Finding characteristic impedance of Tline in HFSS

Hello everybody,
Can anybody help me through this? I've used ADS before to ascertain the characteristic impedance of a transmission line and have used waveports in CPW's.

I'm trying to coax feed (50 Ohm) a 3.6 mm wide line on air dielectric with substrate height of 27 mm. I'm using a driven terminal solution for the coax port.

I've simulated the results (0.5 to 3 GHz ) and have plotted Terminal Z, have introduced a variable with the formula for input impedance but none of the results seem stable at all.

I know what the impedance should be from Txline but I want to reaffirm that with EM simulations.

Any help is appreciated.
Ananth.

ananth shalom,

Why are you using driven terminal solution ? Driven Modal should work just fine for you.

Anyway, I suppose that you are using interpolating sweep. If this is the case click the options button and check the Z0 convergence checkbox

Regards,
Itai

Itai Shalom,
Thanks for the input. No particular reason for me using the driven terminal solution other than the fact that I saw it being used in an antenna simulation in one of the tutorials.

Also, I want to find the impedance of the line I'm feeding through the coax. The convergence would give me the impedance of the coax, not the line, if I'm right.

Lets say I'm feeding a 150 Ohm line with a 50 Ohm coax. How can I see the 150 Ohms characterisitc impedance of the line is my question..

By the way, thanks for the "shalom". I looked it up on the internet.. :)

Ananth.

Hey everyone,
I still haven't found a solution for the problem..
I'm sure there's got to be somebody (of all the HFSS users we've got) who knows how to do this!

Ananth.