CST2013 MWS Examples: Loaded Cavity (Team Workshop Problem 19)

Tetrahedral mesh:

General Description

The eigenmode and Q-factor calculation of the team workshop example #19 ("Microwave Field in a Loaded Cavity") is presented. Furthermore the external Q-factor calculation is performed in the second example.

The structure mainly consists of an air filled cylinder containing a centered dielectric rod. In addition the cylinder is coupled by a small rectangular hole to a rectangular waveguide.

Structure Generation

The background material is defined as perfectly conducting material, the units are changed to millimeters, gigahertz and nanoseconds, and the boundary conditions are set to "electric" in order to model perfectly conducting walls. The structure is created by defining basic shapes like cylinders and bricks. Using the local coordinate system offers the possibility to create the shapes relative to each other.

For the external Q-factor calculation only the first eigenmode is of interest, thus the symmetry conditions for the XZ plane are set to "magnetic" and for the XY plane to "electric".

Mesh Settings

Both the number of lines per wavelength and the lower mesh limit are increased to 20 for the hexahedral mesh. Also for this mesh, in order to obtain accurate results the grid resolution is improved within the dielectric rod by defining the maximum mesh step width in x- and y-direction. Curved element order property for the tetrahedral mesh is set to 2.

Solver Setup

When the eigenmode solver is started, a specific number of the lowest resonance frequencies of the structure are calculated.

The relevant settings are defined using the default values, so that ten eigenmodes are considered.

Solver Setup (External Q)

The simulation is done by using the eigenmode solver JDM and activating the Calculate external Q-factor box. The solver then automatically calculates the first (unloaded) eigenmode, the corresponding external Q-factor and the loaded eigenmode.

Post Processing

The resulting mode information is listed in the navigation tree in the folder 2D/3D Results, subfolder Modes. Here the mode patterns as well as the corresponding eigenfrequencies can be found. The resonance frequencies are also stored in the logfile of the eigenmode solver.

The quality factors are calculated using Post Processing: 2D/3D Field Post Processing Loss and Q .

In case of the external Q-factor calculation in addition the loaded eigenfrequency and external Q-factor are written in the logfile.