Frequency-agile and spectrally sensitive radar transmitter amplifier optimizations

The design and implementation of a first generation evanescent-mode cavity impedance tuner for reconfigurable radar transmitters is presented. The impedance tuner is capable of handling 90 W of radio-frequency (RF) power. The tuner can be used as a reconfigurable load matching network for an amplifier device to maximize the power-added efficiency (PAE) while meeting adjacent-channel power ratio (ACPR) or spectral mask constraints. Algorithms expected to be useful in fast tuning of this device are described, including a modified gradient approach for the optimization of the PAE while meeting constraints on the ACPR. Instead of tuning based on the reflection coefficient, which requires pre-characterization of the tuner, the resonant cavity position numbers of the tuner can be directly adjusted. Initial results are shown using an interval-halving search for optimization of PAE that directly tunes the cavity position numbers to optimize the tuner. This search is more resilient to drift and other repeatability issues that influence characterization. The fast optimization of this tuner is designed to give radar transmitter power amplifiers frequency agility in congested spectral environments.