Broadside coupled traces are a common technique for routing differential pair signals.

Broadside Trace Inductance Explanation

The inductance of broadside coupled traces is easy to calculate. Broadside coupled traces are on adjacent planes and the return is the same width and length of the trace. It is important to note that in industry we can find some differential pairs routed this way to achieve strong coupling but the actual return of the signal is on the power plane. This calculator is for situations where the signal return is on an adjacent trace. The geometry inputs are:

W - Trace Width

T - Trace Thickness

H - Distance between traces

L - Trace Length