simulating baanced transformers in AWR MWO

[Colon]

Hi,

We are having trouble simulating an imported s2p model of a balun in MWO. It seems so simple yet the simulation just doesn;t add up.

Specifically it is a minicircuits ADTL1-15-75. This is a 1:1 75 Ohm tx line transformer with the 4 port model from the manufacturer. But, we actually get the same result if we use a library ideal transformer.

If we go unbalanced-unbalanced we can correctly simulate and see 75 Ohms into both sides no problem. But, if we make the secondary balanced into two 37.5 Ohm ports it all goes wrong. You see 75 Ohms into the primary but each of the two secondary ports see 90 ohms! This is true if you replace one of the secondary ports with a resistive 37.5 Ohm termination. We even tried putting a 180 degree phase shift on one of the secondary ports. We've tried everything we can think of.

Is there something we need to do to simulate this correctly with MWO?

Thanks
James

 

[BigBoss]

You should simulate this transformer with the characteristic impedance which has been defined by manufacturer to get the same result.Otherwise,the s-parameters will be wrong.

 

[Colon]

I thought I was. 75 Ohms unbalanced in on the primary side and 75 Ohms balanced out on the secondary. 75 ohms balanced is equal to two 37.5 Ohms unbalanced outputs, a splitter. This is as intended by the manufacturer. Everything should be well matched. As I said, you can do this with an MWO ideal transformer (with no specified characteristic impedance) and get the same result.

Without this working there is no way to simulate a push pull amp effectively.

Thanks
James