simulate a microstrip in HFSS

Just a simple microstrip...

1. a rectangular ground box (pec)
2. a rectangular substrate box (e.g. ε=2.2)
3. a rectangular conductor box (pec)
4. two rectangular (no box) wave ports (not assigned material), the same width as conductor, the same height as ground+substrate+conductor

After simulation, S21 and S11 are both very bad.....

I understand HFSS sees all faces of the model which are exposed to the outerspace as an E boundary. So I am thinking to add an air box outside the microstrip structure. Since Perfect E boundaries are also on the air box, I think the air box should be much bigger than the microstrip, otherwise it will like a suspended substrate stripline structure.

But the problem is how I can set the wave port into a big air box? HFSS doesn't allow any port set in the material on both sides.

Instead of using air box, I also thought of using "radiation boundaries" on the microstrip itself, but the result is even more ridiculous.

Could any friend here clarify how I can solve this problem? Thanks

just a simple microstrip.....

well brother i see that both the pecs are boxes.which to me sounds a bit corny.pecs(ground and copper) are always been rectangles.and radiation boxes dont let waveports inside of the box.so lump ports has always been the excitation for microstrip.

i hope it helps.since u said ur s11 and s12 are ridiculous i am guessing you dotn have a proper matching network.please look into.

i dont have acess to HFSS now but when i get to school i will look into your design.and post more comments and suggestions.

regards
sajid mohammed.

Hi Sajid,

Thin Rectangular box should be fine for the GND and conductor. Otherwise you cannot assign materials for just rectangular. I am trying to use lumped port and see whether it will be better.

The dimensions of the microstrip is set as a "50 ohm" one, so even it is not that accurate, it should not be away that far...


Lee




ΩΩΩΩΩ

hi lee.

what is the frequency at which you are operating and what is the width of microstrip.

and i am guessin both the sides have lump ports.

Frequency is around 20 GHz and the width of conductor is 1.465mm, which I calcuated for a 50 ohm impendance.

everything seems alrite.just cant figure out whats the matter with the whole messed up s parameters when i did the same simulation with a infinite ground plane with 20 mil thickness of epsilon 2.2 s11 was way below -30dB and s 12 close to 0dB on desinger.

let me look into it more my friend.if u have the solution let me know what was wrong with it.
sajid mohammed.

Added after 51 minutes:

i think i figured the problem.let me upload the file so that u can check with it alrite.

sajid mohammed.

Added after 54 minutes:

i actually redid the whole simulation from the beginning.all the numbers are good. but to my suspicion the duplicating of the rectangles for the lump ports could be a reason for improper result and in the project tree i saw a move command which looked suspicous.i have the file which i have simulated i didnt bother for the length because it is meaningless.

if it really helped .dont forget to add "it helped ".

thanks a lot again.

sajid mohammed.

Hey sajid,

I changed to lumped ports and set a big air box outside, now the result is making sense.

Thank you.

Lee