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How to properly feed Horn antenna with Coax in HFSS?

imtiaz369

imtiaz369

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So, I would like to feed my Horn antenna with coax in my HFSS simulation. But when I do this, the S11 goes below -5.00 dB. My waveguide Cut-off frequency is 21GHz, and my operating range is from 26.5 to 40GHz.

I tried my Coax model only with the waveguide. That time, I got S21 at -1.5dB, which is good. But when I connect it with Horn, why am I getting this kind of response? The Coax impedance is 50 ohms!

S21 - When feed wave guide with the same Coax

1742514758448.png


Horn Feed Response:
1742514808005.png


1742514821190.png
 
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Your question is not clear. You mention S21 insertion loss and then you mention S11 return loss.

Small return loss -10dB or even better -20dB or -30dB means the antenna is matched, that's fine.
 
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volker@muehlhaus said:
Your question is not clear. You mention S21 insertion loss and then you mention S11 return loss.

Small return loss -10dB or even better -20dB or -30dB means the antenna is matched, that's fine.
Click to expand...
Why my question isn't clear to you? I mentioned, "S11 goes below -5.00 dB. My waveguide Cut-off frequency is 21GHz, and my operating range is from 26.5 to 40GHz." -------- It's the case when I feed the horn antenna using a 50ohm Coax!
 
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Hello,

I would suggest looking at the coax to waveguide transition without the horn. Make sure you are satisfied with the response and that there aren't any higher order modes that may be generated that could get trapped in the waveguide and cause the resonances you are seeing.
 
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Kobba said:
Hello,

I would suggest looking at the coax to waveguide transition without the horn. Make sure you are satisfied with the response and that there aren't any higher order modes that may be generated that could get trapped in the waveguide and cause the resonances you are seeing.
Click to expand...
1742588324006.png


I observed the S11 in waveguide. There is no higher order mode between 36-40GHz. But the S11 is below -5dB event the Coax impedance is 50 ohm. What should be the optimization point here! pin length or offset? any good paper or reference for the simulation!
 
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