Apologies for the double posting (in the Founder's Forum), but I'm having no luck getting a response to the following:

I'm looking for clarification on the defined coupling coefficients formula as described in the element help:

K=(Zoe-Zoo)/(2*Zoe*Zoo)=?=(2*Zoe*Zoo)/(Zoe+Zoo)

Also, this formula is different from the voltage coupling coefficient equation:

C=(Zoe-Zoo)/(Zoe+Zoo)

Thanks in advance.

Rocco

I'm looking for clarification on the defined coupling coefficients formula as described in the element help:

K=(Zoe-Zoo)/(2*Zoe*Zoo)=?=(2*Zoe*Zoo)/(Zoe+Zoo)

Also, this formula is different from the voltage coupling coefficient equation:

C=(Zoe-Zoo)/(Zoe+Zoo)

Thanks in advance.

Rocco

The voltage coupling coefficient C is poorly suited for extending a transmission line coupled pair to N coupled lines. Years ago Eagleware was the first software company to provide a model for N coupled lines and they used an exact wire-line equivalent formulation as indicated in the documentation. I seem to remember the proceedure for doing so is described in MYJ.

The resulting coupling coefficient K is similar to but not exactly the same as the voltage coupling coefficient C. In the first equation you repeated from the manual you missed a Zo term. The first equation from the book is

K=Zo/2*(Zoe-Zoo)/(Zoe*Zoo)

Likewise, I believe there is an error in the second formula in the documentaion. A correct alternative formula is

K=(Zoe-Zoo)/(2*Zo)

The coupling coefficient K is related to C by

K=C-(C^5)/400+(C^7)/400

This formula is essentially exact.