What is a patch antenna?
A patch antenna (microstrip antenna) is a flat metal patch printed on a grounded dielectric substrate. A rectangular patch operating in its fundamental TM10 mode is about half a guided wavelength long and radiates from the fringing fields at its two open edges, giving a broadside beam with typical directivity of 6–9 dBi and a narrow impedance bandwidth, often a few percent.[1][2] Practical microstrip arrays were reported by Munson in 1974.[3]
How does a patch radiate?
The patch and ground form a leaky resonant cavity. In the TM10 mode the electric field is maximum and of opposite sign at the two radiating edges; the horizontal fringing components add in phase broadside, so the patch acts like two radiating slots separated by about λg/2.[1]
How are patches fed?
- Microstrip edge or inset feed: simple; inset depth sets impedance, R(y0) ≈ Redgecos²(πy0/L).[1]
- Coaxial probe: feed position chosen for 50 Ω; probe inductance limits thick substrates.
- Aperture coupling: a slot in the ground plane couples a feed line on a separate substrate, separating feed and radiator and widening bandwidth.[4]
- Proximity coupling: a buried line beneath the patch.
What controls bandwidth and efficiency?
Bandwidth increases roughly in proportion to substrate thickness and decreases with permittivity; thick low-εr substrates, foam, stacked patches and aperture coupling widen it. Surface waves grow on thick, high-εr substrates and reduce efficiency. Dielectric loss on FR-4 noticeably lowers gain compared with low-loss laminates.[4][2] See antenna substrates.
Where are patch antennas used?
GNSS receivers (ceramic CP patches), Wi-Fi access points, cellular base-station arrays, satellite terminals, automotive radar and mmWave 5G modules, aircraft and missile conformal arrays. Their low profile and ease of arraying are key advantages.[2][5] For dimensions see microstrip patch design.
Frequently asked questions
How big is a 2.4 GHz patch?
On a substrate with εr ≈ 3.5 it is roughly 32 × 40 mm; on FR-4 a little smaller.
Can a patch be circularly polarized?
Yes, with dual quadrature feeds or single-feed perturbations such as truncated corners.
Why is the ground plane important?
A small ground plane increases back radiation and shifts resonance.
See also
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.
- “Microstrip Antenna Design Handbook”. R. Garg, P. Bhartia, I. Bahl and A. Ittipiboon, Artech House. 2001.
- “Conformal Microstrip Antennas and Microstrip Phased Arrays”. R. E. Munson, IEEE Transactions on Antennas and Propagation, vol. 22, no. 1, pp. 74-78. January 1974.
- “Microstrip Antennas”. D. M. Pozar, Proceedings of the IEEE, vol. 80, no. 1, pp. 79-91. January 1992.
- “Printed Antennas for Wireless Communications”. R. Waterhouse (ed.), Wiley. 2007.