Compensation of amplifier nonlinear phase response to improve wideband distortion cancellation of feedforward amplifiers

Feedforward amplifiers with very good distortion cancellation over narrow bandwidth have been reported. However, if an amplifier in a cancellation loop has a nonlinear phase response, the 180 degrees phase difference between halves of the loop required for perfect cancellation cannot in general be maintained over a wideband if only simple delay line is used. The use of a phase equaliser to improve wideband feedforward cancellation is proposed. Simulated and measured results show a significant improvement in cancellation over the frequency range 1.7-1.9 GHz.