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# Transformer simulation in HFSS

#### goatmxj666

##### Member level 2
Hello,

I'm simulating a transformer right now.

When I simulated the primary and secondary inductor separately, I got an inductance value very close to the ideal value of 500pH.

However, when I stack them together and run the simulation, I got inductance values of 140pH and 180pH respectively.

How can I find the value of an inductor used in a transformer like the one shown below?

The orange layer below is the primary inductor and the green layer above is the secondary inductor.

This is my port setup. (primary ind= Port1, secondary ind= Port3)

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Solution
I think these two equations are same, but results are different.
Sure, your transformer turns are coupled and the load at the secondary will change impedance at the primary. Z11 is the input impedance with the other ports OPEN, 1/Y11 is the input impedance with the other ports SHORTED.
I got inductance values of 140pH and 180pH respectively.
What equations did you use to calculate inductance of primary/secondary?

What equations did you use to calculate inductance of primary/secondary?
I used 'im(1/Y(Diff1,Diff1))/(2*pi*freq)' equation.

I get accurate inductance when I used 'im(Z(Diff1,Diff1))/(2*pi*freq)'.

I think these two equations are same, but results are different.

Do you know the reason?

Perhaps "Mutual Inductance" is high due to tight coupling ??

### goatmxj666

Points: 2
I think these two equations are same, but results are different.
Sure, your transformer turns are coupled and the load at the secondary will change impedance at the primary. Z11 is the input impedance with the other ports OPEN, 1/Y11 is the input impedance with the other ports SHORTED.

### goatmxj666

Points: 2
Sure, your transformer turns are coupled and the load at the secondary will change impedance at the primary. Z11 is the input impedance with the other ports OPEN, 1/Y11 is the input impedance with the other ports SHORTED.
Thank you so much for your response!!

It is really helpful!