# Characteristic impedance from HFSS

1. ## Characteristic impedance from HFSS

hi all,

how can i get the characteristic impedance of a differential line/ differential via from HFSS. Z11 parameter gives you open circuit input impedance. Zot shows the port's terminal impedances.

Or should i have to run two simulations for two models (one with open circuited traces and other with both the traces shorted together) to get Zoc and Zsc. From that i can get Zo=sqrt(Zoc/Zsc).

i did run these simulations and the differential characteristic impedances for differential traces were obtained correctly. :D But i know there should be some other method to obtain characteristic impedance from models easily.

Correct me if i am wrong! Not so conversant with impedances. Any books on this??

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2. ## Re: Characteristic impedance from HFSS

Originally Posted by hardyethan
hi all,

how can i get the characteristic impedance of a differential line/ differential via from HFSS. Z11 parameter gives you open circuit input impedance. Zot shows the port's terminal impedances.

Or should i have to run two simulations for two models (one with open circuited traces and other with both the traces shorted together) to get Zoc and Zsc. From that i can get Zo=sqrt(Zoc/Zsc).

i did run these simulations and the differential characteristic impedances for differential traces were obtained correctly. :D But i know there should be some other method to obtain characteristic impedance from models easily.

Correct me if i am wrong! Not so conversant with impedances. Any books on this??
The easiest way to find Impedance of tranmission line is just define port and calculate port only solution, imho. HFSS will give you the answer as Z0 value in Matrix Data
The Impedance will be equal (in general case) to a relation between maximums of tangential components of E and H fields along any line in z direction.

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