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Main >> Applications >> Sample problems

Microstrip crossover - QuickField simulation example

Mutual capacitance between crossing microstrip traces, quantifying the parasitic capacitive coupling that contributes to high-frequency crosstalk.

Engineering question

How to calculate mutual capacitance in a microstrip crossover?

Answer
Apply opposite potentials to the crossing traces in a 3D electrostatic model and determine their mutual capacitance from the calculated charge.

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Typical applications
PCB microstrip crossovers, multilayer PCB crossings, signal routing crossovers

Microstrip crossover

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Simulation problem

Problem Type electrostatics.

Geometry 3D extrusion.
microstrip crossover model

Equivalent electric circuit:
microstrip crossover circuit

Given
Relative permittivity of air ε = 1,
Relative permittivity of substrate ε = 10,
Strip1 potential U1 = -0.5 V,
Strip2 potential U2 = +0.5 V.

Task
Find the mutual capacitance between strips C12.

Solution
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).

Results
The measured charge q = 1.76e-12 C.
The capacitance is C12 = 1.76e-12 / (0.5 - (-0.5)) = 1.76e-12 F.
microstrip crossover simulation

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