Communications: radio wave antennas – Antennas – Slot type
Reexamination Certificate
1999-08-27
2001-10-16
Wong, Don (Department: 2821)
Communications: radio wave antennas
Antennas
Slot type
C343S768000, C343S872000
Reexamination Certificate
active
06304226
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to antennas. More specifically, the present invention relates to slot antennas used in high-power applications.
2. Description of the Related Art
The individual antenna elements of a wide-scan phased array antenna (e.g., one capable of scanning very wide angles such as +/−45°) must typically be spaced very close together. More specifically, the individual antenna elements must generally be spaced approximately one-half of a free-space wavelength apart from one another. There are a variety of antenna elements that are of such compact design. However, none of the presently available antennas, compact enough for use in a wide-scan phased array antenna, are capable of handling very high average power levels while simultaneously providing very accurate polarization, e.g., circular polarization, over a very large angular region (e.g., +/−50° in both planes). In this connection, there are a number of applications, including high-power wide-scan phased array antennas, that require an extremely compact antenna design that satisfies these constraints. The following brief review of the presently available antenna technology should serve to illustrate the limitations and shortcomings thereof. Circularly polarized patch antennas can be made smaller than one-half of a free-space wavelength, but only through the use of a dielectric, thereby rendering the patch antenna inadequate for high power applications. A circularly polarized ridged waveguide antenna having a slot formed in a surface thereof can be made smaller than one-half of a free-space wavelength. Although such an antenna design can handle high power levels, it is not capable of providing accurate circular polarization.
A rectangular cavity-backed slot antenna can be constructed that can handle high power levels (i.e., no dielectric is required). However, the cross-sectional dimensions of the cavity must be greater than one-half of a free-space wavelength (typically, {fraction (7/10)}th of a wavelength on edge) for the device to be operative. The reason that the dimensions of the cavity must be greater than one-half of a free-space wavelength is due to the fact that in order for the cavity to resonate, the rectangular dimensions must be equal to one-half of a guide wavelength, which is longer than the free-space wavelength.
The size of a conventional cavity-backed slot antenna can be reduced by filling the cavity with a dielectric material, but this introduces substantial losses and renders the antenna inadequate for high average power applications.
Other known antenna designs include those disclosed in U.S. Pat. No. 3,573,834, issued to McCabe et al.; U.S. Pat. No. 4,130,823, issued to Hoople; U.S. Pat. No. 4,132,995, issued to Monser; and, U.S. Pat. No. 5,461,393, issued to Gordon. However, the antennas disclosed in these patents are either too Large, have poor circular polarization performance, and/or can not handle high power levels.
Thus, there is a need in the art for an extremely compact antenna that is capable of handling high power levels and providing very accurate polarization, e.g., for use in high-power applications that require radiation of very accurate circular polarization over a very large angular region (e.g., +/−50° in both planes), such as in wide-scan phased array antennas.
SUMMARY OF THE INVENTION
The need in the art is addressed by the compact, folded cavity-backed slot antenna of the present invention. In one of its aspects, the present invention encompasses an antenna that includes a housing having a plurality of walls forming an enclosure, a slot formed in a first wall of the housing, and, a folded cavity formed in a second wall of the housing opposite the first wall. The folded cavity is preferably a compound cavity that includes a first cavity portion and a second cavity portion joined around their entire respective peripheries by a fold or shelf. Any convenient RF transmission line, e.g., a waveguide or coaxial cables, can be used to inject RF energy into the folded cavity.
In one embodiment, the slot is cross-shaped, and coaxial cables that transmit RF signals that are 90° out-of-phase are used to feed the folded cavity in respective orthogonal directions, whereby the cross-shaped slot produces accurate, circularly polarized radiation.
In another embodiment that was built and extensively tested, the slot is cross-dumbbell-shaped, and a ridged waveguide is used to feed the folded cavity. In this embodiment, an amount of cavity fold is greater in a first direction than it is in a second direction, whereby the folded cavity resonates at different frequencies for RF energy of different polarizations. Further, a coupling post is provided to coupled RF energy of a first polarization to RF energy of a second polarization, whereby the slot produces accurate, circularly polarized radiation.
In both embodiments, at least one of the width and length dimensions of the housing is less than {fraction (7/10)}th of a free-space wavelength and, preferably, both the width and length of the housing are each less than ½ of a free-space wavelength. With either of these embodiments, the antenna is capable of producing very accurate circular polarization and is capable of handling very high average power levels, e.g., 10 kW, thereby making it suitable for high power applications which require extremely compact antenna elements, e.g., wide-scan phased array antennas.
The present invention also encompasses, in another of its aspects, a phased array antenna that includes a plurality of antenna elements each of which is constructed in accordance with the present invention.
REFERENCES:
patent: H1151 (1993-03-01), Peterson, Jr.
patent: 3573834 (1971-04-01), McCabe et al.
patent: 4032921 (1977-06-01), Sikina, Jr. et al.
patent: 4130823 (1978-12-01), Hoople
patent: 4132995 (1979-01-01), Monser
patent: 4200873 (1980-04-01), Seeley
patent: 4242685 (1980-12-01), Sanford
patent: 4451830 (1984-05-01), Lucas et al.
patent: 4573056 (1986-02-01), DuDome et al.
patent: 4733245 (1988-03-01), Mussler
patent: 4935745 (1990-06-01), Mori et al.
patent: 5461393 (1995-10-01), Gordon
patent: 5648786 (1997-07-01), Chung et al.
patent: 6052093 (2000-04-01), Yao et al.
Brown Kenneth W.
Drake Thomas A.
Benman William J.
Lenzen, Jr. Glenn H.
Raytheon Company
Tran Thuy Vinh
Wong Don
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