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.