Phase and Amplitude Modulation in High Efficiency Varactor Frequency Multipliers - General Scattering Properties

The 'presence oj phase and amplitude modulation in the signals oj a varactor jrequency multiplier is analyzed, and some general multiplier properties are derived. The following summarizes one oj the most important results oj this paper. Consider a jrequency multiplier which has the jollowing characteristics: (i) a varactor which has a square-law characteristic, (ii) the order oj multiplication is N = 2n = 2, 4, etc., {Hi) the minimum number oj idlers, and (iv) it is lossless and tuned. It is shown that jor this midtiplier there is no conversion between small-index, low-jrequency amplitude and phase modulation. Therejore, since narrow-band noise jrom external sources will be present at the input and output oj the multiplier, the noise components corresponding to phase modulation oj the carriers can be treated independently oj the noise components corresponding to amplitude modidation. Consider now the input and output noise sidebands corresponding to phase modidation (PM). It is shown that the multiplier behaves with respect to these sidebands as an amplifier with the jollowing properties: (i) a jorward voltage transmission equal to N, (ii) unity reverse transmission, (Hi) an output reflection of 1, --1,3, respectively, jor N = 2, 8, and (iv) no input reflections. .4 s a consequence oj these properties the multiplier is "potentially" unstable with respect to PM. The utility oj the multiplier properties derived in this paper will be illustrated by the discussion in a companion paper in this issue which shows how, in practical cases, instability arises and how it can be avoided.