Filter networks are essential building elements in many areas of RF/microwave engineering. Such networks are used to select/reject or separate/combine signals at different frequencies in a host of RF/microwave systems and equipments. Although the physical realization of filters at RF/microwave frequencies may vary, the circuit network topology is common to all.
At microwave frequencies, the use of voltmeters and ammeters for the direct measurement of voltages and currents do not exist. For this reason, voltage and current, as a measure of the level of electrical excitation of a network, do not play a primary role at microwave frequencies. On the other hand, it is useful to be able to describe the operation of a microwave network, such as a filter, in terms of voltages, currents, and impedances in order to make optimum use of low-frequency network concepts.
It is the purpose of this chapter to describe various network concepts and provide equations [1–10] that are useful for the analysis of filter networks.
2.1 NETWORK VARIABLES
Most RF/microwave filters and filter components can be represented by a two-port network, as shown in Figure 2.1, where V1, V2 and I1, I2 are the voltage and current variables at ports 1 and 2, respectively, Z01 and Z02 are the terminal impedances, and Es is the source or generator voltage. Note that the voltage and current variables are complex amplitudes when we consider sinusoidal quantities. For example, a sinusoidal voltage ...