Date of Award
Spring 1993
Document Type
Thesis - Restricted
Degree Name
Master of Science (MS)
Department
Electrical and Computer Engineering
First Advisor
Richie, James E.
Second Advisor
Arkadan, A. A.
Third Advisor
Ishii, Thomas K.
Abstract
Typically, the sidewalls of a shielded microstrip transmission line are far enough away from the microstrip that their influence on the electromagnetic field is considered negligible. However, certain designs and restrictions require closer shielding to the strip, and the presence of the sidewalls must be accounted for. The influence of sidewall shielding in the proximity of a microstrip transmission line of finite thickness, operating in a quasi-transverse electromagnetic (quasi-TEM) mode, has been investigated using a finite element method, computer simulation program. The analysis assumed infinite length lines. Two dimensional first-order finite elements were used in the discretization of a lateral cross-section of the shielded transmission line. Based on the variational principle, a system of equations was formulatled in terms of the electric scalar potentials at the element vertices. Results show that both the effective permittivity and characteristic impedance of the microstrip transmission line decrease as the sidewalls are moved in closer proximity to the microstrip. This is due to an increased electric flux density in the air region as a result of the sidewall presence. These conclusions are in agreement with literature based on other computer simulation techniques and measured results. The general trend also agrees with the work of other authors in the investigation of the influence of a single sidewall in the proximity of a microstrip of negligible thickness. Two finite element approaches were investigated. The fist one was an eigenproblem formulation for the cases of perfect electric conductors and conductors of finite conductivity. The second finite element approach was based on the electrostatic technique which is a forced excitation method. Only perfect electric conductors were considered for this case. Due to complications with the finite element eigenproblem method, the results presented in this thesis are based on the forced excitation method. Two shielded microstrip transmission line structures were considered in the examination of sidewall influence on microstrips of finite thicknesses. Both microstrip transmission lines were designed to have a characteristic impedance of 50 ohms (unshielded value), and dielectric media which were homogeneous, isotropic, linear, lossless, and nonmagnetic. One transmission line contained a dielectric substrate relative permittivity of 2.50, and the other 9.80. Various strip thicknesses were also investigated. Based on the design parameters of the microstrip transmission lines analyzed, for the quasi-TEM approximation to be valid, the maximum operating frequency was calculated to be 8.50 GHz and 5.47 GHz for the transmission lines with dielectric substrate permittivities of 2.50 and 9.80, respectively.
Recommended Citation
Forest, Francis W., "Sidewall Characteristics of a Shielded Microstrip of Finite Thickness Using the Finite Element Method" (1993). Master's Theses (1922-2009) Access restricted to Marquette Campus. 4578.
https://epublications.marquette.edu/theses/4578