[HFSS Help!] Gain obtained for monopole is higher than theoretical value?

[afterglow18x]

Hi to all the experts out there!:grin:

I have simulated a simple 30MHz monopole antenna with an infinite ground plane and using pec as the material. I have specified my source impedance to be 50ohms. However, I realised my radiation pattern plot has a high realised gain of 5.4694dB at the 90deg direction. I wonder why the antenna has such a high value as compared to the typical 5.15dB, as this means that my simulation is not really accurate. Please kindly enlighten me on my mistake!

Thank you very much.

 

[maxwellian]

How much space are you modeling between the monopole and the absorbing boundaries? I'm not sure about the rules of thumb for HFSS, but sometimes with 3D field solvers you need to have enough space to the absorbing boundaries to keep them out of the near field reactive zone, or you can get some funny results at some angles. Try making the workspace larger to make more space to your absorbing walls. That includes the top. This is a good convergence study to run, to ensure your EM results are convergent.

 

[afterglow18x]

Hi maxwellian!
thank you for your reply.
I have simulated the antenna with a radiation boundary a quarter wavelength away from the monopole, as according to the HFSS guidelines. Simulating one with a boundary half wavelength away also yielded a high gain value not far from 5.4dB. Could there be other factors that have caused this result?