Range and Doppler resolution of a frequency-scanned filter

The paper is an analysis of a radar-signal-processing system¿the frequency-scanned filter¿which is designed to extract both range and velocity information from a single echo. The transmitted signal is a pulse train, which can be represented as a sequence. The echo is processed in a tapped delay line, with the taps weighted according to another sequence. The tap output is modulated by phase-coherent oscillators and summed to form the output. It can be shown that the output is the ambiguity function of the two sequences. By using some well known properties of the ambiguity function, both range and velocity can be estimated from the output, and the errors inherent in this estimation are also calculated. It should be noted that the system is time varying owing to the action of the modulators; this property is emphasised when the system is connected to operate as a frequency analyser. It is also shown that, except for some small and, in practice, insignificant differences, the frequency-scanned filter is equivalent to a bank of matched filters.