Stripline Impedance

Stripline Impedance

A stripline is a trace embedded between two ground planes (an inner layer). Because the trace is completely surrounded by the dielectric, there is no air exposure — the effective dielectric constant equals the bulk value, giving better impedance consistency than microstrip.

The IPC-2141 stripline formula:

Z₀ = (60 / √εr) × ln(4B / (0.67π × (0.8W + T)))

Where:

• εr = substrate dielectric constant
• B = total distance between the two ground planes
• W = trace width
• T = trace thickness

Striplines are preferred for:

• Differential pairs requiring tight impedance control
• EMI-sensitive signals (shielded by ground planes on both sides)
• High-frequency signals above ~1 GHz

Your Task

Implement striplineImpedance(er, B, W, T) where B, W, T are in mm, returning Z₀ in ohms.