Rectangular Microstrip Patch Antenna Calculator
Use this tool to estimate the core dimensions of a rectangular patch antenna for a target resonance frequency. Values are based on common closed-form design equations used for initial PCB antenna sizing.
What this patch antenna calculator does
This calculator helps you quickly size a rectangular microstrip patch antenna. You enter operating frequency, dielectric constant, and substrate thickness, and it returns key layout values including patch width, patch length, effective dielectric constant, fringing extension, and suggested ground plane dimensions.
It also estimates an inset feed location when you supply a target impedance (typically 50 Ω) and an assumed edge resistance. This gives you a practical starting point before electromagnetic simulation and lab tuning.
Equations used in the calculator
These are the classic first-pass equations for a rectangular patch in the fundamental TM10 mode:
Patch width: W = c / (2f) · √(2 / (εr + 1))
Effective permittivity: εeff = (εr + 1)/2 + (εr - 1)/2 · (1 + 12h/W)-1/2
Fringing extension: ΔL = 0.412h · ((εeff + 0.3)(W/h + 0.264))/((εeff - 0.258)(W/h + 0.8))
Effective length: Leff = c / (2f√εeff)
Patch length: L = Leff − 2ΔL
Ground plane estimate: Wg ≈ W + 6h, Lg ≈ L + 6h
How to use the results
1) Build an initial layout
- Draw the patch with the calculated W and L.
- Use calculated Wg and Lg as a minimum board/ground reference.
- Place the feed point (or inset line) using the suggested inset depth when applicable.
2) Simulate before fabrication
Analytical equations are excellent for starting dimensions but they do not capture every real-world effect. Always verify with an EM solver (HFSS, CST, FEKO, Sonnet, ADS Momentum, etc.) before committing to hardware.
3) Tune on hardware
- Frequency is most sensitive to patch length L.
- Impedance match is strongly affected by feed position and feed geometry.
- Nearby plastic, battery packs, cables, and enclosures can detune resonance.
Design tips for better real-world performance
- Use substrate material with controlled dielectric properties for repeatability.
- Keep copper etching tolerances in mind; small dimensional errors can shift frequency.
- Avoid routing noisy digital lines under or near the patch region.
- For compact antennas, expect tradeoffs in bandwidth and efficiency.
- Validate return loss (S11), efficiency, and radiation pattern—not just resonance frequency.
Limitations of closed-form patch calculations
This calculator assumes a simple rectangular patch and a relatively ideal environment. It does not directly model finite ground effects, connector discontinuities, feed-line radiation, substrate loss tangent, anisotropy, or housing interactions. Treat output values as a high-quality first design pass, not final production dimensions.
Quick FAQ
What frequency range can I design for?
The equations are broadly useful across many microwave bands, but manufacturability and losses become critical at higher frequencies. Simulation and measurement are essential.
Why is my measured resonance different from the calculator?
Common causes include dielectric tolerance, copper thickness, solder mask, connector/feed details, nearby objects, and finite ground/board effects.
Is this only for 50 Ω feed systems?
No. You can enter any target impedance and estimate inset feed depth accordingly, as long as your assumed edge resistance supports a valid solution.
Engineering note: all dimensions are approximate. Use this calculator for fast concept sizing, then refine with EM simulation and VNA-based tuning.