Integrated Varactor Tuned Microwave Sources.

Abstract : This report describes the results of a study in which the objectives were to develop varactor-tuned microwave oscillator circuits and planar device technology leading to minimum parasitic monolithic varactor-tuned microwave oscillators (VCOs). A wideband varactor-tuned Gunn oscillator of lumped element construction was developed which tuned from 6.0 GHz to 11.5 GHz, a 63% tuning range based on the midband frequency of 8.75 GHz. This tuning range exceeds that reported previously by others for varactor-tuned oscillators with center frequency in X-band. Although of lumped element construction, the circuit is adaptable to monolithic construction. It consists of series-connected Gunn and varactor chips which are series resonated at the midband frequency by an inductive wire, a wideband lumped element matching section, and lumped element bias sections. Performance data of this circuit using various types of varactors are presented. Excellent tuning linearity occurred when low-high-low IMPATT chips were used as tuning varactors. A deviation of + or - .5% from linear tuning was obtained over a 2.5 GHz range with less than 15 volt change in tuning voltage using these devices. Planar Gunn and varactor devices, developed on this program, were tested in various microwave circuits and found to operate at lower frequencies than conventional Gunns.