Communications: directive radio wave systems and devices (e.g. – Radar ew
Reexamination Certificate
1999-07-09
2001-10-09
Sotomayor, John B. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Radar ew
C342S001000, C342S002000, C342S003000, C342S004000, C342S005000, C342S006000
Reexamination Certificate
active
06300894
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates in general to communication systems, and is particularly directed to a new and improved RF interface structure having a radar cross-section that is electrically controllable, so as to enable an antenna or radome's reflectivity characteristic or ‘signature’ to RF energy to be controllably modified at times other than when the structure is being used in conjunction with the transmission or reception of electromagnetic energy (e.g., receive or transmit communication signals).
BACKGROUND OF THE INVENTION
The survivability of RF transmit/receive systems that are deployable in a hostile environment depends upon their ability to avoid detection by a threat radar. For this purpose, the deployed system preferably employs a configuration and uses ‘stealth’ materials that will minimize its radar cross-section (RCS). On the other hand, because the inherent functionality of a transmit/receive system involves either or both the transmission and reception of RF energy, its operability requires that it exhibit, during some prescribed transmit/receive window, the very characteristic that makes it vulnerable to a threat—i.e., that it reflect electromagnetic energy.
SUMMARY OF THE INVENTION
In accordance with the present invention, this dual objective is effectively accomplished by means of a new and improved electromagnetic energy laminate structure, that may be employed in a variety of electromagnetic energy interface applications, such as, but not limited to use as an antenna reflector, as a radome structure, or the ground plane for an array. As will be described, A DC electric field is applied to the laminate in such a manner as to enable the structure's reflectivity characteristic or electromagnetic energy ‘signature’ to be controllably modified at times other than when it is being used in associated with the transmission or reception of RF energy (e.g., transmit and receive communication signals, radar signals and the like).
For this purpose, the RF interface of the present invention is preferably configured as a relatively compact laminate structure having a core layer of a material having at least one electrical property, such as permitivity, that is electrically controllable in such a manner as to produce a specified modification of the behavior of impinging electromagnetic energy. The specified behavior modification is one of minimally attenuated transmission, maximally attenuated absorption, and highly attenuated or unattenuated reflection.
The core layer preferably comprises a relatively thin (e.g. one-eighth to one-quarter inch) layer of a ferroelectric ceramic material, such as barium strontium titanate (BST). Opposite surfaces of the BST core are coated with micro-thin layers of an electrically conductive material, such as indium tin oxide, that is effectively transparent to electromagnetic energy of the frequency range of interest, such as UHF and SHF frequency bands RF or microwave frequencies typical employed in communication systems or radar systems (e.g., on the order of from 300 MHz to 30 GHz). A differential DC voltage is applied to the thin coatings on the BST core layer, so as to impart a prescribed DC electric field thereacross in accordance with the application in which the laminate structure is employed.
An alternative embodiment of the laminate architecture of the invention has multiple layers of ferromagnetic core material laminated on either side of an intermediate reflective layer and coated on their outer surfaces with thin coating layers. Each of the intermediate and outer surface coating layers may comprise a layer of indium tin oxide. A first potential, such as a ground voltage is applied to the intermediate reflective layer, while the outer thin coating layers are coupled to receive control voltages. As in the single core layer embodiment, the differential voltages and the resulting electric fields applied to the BST layers are selectively defined in accordance with the mode of operation of the multi-laminate structure.
For an application such as a reflector antenna or an array ground plane application, during transmit/receive mode, the magnitude of the differential voltage is set at a value that is effective to render the laminate's ferromagnetic ceramic core highly conductive, and thereby reflective to the RF wavelength being sourced from or received by an associated feed horn, or the array elements. During other times (quiescent mode), the magnitude of the differential voltage is set at a value that is effective render the laminate effectively transparent to RF wavelengths in a broad range of frequencies typical of search radars (e.g., at or below K-band and up to or slightly above K-band (27 GHz)).
When employed in a radome application, during transmit/receive mode of an RF communication system housed within the radome, the laminate's differential voltage is set at a value that renders the radome laminate effectively transparent to a broad band of RF wavelengths. During all other times (quiescent mode), the magnitude of the differential voltage is set at a value that is effective to render the radome laminate effectively absorbent of RF wavelengths, including those lying in a ‘threat’ band of interest, thereby minimizing the radar cross-section of the radome and its interior system components to a search/threat radar. Alternatively, when not in use, the structure may be controllably rendered reflective so as to direct impinging electromagnetic energy away from the transmit source.
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Lynch Michael J.
Newton Charles M.
Walley George M.
Allen Dyer Doppelt Milbrath & Gilchrist, P.A.
Harris Corporation
Sotomayor John B.
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