Influence of second-harmonic frequency termination on Gunn-oscillator performance

Variations of the 2nd-harmonic frequency termination cause the output power of Gunn oscillators to change by a factor of up to five, accompanied by a frequency pulling of a few percent. From detailed impedance measurements it is concluded that the maximum fundamental power occurs if the 2nd-harmonic circuit is tuned near an open-circuit resonance, the total circuit susceptance apparently being somewhat capacitive.