Stripline Trace Impedance Calculator
Calculate characteristic impedance Z₀ of a stripline (embedded) trace sandwiched between two ground planes. Centered and offset variants.
How to Use
- Enter trace width W, total substrate height B (between the two ground planes), trace thickness T.
- Enter dielectric constant εr of the entire substrate.
- Result: Z₀ assuming centered trace. Use offset formula if trace is off-center.
Show Work
Formulas (IPC-2141 / Cohn)
History of Stripline
Robert Barrett at the Air Force Cambridge Research Laboratories developed stripline in 1952 under Seymour Cohn's group as a miniature microwave transmission line. Cohn's 1955 analysis derived the closed-form Z₀ equations still used today. Stripline enabled compact radar-system microwave circuitry in the Cold War era — filters, couplers, and matched amplifiers an order of magnitude smaller than their waveguide equivalents.
The stripline's "TEM mode" propagation (pure transverse electromagnetic, no longitudinal field component) is its key advantage: signals travel at a single velocity set by √εr, with no dispersion and no radiation loss. This made it the preferred technology for precision microwave passive components until surface-mount ceramic and LTCC processes caught up in the 1990s.
Modern PCB stackups on 4+ layer boards use stripline for inner-layer controlled-impedance routing — DDR4/5, PCIe Gen4+, USB4, and all high-speed digital traces above ~1 GHz benefit from stripline's lower radiated emissions and higher isolation vs. microstrip on outer layers.
About This Calculator
Enter width W, full plane-to-plane spacing B, copper thickness T, and substrate dielectric constant εr. The tool assumes centered stripline (equal dielectric above and below) using the IPC-2141 / Cohn-Wadell closed-form equation.
For offset stripline (trace closer to one plane than the other), Z₀ drops — use a field solver or the asymmetric stripline formulas. Comparison readout shows approximate microstrip Z₀ for the same geometry so you can see the ~10-15% difference. Everything runs client-side.
Frequently Asked Questions
Stripline vs microstrip?
Stripline has ground planes above AND below — better EMI shielding, constant εr throughout, but harder to inspect/probe and requires inner-layer routing.
Why lower loss?
Fields are fully contained in the substrate. No fringing to air, no radiation. Typical stripline has ~30% less loss than equivalent microstrip at GHz frequencies.
Centered vs offset?
Centered: midway between top and bottom ground. Offset (asymmetric stripline): closer to one ground. Offset has lower Z₀ for same W, higher crosstalk rejection.
Common Use Cases
RF Backplane
Inner-layer 50Ω lines in multi-GHz backplanes and server motherboards.
PCIe Gen4/5
85-100Ω diff stripline on inner layers for controlled-impedance PCIe routing.
High-Speed Clock
Stripline rejection of external EMI for low-jitter clock distribution.
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