This chapter will show how some of the concepts in Chapter 1 can be further developed into a simple but complete strategy for the design of linear RF power amplifiers. Essentially, a linear power amplifier can be designed using the same basic matching principles used for small signal designs, but with a power-matched output which will not appear to be conjugately matched. In some respects, power amplifier design becomes an analogous process to low noise amplifier (LNA) design, where in order to achieve the best possible noise performance from the device being used, its input will need to be presented with a reflection coefficient which will differ significantly from the conjugate match of the input impedance. In the linear PA case, the device has to be presented with a power match on the output in order to extract the maximum power from the device in question.

In older times, the exact value of the power match impedance at RF and microwave frequencies was regarded as something which could only be measured experimentally. Much like noise match data, this was something which designers had to measure for themselves, or was (preferably) available from the device manufacturer. Thus the art and science of load-pull was founded, and remains with us to this day, in the form of not inexpensive but very powerful computer-controlled measurement systems. This chapter introduces load-pull techniques and their application in linear PA design. Actual load-pull systems and more advanced harmonic load-pull techniques will be discussed further in Chapter...