Microstrip Impedance Calculator

The characteristic impedance (Z₀) of a microstrip transmission line is primarily determined by its physical dimensions (trace width W, dielectric height H, copper thickness T) and the dielectric constant (εr) of the substrate material.

This calculator uses approximations common in the industry. One set of widely used formulas is from Wheeler, or more refined versions by Hammerstad and Jensen. These involve calculating an effective dielectric constant (ε_eff) which accounts for the fact that some of the electromagnetic field lines exist in the air above the trace and some in the dielectric.

For W/H ≤ 1 (narrow traces):

Z₀ ≈ (60 / √εeff) * ln(8H/W' + W'/4H)

For W/H > 1 (wide traces):

Z₀ ≈ (120π / √εeff) / (W'/H + 1.393 + 0.667 * ln(W'/H + 1.444))

Where W' is an effective trace width that accounts for the copper thickness T:

W' = W + (T/π) * (1 + ln(2H/T)) (approximation)

And the effective dielectric constant ε_eff is approximately:

εeff ≈ (εr + 1)/2 + ((εr - 1)/2) * (1 / √(1 + 12H/W))

Note: These are simplified representations. The actual implementation in the calculator might use more detailed or slightly different variations of these formulas for improved accuracy across a wider range of W/H ratios and to account for thickness. Always verify with a more advanced field solver for critical designs.