Negative gain in HFSS, suggestion needed

Hi all,

I am a beginner in using HFSS.
Need your kindly advice and assist if you don't mind.
Currently I'm designing a printed antenna using HFSS, this figure show the antenna structure and geometry:

The problem is the simulation give a negative gain as the result.
I am sure there a mistake in my design (project file) and not in the antenna structure or dimension, because this antenna has already mass fabricated and being used world wide. I just simply use its structure and dimension to check while deepening my understanding in using HFSS.

Please find my HFSS simulation file, hopefully somebody could download and check it. And let me know, where did I get wrong.

Btw, what is the name of this antenna? I just name it printed folded dipole antenna. cmiiw.

Thank you in advance.

Hi

Make the air box larger.
At least lambda/4 on all directions to the nearest structure.

Regards

Hi tyassin,

Thank you for the reply.
I've tried to increase the air box as suggested, however it only affect the return loss result not the gain.
The change of the air box will cause the simulation result especially in return loss or matching condition. So, how big is the air box needed to achieve the best condition which near the real condition (measurement result).

thanks and regards.

Hi

Try simulating the attached file.
The airbox should be at least lambda/4 of your lowest frequency of interest, to the nearest object in your design.

Regards