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# calculate single-sided PCB transmission line impedance?

J

#### Joop

Jan 1, 1970
0
I wondered if trace on a single sided PCB could be optimised to
resemble a 50 ohm transmission line. It will be enclosed largely
between ground areas.

But looking around on the web I have so far only found dual layer
calculators for microstrip or striplines with ground planes.

Does anybody know some calculator, reading material or an simply
example?

Cheers,

Joop

A

#### [email protected]

Jan 1, 1970
0
I wondered if trace on a single sided PCB could be optimised to
resemble a 50 ohm transmission line. It will be enclosed largely
between ground areas.

But looking around on the web I have so far only found dual layer
calculators for microstrip or striplines with ground planes.

Does anybody know some calculator, reading material or an simply
example?

Cheers,

Joop

Hello,
What you want is a co-planar waveguide.
http://www.maxim-ic.com/appnotes.cfm/an_pk/2093

Download the milmega RF calculator, it has a line calculator.

H

#### Helmut Sennewald

Jan 1, 1970
0
Joop said:
I wondered if trace on a single sided PCB could be optimised to
resemble a 50 ohm transmission line. It will be enclosed largely
between ground areas.

But looking around on the web I have so far only found dual layer
calculators for microstrip or striplines with ground planes.

Does anybody know some calculator, reading material or an simply
example?

Cheers,

Joop

Hello Joop,

The program TXLINE can calculate the impedance for a CPW with
or without a ground plane.

I just tried the TXLINE-program for CPW with FR4(Er=4.5).
Z=50 Ohm, no ground plane
W=2mm, gap=0.25mm
Z=50 Ohm, no ground plane
W=3mm, gap=0.35mm

Best regards,
Helmut

CPW=Coplanar Waveguide

J

#### John Larkin

Jan 1, 1970
0
Hello Joop,

The program TXLINE can calculate the impedance for a CPW with
or without a ground plane.

I just tried the TXLINE-program for CPW with FR4(Er=4.5).
Z=50 Ohm, no ground plane
W=2mm, gap=0.25mm
Z=50 Ohm, no ground plane
W=3mm, gap=0.35mm

Best regards,
Helmut

CPW=Coplanar Waveguide

Appcad will also do cpw, with and without flip-side ground plane.

Increasing the gap eventually produces the single trace, single-sided
board case. In older versions of Appcad, as the gap increased the
impedance started going back *down*, but they've fixed that.

Lots of formulas and many programs produce goofy numbers when the
situation deviates from their sweet spot. Negative impedances are a
dead giveaway that something isn't right.

John

J

#### Joop

Jan 1, 1970
0
Hello Joop,

The program TXLINE can calculate the impedance for a CPW with
or without a ground plane.

I just tried the TXLINE-program for CPW with FR4(Er=4.5).
Z=50 Ohm, no ground plane
W=2mm, gap=0.25mm
Z=50 Ohm, no ground plane
W=3mm, gap=0.35mm

Best regards,
Helmut

CPW=Coplanar Waveguide
Thanks, at least I know the right terminology now.
Always nice to be buzzword compliant ;-)

While trying TXLINE I quickly get an error that the substrate height H
should be > 2(w+2g).
Your values only can be reached with super thick PCB material (6mm or
so). What did you specify to get to these numbers? Perhaps I am not
operating the program right.

Joop

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