Re: transmission line z

On Sun, 08 Jun 2025 07:58:14 -0700, john larkin <jl@glen--canyon.com>
wrote:

Suppose you have a slab of FR4 with copper on both sides, standard
ebay stuff. Now shear off a long thin slice. That's a balanced
transmission line.
>
air
__________________ copper
.........................................fr4
__________________ copper
>
air
>
>
>
What's that called?
>
Does anyone know of a calculator that handles this case?

It's just a parallel plate waveguide.

For the TEM mode Z0 = 377*sqrt(ur/er)*(d/w). 

ur/er - substrate permeability/permittivity (relative)
d - dist between copper
w - width copper strip

Formulas for the higher modes also exist.

But I'd have to look them up.