RF Circuit Design, 2nd Edition

Chapter 3: Impedance Matching In The Narrow-Band Case

3.1 Introduction

As emphasized in the previous chapters, impedance matching is the key task in RF circuit design because the main function of the RF block is to ensure maximization of power transfer without any phase shift. The task of impedance matching is to change the original impedance to the standard reference impedance, that is, 50 Ω, or some other desired impedance by constructing an impedance matching network.

There are some basic engineering fundamentals that circuit designers must bear in mind in the process of impedance matching.

First, in real-life RF circuit block designs, the input or output impedance of an RF block may be required to match a certain impedance that is not 50 Ω for cost saving and performance improvement. However, in order to enable the testing of the said RF circuit blocks, the input and output impedances must nonetheless be matched to 50 Ω, which is the standard reference impedance that test equipment manufacturers adopt. Thus, a somewhat complicated design procedure must be used when the actual RF circuit design must match an impedance that is not 50 Ω. This will be discussed in Section 3.6

Second, the impedance matching network could be built by either active or passive parts. It is more desirable to build an impedance matching network using passive parts rather than with active parts because the former is simpler, saves current, and is cost effective compared to the latter. The passive parts ...