Assessing Radome Effect on Crosspol Discrimination

Questions related to the results associated to our different modules and the simulation process.
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rphsia
Posts: 3
Joined: 22 Nov 2017 23:25

Assessing Radome Effect on Crosspol Discrimination

Post by rphsia » 23 Nov 2017 00:26

I'm following the Training Example in "17.1. Example 1: newFASANT Parametric Radomes" which is very useful. I did play around a little with the materials and frequencies, etc. but for the most part I'm using the same model as in the example.

I need some help interpreting and/or presenting the simulated data. My primary interests are the transmission loss and the degradation in axial ratio (or crosspol discrimination) from introducing the radome at specific look angles.

I see that I can plot Circular->Axial Ratio from the Far Field->View Cuts menu. But the result I get seems strange, it starts around 2.0 but later starts jumping all over the place to above 20. I also tried checking the "Antenna Results" box thinking this should plot the antenna axial ratio on its own, but the results look about the same. Shouldn't the Antenna Results show close to perfect Axial Ratio (without the radome), or am I misunderstanding something?

Any help or advice appreciated.

alvaro.somolinos
Posts: 3
Joined: 30 Sep 2016 08:21

Re: Assessing Radome Effect on Crosspol Discrimination

Post by alvaro.somolinos » 24 Nov 2017 11:13

Hello,

The "Antenna Results" box show results of the antenna system without the radome structure.The results that you comment are correct considering that the feeder (alone) is not circular polarized perfectly. Axial Ration can be very high for some angles.

I recommend you create a "Pattern File" with a perfect circular polarization using the DIA file editor to use it as feed. The feed-horn pattern can be modelled as conventional ‘cos^q’ with q=28.
Guide: https://www.fasant.com/en/guides/gui/6. ... /dia-files
dia.png
dia.png (30.69 KiB) Viewed 20230 times
The generated file contains a linear polarization but you can generate circular polarization by placing two pattern file antennas as follows:
Note: The second antenna is rotated 90 degrees and phase 90.
pattern_file.png
pattern_file.png (110.01 KiB) Viewed 20230 times
After simulating click on 'Show results -> Radiation Pattern -> Export as DIA File' and you have the file to use as feed in your radome.
axial_ratio.png
axial_ratio.png (47.34 KiB) Viewed 20230 times

rphsia
Posts: 3
Joined: 22 Nov 2017 23:25

Re: Assessing Radome Effect on Crosspol Discrimination

Post by rphsia » 28 Nov 2017 01:01

Thanks for the detailed info! I tried to follow this step by step but so far I haven't been able to replicate the results you show. My axial ratio plot starts at 0 but immediately jumps to 200 and stays there until close to 180 where it finally drops down.

I think I did everything correctly but maybe I missed something. One thing I noticed was that in the .dia file creator you use REV but later in the "Pattern File" it says 3DE. I did it all in REV, don't know if that matters. Are there any other settings in Mesh or Execute that I might have missed?

alvaro.somolinos
Posts: 3
Joined: 30 Sep 2016 08:21

Re: Assessing Radome Effect on Crosspol Discrimination

Post by alvaro.somolinos » 29 Nov 2017 11:04

Sorry, you have to use the type 'RV2'.

I attached a sample file and the project to create the feed.
Example.zip
(938.64 KiB) Downloaded 974 times

rphsia
Posts: 3
Joined: 22 Nov 2017 23:25

Re: Assessing Radome Effect on Crosspol Discrimination

Post by rphsia » 30 Nov 2017 01:05

Thanks very much for providing the file, that was very helpful in getting further. It seems to be functioning correctly, independent of frequency.

I've now taken the next step and added the "radome". I followed a similar format as the example file, except I used a disk instead of a plane. I have a 0.2" thick piece of foam sandwiched between two thin layers. I've varied the distance between the antenna and the foam from around 0.1" to 1" but it doesn't seem to have much effect. This is at 10-15GHz.

I do see degradation of the axial ratio as a function of angle, but it seems to degrade much faster than the other models and measurement data I'm comparing against. It jumps to 3dB at 60deg, 5dB at 70deg and 8dB at 80deg... the models I'm looking at are much slower, say around 0.5dB at 60deb and 1.5dB at 80deg. Any ideas?

Thanks again!

alvaro.somolinos
Posts: 3
Joined: 30 Sep 2016 08:21

Re: Assessing Radome Effect on Crosspol Discrimination

Post by alvaro.somolinos » 12 Dec 2017 15:57

Sorry for the late reply,

The antenna that I have proposed is a high gain ideal circular polarized antenna. I think that to compare the models with the simulation, you have to feed with the same antenna.

If you want, send us more information about your models to 'webmaster@fasant.com' so I can help you configure the feeding properly.

Best regards,
Alvaro.

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