University:
University of Houston
Course:
PHYS 4356 | Particle and Nuclear Physics
Academic year:

2022
Views:

243

Pages:

12
Author:

Dakota Hubbard

ECE 3317 Applied Electromagnetic Waves Notes 6 Transmission Lines (Time Domain) 1 Note about Books Note: Chapter 10 of the Hayt & Buck book has a thorough discussion of transmission lines in the time domain. Transmission lines is the subject of Chapter 6 in the Shen & Kong book. However, the subject of wave propagation in the time domain is not treated very thoroughly there. 2 Transmission Lines A transmission line is a two-conductor system that is used to transmit a signal from one point to another point. Two common examples: εr z a b Coaxial cable Twin lead A transmission line is normally used in the balanced (or “differential”) mode, meaning equal and opposite currents (and charges) on the two conductors. 3 Transmission Lines (cont.) Here’s what they look like in real-life. Coaxial cable Twin lead 4 Transmission Lines (cont.) CAT 5 cable (twisted pair) 5 Transmission Lines (cont.) Some practical notes:  Coaxial cable is a perfectly shielded system (no interference).  Twin line is not a shielded system – more susceptible to noise and interference.  Twin lead may be improved by using a form known as “twisted pair” (e.g., CAT 5 cable). This results in less interference. E - + + + + - + + Coax - E ρ sa + - - ρ sb Twin lead 6 Transmission Lines (cont.) Microstrip line: a common transmission line for printed circuit boards. w h εr Microstrip line ( a “planar” transmission line) 7 Transmission Lines (cont.) Transmission lines are commonly met on printed-circuit boards. Microstrip line A microwave integrated circuit (MIC) 8 Transmission Lines (cont.) Microstrip line 9 Transmission Lines (cont.) Planar transmission lines commonly met on printed-circuit boards: w εr εr w h Microstrip w Stripline w εr w h Coplanar strips h εr h Coplanar waveguide (CPW) 10 Transmission Lines (cont.) Symbol (schematic) for transmission line: i ( z, t ) + - v ( z, t ) z Note: We use this schematic to represent a general transmission line, no matter what the actual shape of the conductors (coax, twin lead, etc.). Note: The current on the bottom conductor is always assumed to be equal and opposite to the current on the top conductor (but often we do not label the current on the bottom conductor, for simplicity). 11 Transmission Lines (cont.) Four fundamental parameters that characterize any transmission line: z These are the four “per unit length” parameters: 4 parameters C = capacitance/length [F/m] Capacitance between the two wires L = inductance/length [H/m] Inductance due to stored magnetic energy R = resistance/length [Ω/m] Resistance due to the conductors G = conductance/length [S/m] Conductance due to the filling material between the wires 12

Transmission Lines (Time Domain) Ch1

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