Symmetry planes for horn antenna

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PaulUK
Posts: 81
Joined: Wed 28 Oct 2015, 14:23

Symmetry planes for horn antenna

Post by PaulUK » Wed 09 Oct 2019, 14:21

I have written an indepth tutorial for the design of corrugated horn antennas and how they can be simulated with openEMS, and it was suggested that I show how symmetry planes can be used to reduce the size and time for the simulation.

To begin with I just wanted to add a PEC wall normal to the x axis located at x=0. I did this with the -ve x boundary condition. I set the nf2ff not to include the -ve x wall of the nf2ff box. I set the Calcnf2ff to include the mirror olane in the x axis.
However now the radiation patterns are not correct in one plane. They should look like this for 3 cuts.
Hyperbolic Horn Directivity.png
Correct patterns
Hyperbolic Horn Directivity.png (36.8 KiB) Viewed 4904 times
But with one PEC symmetry plane I get this.
Hyperbolic Horn Directivity with PEC symmetry.png
Incorrect patterns
Hyperbolic Horn Directivity with PEC symmetry.png (95.68 KiB) Viewed 4904 times
The script is this attachment. It's a modification to my original script without symmetry.

I would be very gratful if anyone can point out why im not getting the correct radiation patterns in all three cuts. I can't see what I'm doing wrong. Thank you.

Ps, in the tutorial I show equivalent simulation results from CST and HFSS and the results are almost identical! ;)
Attachments
Corrugated_horn_with_mode_converter_options_Symmetry.m
Modified script with symmetry
(22.84 KiB) Downloaded 351 times

thorsten
Posts: 1438
Joined: Mon 27 Jun 2011, 12:26

Re: Symmetry planes for horn antenna

Post by thorsten » Sat 02 Nov 2019, 15:17

Well I do not see an obvious problem. (except the missing mirror for the 3D far fields, but that does not change the cut planes)
I'm running it now, but it takes a while.

What you could try is to run the non-mirrored simulation, but with the cut nf2ff recording and apply the mirror then. This way should be clear that the fields and excitation and so on are fine. Even do this once for +x and -x...

PaulUK
Posts: 81
Joined: Wed 28 Oct 2015, 14:23

Re: Symmetry planes for horn antenna

Post by PaulUK » Sun 03 Nov 2019, 23:21

Hello Thorsten,
Thanks for looking into it. I'll try what you suggest. So if I understand correctly, I simulate the whole model as usual but then to implement the mirrror planes in the nf2ff function and check the patterns?

PaulUK
Posts: 81
Joined: Wed 28 Oct 2015, 14:23

Re: Symmetry planes for horn antenna

Post by PaulUK » Thu 07 Nov 2019, 14:42

I repeated the simulation with the full mesh and made sure that all planes for the nf2ff box are included (set to 1) with all boundaries set to PML_8. I left the CalcNF2FF symmetry plane on normal to the x axis with 'Mirror', {0, 'PEC', 0}. Just one symmetey plane for now.

This time the patterns look almost as the original, but I noticed some low level ripple on the phi=0 plot as shown in the picture.

Does this provide any clues as to what the problem might be?

Edit- It also seems that the gain is 3dB greater.
Hyperbolic Horn Directivity with PEC symmetry but Full Model.png
Ripple at low levels.
Hyperbolic Horn Directivity with PEC symmetry but Full Model.png (90.89 KiB) Viewed 4749 times

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