US 5,442,359 A · Apparatus and method for mitigating range-doppler ambiguities in pulse-doppler radars

Abstract

A method and apparatus for resolving Doppler frequency shift ambiguities in pulse Doppler radar systems provides a radiated signal that is modulated with a periodic waveform having a plurality of pulses within a period, the interpulse intervals between pulses in the period being unequal. Radar target returns are autocorrelated for a plurality of lags, which may include the interpulse intervals and linear combinations thereof. The calculated arguments .theta..sub.Ci of the autocorrelation function are unwrapped by adding 2k.sub..pi., k=0, .+-.1, .+-.2, . . . , to the phase .theta..sub.C1 obtained for the shortest lag T.sub.1 and determining an integer m.sub.k2 from .vertline.(.theta..sub.C2 +2m.sub.k2 .pi.)-(T.sub.2 /T.sub.1).theta..sub.C1 .vertline. <.pi. and then setting .theta..sub.2 =.theta..sub.C2 +2m.sub.k2 .pi.. Phase angles .theta..sub.3, .theta..sub.4, . . . , .theta..sub.m are unwrapped in a similar manner, the integer m.sub.ki being determined from .vertline.(.theta..sub.Ci +2m.sub.ki .pi.)-(T.sub.i /T.sub.i-1).theta. .sub.Ci .vertline.<.pi.. The unwrapped phase angles and the point (0,0) are least mean square fitted to lines of phase angle vs lag for each value of k. The root mean square error of the phase angle offset from each line is determined and the slope of the line with the minimum RMS error is chosen as the Doppler frequency shift from which the velocity of the target is extracted.

Claims7

Dependent claims

A Doppler radar of the type having a stabilized transmitter for transmitting pulse modulated signals and a receiver for receiving radar returned signals further comprising:

waveform generator means coupled to said transmitter for providing a periodic modulating waveform, each period including a plurality of pulses positioned with unequal intervals therebetween, thereby causing periodic pulse modulated radiated signals with each period having a plurality of radiated pulse modulated signals with unequal intervals therebetween;
correlation means coupled to said receiver for performing autocorrelations of returned radar signals, lags for said autocorrelations being equal to said unequal intervals between said plurality of pulses positioned in said period, and for providing signals representative of said autocorrelations, said autocorrelations having an amplitude and a phase;
and
Doppler frequency shift means coupled to receive said autocorrelation representative signals for providing signals representative of Doppler frequency shifts of said returned radar signals.

1 more element

A method of determining velocity of a moving target comprising the steps of:

radiating a signal modulated by a periodic waveform, each period of said periodic waveform including a plurality of pulses positioned with unequal intervals therebetween;
autocorrelating received backscattered returns from said target using lags equal to said unequal intervals to obtain autocorrelations of said received backscattered returns for lags equal to said unequal intervals, each of said autocorrelations having an amplitude and a phase;
and
utilizing said autocorrelations for determining target velocity.

1 more element

Dependencies are inferred from the claim text.

Apparatus and method for mitigating range-doppler ambiguities in pulse-doppler radars

Life of this patent

Apparatus and method for mitigating range-doppler ambiguities in pulse-doppler radars

Life of this patent

Abstract

Claims7