Combline Filter

Coupled Simulation Examples

 

 

Surface power loss distribution

 

Temperature distribution

 

Mechanical deformation

Shifted S-Parameters

 

General Description

This example demonstrates how to perform a parameterized coupled simulation of a narrow band filter, containing two coaxial resonators. The whole simulation workflow involves the coupling of four linked CST-simulation tasks. Due to ohmic and surface losses, the structure is heated. This heating leads to a mechanical deformation, which de-tunes the filter. The final simulation uses the deformation information to compute the shifted S-parameter curves for the heated and deformed structure.

 

Structure Generation

To create the filters housing a shelled brick was created. Afterwards the coaxial connectors were added by defining and mirroring various cylinders. The interior of the filter contains an aperture, created with the brick tool and two cylinders. The regions where fields are most concentrated is where the coaxial feeds are pointing at the resonators cylinders. To obtain accurate results two mesh refinements were defined for the coaxial feeds. The height of the aperture is parameterized and later used for a parameter sweep.

 

Setup Simulation Tasks

The project consists of a master project, which is visible after opening in CST STUDIO SUITE and four simulation tasks, which are basically derived sub projects. To access these simulation tasks one has to switch to the schematic view of the master project:

 

 

All four simulation tasks were derived from the master project and contain further problem-specific settings which are described below:

 

HF FD

The first project is a tetrahedral grid based simulation with the frequency domain solver. Three monitors were defined to record electric-, magnetic- and loss-fields. After the solver process has been finished the thermal surface- and volume-loss distributions are prepared  for the thermal simulation by a template.

 

Thermal

This project uses the thermal loss distributions calculated by the HF FD task to compute a temperature distribution on a hexahedral grid. Besides the loss distributions, convection boundaries were defined on the outer walls of the filters housing.

 

Mechanical

In combination with a reference temperature, this project uses the temperature distribution from the previous one to compute the thermal expansion of the filter. Therefore the coaxial waveguide ports must be fixed mechanically with displacement boundary conditions.

 

HF FD S-Parameter

Finally the mechanical displacement information is used with the sensitivity analysis to compute the S-parameters of the deformed structure. This project is tetrahedral based, since the sensitivity analysis operates only on tetrahedral based grids. The displacement information was imported with the field import source and then linked to the sensitivity analysis.

 

Post Processing

During the workflow a couple of interesting results appear:

Especially the S-parameter curves of the deformed structure play an important role for filter designers. Actually this filter was not designed very well, since the influence of temperature changes affects the electrical filter behavior too much.

 

Parameter Sweep

The example also contains three tables with S-Parameter result curves vs. the height of the aperture:

 

 

This demonstrates that one can easily perform a parameter sweep or an optimization process with the parameterized sequence of simulation tasks.