The Impact of Nonlinear Power Amplifier Load Impedance on Notched Waveforms for Cognitive Radar Spectrum Sharing

Abstract

High-bandwidth waveforms are required to obtain good range resolution in radar applications, yet contiguous bandwidth is often not readily available. To that end, there has been significant effort involved with the design of spectrally notched radar waveforms. However, maintaining the desired notch depth for these optimized waveforms is challenging in actual transmission due to third- and other odd-order nonlinearities in the transmitter power amplifier (PA) Here the effect of the PA is examined for a particular class of transmitter-compatible notched waveforms. Load-pull measurements show that the impedance needed to maximize the power-added efficiency (PAE) and range of the radar system while ensuring a desired minimum notch depth can change significantly for different notch positions and widths. This illustrates the need for reconfigurable power amplifier circuitry in radars for waveform notching applications.