VM120

VM120
Microstrip Transmission Line Capacitance

Overview

Reference:J. Beren, R. Kaires, "EMGAP Solves Electromagnetic Problems Using Finite Element Analysis", Tektronix Internal Publication, Beaverton, OR, May 1983.
Analysis Type(s):Electrostatic Analysis (ANTYPE = 0)
Element Type(s):2D 8-Node Electrostatic Solid Element (PLANE121)
Input Listing:vm120.dat

Test Case

A shielded microstrip transmission line consists of a substrate, microstrip, and a shield. The strip is at a potential V1, and the shield is at a potential V0. Determine the capacitance of the transmission line.

Figure 170: Microstrip Transmission Line Problem Sketch

Microstrip Transmission Line Problem Sketch

Material PropertiesGeometric PropertiesLoading
ε0 = 8.85 x 10-12 F/m
ε1 = 8.85 x 10-11 F/m
a = 10 cm
b = 1 cm
w = 1 cm
V1 = 1.5 v
V0 = 0.5 v

Analysis Assumptions and Modeling Notes

The capacitance of the device can be calculated from electrostatic energy and the applied potential difference as We = 1/2 C (V1-Vo)2 where We is the electrostatic energy and C is the capacitance. The electrostatic energy is available by summing the energies for all the elements in the model in POST1. Additional postprocessing includes displaying equipotential lines and the electric field as vectors.

Results Comparison

TargetMechanical APDLRatio
Capacitance, pF/m178.1179.21.006