Method and apparatus utilizing time-expanded pulse sequences for

Abstract

Pulse sequences from a radar receiver respectively made up of successive start pulses and of successive echo pulses from one or more targets are expanded in time by multiplication with an auxiliary pulse sequence differing slightly in repetition rate from the start pulse sequence. This enables circuits to be used with a lower degree of time resolution that would otherwise be needed, at the cost of proportionally reducing the number of individual measurements of the target distance, a cost which is of no substantial consequence in an anti-collision radar where the closing rates are small compared to the pulse repetition rate. A time-expanded sequence of reference pulses is similarly produced from the oscillator controlling the repetition of the radar pulses and the auxiliary oscillator in order to make the measurements independent of signal propagation times within these circuits. The time-expanded pulses to be evaluated are differentiated and the null passage instant of the differentiated pulses is used to find the maximum amplitude of the pulses and to determine which pulses should be disregarded on the basis of amplitude discrimination. A range gate controlled with reference to the velocity of the vehicle in which the radar is mounted, in combination with certain other factors, is used to exclude interference from irrevalent targets.