Learning Forum

[Behrooz]

Hello!

In HFSS I have designed two Dipole Antenna with 50cm distance between them. When I change the size of the Radiation Box S-parameter results (S11 and S21) are affected. I increased the pass number and initial mesh size but I got the same results. I’m attaching the results.

Please help me in this regard.

Thanks in advance.

Radiation Box.png

[Praneeth]

Hi Behrooz,nPlease ensure that you have at least quarter wavelength distance between the radiating element and the radiation boundary. nKindly refer to Assigning Radiation Boundaries section in the HFSS Help document.nYou can arrive at the optimum distance by increasing this distance and plotting the S-parameters for each distance. You will note that S-parameters are unaffected after a certain distance.nAll the best.nBest Regards,n

[Behrooz]

Dear n Thank you for your comment. I have tried it but there is some problem with S21 when I'm using Radiation boundary (S21 has an unspecified behavior).nIn simple Dipole antenna if we use the FE-BI boundary the result is OK , but If we have some lumped elements (capacitor)  in our structure then we have problem with S Parameter.nn

[Praneeth]

HiArray,nPlease use upload image option to share screenshots for your simulation model and results. We cannot access the attachments in the forum.nBest Regards,n

[Behrooz]

Dear ,nThe simulated results are as below:nn

[Praneeth]

nI think you are plotting the S-parameters for various radiation boundary distances. I am curious to see how you are measuring the distance.nIf so, one probable reason for difference in the S-parameters of different radiation box distances might be the back scattering from the radiation boundary.nThis happens if the sufficient gap is not considered between the antenna and radiation boundary. I would suggest you to increase the radiation distances further till you do not see much difference in the parameters.nYou can also try PML boundary if it is suitable for your model.nAll the best.nBest Regards,nn

[Behrooz]

Dear nI'm plotting the S-parameters for various radiation boundary distances. The distance between antenna and radiation box is changed from 111mm to 400 mm ( lambda is 333mm at 0.9GHz and typically distance of lambda/2=165mm is sufficient)nResults of the S21 parameter are as bellows:nnn

[Praneeth]

nI would suggest you to do a parametric analysis by using a variable for padding distance between your model and radiation boundary and see the response. It looks like your model requires more air padding than a usual case. For FE-BI boundary plots which you have shared, you could see s-parameters plot merely changes as this boundary condition computation is different from radiation boundary. By doing parametric analysis you can find the optimum air padding required for the radiation boundary in your model.nAll the best.nBest Regards,n