Intermodulation noise in solid-state power amplifiers for wideband signal transmission

The results of an investigation of the intermodulation-noise performance of a multistage solid-state power amplifier (SSPA) are presented. It is found that computer calculations of intermodulation noise as a function of output power are in good agreement with laboratory measurements. Appreciable differences are found between calculated and measured values of intermodulation noise as a function of input power, and the net input-output power transfer characteristics for wideband Gaussian noise. On the basis of these measurements, the results suggest that single-frequency AM/AM and AM/PM characteristics do not fully characterize the operation of the SSPA for the signal bandwidths of interest here, particularly with regard to input-output power-transfer characteristics for wideband signals. It is pointed out that the computer simulation is an exact mathematical representation of an instantaneous bandpass nonlinearity with no direct dependence on analytical results. The role of memory in the system operation is discussed.