Crossovers in the digital circuit design cause parasitic capacitance, resulting in high frequency cross talk.
3D problem of electrostatics.
Equivalent electric circuit:
Relative permittivity of air ε = 1,
Relative permittivity of substrate ε = 10,
Strip1 potential U1 = -0.5 V,
Strip2 potential U2 = +0.5 V.
Find the mutual capacitance between strips C12.
To find the mutual capacitances C12 we should switch off all voltage sources and apply opposite potentials on stip1 and stip2.
QuickField simulation gives charge q distribution. The capacitance then can be calculated as C = q / (U2 - U1).
The measured charge q = 1.76e-12 C.
The capacitance is C12 = 1.76e-12 / (0.5 - (-0.5)) = 1.76e-12 F.
See the microstrip_crossover.pbm problem in the Examples folder.