Ultra wideband radar transmitter employing synthesized short pulses

Abstract

A predetermined radar pulse train is formed in space by transmitting individual spectral components thereof. Thus, a train of extremely short pulses is obtained without switching a radio frequency signal on and off at a high rate. A crystal oscillator is coupled to a harmonic generator such as a comb generator. A power divider distributes the output of the harmonic generator to a multiplicity of final filter amplifiers. Each final filter amplifier has a phase-locked VCO circuit that provides frequency accuracy, spectral purity, low noise and frequency stability. Thus, each final filter amplifier provides one of the spectral components of the predetermined radar pulse train. The final filter amplifiers are coupled by duplexers to a broadband multiplexing feed such as a nested cup dipole feed that illuminates a reflector. On receive, the broadband multiplexing feed separates all the spectral components of the incoming pulse train. Each spectral component is coupled to its own narrow band receiver by the duplexers. One receiver is used to amplify and detect each spectral component. The signals from the receivers are coherently combined in a signal processor in which the signals add coherently and the noise signals do not. This provides a processing gain in signal to noise ratio corresponding to the total number of receivers. The output of the signal processor is applied to a radar display.