a bispectral window selectively transmitting and reflecting infrared and millimeter wave (radio frequency) radiation, as well as a reflector antenna arrangement that incorporates such a bispectral window.
BACKGROUND INFORMATION
Attempts have been made in the art to provide a single antenna system that is suitable for transmitting and/or receiving radiations in more than one frequency spectrum or wavelength range. For example, the article “Multispectral (IR/MMW) Dome For seeker Application” by G. Forti, W. Menicacci—S.M.A., A. Novi, G. Simoncini, and L. Calami, OFF. GALILEO, Florence, Italy, pages 157 to 166, as published in the Sixth European Electromagnetic Structures Conference Proceedings, Friedrichshafen, Germany (1991), discloses a rotationally symmetrical Cassegrain-Antenna arrangement which is schematically shown in present FIG.
9
. This conventional reflector antenna arrangement includes a primary or main reflector
101
and a secondary or subreflector
102
arranged symmetrically and coaxially along a common radiation axis CA. Infrared (IR) active elements
104
as well as millimeter wave radiation (RF) active elements
103
are integrated together into a feed horn arranged along the common axis in a typical Cassegrain arrangement. Due to the incorportion of both IR elements
104
and RF elements
103
into the feed horn, both the IR radiation and the RF radiation will be reflected in the same manner along the same path from the subreflector
102
and from the main reflector
101
, and in common along the common axis CA.
With the above described known arrangement, the infrared (IR) signals suffer undesirable side effects, especially in some applications, because it is impossible to optimize the reflectors simultaneously both for the RF radiation and for the IR radiation. For this reason, it becomes necessary to provide a directly radiating aperture for the IR radiation. Such a directly radiating aperture, however, cannot be provided in a system in which the radiation directions or radiation axes of the two radiation spectra are coincident along the common axis CA, because both the exciter as well as the subreflector would necessarily be located in the beam path and thus in the way of a direct radiation of the IR radiation. Furthermore, it has been a continuing problem for conventional antennas to achieve a space-saving integration of a millimeter wave sensor system for RF radiation and an infrared system for IR radiation in a particularly compact arrangement, for example using an offset double reflector antenna arrangement. Particularly, it has not been possible to achieve an acceptable antenna system having the following characteristics: a direct radiating infrared aperture without interference, the smallest possible degradation of the millimeter wave RF signal path, and a coincidence of the radiation beam axes of the two systems externally from the antenna arrangement.
SUMMARY OF THE INVENTION
In view of the above, it is an object of the invention to provide a bispectral window for a reflector, as well as a reflector antenna arrangement using such a bispectral window, which is able to receive and/or transmit both infrared (IR) radiation as well as millimeter wave (RF) radiation without suffering undesirable side effects on the IR radiation, and which has a very compact space-saving arrangement using a comparatively small space for the RF sensor system and for the IR system. The invention further aims to avoid or overcome the disadvantages of the prior art, and to achieve additional advantages, as apparent from the present specification.
The above objects have been achieved in a bispectral window for a reflector for radiation in the infrared (IR) and millimeter wave (RF) ranges, according to the invention. The bispectral window consists essentially of a dielectric material having a low loss factor and a high dielectric constant. Furthermore, the bispectral window comprises respective front and back surfaces that each have a respective rotationally symmetrical aspherical surface contour or shape. The front surface of the bispectral window is arranged on the side of the reflector on which the RF radiation is incident, and the surface contour of the front window surface is optimally matched to that of the surface of the reflector for reflecting the RF radiation. The back surface of the bispectral window has a surface contour that is shaped to achieve an optimal reflectivity for the RF radiation. In this manner, more particularly, the bispectral window is substantially transparent to the IR radiation and substantially reflective for the RF radiation.
The above objects have further been achieved according to the invention in a reflector antenna arrangement including a main reflector having a hole or opening in a central area thereof, and a bispectral window arranged in the hole or opening. The bispectral window is substantially transmissive for IR radiation and is substantially reflective for RF radiation. An RF feed horn, which may include an RF source and/or an RF sensor, is arranged so that RF radiation is reflected from the front surface of the main reflector and the front surface of the bispectral window, from or to the RF feed horn, either directly or via a subreflector. On the other hand, an IR feed or active element, which may include an IR source and/or an IR sensor, is arranged behind the bispectral window that is received in the opening in the reflector. Thus, IR radiation is transmitted through the bispectral window forming an IR aperture, respectively from the IR source or to the IR sensor. The surface contour of the front surface of the bispectral window is substantially matched to and flush with the front surface of the reflector. The back surface of the bispectral window has a surface contour for optimizing the RF reflectivity.
The bispectral window according to the invention, and particularly the arrangement of such a bispectral window in an opening in the central area of a main reflector of an antenna arrangement, achieves a frequency selective separation of the two signal paths of the respective IR and RF radiations. In this manner, the IR signal path does not need to follow the reflection path via main reflector and a subref lector, but instead can be transmitted and radiated directly through the bispectral window representing a direct radiation IR aperture. On the other hand, the RF radiation follows a double reflection path, being reflected from the main reflector including the bispectral window and from the subreflector. Nonetheless, the two radiation beam paths are coincident along a common axis external to the reflector antenna arrangement. By separating the beam paths in this manner, undesirable side effects on the IR radiation can be prevented while maintaining the external common beam axis. Also, the inventive integration of the two systems achieves a very compact and space-saving arrangement while still achieving the above mentioned advantages.
REFERENCES:
patent: 4355313 (1982-10-01), Hubert
patent: 5182564 (1993-01-01), Burkett et al.
patent: 5307077 (1994-04-01), Branigan et al.
patent: 5327149 (1994-07-01), Kuffer
patent: 4010242 (1991-10-01), None
patent: 0583557 (1994-02-01), None
Article entitled “Offset Dual Reflector Antenna” by Y. Mizugutch et al.; IEEE-Proc. Int. Symp. Antennas and Propagation, Stanford, CA, Jun. 1977, pp. 1, 3, 4, 5.
Antenna Handbook, Y.T. Lo, S.W.Lee, New York, 1988, pp. 21-13; Van Nostrand Reinhold Comp.
“Synthesis of dual-offset shaped reflectors for arbitrary aperture shapes using continuous domain deformation”, by B. S. Westcott et al., IEEE-Proceedings, vol. 133, Pt. H, No. 1, Feb. 1986.
“Multispectral (IR/MMW) Dome for Seeker Application”, by B. Forti et al.; 6th European Electromagnetic Structure Conference Proceedings, Dornier/Deutsche Aerospace, Friedrichshafen, Germany, 1991.
Haertinger Erwin
Leupelt Uwe
Schindler Gerhard
Alemu Ephrem
Daimler-Chrysler AG
Fasse W. F.
Fasse W. G.
Wong Don
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