ImpedCalc is a free transmission line impedance calculator. The result is based on formula not 2D field solve, so it can only confirm the accuracy in a relatively range.

Accuracy evaluation
Surface Microstripe
when H=4.5,T=1.2,Er=4.2 and change W. The result is compared with Polar. Surface Mircostrip of ImpedCalc is relatively accurate.

Symmetric Stripline
When H=8 and H =12 while keep T=1.2,Er=4.2 and change W.

The license of this software is Free, you can free download and free use this calculator software.