Microstrip Impedance Calculator

This calculator determines the characteristic impedance of a microstrip transmission line based on its width, height, and dielectric constant. It’s useful for designing PCB traces that match specific impedance values.

Formulas

When (W/H) < 1:

ε_e = (ε_r + 1)/2 + (ε_r – 1)/2 × [1/√(1 + 12 × (H/W)) + 0.4 × (1 – W/H)²]

Z₀ = (60 / √ε_e) × ln(8 × (H/W) + 0.25 × (W/H))

When (W/H) ≥ 1:

ε_e = (ε_r + 1)/2 + (ε_r – 1)/2 × [1/√(1 + 12 × (H/W))]

Z₀ = 120π / [√ε_e × ((W/H) + 1.393 + (2/3) × ln(W/H + 1.444))]

Formula Explanation

• W = width of the microstrip conductor.
• H = height of the dielectric substrate.
• ε_r = dielectric constant of the substrate.
• ε_e = effective dielectric constant.
• Z₀ = characteristic impedance.

Example

Input: W = 2 mm, H = 1 mm, ε_r = 4.5

Result: Z₀ ≈ 52.8 Ω

Who uses it

Helpful for PCB designers and RF engineers ensuring proper impedance matching in high-frequency circuits.