Waveguide adapter simulation

[wettersat]

Hi folks

I am a novice in openEMS and still trying to understand/modify simulation scripts. Until now I have modified scripts to simulate W2IMU dual mode horns.
Has anyone tried to simulate e.g. rectangular waveguide to circular waveguide using a quarter wave plate adapter between? Or only a rectangular waveguide directly connected to a circular waveguide?

[thorsten]

I have played with a SMA to rect waveguide transition but RWG to CWG should be interesting too and should be possible with openEMS (if that was the question). But I have not tried it yet.

[wettersat]

Yes, that was the question. Hmmm, but how?

[Hale_812]

The model of coax to feeding rect-horn works, but needs so dense mesh, that you better put a lumped port just inside the rect. section.
Septum transition should also work just fine, but the circular waveguide is a problem. You will die increasing the mesh for accurate curved surface representation. You can use a cylindrical coordinates, but there will be more problems with rect. waveguide and excitation, which will fall into the center of the model, where... well, nothing is perfect in this world.

[wettersat]

My idea was to "join" both tutorial scripts for circular and rectangular waveguides. But there is the question with the mesh and ports definition. Both ends could be open waveguides, no coax feed needed.

[Hale_812]

Cylindrical coordinates can not be combined with rectangular. You will get stepped surface either in circular, or rectangular section. And it is easier to define circular section in rectangular coordinates, then the opposite.

[wettersat]

Thanks for the hint.

[thorsten]

I agree, you should just do this in the "normal" mesh. Both types of ports should work fine. You "only" need to come up with a transition. But the RWG TE01 und the CWG TE11 mode should be similar enough that this should not be too difficult?

[wettersat]

Last weekend I studied some openEMS scripts (again). A rect-to-rect transition should be able to do (or a cir-to-cir transition), that's an easy job.

For a better understanding. I need only 1 port for a rec-to-cir transition, but which one?
[CSX, port{1}] = AddCircWaveGuidePort( CSX, 0, 1, start, stop, 'z', a*unit, b*unit, 'TE11', 1);
or
[CSX, port{2}] = AddRectWaveGuidePort( CSX, 0, 2, start, stop, 'z', a*unit, b*unit, 'TE01', 1);

Should I use the TE01 mode if the port is within the rec-waveguide?
Should I use the TE11 mode if the port is within the cir-waveguide?

[Hale_812]

I guess, you are transiting From Rect to circ, and not back? so, isn't it obvious?

Or (probably), knowing approximate impedance you can add a lumped port along the expected field line corresponding the mode. It just creates a E field by driving the current through the port resistor.