Pulse Compression by Means of Linear- Period Modulation

ln applications where large time-bandwidth products and high target speeds combine, linear FM pulsecompression systems used in radar or mar der considerable lases in performance. This.paper deals with the problem of wide-band signal optimizintion far the purpose of minimizing signal degradation resulting from Doppler dirtortion effects. The equation for the instantaneous frequency of a Doppler-transformed signal is derived. The optimum frequency-modulation law is then shown to be the linear period modulation (it can be with equal rights called hyperbolic frequency modulation or logarithmic phase modulation). It is interesting to note that some kinds of bats use this type of signal in their "mar." Exact and approximate expres- siom far the spectrum of a linear-periad-madulated rectangular pulse are given, and the shape of the compressed output pulse is comidered. Signal degradation due to Doppler distortion is shown to be negligible in the case of linear-period-modulation pulses. The influence of pulse envelope on the compressed signal waveform is discussed, and envelope-optimization examples are presented. A possibility far active generation of the optimum signal is mentioned. Significant properties of linear FM and linear-period-modulation pulse compression systems are compared.