Calculating Capacitance of overlapped transmission lines in Sonnet

Hi guys

New here, and new to circuit simulations. Just jumped fields so taking some time to get up to speed.

I'm currently attempting to pull capacitance in Sonnet for a microstrip transmission line with ports 1 to 2, with a 3rd port with a second transmission line
capacitively coupled using a dielectric brick and an edge via to overlap the first transmission line.

I've run simulations with a capacitive overlap between 2 ports to obtain the capacitance using Sonnets equation:

C1=1.0E12/(2*_PI*_FREQ*(1/Y11))

is it a case of the same but between ports 3 and 1:

C2=1.0E12/(2*_PI*_FREQ*(1/Y31))

I'm unsure with respect to a 3 port system if this is correct or if there are any factors I haven't considered.

Any advice would be appreciated, project file included.

Thanks

Ben

Hi Ben,

when I look at your model in Sonnet Lite, I see no reference planes, so all the feedline is included in results. Is this on purpose?

Your equation with Y31 looks wrong to me here, because using Y31 implies that port 2 is shorted to ground. Why do you simulate this with 3 ports, and don't simplify to 2 ports?

Best regards
Volker

Hi Volker

I have been switching between reference/no-reference. You're right, purely for this purpose I should add reference planes.

I'll simplify the model and see how I get on.

Thanks you for the advice.

Ben