How do you design a microstrip patch antenna?

From RF Design Wiki · By the RF Design Wiki editorial team · Published October 21, 2026 · Last reviewed October 21, 2026 · How we research

A microstrip patch is a metal rectangle on a grounded substrate that resonates when its length is about half a guided wavelength. Standard transmission-line-model equations give width W = (c/(2f_r))·√(2/(ε_r + 1)) and length L = c/(2f_r√ε_eff) − 2ΔL, where ΔL is the fringing extension (Hammerstad’s formula).^[1]

What is the fringing extension?

ΔL/h = 0.412·(ε_eff + 0.3)(W/h + 0.264) / ((ε_eff − 0.258)(W/h + 0.8)), with ε_eff from the microstrip formula using W/h. The fields fringing at the radiating edges make the patch electrically longer than its physical length.^[1]

How are patches fed?

Inset microstrip: notches into the patch to reach a 50 Ω point.
Coaxial probe: pin from below; impedance set by position.
Aperture coupled: slot in the ground plane, feed on another layer; wider bandwidth, isolates feed radiation.
Proximity coupled: feed line beneath the patch.

What bandwidth and gain do patches have?

Thin patches are narrowband, often a few percent; bandwidth increases with substrate thickness and lower ε_r. Gain is typically about 5–8 dBi. Stacked patches, parasitic elements and thick foam substrates widen bandwidth. Circular polarization uses truncated corners or dual feeds in quadrature.^[1]

Frequently asked questions

What is a typical patch size at 2.4 GHz on FR-4?

Roughly 29 mm long, since half a guided wavelength is about 3 cm.

Why are patches narrowband?

They are high-Q cavities with radiation from narrow edge slots.

Are patches used in arrays?

Yes, widely in phased arrays and 5G mmWave modules.

References

Online sources accessed October 21, 2026; printed works cited by edition. See all sources.

“Antenna Theory: Analysis and Design, 4th ed.”. C. A. Balanis, Wiley. 2016.

Categories: Antennas and propagation

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