Network Analysis 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 equipment. Although the physical realization of filters at RF/microwave frequencies may vary, the circuit network topology is common to all. At microwave frequencies, 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 | Microstrip Filters for RF Microwave Applications. Jia-Sheng Hong M. J. Lancaster Copyright 2001 John Wiley Sons Inc. ISBNs 0-471-38877-7 Hardback 0-471-22161-9 Electronic CHAPTER 2 Network Analysis 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 equipment. Although the physical realization of filters at RF microwave frequencies may vary the circuit network topology is common to all. At microwave frequencies 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 that are useful for the analysis of filter networks. NETWORK VARIABLES Most RF microwave filters and filter components can be represented by a two-port network as shown in Figure where V1 V2 and I1 I2 are the voltage and current variables at the 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 at port 1 is given by v1 t V1 cos t p We can then make the following transformations v1 t V1 cos wt Re V1jt Re V1ej t 7 8 NETWORK ANAYLSIS Z01 Es b -------- a1------ Two-port network V2 ------ a2 Z02 A A ---- FIGURE Two-port network showing network variables. where Re denotes the real part of the expression that follows it. Therefore one can .
