Two-wire balanced TL characteristic impedance calculator

The calculation is by the following equation

Quite often on the internet you can find calculators of a two-wire balanced TL using a simplified calculation formula:This formula is a simplification of the first part of the first formula. If D is much greater than d, then the unit under the square root can be neglected and we arrive at the second formula. However, with this simplification, the calculation error will be no worse than 1% only for lines with a characteristic impedance of at least 300 Ohm. For TL with a small gap g, calculators based on this simplified formula give an incorrect result. Why it was so simplified - it is not clear. Perhaps it stretches back from the era of slide rules.

This calculation (as well as the calculation of many other RF TL) is implemented in our Android app "Characteristic impedance", which you can download by clicking or scanning the QR code below. The app allows you to get additional parameters of a TL.

Related links:

• Parallel Circular Conductor Transmission Line Calculator by Serge Y. Stroobandt, ON4AA, the calculator uses the same formula and allows you to reverse the calculation;