I am simulating a coupled line in momentum and I dont know how to compute the even mode and odd mode impedances.

The structure consists of a simple pair of coupled lines.

For the even mode impedance computation, I set up the ports on each side as common mode ports with 50 ohms impedance and the association is the port below/above it.

I looked at the input impedance and the answer is far off from the required answer.

Same situation with odd mode using differential ports.

Please help me.

The structure consists of a simple pair of coupled lines.

For the even mode impedance computation, I set up the ports on each side as common mode ports with 50 ohms impedance and the association is the port below/above it.

I looked at the input impedance and the answer is far off from the required answer.

Same situation with odd mode using differential ports.

Please help me.

Zodd = [det(Z)*(Z11+Z22-Z12-Z21)]/(sqr(Z11)+sqr(Z22)-sqr(Z12)-sqr(Z21))

Zeven = det(Z) / (Z11+Z22-Z21-Z12)

with:

det(Z) = determinant of the Z-matrix = Z11*Z22-Z21*Z12

sqr = square

The common mode impedance Zcm = Zeven/2

and the differential mode impedance Zd = 2 Zodd

In the symmetric case, like your example below, we have

Z11=Z22 and Z12=Z21.

The formulas become:

Zodd= Z11-Z12

Zeven= (Z11+Z12)/2

Zdm = 2 * (Z11-Z12)

Zcm = (Z11+Z12)/4

These formulas are based on voltage and current

laws in microstrip conductors, they are NOT valid

for slotlines. In slotlines the following formulas

hold:

Zodd=det(Z)/(Z11+Z22+Z12+Z21)

Zeven = [det(Z)*(Z11+Z22+Z12+Z21]/[sqr(Z11)+sqr(Z22)-sqr(Z12)-sqr(Z21)]