Stripline Impedance Calculator
Calculate the characteristic impedance, propagation velocity, delay and wavelength of a symmetric stripline using standard stripline equations.
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Math
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Related
Enter parameters and click Calculate to view results
Formula & Theory
Z₀ = (30pi / √epsilon r) / (w/b + 0.441) for w/b ≤ 0.35This formula is used to calculate antenna parameters for stripline impedance calculator.
Overview
The Stripline Impedance Calculator computes the characteristic impedance, propagation velocity, delay, and guided wavelength of a symmetric stripline PCB trace — a copper trace sandwiched between two ground planes, fully enclosed within the dielectric. Enter the dielectric height from the trace to each ground plane, trace width, copper thickness, relative permittivity (epsilon r) of the PCB substrate, and operating frequency, and the calculator returns the characteristic impedance in ohms along with the effective trace width, width-to-height ratio, velocity factor, propagation velocity, propagation delay per meter, and guided wavelength. This is essential for PCB designers and RF/microwave engineers laying out controlled-impedance traces for high-speed digital signals, RF signal routing, and any board where matching a specific impedance (commonly 50 ohms single-ended or 100 ohms differential) is critical to signal integrity.
Input Guide
Enter Dielectric Height to Each Ground Plane exactly as shown on the calculator. Confirm every unit, selected option, and decimal position before calculating so the stripline impedance result matches the intended transmission lines design case.
Output Guide
The output section reports Characteristic Impedance, Effective Trace Width, Width / Height Ratio (w/b), Velocity Factor, Propagation Velocity, Propagation Delay, Guided Wavelength for the values you entered. Use these values as design targets, then compare them with available space, component limits, feed system behavior, installation environment, and measured performance before finalizing the design.
How This Calculator Works
The Stripline Impedance applies Z₀ = (30pi / √epsilon r) / (w/b + 0.441) for w/b ≤ 0.35 to the entered values. Calculate the characteristic impedance, propagation velocity, delay and wavelength of a symmetric stripline using standard stripline equations. Use the result as a first-pass transmission lines target, then validate it against losses, tolerances, mounting, nearby conductors, feed-line effects, and measurement conditions.
Design Notes
Stripline differs from microstrip in that the signal trace is fully enclosed between two ground planes rather than exposed on the board's outer surface, which shields it from external interference and gives it a more uniform, dispersion-free electromagnetic environment — at the cost of requiring an internal PCB layer and making the trace harder to probe or modify after fabrication. This calculator uses the standard closed-form stripline impedance equations (Z₀ = (30pi / √epsilon r) / (w/b + 0.441) for narrow traces where w/b ≤ 0.35, switching to a different formula for wider traces), where b is the total dielectric thickness between the two ground planes and w/b is the trace's width-to-height ratio — a key design variable, since narrower traces relative to the dielectric spacing produce higher impedance, and wider traces produce lower impedance. Because the signal is symmetric between two ground planes, stripline propagation velocity depends only on the dielectric constant (v = c / √epsilon r) and is independent of trace width, unlike microstrip where the effective dielectric constant is a mix of substrate and air.
Build and Tuning Notes
Use the calculated trace width as a starting point for your PCB stackup, then verify the result against your fabricator's actual dielectric constant and layer thickness tolerances, since epsilon r and copper thickness can vary meaningfully between PCB manufacturers and material lots, directly shifting the achieved impedance from the calculated target. For controlled-impedance boards, always confirm your fabricator's capabilities and request impedance verification (typically via TDR testing) on production boards, since stripline impedance is sensitive to small manufacturing variations in dielectric thickness and etching tolerance on the trace width. When routing differential pairs or matched-length RF traces in stripline, also account for the calculated propagation delay per meter to maintain proper timing and phase alignment between parallel traces, since even small length mismatches translate into timing skew or phase error at high frequencies.
Inputs used by this calculator
- Dielectric Height to Each Ground Plane — use mm.
- Trace Width — use mm.
- Copper Thickness — use mm.
- Relative Permittivity (epsilon r).
- Frequency — use MHz.
Frequently Asked Questions
How do I calculate stripline characteristic impedance?
Stripline characteristic impedance is calculated from the trace width, total dielectric thickness between the two ground planes, and the substrate's relative permittivity, using the standard formula Z₀ = (30pi / √epsilon r) / (w/b + 0.441) for narrow traces (w/b ≤ 0.35). This calculator applies the correct formula automatically based on your entered dimensions.
What is the difference between stripline and microstrip?
Stripline is a fully enclosed trace sandwiched between two internal ground planes, while microstrip is an exposed trace on the outer layer of a PCB with a ground plane only on one side. Stripline offers better shielding and more uniform propagation characteristics, while microstrip is easier to fabricate, probe, and modify.
What impedance is typically targeted for PCB traces?
50 ohms single-ended impedance is the most common target for RF and high-speed digital signal traces, while 100 ohms differential impedance is standard for differential pair signaling such as USB, Ethernet, and high-speed serial links, though the target depends on your specific interface and design requirements.
How does trace width affect stripline impedance?
Wider traces relative to the dielectric spacing between ground planes produce lower characteristic impedance, while narrower traces produce higher impedance. This inverse relationship means impedance can be tuned by adjusting trace width for a given PCB stackup and dielectric material.
Why is stripline propagation velocity independent of trace width?
Because a stripline trace is fully surrounded by a uniform dielectric material between two ground planes, its propagation velocity depends only on the substrate's relative permittivity (v = c / √epsilon r), unlike microstrip where the effective dielectric constant is a mix of the substrate and the air above the exposed trace.
Why might my fabricated PCB trace not match the calculated impedance?
Actual dielectric constant, copper thickness, and etching tolerances can vary between PCB manufacturers and material batches, causing the fabricated trace's real impedance to deviate from the calculated target. Controlled-impedance boards should be verified with TDR testing, and design margins should account for your fabricator's stated tolerances.
Alex Warren
B.Sc. in Electrical & Electronic Engineering (EEE)
Alex specialises in antenna design and wave propagation. His expertise helps ensure these calculators present practical RF concepts, useful design estimates, and clear engineering guidance for students, HAM operators, and wireless professionals.