Use of noise radar in High PRF mode for far range surveillance

Abstract

Pulse radar is a widely used type of remote sensors. Estimations of both range and velocity of a moving target are the main capabilities of the coherent pulse radar. Known difficulties in design of coherent pulse radar are the range and Doppler ambiguities in measurements of high velocities for long range targets. This is a consequence of the contradictory requirements to the choice of pulse repetition interval (PRI) which is inverse of the pulse repetition frequency (PRF) needed for unambiguous measurement of target's range and velocity: the first one requires the pulse repetition interval exceeding the time of radar signal round trip propagation to the most distant target whereas unambiguous measurement of velocity requires pulse repetition interval to be smaller than the half of the Doppler frequency period which is defined by target velocity value. In practice, surveillance radar system requirements may lead to situation where no PRI can be chosen to fulfill both relations. This leads to design radar operating in so called High PRF mode when PRF is chosen so that several pulses are transmitted during the time of signal round trip propagation towards a most distant target. High PRF mode requires solving the problems of range ambiguity. One of the methods currently used for solving this problem is to generate of several bursts with various PRF and, later, to do a joint processing of the information about target detections made by each of the bursts [1]. This approach enables to solve the ambiguities with certain loss in the system power budget because the operation time and, consequently, energy should be split between the bursts, by each of which the target should be detected. Other approach uses PRF jitter and further processing of the data using compressive sensing algorithms [2]. This solution enables to solve ambiguity problems and to detect fast targets at long range, but with increased complexity of algorithm resulting in high costs both in implementation and in computational load. In another implementation [3] it is stated that pulse noise radar is free of range ambiguity due to the fact that the sounding signal and the reference for each pulse are random. Apart of that, noise signal may offer to a radar engineer such benefits as interference robustness and increased covertness.