Varactor Tuned Gunn o s c i l l a t o r s and c h i p -l e v e l IMPATT diode power combiners have been f a b r i c a t e d a t frequenTechniques f o r t h e design and f a b r i c a t i o n o f such c i r c u i t s The b e s t lumped-element VCO tuned from 6 t o 11.3 GHz w i t h A six-mesa s e r i e s -p a r a l l e l a r r a y o f GaAs IMPATT diode chips generated 22.5

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MANY IMPROVEMENTS have been made in the instantaneous and tuning bandwidths o f certain microwave components in the past few years. In general, these improvements can bc directly attributed to circuit simplifications involving: elimination of dispersive transmission media, whenever possible, climination of distributed components of dimcnsions that arc appreciable fractions of a wavclcngth, and replacement of thcsc: elements with lumped or nearly lumped tuning and matching elements. This paper will describe a varactor-tuned Gunn oscillator which was designed with these factors considered of utmost importance in the overall design. OSM output connector and a copper holder along which a 0.25" wide x 0.1" deep channel was machined. All circuit components were mounted within this channel. An indication of the relative siLe of thc circuit can be obtained from the flange of the OSM connector which is 1/2" square. The center conductor of the connector makes contact to a gold pad which is TC bonded t o a 30 pF dc blocking capacitor, of Si02 construction, mounted on a 30-mil high quartz post. One end of a gold foil is sandwiched between the bottom of the blocking capacitor and the top of the quartz post and the other end connects to the first capacitor of a matching circuit which consists of two cascaded 71 sections each equivalent to a 20-ohm eighth wavelength line. The matching capacitors were made by metalizing quartz etched to a thickness of approximately 1/2 mil. The composite matching circuit consists of two 0.37 p F capacitors and a 0.74 p F center capacitor, connected together by short lengths of wires having nominal inductance per connection of 0.25 nII. A 1-mil gold wire of sufficient length to provide resonance at thc center frequency connects the innermost matching capacitor to the tuning varactor which is mounted on a gold pad of an insulating diamond. A short length of wire connects this floating pad to the top of the Gunn chip which is mounted on a fully metalized diamond. The Gunn and varactor chips are both biased through identical circuits, each consisting of a series inductor and a 30 p F RF bypass capacitor. The bias circuit inductors are miuature solenoids approximately 10 mils in diameter, consisting of 5 to 8 turns of gold wire of sufficient size to bias the respective devices.terminated in a 50-ohm load, plotted as a function of frequency, is shown in Figure 2. Also plotted for comparison is the impedance of a 50-ohm load transformed through a 20-ohm transmission line whose length is a quarter wavelength at 9 GHz.