How does ground-plane size affect an antenna?
For monopole-type antennas, including IFAs, PIFAs and chip antennas, the ground plane is half of the antenna: its currents radiate and its size sets resonance, bandwidth and efficiency. In phones below about 1 GHz the chassis dominates radiation, and its fundamental resonance occurs when the chassis length is about half a wavelength.[1][2]
How does ground size change performance?
- Too small: resonance shifts up, bandwidth and efficiency fall, and current spills onto cables.
- Near λ/2 long: the chassis resonates; bandwidth is maximized when the antenna couples well to this mode.
- Large: the monopole approaches image-theory behavior with the beam tilted upward on a finite plane.[1]
What about patches and directional antennas?
A patch on a small ground plane radiates more backward, has lower gain and a shifted resonance; ground planes extending about λ/4 or more beyond the patch edges are a common guideline. Ground-plane edges diffract and create pattern ripple.[3][2]
How do designers analyze chassis effects?
Characteristic mode analysis identifies the natural current modes of the chassis and where to place couplers to excite them. Full-wave simulation of the entire device, including battery, display and enclosure, is standard practice.[1]
Frequently asked questions
Why does my antenna work on the eval board but not mine?
Your ground plane differs in size or shape, changing resonance and efficiency.
Does a ground plane need to be solid?
Large gaps and slits change current paths; stitching layers with vias keeps it electrically solid.
How small can the ground be at 868 MHz?
Very small boards severely limit efficiency; vendor guides give minimum sizes for each design.
See also
References
Online sources accessed October 21, 2026; printed works cited by edition. See all sources.
- “Modern Small Antennas”. K. Fujimoto and H. Morishita, Cambridge University Press. 2013.
- “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.