Abstract In an AMTI adaptive array, each array antenna element is connected to an element circuit which multiplies the contribution of each antenna element to the total return by a weight. The element circuits and further signal processing circuitry comprise the array processor. The element circuits include well-known cross correlator control loops. In accordance with the present invention, a signal whose pulse repetition interval to pulse repetition interval doppler phase shift is 180* out of phase with clutter returns is supplied to a control loop. Thus even with clutter at or near the look angle, mainlobe gain is maintained. Consequently, a ''''two pulse'''' MTI circuit utilizing a single delay line in each element circuit may be utilized rather than a two delay line element circuit which would normally be required to provide a signal to noise ratio value indicative of mainlobe gain which would be required for compatability with further MTI processing circuitry.
An adaptive AMTI processor for receive-mode operation with an array antenna, comprising, in combination: a plurality of element circuits connected, one each, to the respective antenna elements, each said circuit including a delay line arranged to receive the output from the antenna element, a pair of cross-correlator control loops connected respectively to the input and output of said delay line, weighting feedback means connected to said cross-correlator control loops and incorporating beam-forming circuit means operable to control the gain of said cross-correlator control loops to suppress signal returns incident upon said antenna from all directions other than the angle of a narrow arc centered about the antenna boresight, and phase shift means also incorporated in said weighting feedback means for introducing into the feedback signal path a phase shift approximately 180* greater than the phase difference between corresponding clutter return signals appearing at the input and output of said delay line; an AMTI canceller circuit; and summing circuit means for combining all outputs from said crosscorrelator control loops and passing the resultant signal to said AMTI canceller circuit for processing.
Claim 2
Dependent Claim
180 words
An adaptive AMTI processor for receive-mode operation with an array antenna, comprising, in combination: a plurality of element circuits connected, one each, to the respective antenna elements, each said circuit including a delay line arranged to receive the output from the antenna element, a pair of cross-correlator control loops connected respectively to the input and output of said delay line, weighting feedback means connected to said cross-correlator control loops and incorporating beam-forming circuit means operable to control the gain of said cross-correlator control loops to suppress signal returns incident upon said antenna from all directions other than the angle of a narrow arc centered about the antenna boresight, and phase shift means also incorporated in said weighting feedback means for introducing into the feedback signal path a phase shift approximately 180* greater than the phase difference between corresponding clutter return signals appearing at the input and output of said delay line; an AMTI canceller circuit; and summing circuit means for combining all outputs from said crosscorrelator control loops and passing the resultant signal to said AMTI canceller circuit for processing.