Linearization of class AB amplifiers for QAM-type modulation

The use of Frank waveform codes in radar applications is well known. These codes are phase modulation based, with the number of phase steps dependent on the order of the code. Amplitude shaping techniques are applied to the modulation bits to reduce the sidelobe levels and constrain the bandwidth of the transmitted signal. This combination of amplitude shaping and phase modulation of the waveform results in a QAM-like waveform. Furthermore, a subset of polyphase codes has a power envelope that will transit through zero power. This class of waveform presents a significant design challenge to the RF engineer for pulsed, high power transmission when the occupied bandwidth is constrained by limited spectrum. In this paper we describe the results of the linearization of a commercially available HF high power class AB amplifier for use with Raytheonpsilas high frequency surface wave radar (HFSWR) system.