I am designing a patch antenna using coax feed in HFSS. I read in posts that dimensions of radiation box should be more than lambda/4 from the edges of the radiating structure. So I did like that and after that I changed the height of radiation box from lambda/4 to more than lambda/2 in steps. I found that each height I get different S11 plot, the resonant frequency was same but S11 dB magnitude was varying, so I was not able to find the correct height of radiation box. Can somebody help in how to select the radiation box dimensions.
I am not aware of HFSS specific implementation.
However, if you have a powerful enough PC you can keep the same mesh density end and gradually increase the BOX dimension. At some point, you will find that the S11 does not change with the BOX size increase. That will be the correct answer.
Hello,
you should be chosen the size of air box, lambda/4 larger than substrate or your design. your design should be completely inside of air box.
If suppose your dimension is Ax Bx C (length*width*height)
then radiation box dimension is ((A+2*lambda/4)x (B+2*lambda/4)x (C+2*lambda/4)).
Thanks,
One approach to finding the correct dimensions for the radiation box is to start with a large box (greater than λ/4) and then gradually decrease the size of the box in small steps (for example, by 0.1λ or 0.2λ). After each step, re-run the simulation and plot the S11 parameter. Compare the results and look for any changes in the resonant frequency or the S11 dB magnitude, and select the dimensions that give the most accurate and consistent results. Additionally, you can use some other parameters like return loss to check the simulation results and compare them with the expected values.
In the latest version of HFSS, we get option of drawing radiation box (right click on the mouse by keeping cursor on the antenna design and choose Radiation Box, it will ask for central frequency, then specify your resonant frequency then you will get Radiation box.
As It was rembering form reading in reference before that the high of microstrip must be about 0.1 lambda
https://youtu.be/A3mMfW5tenc
You can use draw option / or insert open boundary option
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