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Solution Number: 909
Platform: All Platforms
Applies to: Electromagnetics Module, RF Module
Versions: 3.3, 3.4
Created: December 17, 2002
Last Modified: August 15, 2008
Categories: Electromagnetics
Keywords:

Problem Description

Can COMSOL Multiphysics be used for TEM mode analysis?

Solution

Yes, you can make a TEM, or rather quasi-TEM mode analysis of microstrip line cross sections by using the "Hybrid-Mode Waves" application mode in the RF Module. This application mode computes the eigenmodes and propagation constants for transmission lines such as microstrips and coaxial cables. It uses a full hybrid mode problem formulation and vector elements which allows for a correct and accurate treatment of transmission line and waveguide cross sections with inhomogeneous and even discontinuous permittivity or refractive index profiles. The application mode solves for the quasi-TEM modes, as well as TE, TM, and hybrid modes. This means the application mode can also be applied to general inhomogeneous dielectric waveguide cross sections.

The example model microstrip_port.mph shows a microstrip port simulation in COMSOL Multiphysics with the computed propagation constant and field distribution.

Click to enlarge The field distribution of a microstrip port. The surface plot shows the z component of the electric field and the arrow plot shows the magnetic field.
Click on image to enlarge.

Full 3D wave propagation and mode analysis can be handled in the 3D Electromagnetic Waves application mode, which is also in the RF Module. This application mode allows for arbitrary excitations of the input ports using closed analytical expressions (like C*exp(-k*(x^2+y^2+z^2)) for Gaussian profiles), port eigenmodes computed in 2D, or constant values of the field components, for plane waves. Common rectangular, circular and coaxial eigenmodes are featured as predefined selections. Furthermore, a lumped port boundary condition (new in COMSOL Multiphysics 3.4) provides excitation by a set voltage. 

The Waveguide Adapter model in the Model Library of the RF Module shows how to set up and run a 3D simulation with a port eigenmode excitation. Lumped ports and 3D transmission line modeling are demonstrated in the Microstrip in PCB model.

In addition, axisymmetric TEM wave propagation and mode analysis can be made by using the Axisymmetric TM Waves application mode. TEM waves fall under the class of waves handled by this application mode.

Related Files

microstrip_port.mph 784 KB


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