Learning Forum

[Pratik Deb]

Hello all,

So, this is a very basic level question. I was designing a 50ohm micristrip line at 5GHz frequency using Ansys HFSS in Ansys Electronic Desktop 2022-R2 with the help of this youtube video (https://www.youtube.com/watch?v=LOQePJnB_9Q&ab_channel=RFDesignBasics). The video uses this link to calculate the dimensions for the substrate and the copper trace: https://www.emtalk.com/mscalc.php.

Now, my question is, how do I verify that the design is actually a 50ohm microstrip line? Do I plot the Z parameters (Z(1,1)) to see if there is peak at 5GHz of 50Ohms? I did that but the value of Z(1,1) is not 50ohms.

Thank you!

[Connor Pope]

Try plotting the time domain reflection (TDR) of your microstrip line. If you switch your domain from "Sweep" [the name of your Analysis] to "Time" you can then plot the TDR. 

Once you've selected "Time" as your domaine, you can selected "Terminal TDR Impedance" which will plot the time domain reflection vs time. For a straight microstrip line it should be relatively flat. You can switch the settings for the TDR plot under "TDR Options..." which should be ungreyed after you switch your domain to time.

[Pratik Deb]

Hello,

Thank you for your response. I did not have the option to plot "Terminal" parameters like your screenshot when I switched to time domain but there was an option to plot TDR impedance (See screenshot below):

 

So I plotted the TDRZ(1) (abs) (Screenshot below):

So, since at the 0 sec, we can see that the TDRZ(1) value is 49.5 ohms, this is how I verify that my microstrip line structure is actually 50ohms, right?

Again, thank you for your help.

[Dan Dvorscak]

Another viable option would be to export the s-parameter model into AEDT Circuit and use the TDR probe in that tool. Which has the advantage that if you are looking to include this as part of a larger channel model, you can include those models as well to get a feel for the entire strucutre. 

[Pratik Deb]

Thank you. I have used Ansys Circuit Design before where I had took my model from HFSS to Circuit Design and added passive elements there and used the option "push excitations" and later observed results in HFSS again. I don't have much experience in using the Ansys Circuit Design option but I will try to do what you suggested.

[Dan Dvorscak]

Hi Pratik. Ah, pushing excitations back to HFSS is really only used for field plotting. It does not impact results like s-parameters or TDR plots. To do a TDR of that combined structure, you must do it in the Cicuit tool. There is an example TDR project in the examples in the Circuit/Signal Integrity folder if you need a reference. 

[Pratik Deb]

Hi Dan, thank you for the explanation. Any chance you could link those TDR example projects that you just mentioned?

 

 

 

[Dan Dvorscak]

I can't send the exact link. But you can get to this by clicking on the Open Examples Icon in the AEDT File Menu:

 

Navigating to the Circuit/Signal Integrity folder:

And then opening the TDR_Example project:

 

 

 

[Pratik Deb]

Thank you Dan! I thought you meant examples from the Ansys Learning Hub website, that's why I had asked for a link. I will check out these examples.