6.1: Introduction

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The maximum transfer of signal power is one of the prime objectives in RF and microwave circuit design. Power traverses a network from a source to a load generally through a sequence of two-port networks. Maximum power transfer requires that the Thevenin equivalent impedance of a source be matched to the impedance seen from the source. That is, the source should be presented with the complex conjugate of the source impedance. This is achieved by designing what is called a matching network inserted between the source and load. As long as the load has some nonzero real part (and so can dissipate power), a matching network can always be found. Design of the matching network is called impedance matching.

Section 6.2 describes two common matching objectives. Then design approaches for impedance matching are presented first with an algorithmic approach in Sections 6.3–6.6 and then a graphical approach based on using a Smith chart in Sections 6.7–6.9.