GB1329002A - Microwave oscillator circuit including a bulk-effect negative- resistance device - Google Patents

Abstract

1329002 Bulk effect oscillators VARIAN ASSOCIATES 3 Sept 1970 42309/70 Heading H3T [Also in Division H1] A microwave oscillator has a pair of variable lumped capacitors 5, 6 connected in shunt with and at opposite ends of a strip transmission line 7 to define a half wavelength resonator 3 open circuited at its ends and tuned to a fundamental mode of resonance at the operating frequency of the oscillator and a bulk effect device 14 connected in shunt with and at a point intermediate the length of the line 7 near the voltage null of said resonator for the fundamental mode of resonance for matching the impedance of the device 14 to the impedance of the resonator 3. The product of capacitance and self inductance (C 1 L 1 or C 2 L 2 Fig. 2, not shown), of the capacitors 5, 6 at the second harmonic of the operating frequency of the oscillator is greater at one end than the other end of the line 7 so as to position one of the voltage nulls of the second harmonic nearer than the other to the position of the device 14 such that during operation the total electric field between the terminals of the device causes the current in the device to be substantially a square wave at the fundamental operating frequency. The strip line 7 is formed of silver plated copper strips 9, 12 separated by a gold plated tungsten mesh screen 13 and supported by thermally conductive electrically insulative tabs 11, such as of beryllia. A silver plated copper capacitive loading ridge 15 supplies pulsed bias from conductor 18 to the bulk effect device 14, such as GaAs Gunn diode, via a strip of solder foil (17, Fig. 5, not shown), or a tellurium copper stud (16, Fig. 6, not shown). The foil (17) or stud 16 and slabs 11 provide heat sintering for the diode 14. Capacitive ridge 15 reduces the surge impedance of the line 7 to prevent avalanche current flowing when oscillations first begin and facilitates starting at the fundamental frequency. The amplitude of the second harmonic voltage must be sufficient to combine with the fundamental voltage wave so that the total electric field across the diode 14 is above the threshold for microwave oscillation for a first half cycle and then slightly below this threshold to delay domain formation during a second half cycle of fundamental frequency. Also the total voltage of the fundamental and second harmonic should be arranged to be less than the avalanche voltage so as to avoid failure of the device. A pair of lumped trimmer capacitors 23, 24 similar to trimmers 5, 6 are tuned to the fundamental to provide output via coaxial line 26, 27 but are detuned with regard to the second harmonic to reduce the coupling of the second harmonic to the load. To increase the output power of the oscillator a plurality of Gunn effect diodes can be connected in parallel. Preferably the diodes have a transit time mode frequency of operation within Œ30% of the operating frequency of the oscillator. U.S.A. Specification 3,416,099 is referred to.