Communications: radio wave antennas – Antennas – Slot type
Reexamination Certificate
2000-02-02
2001-05-29
Ho, Tan (Department: 2821)
Communications: radio wave antennas
Antennas
Slot type
C343S7000MS, C343S846000
Reexamination Certificate
active
06239762
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to array antennas, and more particularly to co-located or common-aperture antenna arrays operating at disparate frequencies.
BACKGROUND OF THE INVENTION
For some applications, it is desirable to be able to use the same aperture area for a plurality of array antennas. In such interleaved or common-aperture arrangements, the operation of each array antenna is complicated by the presence of the other array, which adds mutual coupling between elements and interelement spacing problems. This problem is particularly acute when elliptical or circular (or dual linear) polarization is desired. Such a situation is described in U.S. Pat. No. 5,258,771, issued Nov. 2, 1993 in the name of Praba, in which two separate arrays of helical antennas, operable at different or disparate frequencies, are interleaved on (or using) the same ground plane. As described by Praba, the mutual coupling problem is solved, at least in part, by making the antenna elements of opposite hands of polarization. Grating lobes attributable to spacing of antenna elements are reduced by designing the helices so that the radiation pattern of the individual elements superposes nulls over the grating-lobe peaks. It should be understood that the ground plane, as described by Praba, has dual uses, the first being as a physical support for the antennas. The second use of the ground plane is equally important, if less obvious, and that is the use as an electrical terminus or ground, which allows the individual antenna feeds to be accomplished by means of transmission-line structures. Those skilled in the art know that it is very important in many contexts, including the electrical feed of antennas, to form the structures as transmission lines rather than as simple electrical conductors. In this context, the term “transmission line” connotes various factors such as low standing-wave ratio (SWR), controlled impedances (either the same at each point along the transmission line, or with at least somewhat matched transitions between different impedance levels), and low leakage or losses, except at locations where signal power transfer is desired.
A multiband phased-array antenna consisting of an L-band microstrip patch array interleaved with a linearly-polarized X-band slot array is described in an article entitled A Multiband Phased Array Antenna, by Edward, B. J., et al., published in Proceedings of the Sixteenth Annual Antenna Applications Symposium, Sep. 23-25, 1992. Such antennas are more desirable than helical antennas for those situations in which a planar or two-dimensional structure is preferred to a three-dimensional structure such as that of the Praba arrangement.
Improved interleaved antenna arrays are desired.
SUMMARY OF THE INVENTION
In its most general form, the invention lies in a crossed-slot antenna in a first ground plane, where the crossed-slot antenna has a first feed. The first feed is in stripline form, including a second ground plane, which underlies a portion of one of the orthogonal slots of the crossed-slot antenna for exciting a first polarization. A conductive lip of the other slot extends through the plane of the first feed, and opens through the second ground plane. A second feed includes conductors underlying the extended other slot. In a preferred embodiment, the feeds for the first and second slots are balanced. In a particularly advantageous embodiment, an array of such crossed slots is co-located with an array of enhanced-gain patch antennas.
More specifically, a crossed slot antenna arrangement according to an aspect of the invention includes a first ground plane or ground layer having radiating and nonradiating broad sides. The first ground plane defines a crossed slot antenna having first and second mutually orthogonal linear slots. These slots cross at a junction. Each of the linear slots includes a first and second portion. In a particular embodiment, the first and second portions of each linear slot are colinear, and separated by the junction. The crossed slot antenna arrangement also includes a first electrically conductive feed lying parallel with, and adjacent, the nonradiating side of the first ground plane, and extends across the first portion of the first linear slot for excitation thereof. A first dielectric layer lies between the nonradiating side of the first ground plane and the first electrically conductive feed, as a result of which, or whereby, the first electrically conductive feed takes on the general form of a first transmission-line structure. In a particular embodiment, the structure as so far recited is that of microstrip. A second electrically conductive feed lies parallel with the first ground plane and extends across the first portion of the second linear slot for excitation thereof. A second ground plane lies between the second electrically conductive feed and the first electrically conductive feed, thereby providing a second ground plane for the first transmission-line structure, and whereby the second electrically conductive feed takes on the form of a second transmission-line structure. In the particular embodiment, the presence of the second ground plane transforms the microstrip form of the first feed into a stripline structure. A second dielectric layer lies between the second electrically conductive feed and the second ground plane. A third ground plane extends parallel with the first ground plane, adjacent to the second electrically conductive feed, at a location remote from the second dielectric layer, for thereby providing a second ground plane for the second transmission-line structure. In the particular embodiment, the presence of the third ground plane transforms the second feed into a stripline form. An electrically conductive interconnection is coupled to at least the first portion of the second linear slot and to the third ground plane, without contacting the first and second electrically conductive feeds, for electrically interconnecting the second linear slot with the second transmission-line structure.
In a particular version of the crossed slot antenna arrangement, the first electrically conductive feed includes a further portion extending across the second portion of the first linear slot for excitation thereof, the further portion of the first electrically conductive feed including power splitting means for feeding the first and second portions of the first slot with substantially equal amplitudes. In another version of the crossed slot antenna arrangement, the second electrically conductive feed includes a further portion extending across the second portion of the second linear slot for excitation thereof, and the further portion of the second electrically conductive feed including power splitting means for feeding the first and second portions of the second slot with substantially equal amplitudes.
In a particular atavar of the invention, the first and second feeds are interconnected by a phase-shifting arrangement, for shifting the relative phases of signals provided by the first and second feeds to about 90° at a frequency within the operating frequency range of the crossed slot antenna arrangement.
In a yet further hypostasis of the invention, the crossed slot antenna arrangement further comprises a second electrically conductive interconnection arrangement coupled to at least the first portion of the first linear slot and to the second ground plane, without contacting the first and second electrically conductive feeds, for aiding in electrically interconnecting the first linear slot with the first transmission-line structure.
In a particularly advantageous version of the crossed slot antenna arrangement further includes at least one additional dielectric layer lying adjacent the radiating side of the first ground plane, the additional dielectric layer carrying a plurality of patch antennas overlying the radiating side of the first ground plane at locations other than those of the first and second slots, for radiating at a frequency higher than the operating frequency of the crossed slot anten
Ho Tan
Lockheed Martin Corporation
Meise W. H.
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