Resonant Pulse-Shaping Power Supply for Radar Transmitters

Typical radar transmitter signals are frequency-modulated with pulsed constant-amplitude envelopes in order to optimize radio-frequency power amplifier (RFPA) efficiency, which results in spectral broadening and power radiated outside of the radar frequency band. This problem can be alleviated by using an appropriately shaped pulse envelope, provided that high-efficiency operation of the radar transmitter is maintained. This paper introduces a pulse-shaping power supply for RFPAs in radar transmitters which enables high efficiency while reducing the spectral emissions. The pulse-shaping power supply is a simple switched resonant circuit capable of approximating a Gaussian pulse envelope waveform. Operating principles are presented and a state-plane-based design approach is described for the resonant pulse-shaping power supply, which enables improved waveform quality and efficiency. An experimental prototype with efficiency greater than 90% is used to supply a 2.14-GHz GaN RFPA. The RFPA efficiency of up to 76%, overall transmitter efficiency of up to 67%, and output signal having high spectral purity demonstrate feasibility of a high-efficiency, high-performance radar system.