Dear friends... I have designed several very compact antennas from reputed journals in HFSS. But I am getting the negative gains for low-frequency band (3GHz to 4 GHz). I could not find the solution for it. please help me in this regard. I am attaching you the reference paper and design file for your reference.please find the attachments.
The radiation box should always have at least a quarter wavelength in the embedding medium (usually a vacuum) between the closest radiating edge and the closest edge of the box, at the lowest frequency. A larger radiation box shouldn't be an issue, it might just take longer to simulate.
Dear Saka
I checked your simulation files and there were a couple of things you should consider. You need to take time an get familiar with HFSS setup. It looks simple at the first glance but disregarding any of them will give you inaccurate result. I will list a handful of them which should solve your issue at this step:
1. Replace the wave port with a lumped port limited between ground plane and center line with integrated line defined. Do not exceed this boarders.
2. In Analysis>setup>Options you have specified the "Minimum Number of Passes" and "Minimum Converged Passes" to be one. That is why your simulation finishes pretty fast. Change them to 15 and 8, respectively.
3. In Analysis>setup>sweep you chose the "Fast" for sweep type. It is for a quick look at the S-parameters. If you seek radiation pattern at other frequencies you should choose "Discrete" which solves the whole geometry at any separate frequency. Many frequencies takes too much.
Go ahead, I hope they work.
https://www.researchgate.net/post/What_is_the_basic_formula_for_calculation_of_the_Airbox_dimension_during_the_simulation_of_any_antenna_structure_in_HFSS
Hope this will help you
Basically, according to HFSS manual, height of Rad_Box >= lamda/4 where lamda is operating frequency (solution frequency). Suppose your operating frequency is frc and range of simulation is from fr1 to fr2. Then fr1
Dear sudipata maity sir, Thank you for your replies. Have you faced this problem when designing very compact antennas in HFSS ( typically around 20mm*20mm*1.6mm).I have checked your suggestion but nothing changed.
We have HFSSv13 and you are using HFSSv15. Due to that reason, I'm unable to see EXACT HFSS structure what you have drawn. Negative gain is quite possible to insufficient amount of ground plane. Even, in case of DRA, I found -4 to -3dB. Then, I increased the size of ground plane monotonically. I got finally 6dB.
Maity sir, I have attached the step files of my design i think you can see my design models now. please find the attachments sir.
Dear suhas Dinesh, Yes that is what i am looking for. can you please tell me what i have to do to get that response.
1. It is not the problem of the radiation boundary.
2. Adjust your Analysis setup: Set solution frequency to the upper bound that is 20 GHz. That is to make the mesh size as small as possible.
3. Set the number of passes to 20.
4. Set maximum delta S = 0.02.
5. Set sweep type to interpolating sweep, step size to 0.01.
Now, you are good to go!
dear dinesh....i simulated using discrete sweet i got -10dB bandwidth from 3.19GHz to around 12 GHz. in the reference paper they got the bandwidth from 2.9–13.7GHz. Moreover total gain is negative at 3.2 GHz. how can we address this problem
The gain plot is with the slot embedded in the structure. Your's has no slot.
dear Dinesh, i think by introducing a slot in the patch for a particular frequency, the gain will be affected at that frequency, isn't it?. Not only for this antenna i getting this problem for few more antennas also.
Dear friends, i have a PIFA antenna operate at 5 band frequencies, i simulated it on CST Mws and i exported their file from the CST Mws to the HFSS, but i found a problem with the dimensions of the radiation box, knowing that their low frequency is 0.9GHz and their high frequency is 2.8GHz, any help on how to calculate the dimensions of the radiation box ?
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