Patch antenna input form
This tool targets a rectangular microstrip patch operating in the TM10 mode. It gives fast design dimensions for early engineering evaluation.
Formula used
1) Patch width
W = c / (2fr) × √[2 / (εr + 1)]
2) Effective dielectric constant
εeff = (εr + 1)/2 + (εr - 1)/2 × (1 + 12h/W)-1/2
3) Fringing extension
ΔL/h = 0.412 × [(εeff + 0.3)(W/h + 0.264)] / [(εeff - 0.258)(W/h + 0.8)]
4) Effective and actual patch length
Leff = c / [2fr√εeff]
L = Leff - 2ΔL
5) Ground plane estimates
Wg = W + 2Nh
Lg = L + 2Nh
6) Inset feed estimate
y0 = (L/π) × cos-1√(Rtarget / Redge)
These equations are standard first-pass rectangular microstrip patch relations. Final products should still be tuned in a full-wave simulator and validated against fabrication limits.
How to use this calculator
Step 1
Enter the target resonant frequency and choose GHz or MHz. Use the same frequency intended for your antenna operating band.
Step 2
Enter the substrate dielectric constant and substrate height. These values strongly affect patch size, fringing fields, and feed behavior.
Step 3
Set a target feed impedance, usually 50 Ω. Then provide an estimated edge impedance for the inset-feed approximation.
Step 4
Choose the ground extension factor per side. A value of 3 gives the common quick estimate of adding 6h overall.
Step 5
Submit the form. Review the dimensions above the form, inspect the chart, and export the table as CSV or PDF.
Example data table
These examples are illustrative first-pass values generated from the same design equations used by this page.
| Case | Frequency | εr | h (mm) | Width (mm) | Length (mm) | Ground Width (mm) | Ground Length (mm) |
|---|---|---|---|---|---|---|---|
| Wi-Fi patch on FR4 | 2.4 GHz | 4.4 | 1.6 | 38.01 | 29.42 | 47.61 | 39.02 |
| 5.8 GHz low-loss board | 5.8 GHz | 2.2 | 1.6 | 20.43 | 16.47 | 30.03 | 26.07 |
| GNSS style substrate | 1.575 GHz | 2.2 | 3.2 | 75.24 | 62.50 | 94.44 | 81.70 |
Frequently asked questions
1) What does this calculator estimate?
It estimates the key first-pass dimensions of a rectangular microstrip patch antenna, including patch width, patch length, effective length, ground plane size, and a basic inset feed position.
2) Why is effective dielectric constant lower than εr?
Patch fields do not stay fully inside the substrate. Some fringing fields travel in air, so the effective dielectric constant becomes lower than the actual substrate dielectric constant.
3) Why does substrate height matter so much?
Substrate height changes fringing, impedance behavior, bandwidth trends, and physical size corrections. A thicker substrate often changes the required length and the ground dimensions noticeably.
4) Is the inset feed result exact?
No. It is an engineering estimate based on a simplified resistance model. Use it as a starting point, then refine the feed with simulation, measurement, and fabrication-aware tuning.
5) Can I use this for circular or slot patches?
No. This page is designed for a rectangular microstrip patch in the dominant mode. Other geometries need different field models and different design equations.
6) Does the calculator include losses and full-wave coupling?
Not fully. It focuses on geometric design equations. Radiation efficiency, surface waves, conductor losses, and nearby structures still require electromagnetic simulation or measurement.
7) What edge impedance should I enter?
Use a reasonable design estimate from your reference method, prior build, or simulator. Many early designs start around a few hundred ohms, then adjust after refinement.
8) What should I verify before manufacturing?
Check board tolerance, copper thickness, connector placement, feed geometry, finite ground effects, enclosure detuning, and the final resonant frequency after full-wave simulation.