Slow wave line simulation in HFSS/Sonnet/Momentum

Hi all,

I have couple of questions regarding slow wave line and simulating them in EM simulators.
From most papers I understand that the floating strips are always kept as near as possible.

I want to simulate the following in HFSS or sonnet or momentum:

1. A grounded CPW structure and would like to see the effect of the width of the floating strips and the spacing between the strips and its impact on the slowing effect.


Some kind of screenshot for the setup would be very helpful. I hope the experts here can help me in this.

Cheers!
Neel

The slowing effect is due to the dielectric constant. For quasi-TEM like CPW, CPWG, microstrip, the nonisotropic medium (fields partly in air, partly in dielectric) can be approximated or simplified as an isotropic medium with an effective dielectric constant. The effective dielectric constant will be somewhere between the values for air and the dielectric constant of the substrate. Wider lines will contain more of the fields in the substrate so the effective dielectric will get closer to the dielectric constant of the substrate and the wave will be slower. The spacing and widths of the lines generally need to be set at values that will achieve the desired impedance and not necesarily "as close as possible".

Thanks for your inputs. When you say "The spacing and widths of the lines generally need to be set at values that will achieve the desired impedance and not necesarily "as close as possible".". I can imagine the impedance would depend on the width but will the spacing of the floating strips have an impact on the impedance. I thought it will impact more on the wave speed. Do you have some idea on how to simulate it in HFSS? I would like to sweep the width and spacing of the floating strips. Even some inputs in Sonnet or momentum will help?

HFSS comes with some examples. Go to File->open examples->Transmission lines->coplanar_wg_w_ground.hfss also look up the help topic under examples and go through the tutorial. Should get you started.

I think redintransit is talking about effective permittivity in microstrip lines, and not about slow wave lines?

Many years ago, I had supported a customer with simulating slow wave lines in Sonnet. Maybe the attached document helps to get started.