PCB Coplanar Waveguide Calculator

Calculator Inputs

Dimension Unit

Structure Type

Trace Width

Gap To Side Ground

Substrate Height

Copper Thickness

Dielectric Constant

Frequency GHz

Line Length

Loss Tangent

Conductivity MS/m

Target Impedance Ohms

Formula Used

The calculator uses a quasi-static coplanar waveguide model. It estimates the elliptic modulus as k = W / (W + 2S). The complementary modulus is k' = √(1 - k²). The characteristic impedance is estimated with Z₀ = 30π K(k') / [√εeff K(k)].

Finite substrate height is included with a second modulus based on hyperbolic sine terms. Copper thickness adjusts the effective trace width and gap. Propagation delay uses td = √εeff / c. Guided wavelength uses λg = c / [f√εeff]. Loss uses approximate conductor and dielectric loss terms.

How To Use This Calculator

Enter trace width, side gap, substrate height, and copper thickness using one selected dimension unit.

Choose standard coplanar waveguide or grounded coplanar waveguide. Enter dielectric constant and loss tangent from the laminate data sheet.

Add frequency, line length, copper conductivity, and target impedance. Press Calculate. The result appears above the form and below the header.

Use CSV for spreadsheets. Use PDF for quick design notes, calculation records, or layout review reports.

Example Data Table

Use Case	Width mm	Gap mm	Height mm	Er	Frequency GHz	Target Ohms
RF test trace	0.35	0.18	0.80	4.20	2.40	50
Thin laminate launch	0.20	0.12	0.30	3.66	5.80	50
Wide low loss guide	0.60	0.30	1.20	3.00	1.00	75

Advanced PCB Coplanar Waveguide Planning

A coplanar waveguide places the signal trace and ground copper on the same surface. The return path sits beside the trace. This layout is useful for RF boards, probes, antennas, filters, and fast digital launches. It gives easy access to shunt parts. It also reduces via transitions when surface ground is continuous.

What the Inputs Mean

Trace width controls capacitance and current crowding. Gap controls electric field strength between the trace and side grounds. Substrate height changes how much field enters the dielectric. Dielectric constant sets wave speed. Copper thickness changes the effective width. Frequency affects wavelength and skin depth. Loss tangent estimates dielectric loss. Conductivity estimates conductor loss.

Why the Estimate Matters

Controlled impedance keeps reflections low. It also improves matching between connectors, amplifiers, filters, and antennas. A small change in gap can shift impedance strongly. A thicker substrate can raise field spread. A higher dielectric constant usually lowers impedance and slows the signal. This calculator lets you test those changes before layout review.

Design Notes

Keep the side grounds wide and well stitched. Use many ground vias near the guide. Avoid sudden neck downs. Add tapered transitions when moving into pads. Include solder mask effects when final accuracy is critical. Fabrication tolerance should be checked with the board supplier. At microwave frequencies, roughness, plating, mask, and connector launch geometry may dominate the final result.

Using the Results

Use impedance for matching targets. Use effective dielectric for delay and wavelength. Use electrical length when building stubs, resonators, or phase sections. Use loss estimates for early budgeting. They are not a substitute for a field solver. Still, they give a fast and transparent engineering reference. Save CSV files for spreadsheets. Save PDF files for design records and review packages.

Practical Accuracy

For early work, enter nominal dimensions first. Then repeat the check with minimum and maximum fabrication limits. This shows impedance spread before ordering boards. Compare the output with your target stackup notes. For production RF work, confirm the structure with a solver and measurement coupon. Use the calculator to document assumptions, compare alternatives, and find sensitive inputs quickly. It is especially helpful during schematic and placement decisions. Small checks often prevent costly board spins.

FAQs

What is a PCB coplanar waveguide?

It is a transmission line where the signal trace and ground conductors sit on the same PCB layer. The gap between them helps set impedance.

What impedance should I target?

Many RF systems use 50 ohms. Some video, antenna, or special systems may use other targets. Always match the connected system requirement.

Does solder mask affect the result?

Yes. Solder mask can change effective dielectric constant and impedance. This calculator gives an early estimate. Use a solver for final masked designs.

Why does the gap matter so much?

The side gap controls electric field concentration. A smaller gap usually lowers impedance and increases capacitance between the trace and grounds.

What is effective dielectric constant?

It is the dielectric value seen by the wave. Fields travel partly in air and partly in laminate, so the effective value differs from Er.

Is this calculator a field solver?

No. It uses closed form approximations. It is useful for planning, comparison, and documentation. Critical RF boards need solver checks and measurement.

How should I use loss results?

Use them for early budgeting. Real loss also depends on copper roughness, plating, solder mask, connectors, launches, bends, vias, and fabrication quality.

Can I export my results?

Yes. After calculation, use the CSV button for spreadsheet work. Use the PDF button for reports, reviews, or saved design records.