Effects of power amplifier nonlinearities on the radar ambiguity function

The radar ambiguity function describes the possibility of errors in range and Doppler detection for targets of certain range-Doppler combinations. Nonlinear power amplifiers in radar transmitters provide many undesirable effects, including spreading of the radar spectrum. Based on the known impacts of the power amplifier nonlinearities on the waveform and spectrum that is transmitted, this paper assesses the related impacts on the ambiguity function and, therefore, on the estimation precision capabilities of the radar. Simulation results for nonlinear microwave power-amplifier transistor models are presented to illustrate the theory that is presented. Simulations using a Gaussian Barker code implementation show that amplifier nonlinearities cause widening of ambiguity content in the Doppler dimension, widening of range sidelobes, and deepening of range and Doppler nulls. The theory and observations presented in this paper are expected to find significant application in radar waveform optimization to provide desired ambiguity-function properties while maintaining spectral compliance.