7e Applied EM by Ulaby and Ravaioli 2. Transmission Lines 7e Applied EM by Ulaby and Ravaioli
Types of Transmission Lines
Fields of Transmission Lines
Transmission Lines = Roads for Wave A transmission line connects a generator to a load Transmission lines include: Two parallel wires Coaxial cable Microstrip line Optical fiber Waveguide etc.
- Dispersion (분산 = 주파수에 따른 불균일 특성) - 분산이 크면 신호왜곡 증가 - Distortion (신호왜곡)
Modes in Transmission Line Mode: 전기장의 분포형태 - TEM (transverse electromagnetic) mode: Ez = 0, Hz = 0, # of conductors > 1 fc = 0 (차단 주파수), Example = coaxial cable TEM mode - Quasi-TEM: TEM with mixed dielectric, fc (cutoff frequency) = 0 Example = microstrip line - TE (transverse electric) mode: Ez = 0, fc > 0, Example = rectangular waveguide - TM (transverse magnetic) mode: Hz = 0, fc > 0, Example = coaxial TM01 mode - Hybrid mode: TE+TM, fc > 0, Example = optical fiber HE11 mode
Electric and Magnetic Fields in A Transmission Line - 전송선에는 전기장 파동, 자기장 파동이 진행 - 회로이론 적용을 위해 전송선의 전압, 전류 개념 적용 Voltage and Current: obtained from E and H
Transmission Line Circuit Model
Transmission Line Parameters: R, L, G, C R', G', C' from electrostabics; L' from magnetostatics Expressions will be derived in later chapters
Transmission-Line Equations ac signals: use phasors Telegrapher’s equations
Phase constant complex propagation constant attenuation constant (전파상수) (감쇠정수) (위상정수)
(특성임피던스)
Example 2-1: Air Line
Lossless Transmission Line Lossless Line: Lossless TEM Line:
Material Parameters in Transmission Lines - Conductor (도체, 금속) - Dielectric (유전체,플라스틱)
Low-Loss Transmission Lines
Distortionless Transmission Line
Distortionless Transmission Line: Heaviside Condition
Reflected Wave In general: wave along +z because coefficients of t and z have opposite signs wave along –z because coefficients of t and z have the same sign
Microstrip Line - A Quasi-TEM line Quasi-TEM : Ez & Hz very small Phase velocity in dielectric: Phase velocity for microstrip:
Microstrip (cont.) s = w/h
Coaxial Transmissioni Line (TEM Line)
Skin Depth (AC Resistance) Table: Copper (Cu) skin depth