Using HFSS to simulate EM reflection coefficient, which method is correct?

Hi everyone,

I want to use HFSS to simulate the electromagnetic reflection coefficient of a multi-layer structure (namely electromagnetic absorber), the thickness of each layer of which is about 5 mm, made by dielectric material. The electromagnetic wave, the frequency of which is about 5 GHz, is normal to the planar interface. Our design objective is to attenuate electromagnetic wave reflection.

I created two models described as following:
The first model, as shown in the attachment——the first model, consists of a two-layer structure and an air box. The air box include the structure, and the bottom surfaces of the air box and structure are coplanar, the corresponding surfaces of two components in other directions are at a distance of 50 mm. Assign radiation boundary to the air box, choose the bottom face of the structure, which is coplanar to the air box, as the waveport.
The second model, as shown in the attachment——the second model, is similar to the first model. All the corresponding surfaces of two components are at a distance of 50 mm. Assign radiation boundary to the air box, too. Choose the top and bottom face of the air box as the waveport.
I extract S11 of the two model, but the magnitude is very different.

Could you tell me which method is correct? If both are improper, could you give any suggestion to create a correct model?

Thank you in advance for your help!
With best wishes!
Cherne-he

Hi,
second model seems be correct. you do not need to assign two wave port for two sides of your structure, one port is enough. it is important that the boundary condition of the air box in the port side be selected as "incident field" (not "radiation only").

Hi Vahidqc,

Thank you for your warm reply. Your suggestions are very useful. Is the wave port assigned for side of air box?

Regards,
Cherne-he

vahidqc said:

Hi,
second model seems be correct. you do not need to assign two wave port for two sides of your structure, one port is enough. it is important that the boundary condition of the air box in the port side be selected as "incident field" (not "radiation only").

Click to expand...

if the back side of your ports are PEC,the waveport is ok,else you must use lumped port

Hi ehsan_faal,
I want to extract S11, so I must assign wave port. The material of multi-layer structure is dielectric. Is it correct that I assign wave port for the surface of air box? If it is right, should I assign wave port for the surface of air box, or create a sheet on the surface of air box, then assign wave port for the sheet? And the size of the port is as large as air box surface’s. Any suggestion?
Thanks in advance!

ehsan_faal said:

if the back side of your ports are PEC,the waveport is ok,else you must use lumped port

Click to expand...

i think if u assign wave port to face of air box ,size of ports in your design is bigger than it's usual,
it's better u create a sheet on the surface of air box and then assign your ports.

Hi ehsan_faal,

I created a sheet, the size of which is 10 mm*10 mm as is smaller than former's 200 mm*200 mm, on the face of air box. Then assign the port on it. The face is coplanar to multi-layer's bottom face. The E field is attached. But i don't know how to modify the size of port according to the E field figure.
Thank you.

ehsan_faal said:

i think if u assign wave port to face of air box ,size of ports in your design is bigger than it's usual,
it's better u create a sheet on the surface of air box and then assign your ports.

Click to expand...