Conditions of Oscillation for Waveguide Mounted Tunnel Diodes

Double frequency oscillation was observed in a waveguide mounted tunnel diode circuit, due to the frequency dependency of the waveguide´s distributed parameters. A general analysis of the frequency dependent diode load is made and conditions of oscillation are formulated. The analysis is extended to a 1N3219A diode mounted in a tapered RG-52/U waveguide used as an oscillator. The load impedance to the tunnel diode is derived with the diode mounted at the center of the waveguide. A numerical example involving the RG-52/U waveguide mount is presented verifying the existence of double frequency oscillation and exemplifying the oscillation conditions stated. Off center diode mounting is examined. It is concluded that the waveguide mount´s distributed parameters are highly frequency dependent at the center of the guide and thus double frequency oscillation can exist when a tunnel diode is mounted at that point. With the diode mounted at any other point, only one oscillation frequency can be observed. The frequencies of oscillation of a waveguide mounted tunnel diode oscillator are determined only by the real roots of the resistive component of the total tunnel diode load impedance.