Modern Microwave Circuits
Including over 1,200 equations and more than 300 illustrations, this invaluable book explains how microstrip circuits are built and provides in-depth coverage of computer-aided simulation and underlying theories.
TABLE OF CONTENTS Modern Microwave Circuits
1.10: IMPEDANCE MATCHING
1.10 IMPEDANCE MATCHING
There are two different concepts of impedance matching in microwave engineering. The first one refers to terminating a transmission line with the characteristic impedance of the line. The second one refers to terminating a general source with the complex conjugate of the source impedance. The latter concept is the fundamental requirement of maximum power transfer. Note that depending on the context, one should distinguish these concepts from each other. In this section, we will investigate the problem of terminating a source with the complex conjugate of its output impedance. Note that the term source is used in a general sense here; it represents any network (amplifier, filter, and so forth) connected to a load resistance.
In order to terminate a general source with the complex conjugate of its output impedance, the load resistance (usually 50 ohms) must be transferred to the required value by means of an appropriate network which can be distributed or lumped. This network is called a matching network, and there are many ways of implementing it. Depending on the bandwidth requirement, the matching network can be quite complicated. Matching using stubs is the most basic form of matching networks and will be discussed first.
1.10.1 Single-Stub Matching
Single-stub matching employs a transmission line and a stub as shown in Figure 1.30. The stub can be implemented as a short- or open-circuited stub. For simple, discrete microwave amplifier designs, the short-circuited stub can be advantageous because one can feed the amplifier biases from...
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