The Mode-Locked SAW Oscillator

Abstract

The mode-locked SAW oscillator is a new type of signal source, one which generates a stable and highly coherent pulsed rf output. The new device is analogous to the self mode-locked microwave oscillator described by Cutler in 1955 and the mode-locked lasersintroduced by Hargrove, %&. in 1964 and by DeMaria, st. in 1967. the reciprocal of the decay time and usually deemed undesirable, are synchronized by inserting a nonlinear element, a signal expander, into the feedback loop. The synchronized spectral lines, whose number are governed by the bandwidth of the SAW transducers, combine to form a precise train of short rf pulses,with a repetition rate equal to the reciprocal of the delay time.frequency is a precise harmonic of the pulse repetition rate. The precision, highly synchronized, comb spectrum is a feature which could prove important for frequency synthesis in programmable frequency hopping systems. Experiments with mode-locked oscillators operating near 100 MHz with 50 ns pulse widths, 0.56 MHz repetition rates and comb spectrums spanning more than 20 MHz are described.In operation, the multiple modes of oscillation, spaced by Furthermore, the rf

High Frequency Signal Sources Using Surface Acoustic Wave (SAW) Technology.

“…The signal sources include : 1) a Mode Locked SAW Oscillator (Ref. 1) at 333 MHz generating a comb spectrum with 9 precision lines spaced by 3 MHz , 2) a Mode Locked SAW Oscillator at 828 MHz generating a comb spectrum with 10 precision lines spaced at 24 MHz , and 3) a single frequency source at 19813 MHz. These three sources will provide the primary signals for a new approach to frequency synthesis that is made possible by the electronically controlled SAW filter technology under development at RADC /ET, Hanscom AFB (Refs.…”

“…The expander circuit includes a varactor (as the nonlinear element ) that is integrated with the delay line at the SAW transducer (Ref. 1). The presence of a large signal ( the circulating rf pulse) and the reference signal causes the required expander action to maintain the short pulse width .…”