Hi,

I am trying to find zin of a simple circuit using stoz function, but it does not work. However, if I use two small microstips then the results will be correct. Please see the attached schematics and results. I was wondering if any of you have any explanation for that. Thank you,

Mojtaba

I am trying to find zin of a simple circuit using stoz function, but it does not work. However, if I use two small microstips then the results will be correct. Please see the attached schematics and results. I was wondering if any of you have any explanation for that. Thank you,

Mojtaba

Z-parameters are defined with an OPEN at the other ports. This isn't a good way to measure a pure series element, because Z11 and Z22 would be a perfect open in this case. Dividing by that Z22 (infinity) gives an invalid result (zero). This explains why your Z-parameter math fails for the testcase (ideal series L).

As you have already found out, it helps to add some shunt elements, so that Z11 and Z22 are not infinite. Then, you still have some numerical noise but results start to make sense. For a real line with series L and shunt C, it should work fine.