Wideband operation of nonlinear solid-state power amplifiers — Comparisons of calculations and measurements

Calculations of intermodulation (IM) noise and input/output power-transfer characteristics for a number of different nonlinear Solid-State Power Amplifiers (SSPAs) are found to be in very good agreement with measurements. The calculations are based on the measured AM/AM and AM/PM characteristics, and include results of a computer simulation, and analytical results based on modeling the SSPA as an ideal envelope limiter. The results demonstrate that the calculations predict wideband performance characteristics of nonlinear amplifiers for arbitrary input signal configurations and operating conditions, as well as provide a basis for comparison against which anomalous behavior can be identified. Earlier results, in which anomalous behavior of an SSPA was observed to result in significant performance degradation, are discussed in the light of these new results. A simple analytical criterion is developed for evaluating measurements to identify such degradation. The effect of AM/PM conversion is investigated and found to cause significant degradation in IM performance only at low power levels for typical SSPAs. In the vicinity of saturation, and above, the contribution to IM noise due to AM/PM conversion is found to be very small in comparison with that due to the saturating AM/AM characteristic.