Continue to Site

Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Frequency Range in CST? Different results

Status
Not open for further replies.

mbroell

Newbie level 3
Newbie level 3
Joined
Jul 28, 2009
Messages
3
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,281
Location
Germany
Activity points
1,305
cst 500thz

Dear users,
using transient solver in CST Microwave Studio I have the following problem:
I would like to calculate S-Parameters through a metallic periodic structure in the visible/near infrared. I use two ports in a waveguide to excite the signal and to detect the reflected/transmitted intensity. Unfortunately S-parameters change when I set the lower frequency in "frequency range" to 0THz. If the lower frequency is finite (i.e. 1 or 250THz) no change in S-Parameters is visible. On the other hand I have heard, that simulations run faster and more accurately when setting the lower frequency limit to 0 THz.

So my question is: Which results can I trust more?

Attached to this post you can find the simulated S-parameters for a lower frequency of 0Thz and 1THz respectively. The upper frequency was 500THz. Especially in the region of 300THz which is of special interest in my case, large differences in the S-parameters appear.
Thanks a lot for your support,
Markus.
 

frequency range of hindi

mbroell

Are you using the same solver accuracy setting for both cases? You may try increasing the solver accuracy of the lower freq=1THz case by 20dB and see if the results begin to converge with the lower freq=0THz case.
 

cst frequency range setting

Hi Dave,
sorry for the late reply, the simulation takes a while. Unfortunately the S-Parameters do not converge, even for a higher accuracy. In the case of 1THz I have a clear resonance behaviour at about 390THz. This resonance has disappeared if I take 0THz as lower frequency. Is there any physical meaning why results are different for different frequency ranges? Why is it favourable to take 0THz as lower limit?
 

Re: Frequency Range in CST?

[quote="Is there any physical meaning why results are different for different frequency ranges? Why is it favourable to take 0THz as lower limit?[/quote]

I would take the lower freq=0THz case as more accurate. Remember, T=1/df, where df = bandwidth of signal, so the bandwidth of the lower freq=0THz case is larger and at the same time the simulation will be shorter.

I do see a small, but distinct resonance, at around 340THz in the lower freq=0THz case, which is probably the same ripple that you see in the lower freq=1THz case. In my opinion, the smoothing you see in the lower freq=0THz case is because of the increased bandwidth of the excitation signal.

Since you increased the solver accuracy of the lower freq=1THz model and it is already well converged, one more thing to try is to run the lower freq=0THz case with an increased solver accuracy of 20dB and see if the resonances which get deeper and shift up in frequency a little. By increasing the simulation time you are the solver is forced to integrate the S-parameters using more data points and you may see an overal improved resolution in the frequency domain.
 

Status
Not open for further replies.

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top