This invention relates generally to Gunn diode oscillators, and more particularly, to Gunn diode oscillators that may be tuned by a varactor. Varactor-tuned Gunn diodes are important components used as local oscillators in receivers and as power/driver stages in transmitters. Basically, varactor tuning provides a means for varying the frequency of the oscillator in accordance with the value of a dc bias signal applied to the varactor. The combination of a Gunn diode and a varactor functions as a voltage-controlled oscillator (VCO), which may be used in a phase-locked loop to lock onto a received carrier signal, or may be used to tune an oscillator over a wide range of frequencies.
In most communications systems operating at extremely high frequencies, typically in the millimeter-wave region, it is desired to minimize the weight, size and cost of the components. Most millimeter-wave Gunn VCO's are limited to configurations employing waveguides, which are inherently difficult to make a low cost and in small sizes. For example, power outputs of 100-150 milliwatt (mW) have been achieved using waveguide techniques at Q-band frequencies (33 to 50 gigahertz).
However, the use of millimeter-wave integrated circuits (MIC) for the same purpose has not been particularly successful. MIC devices are, of course, smaller, lighter and, when fabricated in relatively large quantities, less costly than their waveguide counterparts. However, MIC oscillators have in the past employed microstrip configurations, in which a conductive strip is disposed on a dielectric substrate. Such devices are subject to excessive circuit losses. Typical power outputs in the Q-band frequencies have been below 50 mW. For example, a 40 mW microstrip configuration is described by David Rubin in "Varactor-Tuned MillimeterWave MIC Oscillator," IEEE Trans. on Microwave Theory & Tech., Vol. MTT-24, Nov. 1976, pp. 866-67.
It will be appreciated from the foregoing that there is a need for improvement in the field of MIC oscillator devices for use in the millimeter wave region. The present invention satisfies this need.