Language: EN
Stripline calculator
A stripline is a track on an inner layer, halfway between two ground planes. The planes shield it, so it radiates very little, which suits fast digital signals and RF routed inside the board. Change any value and the results update at once.
Results
- Characteristic impedance
- – Ω
- Effective dielectric constant
- –
- Wavelength on the line
- – mm
- Quarter wavelength
- – mm
PCB materials
Typical dielectric constants (Dk) and loss tangents (Df). For Rogers laminates, use the design Dk for impedance. For FR-4, the value depends on the glass weave, the resin and the frequency, so use the one from your PCB maker’s stackup when you have it.
| Material | Type | Dk | Df | At | Use this Dk in the calculator |
|---|---|---|---|---|---|
| FR-4 (generic) | Standard | 4.2–4.7 | 0.015–0.020 | 1 GHz | |
| Rogers RO4003C | RF | 3.38 (design 3.55) | 0.0027 | 10 GHz | |
| Rogers RO4350B | RF | 3.48 (design 3.66) | 0.0037 | 10 GHz | |
| Rogers RO3003 | RF | 3.00 | 0.0010 | 10 GHz | |
| Rogers RO3006 | RF | 6.15 (design 6.5) | 0.0020 | 10 GHz | |
| Rogers RO3010 | RF | 10.2 (design 11.2) | 0.0022 | 10 GHz | |
| Rogers RT/duroid 5880 | RF | 2.20 | 0.0009 | 10 GHz | |
| PTFE (generic) | RF | 2.1 | 0.0002–0.0005 | 1–10 GHz | |
| Polyimide (flex) | Flex | 3.2–3.5 | 0.002–0.005 | 1 kHz–1 GHz | |
| Alumina 96% | Ceramic | 9.0–9.6 | 0.0002–0.0005 | 1 MHz–10 GHz | |
| Alumina 99.6% | Ceramic | 9.7–9.9 | 0.0001–0.0002 | 1 MHz–10 GHz |
How it’s calculated
For a centred track and a copper thickness of zero, the impedance has an exact solution by conformal mapping, from S. B. Cohn, “Characteristic Impedance of the Shielded-Strip Transmission Line” (IRE Transactions on Microwave Theory and Techniques, 1954). K is the complete elliptic integral of the first kind. The field is all inside the substrate, so εeff equals εr.
k = 1 / cosh(πW / 2B)
k' = √(1 − k²)
Z0 = 30π / √εr · K(k) / K(k')
εeff = εrKeep its limits in mind.
- The copper thickness is taken as zero. Real copper lowers the impedance, more than on outer layers, because the planes are close.
- The track is taken as exactly halfway between the planes. On real stackups it often isn’t (offset stripline), which changes the impedance.
- The core and the prepreg around the track often have different Dk. Use a value between them, or the one your PCB maker gives for that layer.
- For a final design, ask your PCB maker to check the impedance with their own stackup.