Designing transmitters for spectral conformity: power amplifier design issues and strategies

Spectral constraints placed on radar systems by regulatory agencies require the design of highly linear amplifiers. Spectral spreading in power amplifiers is a result of transistors operated in the non-linear regime to optimise efficiency. Various methods are employed by power amplifier designers to maximise both linearity and efficiency. The methods of predistortion, feedforward, envelope tracking, Doherty and `linear amplification using non-linear components` are discussed in this article. Trade-offs and challenges inherent in these design approaches are surveyed.