Mode-locked, surface acoustic wave oscillator

Abstract

A mode-locked surface acoustic wave oscillator (MLSO) provides mode-locked, phase coherent RF signal pulses through a regenerative closed loop RF signal path which includes a surface acoustic wave (SAW) delay line having a piezoelectric substrate and a pair of signal transducers relatively disposed at a determined SAW propagation distance along a major surface thereof, an RF amplifier to provide in phase amplification of the RF pulse, and a signal expander circuit for providing an increase in the harmonic frequencies of the RF signal pulse and an increased RF pulse frequency bandwidth. The pulse repetition frequency is determined by the signal propagation time delay, provided primarily by the SAW delay line. The delay line transducers establish the center frequency of the RF signal pulse and the bandwidth of the regenerative loop limits the minimum obtainable RF pulse width. An alternative embodiment of the MLSO includes a secondary loop which provides automatic generation of a synchronized trigger pulse having a pulse repetition frequency (PRF) derived from the RF signal pulse circulating in the regenerative loop. The synchronized trigger modulates the RF signal in the regenerative loop at a PRF equal to the reciprocal of the time delay of the SAW delay line, to further enhance the frequency mode-locked operation.