HFSS: mm-Wave Finite Ground Coplanar Waveguide

Hello,

I have been trying to simulate a FG-CPW at frequencies in the mm-wave band 190-310 GHz, with the aim of determining the amount of radiation loss from the CPW transmission line. The dimensions of the CPW are w = 2 um, g = 1 um and wg = 3 um, on a 300 um thick Si substrate. The conductors are 2D sheets assigned with a PerfE boundary condition and the substrate is defined with

_R = 11.9 only (tan

= 0). There is no ground plane on the underside of the substrate and there is a radiation boundary condition on all faces of the vacuum box, spaced

/2 away from the transmission line.

I am currently using modal solution setup with a waveport (WP) excitation, but am having a bit of trouble exciting the structure. I have spent a bit of time searching forums and tutorials on how to excite a FG-CPW, but non of the recommendations are applicable. For example, the standard recommendation for the height of the WP is ~ 10*substrate height, which would result in a WP height of 3 mm, which is much greater than

/2. I have tried cutting "fingers' in the WP to ensure that the two ground planes are at the same potential, and also simulated the first five modes to determine whether the correct CPW mode is being excited.

After taking all the advice and experimenting, I'm still unsure as to whether I am exciting the transmission line correctly, therefore if anyone has any advice, it would be greatly appreciated.

If there's any other information you need, let me know. I am able to upload my HFSS file if needed.

Thank you for your time,

bazza1988

Use Driven Terminal rather than Driven Modal for your excitation... I have also attached an example file that shows several setups for various transmission lines in Driven Terminal.

Have Fun

Thank you for your reply, but I'm not sure this is what I was looking for.

I believe I have found a solution to the problem using the driven modal set-up, which involves modifying the dimensions of the port such that the waveport "see's" the three conductors and "catches" the CPW mode.

Cheers,

Bazza1988

Hello tallface65,

I saw your post in edaboard regarding finite ground CPW . I have also the same problem . I am using HFSS . I am not getting proper result. I want to simulate a W band 50 ohms CPW line. My problem is on changing the waveport size , the impedance of the CPW also changes for the fixed dimensions , so how can I exactly get the CPW dimensions for 50 ohms . My subs is er=3.38 and thickness=0.203mm.

Also I am attaching the hfss file that I made.
PLz help me in solving it


Thanx in advance