HFSS Slot antenna problem

[trichop]

Hi everyone,
I am working on a problem lately without any success.
I am simulating on HFSS a slot antenna which is located on the air/dielectric (silicon, er=11.7) interface.
I try to calculate the radiation pattern in the dielectric half-space but the directivity I am getting is very low compared to what I am expecting.
For example, for a typical double slot antenna, max directivity should be around 10dB and I get 4dB.
I have the same problem with every slot antenna I simulate.

FYI:
I conducted the runs using both absorbing boundaries or PML.
I tried also having the metal surface finite (smaller than the air/dielectric box)
or letting it protrude into the absorbing boundary or PML.

Do you have any suggestions?

Thank you.

 

[usman_mahfooz]

Can you upload the design file. What type of port you are using. Are you using PEC as antenna conductor material?

 

[trichop]

I used lumped port and PEC as the antenna conductor.

Thank you.

 

[sharonma]

1. If you are using a double slot antenna with more than one port, make sure that the excitation phases are correct.
2. Silicon is a VERY lossy substrate, try comparing the same antenna using metal over air (radiating slot) and compare to text book exact solution (e.g., Balanis).
When you have a good agreement between the solutions change back to silicon

 

[trichop]

Thanks for the response sharonma.
I doubt the problem is the silicon substrate because in the HFSS model I am using conductivity of silicon is set to 0.
I am also using one lumped port excitation.

Thank you.