Mcdonnell Douglas Corporation

Jesse C James

James B Blackmon, Jr

A synthetic aperture radar's surveillance is defeated by electronic camouflage that employs a protective shield to cover an intended target. The shield intercepts and modifies the interrogating radar pulses by modulating incident radar pulses to produce radar echoes shifted in Doppler frequency, whereby the returned echoes give a false depiction of the target, even to smearing the radar display. New structures are presented that exhibit variable reflectivity and variable dielectric characteristics of particular use in the foregoing and other electronic systems.

Synthetic aperture radar smearing

Novel test mounts are defined for a radar cross section testing apparatus that allows a supported object to be tested without interference from the test mount. This includes prescribing a diameter of about 0.61 wavelegths for a cylindrical test mount; maintaining a ratio for the test mount's characteristic dielectric constant and magnetic permeability of about one; and/or installing a frequency transposing apparatus to convert the frequency of radar pulses directed toward the test mount to off-frequency echoes.

Low RCS test mounts

Microwave devices incorporate at least one photosensitive baffle that is selectively illuminated changing the baffle's electronic characteristic from being transparent to being reflective of microwave energy. The baffle serves as a gate, tuning element, reflector and the like. Various forms of photosensitive baffles and microwave devices are presented.

Electronic baffle and baffle controlled microwave devices

The method and apparatus precisely identifies and locates an object which resonates in response to signals of at least one and, more typically, two resonant frequencies. The locating apparatus includes a transmitter for concurrently transmitting signals having a resonant frequency and signals having a non-resonant frequency toward the resonant object. The locating apparatus also includes at least two receivers for receiving reflected signals having the resonant frequency and the non-resonant frequency. The locating apparatus further includes a signal processor for locating the resonant object based upon the reflected signals detected by the receivers. The signal processor has multiple channels, one of which is associated with each receiver, for separately processing the reflected signals received over time by each of the receivers. Within each channel, the signal processor significantly reduces signal clutter based upon respective differences between the reflected signals having the resonant frequency and the reflected signals having the non-resonant frequency which were received by the respective receiver. By reducing signal clutter in the received signals, the locating apparatus identifies and locates the resonant object with more precision.

Method and apparatus for precisely locating a resonant object

Novel test mounts are defined for a radar cross section testing apparatus that allows a supported object to be tested without interference from the test mount. This includes prescribing a diameter of about 0.61 wavelengths for a cylindrical test mount; maintaining a ratio for the test mount's characteristic dielectric constant and magnetic permeability of about one; and/or installing a frequency transposing apparatus to convert the frequency of radar pulses directed toward the test mount to off-frequency echoes.

Microwave devices incorporate at least one photosensitive baffle that is selectively illuminated, changing the baffle's electronic characteristic from being transparent to microwave energy to being reflective thereof. That action selectively alters an electronic characteristic of the microwave device. The effect is shown applied in a number of devices, including a back lobe antenna. Undesired back lobes occuring at a principal frequency are reduced in a back plane antenna by alternately coupling and decoupling an extension to the antenna's back plane at a rate sufficiently high enough to shift the back lobes to adjacent frequencies. A photoelectrically controlled baffle suitably serves as the extension.

One or more antenna elements are submerged beneath a faired cover over a roof supporting member of a motor vehicle or hidden behind or as part of the front grill. Usually a conductive support extends behind the antenna elements and are electrically isolated therefrom to form the ground plane of the antenna. In some cases the antennas can be the structural members electrically isolated from the remainder of the body, but physically connected thereto. RF absorbers may be positioned spaced from radiating antenna elements to prevent antenna cross talk and exposure of occupants of the vehicle to high RF power densities. The antenna elements are especially useful in providing collision avoidance radar.

Hidden vehicle antennas

Placed in electrical circuit in shunt of the electrodes that supply current to a protected device and optically coupled to the location in the protected device where an electric arc is most likely to occur, a photosensitive device, responsive to illumination created by such an electric arc, switches to a conductive state, thereby short circuiting the electrodes feeding current to the arc and the arc is quickly extinguished.

Arc suppressor

Improvement of radar sign-to-noise ratio and detection sensitivity in radar systems is achieved by methods employing the subtraction of the unwanted radio frequency interference, RFI, or 'clone' signals thereof, from the total received signal. The Clone signals are appropriately adjusted in phase and amplitude, and are obtained from an auxilliary broad beam antenna or from a delayed sample from the system's principal antenna. When multiple RFI signals at different frequencies are present, the entire receive band is subdivided into a plurality of frequency sub-ranges.

RFI suppression circuit and method

An adjustable phase shifter is formed of an RF transmission line having an internal cavity, in which the phase shift produced is determined in part by a mound of flowable dielectric material in the internal cavity. An inlet tube defines a chute for dispensing the dielectric material into the internal cavity and a capped outlet tube connected to a bottom end of the internal cavity defines another gravity chute through which the dielectric material is removed to lower the height of the mound, when the cap is removed from the tube. The electrical length of the phase shifter is increased with addition of dielectric material and decreased with removal thereby varying the effective length of the RF transmission line and the phase shift produced on the RF that propagates therethrough.

High power RF phase shifter

An interceptor's point of impact on a targeted missile is quickly revealed in the milliseconds preceeding and following the impact by illuminating the target with radar signals at a high pulse repetition rate and observing the reflected radar echoes on an A-scope display. The position within the returned radar echo of a double echo and related changing phenomenon indicates the point of impact. Failing intercept, the miss distance is computed from the relative slant ranges to the targeted missile, the interceptor, and the double echo. The type warhead killed is revealed by a spectrograph slaved to the radar's antenna. Various techniques assist with the interpretation of the displayed patterns, including subtraction of previously stored patterns and display of the difference, display of characteristic patterns of various known missiles and interceptors stored in 'look up' tables, and neural networks.

Growing community of inventors

Huntsville, AL, United States of America

Jesse C James