Output Networks for Radio-Frequency Power Amplifiers

At high frequencies a transformer consisting of primary, secondary, and mutual inductances cannot be constructed to match a generator effectively to a resistive load. By introducing capacitative elements, such a match can be obtained. The design of reactance networks to connect a resistive load efficiently to a source of power can be carried out most conveniently by the theory of image impedances. Such reactance networks can provide not only for high efficiency but can also attenuate undesired harmonics. A variety of configurations can be designed to accomplish the desired result. The network can also be arranged to provide extremely high attenuation at design ated frequencies. The most efficient network is one designed for critical coupling, assuming a constant Q for the inductances. The efficiency also depends on the impedance ratio.