Designing for spectral conformity: Issues in power amplifier design

Spectral constraints placed upon 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 nonlinear regime to optimize efficiency. Several different methods are employed by power amplifier designers to maximize both linearity and efficiency. The methods of predistortion, feedforward, envelope tracking, Doherty, and “Linear Amplification Using Nonlinear Components” (LINC) are discussed in this paper. Tradeoffs and challenges inherent in these design approaches are surveyed.