incorrect S11 results- microstrip transmission line in HFSS

microstrip transmission line hfss

Hi

I have a simple 21mm long microstrip line in HFSS(PEC) whose width,W = 0.168 mmm . I haver drawn this structure over a Ground plane (PEC) where dielectric thickness between microstrip and ground plane is 0.1mm.

When i compare the S11 results from HFSS with ADS then the ADS results are around -40 dB while HFSS results for this structure are -25 dB. I have used waveports at the ends of the microstrip with the suggested dimensions of 10*W and 8*height of dielectric.

Even after I increase my port accuracy to about 0.01 % also the results still dont match. I calculated the microstrip dimensions using linecalc from ADS.

I would reallt appreciate some help on this because I have tried everything I know and still can not make the S11 results coincident..

thanks a lot

Re: microstrip transmission line hfss

Hi

I had the same problem. But as far as I remember, select the " Renormalize all modes" in ports definition. Maybe doing this will not give you the same results, but I believe that you should do this.
Since in ADS the port impedance is 50 ohm.

Hamid

I had the same problem and i tried everything i know to fix it, but nothing...
Does ADS have a better performance than HFSS?

Actually I also once believed that I did everything that I knew to fix the problem. That time I believed that ADS was better than HFSS.
But finally I fixed the problem. The results should not be the same but if the discrepancies between ADS results and HFSS results are too much, there
is a problem with your model either in ADS or in HFSS.
Most of the time the problem lies in the HFFS model. In my case the problem was: transmission line was very close to the air box in HFSS.

I've heard that the port impedance measuring is not reliable in HFSS except you take care of any situation individually from your experience and skills. which is only applicable in case you almost know the result. I have the same problem for finding the port impedance of a microstrip balun.

I think the impedance of the waveport is not equal to 50 ohm and it is not constant through out the frequency range of simulation. So,renormalizing the waveport impedance to 50 ohm will give you better results in HFSS. And increase the solution frequency.

sv1437: that's right
AN56: No, it's not the case. You should just study some port tutorials especially for microstip line. One useful test is measuring port impedance and input impedance (by adding some equations to the calculator of HFSS), now if both of them are like 50 ohm, you are done.

---------- Post added at 09:47 ---------- Previous post was at 09:46 ----------

For the input impedance case, ports should not be renormalized.

hi ......
do you have a HFSS Tutorials.....
Thanking you.....

gopigopinath10 said:

hi ......
do you have a HFSS Tutorials.....
.....

Click to expand...

This is for version 10 but still usefull