Language: EN
Microstrip calculator
A microstrip is a track on an outer layer with a ground plane underneath, the most common controlled-impedance line on a PCB. 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
The calculator uses the closed-form formulas from E. Hammerstad and Ø. Jensen, “Accurate Models for Microstrip Computer-Aided Design” (IEEE MTT-S International Microwave Symposium, 1980). η0 is the impedance of free space, about 376.73 Ω.
u = W / H
a = 1 + ln((u⁴ + (u/52)²) / (u⁴ + 0.432)) / 49 + ln(1 + (u/18.1)³) / 18.7
b = 0.564 · ((εr − 0.9) / (εr + 3))^0.053
εeff = (εr + 1)/2 + (εr − 1)/2 · (1 + 10/u)^(−a·b)
f(u) = 6 + (2π − 6) · exp(−(30.666 / u)^0.7528)
Z0 = η0 / (2π · √εeff) · ln(f(u)/u + √(1 + (2/u)²))Keep its limits in mind.
- The copper thickness is taken as zero. Real copper lowers the impedance a little.
- It’s quasi-static, without dispersion. At several GHz the effective dielectric constant rises slowly with frequency.
- Solder mask over the track lowers the impedance by a few percent. Losses and copper roughness aren’t included.
- For a final design, ask your PCB maker to check the impedance with their own stackup.