The chapter covers main characteristics of the devices used in power amplifiers (PAs) and provides basic knowledge about the specifications of these devices and the transistor models that are used in PA designs. The Preface covers the basic characteristics of main semiconductor device types used in PA designs. These devices have been in use for many decades, the technology of which is well established and its production is repeatable with high yield. Now, these devices show really impressive results. They work up to the terahertz region and can deliver kilowatts of power at low radio frequencies (RF). Probably one of the most promising devices now is the GaN high-electron-mobility transistor (HEMT), and they yield high-power and high-frequency results in number of applications. There are a plenty number of literature on these devices regarding how to design PA, and using these transistors has put a tremendous success in its field. A very small part of these references is listed here. The models come in small signal (SS), large signal (LS) categories, and for all these devices, extraction procedures, software is available.

Real frequency matching network design techniques require the “Darlington synthesis” of positive real immittance functions. Therefore, this chapter is devoted to “automated Darlington synthesis” to construct lossless matching networks with lumped and distributed elements. In this chapter, several high precision lowpass/bandpass/high-pass LC (Inductor L, Capacitor C) ladder synthesis algorithms are presented. Novel algorithms directly work on the driving-point input immittance or bounded-real reflection functions which describe any kind of cascade-connection LC ladders, perhaps with Brune and C-sections in resistive termination. The crux of the idea is that, at each step of the proposed synthesis methods, a simple pole at DC, or at infinity, or at a finite frequency is removed; then, the remaining immittance function is corrected using what we call is the parametric method. At this point, parametric method warrants the exact LC ladder nature of the remaining immittance function. Thus, at the end of synthesis process, an LC ladder is obtained with high numerical precision.

The Chapter introduces novel techniques to design wideband amplifiers employing “real-frequency techniques" (RFTs). In essence, RFTs are wideband semi-analytic design methods to realize lossless matching networks and real frequency (RF) and microwave amplifiers with optimum circuit topologies. After an introductory section, the Chapter discusses: a simplified real-frequency technique (SRFT) to design microwave amplifiers, a SRFT single-stage microwave amplifier design algorithm, amplifier stability, design practical aspects, ultra-wideband microwave amplifier design using commensurate transmission lines, characteristic impedances physical realization, characteristic impedance calculations, an algorithm for broadband multistage microwave amplifiers design via SRFTstep-by-step multistage amplifier design, a microwave power amplifier with mixed lumped and distributed elements design.