Reduction of radar antenna area

Abstract

The traditional minimum antenna area limit for synthetic aperture radar (SAR), imposed by ambiguity considerations, is eliminated by using a transmitter format providing distinguishable sub-pulses. Signal formats which are feasible for implementing such sub-pulses include frequency-division (i.e., a distinct frequency band is used for each sub-pulse), and code-division (i.e., sub-pulses occupying the same frequency band are grouped in distinguishable combinations). The nominal pulse period is divided into N sub-pulses, and the sub-pulse group is transmitted with the nominal pulse repetition frequency (f.sub.p). The range ambiguities are determined by the repetition rate of the sub-pulse group (f.sub.p) and the azimuth ambiguities are determined by the repetition rate of the sub-pulses (N.f.sub.p). The antenna is capable of sampling a Doppler bandwidth that is a factor of N times the traditional value and the antenna area can be reduced by a factor N from the limiting value presently used in SAR antenna design. A reduction in antenna length by a factor of N, for example, can be obtained at the expense of a signal-to-noise decrease of N and an increase in signal bandwidth by the same factor. Alternatively, the same antenna length reduction of N and an increase in signal-to-noise by a factor N can be obtained using the original bandwidth if the resolution is degraded by N.