Characterisation of nonlinear 2-ports for the design of class-C amplifiers

A method of characterising a nonlinear 2-port based on the `multiple-sinusoid-input describing function¿¿ technique is proposed. For simplicity, the effects of the third and higher harmonics are ignored and the nonlinear 2-port is treated as a linear 4-port. The S-parameters of the 4-port are measured, and the `effective¿¿ 5-parameters of the nonlinear 2-port are expressed in terms of the 2nd-harmonic terminations. The effects of the 2nd-harmonic reactance terminations on the fundamental-frequency 5-parameters are investigated, and a strategy for optimising the performance of a class-C amplifier is described.