Use the effective dielectric constant for microstrip
The effective dielectric constant is what sets propagation delay and wavelength on a microstrip line. It depends on the geometry as well as the substrate material.
Effective dielectric constant
Calculate the effective dielectric constant of a microstrip line, including conductor thickness and dispersion.
Manufacturer stack-up referenceJLCPCB and PCBWay
Choose a board, check its layers, then apply the values you need. Two-layer presets use an estimated core thickness. Your browser remembers the selected board and signal layer.
If no value is shown, enter the dielectric constant agreed with your PCB manufacturer. These impedance models use a single value for Er.
Layer details
| Layer | Material | Thickness (mm) | Er |
|---|
Includes common two-layer FR-4 presets from 0.4 to 2 mm with 1 or 2 oz copper, 298 PCBWay constructions with 4 to 18 layers, and 36 JLCPCB 1.6 mm constructions with 4 or 6 layers. The JLCPCB multilayer entries use 1 oz outer copper and 0.5 oz inner copper. For other JLCPCB options, see the manufacturer’s calculator. Confirm the construction for your order. The calculations do not include solder mask or manufacturing corrections.
Result
Enter your values to calculate a result.
A microstrip field passes through both air and dielectric. The effective dielectric constant describes the combined effect. It differs from the dielectric constant of the laminate alone.
Illustration only. Not to scale.Effective dielectric constant
N/A
Characteristic impedanceN/A
Propagation delayN/A
Inductance per lengthN/A
Capacitance per lengthN/A
Method and assumptions
The result uses the Hammerstad–Jensen effective-permittivity expression with conductor-thickness correction. For microstrip, the effective dielectric constant is lower than the substrate Er because part of the field is in air.
- Frequency dispersion uses the Kirschning–Jansen model, valid for Er ≤ 20.
- Use the PCB manufacturer’s layer stack and material data for controlled-impedance work.