Evaluate coplanar waveguide impedance from substrate and geometry. Get effective permittivity, wavelength, and propagation speed. Simple exports and examples make technical checks easier today.
| Width (mm) | Gap (mm) | Height (mm) | Thickness (mm) | Er | Freq (GHz) | Z0 (Ω) | εeff | λg (mm) |
|---|---|---|---|---|---|---|---|---|
| 1.50 | 0.20 | 1.60 | 0.035 | 4.30 | 2.40 | 49.033 | 2.559 | 78.084 |
| 2.20 | 0.25 | 0.80 | 0.018 | 3.48 | 5.80 | 56.208 | 1.945 | 37.058 |
| 0.90 | 0.15 | 0.50 | 0.018 | 2.20 | 10.00 | 69.035 | 1.500 | 24.479 |
The calculator uses a quasi static coplanar waveguide model.
1. Thickness corrected dimensions:
weff = w + Δw
seff = s - (Δw / 2)
2. Main modulus term:
k = weff / (weff + 2seff)
k′ = √(1 - k2)
3. Effective permittivity:
εeff = 1 + q(εr - 1)
q = 0.5 × [K(k1) / K(k1′)] × [K(k′) / K(k)]
4. Characteristic impedance:
Z0 = (30π / √εeff) × [K(k′) / K(k)]
5. Propagation values:
vp = c / √εeff
λg = vp / f
K() is the complete elliptic integral of the first kind.
A CPW impedance calculator helps engineers study coplanar waveguide behavior before fabrication. It estimates characteristic impedance from conductor width, slot gap, substrate height, thickness, and dielectric constant. That makes early microwave planning faster. It also reduces guesswork during board layout, antenna feeds, test fixtures, and RF transitions.
CPW lines place the signal strip and ground conductors on the same surface. Electric fields spread through air and substrate together. Because of that, geometry strongly changes impedance and effective permittivity. A wider center strip usually lowers impedance. A larger slot usually raises impedance. Substrate properties also shift phase velocity and guided wavelength.
This calculator reports characteristic impedance, effective permittivity, phase velocity, and guided wavelength. Those outputs help compare target designs against common system values such as 50 ohms or 75 ohms. They also help when checking whether a trace is electrically short or long at a selected frequency.
The model uses standard quasi static coplanar waveguide relations with complete elliptic integrals. First, the tool builds modulus terms from corrected width and gap values. Next, it estimates the field filling factor inside the dielectric. Then it computes effective permittivity. Finally, it derives impedance from the elliptic integral ratio and uses frequency to estimate guided wavelength.
Real structures can differ from theory. Solder mask, metal roughness, conductor loss, finite ground width, enclosure effects, and nearby parts can shift the final result. Very high frequencies also increase sensitivity to manufacturing tolerance. That is why a fast CPW impedance estimate should guide layout choices, but not replace field solver validation for critical hardware.
Use this tool during concept design, stackup review, and design optimization. It is useful for RF boards, sensors, resonators, measurement coupons, and communication hardware. You can test several width and gap combinations quickly, export results, and compare examples. That improves trace planning and supports cleaner impedance control decisions during daily engineering work.
CPW impedance is the characteristic impedance of a coplanar waveguide. It describes how voltage and current travel along the line. Designers usually target a standard value, such as 50 ohms, for matching and low reflection.
The center strip width and slot gap shape the electric field. A wider strip usually lowers impedance. A wider gap usually raises impedance. Small geometry changes can shift results noticeably at microwave frequencies.
The dielectric constant changes how strongly the substrate stores electric energy. Higher relative permittivity usually lowers phase velocity and guided wavelength. It also changes effective permittivity, which affects impedance calculations.
In this quasi static model, frequency mainly affects guided wavelength. The characteristic impedance is driven mostly by geometry and material values. Real high frequency dispersion can add small differences in practical structures.
Yes. This calculator applies a simple thickness correction before the main CPW equations. That gives a more realistic estimate than a zero thickness assumption, especially when copper thickness is not negligible.
Use it for fast planning, comparison, and review. Final release work should still be checked against fabrication limits, stackup data, and an electromagnetic solver when the design is highly sensitive.
You can enter dimensions in meters, centimeters, millimeters, micrometers, or mils. Frequency can be entered in hertz, kilohertz, megahertz, or gigahertz. The calculator converts values internally to SI units.
Exports help document assumptions, compare iterations, and share quick reports. CSV works well for spreadsheets. PDF is useful for reviews, handoff notes, and keeping a simple record of a chosen CPW geometry.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.