Re: Asymmetric Stripline / Microstrip online calculators for impedance and velocity

On 5/20/2025 11:38 AM, Joe Gwinn wrote:

On Tue, 20 May 2025 11:20:05 -0400, bitrex <user@example.net> wrote:
 

On 5/20/2025 11:15 AM, bitrex wrote:

On 5/20/2025 11:00 AM, Mike Perkins wrote:

On 20/05/2025 15:56, bitrex wrote:

On 5/20/2025 10:06 AM, Mike Perkins wrote:

On 20/05/2025 14:53, Mike Perkins wrote:

>
I can find numerous calculators that provide impedance for the
above structures, but are there any that give propagation velocity
too?

>
After numerous failed searches I found:
   https://www.multekpcb.com/calculators/
>

>
I think the stripline would have to be pretty far off-center for the
phase velocity to be much different than c/sqrt(Er); in pen-and-paper
analysis to derive the relatively simple equations for characteristic
impedance, the dominant propagation mode is considered to be TEM.
>
If the geometry is so screwy that it can't be well-approximated by
TEM the characteristic impedance equation is wrong, also.
>
I don't know what "asymmetric microstrip" is..?

>
I would hope the calculators cope with standard Stripline and Microstrip.
>
>
I just needed details for Asymmetric Stripline and standard Microstrip.
>
>

>
In the asymmetric stripline calculator you posted the propagation delay
is calculated from the relative permittivity of the substrate alone,
just so you know it's not returning anything different for that than the
standard one.

>
IOW the phase velocity of the TEM mode is taken as a given to develop
the pen-and-paper equations for the capacitance, and and thereby the
characteristic impedance of both the symmetric and asymmetric stripline.

 It's not just the relative permittivity of the substrate, as part of
the EM field is in air.  In some designs this is small enough to
ignore the air part, but this must be determined, not just assumed.
 Joe

The model of stripline amenable to pen-and-paper calculation has a conductor floating between two ground planes on the z axis, and dielectric to infinity in the xy plane, there's no field in the air in that model.
The microstrip model has field in air and is only quasi-TEM but they're not the same thing. What the hell is a "asymmetric microstrip" anyway?!
Not sure what y'all think these online calculators are doing. They're just automating the kind of pen-and-paper derived equations you can find in the textbooks, which make a number of assumptions to make the problem tractable to closed-form analysis.