Microwave devices and components

7.1 Introduction

A transmission line is a system of conductors which connects two points by means of electromagnetic energy which travels along the system. A system may include wires which carry 240 V/50 Hz mains supplies to consumers, or it may consist of lines which feed thousands of watts to a transmitting antenna. There are various kinds of transmission lines in use - the twisted pair, twin lead and coaxial, to mention a few. Twin-wire lines are often used for carrying radio frequency power to transmitters, while coaxial cables are commonly employed for low-power applications such as coupling receivers to their antennas.

Consider Fig. 7.1 in which a transmission line is connected between a generator and a load. In this circuit a section of transmission line is used and takes on the characteristics of a T-network. The components shown are not lumped components connected into the transmission line as such, but inherent parameters which manifest themselves when energy is propagated along the transmission line.

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