Inset-Fed Patch Antenna Calculator

Antenna and substrate inputs

Calculation mode

Target frequency

Frequency unit

Substrate preset

Relative dielectric constant, εr

Substrate thickness

Dimension unit

Dielectric loss tangent

Conductor conductivity, S/m

Conductor thickness

Existing patch width

Existing patch length

Inset feed and impedance options

Desired feed impedance, Ω

Source impedance, Ω

Patch-edge resistance model

Manual edge resistance, Ω

Manual inset depth

Total inset opening width

Feedline length

Ground margin factor × h

Automatically calculate matched inset depth

Sweep, tolerances, and output

Sweep start

Sweep end

Sweep points

Acceptable VSWR limit

Return-loss limit, dB

Decimal places

εr tolerance, ±

Substrate tolerance, ±

Patch etching tolerance, ±

Inset tolerance, ±

Feed-width tolerance, ±

Download CSV automatically after five seconds

Formula used

Quantity	Formula
Patch width	W = c ÷ (2f_r) × √[2 ÷ (ε_r + 1)]
Effective permittivity	ε_eff = (ε_r + 1) ÷ 2 + (ε_r − 1) ÷ 2 × (1 + 12h/W)^−1/2
Length extension	ΔL/h = 0.412 × [(ε_eff + 0.3)(W/h + 0.264)] ÷ [(ε_eff − 0.258)(W/h + 0.8)]
Patch length	L = c ÷ [2f_r√ε_eff] − 2ΔL
Inset resistance	R_in(y) = R_edge cos²(πy/L)
Matched inset	y = L/π × cos⁻¹√(Z₀/R_edge)

How to use

Select design or existing-antenna analysis mode.
Enter frequency, substrate properties, and preferred units.
Choose automatic or manual patch-edge resistance.
Set feed impedance, inset options, and fabrication tolerances.
Calculate, inspect warnings, then export fabrication dimensions.
Verify the final design using simulation and measurement.

Example designs

Application	Frequency	Substrate	Typical εr	Starting thickness
Wi-Fi and Bluetooth	2.45 GHz	FR-4	4.4	1.6 mm
ISM telemetry	915 MHz	FR-4	4.4	1.6 mm
GPS L1	1.57542 GHz	RO4003C	3.55	1.524 mm
5.8 GHz ISM	5.8 GHz	RO4350B	3.48	0.762 mm

Frequently asked questions

What does an inset feed accomplish?

It moves the feed toward a lower-resistance patch location. This supports direct impedance matching without an external transformer.

Why is the patch-edge resistance estimated?

Closed-form resistance models simplify a distributed radiating structure. Simulation usually improves the final feed-position estimate.

Can this calculator replace electromagnetic simulation?

No. It supplies practical starting dimensions and sensitivity guidance.

Why can measured resonance shift?

Permittivity, etching, connectors, solder, and nearby objects alter fields. Enclosures and finite grounds also change measured performance.

Should the inset gap equal feedline width?

The opening must provide feedline clearance and manufacturable spacing. Coupling changes when side gaps become very narrow.

Which substrate is best?

Low-loss laminates improve efficiency and dimensional repeatability. FR-4 remains economical for many prototypes.

How large should the ground plane be?

A common starting margin is six substrate thicknesses. Larger grounds may improve pattern stability and matching.

Why does substrate thickness affect bandwidth?

Thicker substrates usually increase fringing and bandwidth. Excessive thickness can excite unwanted waves and radiation.

How should the prototype be tuned?

Measure S11 with a calibrated vector network analyser. Trim cautiously and document every dimensional change.

What feed connector should be used?

Choose a connector rated beyond the operating frequency. Model its launch geometry during detailed simulation.

Engineering note: These results use analytical approximations. Verify dimensions with full-wave simulation, calibrated VNA measurements, and prototype tuning before production.