2. A search system for detecting moving targets, in chaff, and including a ransmitter for reflecting bursts of randomly phase coded, electromagnetic energy from a target, and a receiver, said receiver comprising A delay line having a plurality of output taps thereon, Means for applying said reflected bursts to said delay line, A plurality of phase shifters which are preset in accordance with the phase coding of said transmitter, Each phase shifting means being connected to a different output tap of said delay line, said plurality of phase shifters removing said phase coding from said bursts and providing a pure Doppler signal output, and Display means operably connected to receive the output from each of said phase shifting means for indicating the Doppler shift introduced by the target to each pulse of said burst.
A radar system is disclosed utilizing digital techniques for implementing a moving target indicator (MTI) or pulse doppler type of radar system. More specifically, the radar system includes an MTI filter or canceler circuit for suppressing clutter signals corresponding to stationary and/or relatively slow-moving targets, while providing an output signal indicative of echo signals received from relatively fast-moving targets. The canceling circuit of this invention achieves moving target detection with digital apparatus having a capability of processing only a limited number of digital bits. The MTI filter of this invention incorporates modulo-N components having a modulus or linear range so that the minimum detectable signal of interest lies therein. The higher magnitudes of signals corresponding to echo signals received from stationary and/or slowly-moving objects will be canceled by the canceling circuit, normally. If echo signals are developed from moving targets that are of higher magnitudes than the modulus, these signals will be "aliased" by the modulo-N components about the levels N/2 and -N/2 to provide a noise-like output. Regardless of the amplitude of the echo signals derived from a relatively fast-moving target, detecting means is provided to detect the absence or presence of such signals.
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.
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.
An impulse interference suppression circuit for use in combination with an -pulse Moving Target Indicator system comprising a gate connected to block the output signal from the MTI system when energized, and a circuit for taking the magnitudes of successive echo return signals, subtracting the magnitudes of consecutive echo signals to remove clutter, comparing the consecutive difference signals from such subtractions against each other, and generating and applying a blocking signal to the gate if the difference between the subtraction difference signals is above a given threshold level.
