Stripline Impedance

Formula

Description

A stripline is a transmission line embedded between two ground planes inside the PCB stackup. Unlike microstrip which has dielectric on one side and air on the other, stripline is fully surrounded by dielectric, resulting in a homogeneous propagation medium with well-controlled impedance and lower radiation. Stripline impedance depends on the dielectric constant, the distance between ground planes, and the trace geometry. Stripline routing is preferred for sensitive high-speed signals because the ground planes provide excellent shielding from external noise and minimize crosstalk.

Variables

• Z0 — Characteristic impedance (Ω)
• εr — Relative dielectric constant
• h — Total distance between ground planes (mm)
• w — Trace width (mm)
• t — Copper thickness (mm)

Practical Notes

Stripline has about 40% lower propagation velocity than microstrip due to being fully immersed in dielectric. For FR-4 with εr = 4.2, a 50Ω stripline requires a wider trace than a 50Ω microstrip for the same dielectric thickness. Dual stripline uses two signal layers between three ground planes to increase routing density. Consult your PCB fab stackup data for accurate εr values.