advertisement

Microwave Engineering Ch.2 Transmission Line Theory (1/2) Prof. Jong-Won Yu KAIST http://rfss.kaist.ac.kr Chap 2. Transmission Line Theory z Plane Wave Propagation Orientation of the Ε , H, and k = k0 n vectors for a general plane wave. Plane wave reflection from a lossy medium; normal incidence 2 . Chap 2. Transmission Line Theory z Two-wire line z Coaxial cable 3 Chap 2. Transmission Line Theory z Microstrip line 4 Chap 2. Transmission Line Theory z High frequency implies spatial voltage distribution z Voltage has a time and space behavior. z Space is neglected for low frequency applications. z For RF there can be a large spatial variation. z For low frequency (1MHz) y Kirchhoff’s laws apply z For high frequency (1GHz) y Kirchhoff’s laws do not apply anymore 5 Chap 2. Transmission Line Theory z Kirchhoff’s laws on a microscopic level Conductor Appropriate Circuit model Transmission Line M d l takes Model k iinto account liline llosses and d di dielectric l i llosses 6 Chap 2. Transmission Line Theory z The Lumped-Element Circuit Model for a Transmission Line z T/L is a distributed network, Voltages and currents can vary in magnitude and phase over its length Voltage and Current Definitions z Lumped-element Equivalent CKT Using K.V.L & K.C.L 7 Chap 2. Transmission Line Theory z Wave Propagation on a Transmission Line Time Harmonic Case Wave Equations for V & I Coupled Eqs Propagation constant Wave propagation in the +z direction Solutions Characteristic Impedance 8 Chap 2. Transmission Line Theory z Characteristic Impedance, Wavelength & Phase velocity Z=V/I z Characteristic Impedance p is the ratio of voltage g to current of either wave independently. z Time domain waveform Wavelength Phase velocity 9 Chap 2. Transmission Line Theory z Transmission-line parameters z R,L,G,L are given per unit length and depend on geometry 10 Chap 2. Transmission Line Theory z Coaxial Cable z Characteristic Impedance z Velocity Factor y Whenever you apply a signal to a transmission line line, the inductance and capacitance of that line will cause signal to travel more slowly that it would in free space 11 Chap 2. Transmission Line Theory z Microstrip Line 12 Chap 2. Transmission Line Theory z Lossless Transmission Line Lumped-element Lumped element Equivalent CKT 13 Chap 2. Transmission Line Theory z Terminated T/L : Reflection Coefficient The total voltage and current on the line Th ttotal The t l voltage lt and d currentt att th the lload d R fl i Reflection C Coefficient ffi i Solving for The total V & I on the line in terms of the refection coefficient A super position of an incident and reflected wave Standing waves 14 Chap 2. Transmission Line Theory z Terminated T/L : Input Impedance Input impedance at 15 Chap 2. Transmission Line Theory z Terminated T/L : Return Loss, SWR The total V & I on the line in terms of the refection coefficient Incident power Th ti The time-average power flow fl along l the th liline att th the point i tz Purely imaginary The return loss (RL) The Standing Wave Ratio (SWR) 16 Chap 2. Transmission Line Theory z Lossless T/L : Short Termination V l Voltage Current 17 Chap 2. Transmission Line Theory z Lossless T/L : Short Termination 18 Chap 2. Transmission Line Theory z Lossless T/L : Open Termination Voltage Current 19 Chap 2. Transmission Line Theory z Lossless T/L : Open Termination 20 Chap 2. Transmission Line Theory z Lossless l T/L : A half-wavelength line does not alter or transform the load impedance, regardless of the characteristic impedance z Lossless T/L : Impedance Inverter Open impedance Short impedance 21 Chap 2. Transmission Line Theory z Insertion Loss Consider the reflection and transmission at the junction of two T/L with different Zo Equating voltages at z=0 Insertion Loss (IL) 22 Chap 2. Transmission Line Theory z Homework #1 z Deadline : 9/16 1:00pm z D.M.Pozar :Microwave Engineering 3rd Ed. z Problem Problem Problem Problem z z z 2.6 2.7 2.8 2.9 (Page87) (Page87) (Page87) (Page88) g 23