Calculate trace impedance for microstrip, stripline, and coplanar waveguide structures using IPC-2141 / Wadell formulas.
Trace impedance is the characteristic impedance of a PCB transmission line, determined by the trace geometry (width, thickness), dielectric material properties, and layer stackup. Controlled impedance is critical for high-speed digital signals (USB, DDR, PCIe, Ethernet) and RF circuits to minimize reflections and signal integrity issues.
A microstrip is a trace on an outer layer with a ground plane below. It's the most common transmission line type, easy to manufacture, but has higher radiation loss at high frequencies.
A stripline is a trace embedded between two ground planes inside the PCB. It offers better shielding and lower crosstalk than microstrip, but is harder to achieve exact impedance.
A grounded coplanar waveguide (GCPW) has a signal trace with ground planes on both sides on the same layer, plus a ground plane below. It offers excellent high-frequency performance and is widely used in RF/microwave designs.
1. Select the transmission line structure type.
2. Enter trace width (W), thickness (T), dielectric height (H), and dielectric constant (εr).
3. For differential or GCPW, enter the spacing (S).
4. Optionally enter frequency for loss estimation.
5. Results update in real-time as you type.
Microstrip uses the Hammerstad-Jensen model. Stripline uses the Wadell formula. GCPW uses conformal mapping with the Hilberg approximation for elliptic integrals. All are standard IPC-2141 methods.
For typical PCB geometries, accuracy is within 2-5% of full-wave electromagnetic simulations. For critical designs, verify with your PCB manufacturer's impedance modeling tools.
Standard FR-4 has εr ≈ 4.2-4.5 at 1 GHz. The value decreases slightly at higher frequencies. Use your laminate vendor's datasheet for best accuracy.
It depends on your stackup. For a typical 4-layer FR-4 board with 0.2mm dielectric, roughly 0.3mm trace width gives ~50Ω microstrip. Use this calculator with your exact stackup parameters.
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