Dear

I am suggesting you to check the boundary conditions setting.

But for which design the two graphs belong to?

Thanx for reply Mr.Salah .Could u explain more what u mean by boundary conditions  setting. The design is for 79 Ghz SRR.

Dear

Actually I am using SEMCAD X, but as I understand, making the same numerical computation with two different software any not give the same results. I am afraid you are not defining your boundary conditions the same in the two software. Here, I mean the Absorbing Boundary Conditions (ABC). The ABC are set as a uniaxial perfectly matched layer (UPML) mode with different strength thickness.

Thanx for explanation Mr.Salah

Dear Bassem,

I want firstly to know :

witch CST did you use? microwave or microstripes?

also,

witch setup frequency you made in HFSS and also witch sweep  type (fast ? discrete?) and also the sweep step? It can made great differences.

a priori there is a problem with the frequency setup

don't forget to tell us also the application the antenna is dedicated to and also the function frequencies

Dear Abdelhakim,

I used CST microwave CST-MWS

for HFSS

 frequency setup=linearcount  ''type'' 

Sweep type=Fast 

Sweep step=70-90 GHZ

Application is Automotive radar 

Dear bassem.

You didn't give me the setup frequency you used in HFSS. It will be the source of problem because you have in both figures closer pics with S11 values different.

Try please that setup configuration:

Frequency setup =  79 Ghz (arithmetic mean)

Sweep interval = 77-81 Ghz

 sweep step = 20 Mhz 

Dear Abdelhakim,

Check the figures please

I can read difficult image

Choose 0.01 or 0.02 Ghz insread of 0.1 Ghz for the  step

Make the simulation and tell me after the results

If you are interested only for the 77-81 Ghz band make the simulation only in this band . but to compare between two simulation, it's recommended to do it in the same configuration conditions.

I insist to do a small step like 10 or 20 Mhz and if you have strong machine do the sweep type = Discrete and not fast

Dear Basem,

There is news about your simulation with the proposed configuration?

have a nice luck.

Dear Abdelhakim ;

Unfortunately .There is no improvement ..Really I feel lost. HFSS is very bad compared to CST .

Don 't worry my brother. Send me the screen capture of your results

Or if you are sure you did a good CST simulation, 

I propose you to send me the hfss file to try to help you. I have hfss 10. 

I think the issue will be related to the mishing and the mish size you use in both programs as you know that both programs are using different numerical methods, i.e. FEM and FIT.

Dear Osama;

I used the defaults mishing for both CST and HFSS, so Do u have any suggestion to slove that problem or any change of mishing ?

Dear aqlan,,

If you can send me the hfss file on my researchgate account, i can view the problem and try to find the solution.

Dear Abdelhakim ;

Sorry, I cant right now .Many thanx for help and explanation .

I advise you this time to change the frequency setup and make it equal to 77.5 GHz or exactly the desired value corresponding to the peak you have in CST simulation corresponding to -45 dB and make the frequency in exact value expressed in MHz (it's more accurate than the Ghz)

good luck

You can inform me if there is any improvement

Allah help you

In my experience with HFSS you want to set your solution frequency to the highest frequency of evaluation.  So in your case 90 GHz (or thereabouts) appears to be your highest evaluated frequency, rerun your HFSS model but with 90 GHz as your solution frequency.  Let me know if you are able to resolve your problem.  Also, more details about each simulation would be helpful!

Basem Aqlan : Did you find the solution to your problem. If yes, would you kindly share it with me since I am also facing a similar issue?

El Ouadih Abdelhakim : I am facing a similar problem. I tried all possible solutions but in vain. Would you kindly also help me to find the solution?