Phase and Amplitude Modulation in High-Efficiency Varactor Frequency Multipliers of Order N = 2n- Stability and Noise

A general analysis of the stability conditions of frequency multipliers of order N = 2nis presented. The frequency multipliers to be considered are harmonic generators which use varactor diodes as nonlinear elements. The type of instability investigated is that which causes spurious tones to appear at the output of a multiplier in the vicinity of the desired harmonic. It arises because an efficient multiplier is potentially unstable with respect to the quadrature components of its sidebands. This paper shows how instability arises and how it can be avoided. One of the main results is that, to obtain stability in practical cases, it is sufficient that the bandwidths of the various resonant circuits satisfy some simple conditions.