TABLE OF CONTENTS This chapter describes circuit parameters that are based on power flow. The open-circuit Z-parameters and the short-circuit Y-parameters are used in many of the circuit computer-aided design (CAD) programs. We can calculate the network parameters of circuits made from well-known components such as resistors, capacitors, and inductors. However, the circuit parameters of transistors and other types of semiconductors must be measured. As frequencies rise, it becomes increasingly difficult to measure voltage and current on the ports of a circuit.
This chapter introduces transmission lines and the mathematical expression that is used to describe their voltage and current. A detailed discussion of the electromagnetic foundation of transmission line theory is beyond the scope of this book. Instead, we focus on the propagation of power and signals and show how the power flow relates to voltage and current at any point along a transmission line. Transmission lines are an integral part of the transmission of power and signals in high-frequency circuits. In microwave circuits, rather than using resistors, capacitors, or inductors, transmission lines are employed to connect components and produce a complex impedance.
Further, we will develop another set of circuit parameters based on power flow in a transmission line. Whereas voltage and current are difficult to measure at microwave frequencies, power flow can be measured easily with directional couplers. Scattering parameters, or S-parameters, are ratios of power flow amplitude and phase in a circuit. S-parameters are usually listed in the transistor's data sheets. Since S-parameter power vectors are related...
