USA as Represented by Secretary of the Navy

Other

Bernard L Lewis

Frank F Kretschmer, Jr

Ben H Cantrell

James P Hansen

Irwin D Olin

Dean D Howard

The present invention describes a system for counteracting countermeasures against radar detection. Two known countermeasures are &ldquo;phase front tilting&rdquo; and &ldquo;isotropic scattering.&rdquo; The invention accomplishes this counteraction by deliberately producing a tilt in the phase front of the transmitted energy. This causes the phase front tilting countermeasure itself to become a tracking signal source for the radar system. The isotropic scatterer types of countermeasures are insensitive to the phase front of the transmitted energy and hence produce return signals which may be distinguished from a true radar echo return signal which is highly sensitive to the phase front of the transmitted energy. Thus this invention provides a radar system having a high degree of immunity to radar countermeasure devices.

Radar system

A system for instrumenting time sampled predicting interference suppression, particularly in a side-lobe canceller system. Main and auxiliary channel signals are supplied to a canceller loop where correlating weights are sampled just prior to a radar pulse transmission on command of a radar pretrigger pulse. A sampling circuit stores both current and past weights and combines the current weight with the integral of the difference between the current and past weight to form predicting weights over each pulse repetition period. The predicting weights are used to form a translating signal for operating on the auxiliary channel interference signal so that it will cancel the interference in the main channel. By sampling just prior to radar pulse transmission and forming the predicting weights, cross modulation of clutter and antenna scan error can be reduced in order that a side-lobe canceller may be used compatibly with Moving Target Indicators.

Predicting coherent sidelobe canceller

A moving target indicating system wherein a pulse source which generates radiofrequency drive pulses at a predetermined pulse repetition frequency is connected to the inputs of a pair of channels. The first channel includes a phase-dispersive filter having a first phase-slope dispersion characteristic, while the second channel has a phase-dispersive filter having a phase-slope dispersion characteristic which is the negative of that of the first filter. A pulse group comprising the output of the first and the second channels is transmitted periodically as each drive pulse is applied. The pulse repetition frequency is sufficiently low that when transmitted, echos of only one pulse of each group are received at a time. Due to the 'matched' or 'conjugate' phase-dispersive characteristics of the filters in the respective channels, the first channel operates in reception upon the reflected pulse originally generated in the second channel and compresses it thus resynthesizing or reconstituting a short duration pulse like the original, while the second channel operates in reception upon the reflected pulse generated in the first channel, compressing it to reconstitute a short duration pulse like the original. A canceler is switched between the outputs of the first and second channels to receive the two resulting reconstituted pulses of each group. In the usual application, fixed target information is cancelled out and moving target information is derived for application to a display device.

Moving target indicator with no blind speeds

An MTI with no blind speeds which compensates for antenna scan modulation. his design includes circuitry for generating and transmitting consecutive first, second and third doppler-tolerant FM pulses, wherein the first and third FM pulses have a given dispersion characteristic, and the second FM pulse has a dispersion characteristic which is the complex conjugate of the first and third FM pulses. Circuitry is then provided for receiving and compressing the first, second, and third echos from the first, second, and third pulses, respectively. Finally, a processing circuit is used to effectively add the first and third echo pulses and to subtract twice the second echo pulse from this sum to effect the detection of the moving target.

Three-pulse MTI without blind speeds

A sidelobe suppression system including an antenna with a variable phase ter, a transmitter for transmitting an expanded phase-coded pulse, a receiver for receiving target echos, a pulse expander/compressor for phase coding the expanded transmitted pulse with a phase code, P, and for compressing target echos with unscrambled phase code P and a control unit for shifting the phase center of the antenna to scramble the phase codes of the expanded pulses transmitted into the antenna sidelobes.

Coherent antenna sidelobe suppression system

A radar interference circuit which rejects both continuous noise and shorulse interference signals. A plurality of omni-directional antennas are placed around the main directional radar antenna and connected in differing sets to a plurality of canceller means to each of which the main antenna signal is also connected. The canceller means for each set of three Omnis and the main antenna cancels out the white-noise interference received by that group of antennas. The outputs of the plurality of canceller means are then taken in different sets of two each, subtracted and compared to a threshold signal. If one or more comparator outputs are above the threshold, signifying that the antenna pulse signal is being received through the sidelobes of the antenna patterns, the outputs of these comparators will be a one signal and the OR gate, to which the comparator outputs are fed, will provide an output to blank the radar. Thus, short-pulse signals arriving through the sidelobes of the antenna patterns are rejected as interference signals.

Method and means for short pulse interference rejection

An electronic countermeasure system carried aboard a target that creates se targets in front of and/or behind the target. The radar's transmitted signal is repeated back to the radar with a frequency effect, which induces the range-doppler coupling feature of the pulse-compression circuit to compress early or late by the ratio of the frequency offset to the radar receiver bandwidth times the uncompressed pulsed length of the radar signal.

ECM for long-range radars

A technique for improving sidelobe canceller performance by blocking the canceller output signal upon sensing reduced main channel interference accompanied by an increased sidelobe canceller output. Two signal processing networks form the difference between successive output signals from a radar antenna and sidelobe canceller respectively. The difference signals are multiplied together and the product used to control passage and preclude utilization of the canceller output signal when reduced jamming interference occurs.

Technique for processing interference-contaminated radar energy

An MTI radar based on a comparison of the Doppler shifts of the original signal and a phase-reversed signal using pulse compression wherein the received signal is phase detected for in-phase and quadrature components relative to the IF. A Doppler-corrected pulse compressor produces a magnitude signal for the Doppler shift of the received signal from the sequence of in-phase and quadrature components. Another Doppler-corrected pulse compressor produces a magnitude signal for the Doppler shift of the received signal from the conjugates of the sequence of in-phase and quadrature components. The magnitude signal of the same Doppler shift of the two compressors are compared and the difference is the output of the MTI.

High frequency MTI radar

A canceller system having four or more signal sources with correlated coments uses signals from three of the signal sources to cancel correlated components from the signal of the fourth signal source. The canceller apparatus includes a main cancellation channel with serial cancellers and a preprocessing arrangement of cancellers made up of M auxiliary channels each having M-1 serial cancellers. Each of the M auxiliary channels outputs is decorrelated from each other auxiliary channel output and each is provided as an input to one of the main channel serial canceller.

Adaptive decorrelating sidelobe canceller

A pulse-compression, MTI, doppler-radar system for determining target velty information from a single target-return pulse is improved by the addition of a pulse-compression filter consisting of at least two pulse compressors and by the addition of a phase-comparison processor. The pulse compressors simultaneously pulse-compress separate portions of the single target-return pulse. The phase-comparison processor then determines the phase difference between the compressed pulses to obtain the target velocity information.

Phase-coded monopulse MTI

A sidelobe canceller system utilizing directional auxiliary antennas and e delays allows the spacing between the auxiliary antennas and a main radar antenna to be increased. This improves cancellation of multiple interference signals from the sidelobes of the main antenna.

High-resolution sidelobe-canceller auxiliary antennas

A system for cancelling jammer signals entering the mainlobe of a monopulse adar and providing target locations with respect to the jammer position comprising for a sequential lobing embodiment: measuring the angular position of the jammer in the radar's mainlobe via the use of monopulse sum and difference signals, pointing the radar antenna so that the jammer is positioned within the 3 dB points of the mainlobe of the monopulse antenna, converting the sum and difference echo signals received with the antenna in this position from the next radar transmission into a second set sum and difference signals, applying this second set of sum and second set of difference signals to the inputs of an adaptive canceller to cancel the jamming signal therein and storing these signals in time sequential order, changing the orientation of the radar antenna by a small arbitrary elevation angle, converting the sum and difference echo signals received with the antenna in this new position from a third radar transmission into a third set of sum and difference signals, applying this third set of sum signals and third set of difference signals in reverse order relative to the second set of signals to the inputs of an adaptive canceller to cancel the jamming signal therein, reading out the adaptively cancelled stored echo signals from the second radar transmission into one input of a divider in time coincidence with the application of the adaptively cancelled echo signals from the same targets from the third radar transmission to the other input of the divider to obtain ratio signals proportional to the elevation angle separating the individual targets from the jammer.

Jammer reference target measurement system

A digital, open-loop, sidelobe canceller system includes an arrangement of uxiliary-channel preprocessing cancellers and a series of main-channel cancellers in which specific cancellers average a different number of samples for cancelling both barrage (continuous) jamming and false-target-repeater jamming, which enter the sidelobes of a radar antenna. The preprocessing cancellers and each of the main-channel cancellers, except the last succeeding main-channel canceller, use long-time averaging (averaging over a large number, n, of samples of the main and auxiliary signals, where n&gt;&gt;2) for removing barrage jamming from the main signal. The last succeeding main-channel canceller uses short-time averaging (averaging over approximately 2-4 samples) for removing false-target-repeater jamming from the main signal.

General purpose sidelobe canceller system

A pulse-compression, MTI, doppler-radar system for determining target velty information from a single, frequency-coded uncompressed target-return pulse includes a coded modulator, two pulse compressors, and a phase-comparison processor. The coded modulator generates for transmission an uncompressed pulse with the first and second halves of the pulse coded with the even and odd harmonic sidebands of a pulse repetition frequency, respectively. The first and second halves of the pulse returning from the target are pulse compressed simultaneously by the two pulse compressors. The phase comparison processor then determines the phase difference between the compressed pulses to obtain the target velocity information.

Growing community of inventors

Oxon Hill, MD, United States of America

Bernard L Lewis