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Grounded CPW Line Calculator
Estimate grounded coplanar waveguide impedance, effective dielectric constant, propagation delay, wavelength, and electrical length from signal width, gap, dielectric constant, and substrate height.
Input Parameters
Results
For RF layouts, combine this estimate with controlled stackup data and via-stitching rules.
Equations Used
CPW Geometry:
k = a / b, where a = W/2 and b = W/2 + gap.
Grounded Correction:
A second conformal-mapping term is added for the lower reference ground plane.
Characteristic Impedance:
Z0 is estimated from elliptic integral ratios and effective dielectric constant.
Propagation Velocity:
v = c / sqrt(εeff)
Electrical Length:
Electrical length = 360 deg × frequency × delay
Frequently Asked Questions (FAQ)
Q1: What is grounded CPW?
Grounded coplanar waveguide uses a center signal trace, adjacent top-layer ground pours, and a lower reference ground plane.
Q2: Why does gap matter so much?
A smaller gap increases capacitance and usually lowers impedance.
Q3: Is CPW more accurate than microstrip for RF?
CPW can provide better ground access and controlled return current, but it still requires stackup-specific verification.
Q4: Does via stitching matter?
Yes. Ground via spacing strongly affects real CPW performance, especially at RF and microwave frequencies.
Q5: Can this replace a field solver?
No. It is a quasi-static estimate for early design checks.
Q6: What target impedance is common?
50 ohms is common for RF feed lines, but the target depends on the system.
