Selected problems of processing a radar signal with a LFM-FSK modulation

Abstract

An operational model of continuous-wave radar designed for detection of stationary and moving objects in the air was built at the Institute of Aviation. The LFM-FSK modulation of radiated signal was selected, due to its advantages (short measurement time, not very complicated algorithm of calculations, the possibility of simultaneous measurement of the range and velocity of multiple objects). The modulation waveform is composed of two intertwined strictly linear or stepwise sweeps. Two adverse phenomena (the mutual influence, resulting from not perfect transmittance of receiver channel, of the samples related to even and odd steps of the transmitted signal and the leakage of transmitted signal into the receiver antenna causing an excessive increase of receiver output dynamic range) were encountered during the development process. The issues relating to them are presented in the paper. The first issue was solved by the use of a pre-compensation digital filter. The dynamics of the leakage signal was reduced by mixing of quadrature output signals of the radar head in a proper proportion, and by using the dome made of foam material, instead of a laminate one, which was designed initially.

Keyword : radar signal, modulation, unmanned aerial vehicle, compensational method