Transmission Line Analysis - University of San Diegoekim/e194rfs01/lec03ek.pdfEEE194RF_L3 194 2...
Transcript of Transmission Line Analysis - University of San Diegoekim/e194rfs01/lec03ek.pdfEEE194RF_L3 194 2...
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Transmission Line Analysis
• Propagating electric field
• Phase velocity
• Traveling voltage wave
)cos(0 kztEE XX −= ω
Time factor
Space factor
r
p
cfv
εεµλ ===
1
k
kztEtzV X
)sin(),( 0
−=
ω
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High frequency implies spatial voltage distribution
• Voltage has a time andspace behavior
• Space is neglected for lowfrequency applications
• For RF there can be a largespatial variation
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Generic way to measure spatial voltage variations
• For low frequency (1MHz)Kirchhoff’s laws apply
• For high frequency (1GHz)Kirchhoff’s laws do notapply anymore
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Kirchhoff’s laws on a microscopic level
• Over a differential sectionwe can again use basiccircuit theory
• Model takes into accountline losses and dielectriclosses
• Ideal line involves only Land C
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Example of transmission line: Two-wire line
• Alternating electric fieldbetween conductors
• alternating magnetic fieldsurrounding conductors
• dielectric medium tendsto confine field insidematerial
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Example of transmission line: Coaxial cable
• Electric field iscompletely containedwithin both conductors
• Perfect shielding ofmagnetic field
• TEM modes up to acertain cut-off frequency
E
H
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Example of transmission line: Microstip line
Cross-sectional view
Low dielectric medium High dielectric medium
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Triple-layer transmission line
Conductor is completely shielded between twoground planes
Cross-sectional view