Estimation of practical inter-modulation rejection values in a multi-loop feed-forward microwave power amplifier using Monte-Carlo method

Feed-forward is one of the best methods for linearizing microwave power amplifiers, but due to device tolerance in implementation of the system components, the practical Inter- Modulation Rejection (IMR) value may differ quite much from the theoretical IMR value. One of the methods to improve the practical performance of the system is using the multi-loop configuration. Here we have introduced the multi-loop feedforward systems and we have estimated the practical IMR values of the system using Monte-Carlo analysis. As the analysis shows, although the number of components in a multi-loop system is increased with respect to a simple feed-forward system, but the difference between the practical value and the theoretical value of the IMR for the two systems is almost the same. Therefore a multi-loop feed-forward system with higher practical IMR may be applicable for linearizing a microwave power amplifier. Simulations with ADS show one can expect a multi-loop feedforward system designed for an ideal 39 dB IMR after implementation with usual techniques, may have 29 dB rejection, which is an acceptable value for a linearization system.