Transmission Line Basics II - Class 6.ppt

Transmission Line Basics II - Class 6 Prerequisite Reading assignment: CH2 Real Computer Issues Agenda The Transmission Line Concept Transmission line equivalent circuits and relevant equations Reflection diagram equation Loading Termination methods and comparison Propagation delay Simple return path ( circuit theory, network theory come later) Two Transmission Line Viewpoints Steady state ( most historical view) Frequency domain Transient Time domain Not circuit element Why? We mix metaphors all the time Why convenience and history Transmission Line Concept PC Transmission Lines Key point about transmission line operation Examples of Transmission Line Structures- I Cables and wires (a) Coax cable (b) Wire over ground (c) Tri-lead wire (d) Twisted pair (two-wire line) Long distance interconnects Segment 2: Transmission line equivalent circuits and relevant equations E H Fields – Microstrip Case The signal is really the wave propagating between the conductors Transmission Line “Definition” General transmission line: a closed system in which power is transmitted from a source to a destination Our class: only TEM mode transmission lines A two conductor wire system with the wires in close proximity, providing relative impedance, velocity and closed current return path to the source. Characteristic impedance is the ratio of the voltage and current waves at any one position on the transmission line Propagation velocity is the speed with which signals are transmitted through the transmission line in its surrounding medium. Presence of Electric and Magnetic Fields Both Electric and Magnetic fields are present in the transmission lines These fields are perpendicular to each other and to the direction of wave propagation for TEM mode waves, which is the simplest mode, and assumed for most simulators(except for microstrip lines which assume “quasi-TEM”, which is an approximated equivalent for transient response calculations). Electric field is established