Ground Coplanar Waveguide Calculator

Enter Waveguide Values

Center Trace Width

Side Gap

Substrate Height

Copper Thickness

Relative Permittivity

Loss Tangent

Frequency

Line Length

Conductor Conductivity

Copper Roughness RMS

µm

Input Power

dBm

Target Impedance

Solver Mode

Thickness Correction

Formula Used

This calculator uses a quasi-static grounded coplanar waveguide model. The center strip width is W. The side gap is S. The substrate height to the lower ground plane is H.

k = W / (W + 2S)

k1 = sinh(πW / 4H) / sinh(π(W + 2S) / 4H)

q0 = K(k) / K(k') and q1 = K(k1) / K(k1')

εeff = 1 + (εr - 1) × q1 / (q0 + q1)

Z0 = 60π / [sqrt(εeff) × (q0 + q1)]

Here K is the complete elliptic integral of the first kind. Loss values are engineering estimates. Final RF layouts should be checked with measured stackup data.

How to Use This Calculator

Enter the center trace width, side gap, substrate height, and copper thickness.
Add the dielectric constant and loss tangent from the laminate data sheet.
Set the operating frequency and line length.
Choose a solver mode if you want a target impedance estimate.
Press the calculate button. The result appears below the header and above the form.
Download the CSV or PDF file for design records.

Example Data Table

Material	εr	Height	Width	Gap	Frequency	Typical Use
FR-4 estimate	4.20	0.80 mm	1.20 mm	0.20 mm	2.40 GHz	General RF boards
Low loss laminate	3.48	0.762 mm	1.35 mm	0.25 mm	5.80 GHz	Microwave modules
Thin RF core	3.00	0.254 mm	0.45 mm	0.12 mm	10.00 GHz	Compact launches

Ground Coplanar Waveguide Guide

Why This Line Matters

A grounded coplanar waveguide is common in RF boards. It places a center trace between two side grounds. A solid reference plane also sits below the substrate. This structure gives tight field control. It also helps routing around components and vias. Designers use it for antennas, filters, mixers, and high speed modules.

Important Geometry Choices

The center width and side gap set most of the impedance. A wider trace lowers impedance. A wider gap raises impedance. Substrate height changes the pull of the bottom plane. Copper thickness also matters on real boards. Very thin gaps may be hard to etch. Very wide gaps may weaken ground coupling. Always match the calculator output with fabrication limits.

Material And Frequency Effects

Dielectric constant controls wave speed. Higher values shorten wavelength and lower impedance. Loss tangent estimates dielectric heating. Conductivity and roughness estimate conductor loss. At higher frequency, skin depth falls. Current moves near copper surfaces. Rough copper can add visible loss. These values are approximations, but they help early decisions.

Layout Practice

Keep ground vias close to the line. Use via fences near transitions and connectors. A common spacing target is below one twentieth wavelength. Avoid sudden width changes. Taper unavoidable changes slowly. Keep solder mask choices consistent. Mask can slightly shift impedance. Leave room for connector pads and launch tuning.

Using Results Wisely

The calculator gives impedance, effective permittivity, delay, wavelength, and losses. It can also solve a width or gap near a target impedance. Treat results as design guidance. Real boards vary with laminate tolerance, etching, plating, and assembly. Use field solvers for final microwave launches. Measure prototypes when the design is critical.

Practical Review

Check the table for comparable stackups. Then adjust width, gap, and height. Review electrical length before routing. Confirm loss across the real line length. Export the data for notes. Share the estimate with your board shop. Clear dimensions make production easier and reduce tuning work later.

Final Check

Common Mistakes

Do not copy values from another board without checking stackup data. Small dielectric changes move impedance. Ignore plating only for rough estimates. Confirm gap clearance near pads. Keep return paths continuous. Review manufacturing rules before ordering panels.

FAQs

What is a grounded coplanar waveguide?

It is a transmission line with a center conductor, side grounds, and a lower ground plane. It is used for controlled RF routing on printed circuit boards.

Why does the side gap matter?

The side gap controls electric field distribution. A larger gap usually raises impedance. A smaller gap usually lowers impedance and increases ground coupling.

What value should I use for dielectric constant?

Use the laminate data sheet value at the closest operating frequency. FR-4 varies widely, so measured or supplier confirmed data is better for RF work.

Does copper thickness affect impedance?

Yes. Thicker copper changes the effective trace width and gap. The effect is stronger when gaps are small or trace dimensions are very tight.

Can this replace a field solver?

No. This is an engineering estimate. Use a field solver and prototype measurements for final microwave launches, antennas, filters, or critical production designs.

Why is via fence spacing shown?

Ground via fences help connect top ground to the lower ground plane. Spacing below one twentieth guided wavelength is a common starting point.

What is effective dielectric constant?

It is the dielectric value seen by the traveling wave. Fields exist partly in air and partly in the substrate, so the value differs from εr.

Why are loss values approximate?

Loss depends on laminate quality, copper finish, roughness, plating, solder mask, and frequency. The calculator gives a useful estimate for early design comparison.