Some Considerations of Stability in Lossy Varactor Harmonic Generators
01 July 1968
A serious limitation to efficient wideband harmonic generation with varactor diodes is that instability in the multiplier might cause the generation of spurious tones.1 It is the purpose of this paper to study the effect of losses on stability of abrupt-junction varactor frequency multipliers of order N = 2" = 2, 4, and so on, with the minimum number of idlers. The type of instability considered here is the one discussed in Refs. 2, 3, and 4. It produces undesired low-frequency fluctuations in the amplitude and phase of the output harmonic and is caused by the time-varying elastance of the varactor, which is potentially unstable with respect to phase perturbations. The stability conditions of lossless abrupt-junction varactor multipliers have already been extensively discussed elsewhere in Refs. 3 and 4. More precisely, these works have shown that, in the absence of any losses in the varactor diode, the frequency characteristics of the input, output, and idler circuits must satisfy certain restrictions in order that the multiplier be stable. The main objective of this 887