Introduction to the Real Frequency Technique

The real frequency technique (RFT) is an optimum solution to broadband amplifier equalization problems. This chapter provides a complete description of the RFT for the case of multistage microwave amplifier design for the simultaneous optimization of transducer gain and voltage standing wave ratio (VSWR). The simple formalism of the RFT allows optimizing many performance parameters of single- or multistage microwave amplifiers. There exist many optimization routines but one that was found to work well in the case of microwave amplifier design is to use a single-valued error function based on a sum of squares and an optimization algorithm based on a Levenberg-Marquardt-More technique for solving least-squares problems. At low frequencies, microwave GaAs MESFETs are unstable and are virtually impossible to match over large bandwidths. It is thus necessary to use either a lossy matching or RL feedback technique to reduce terminal impedances and stabilize the transistor.