What is an antenna radiation pattern?
A radiation pattern is the spatial distribution of a quantity that characterizes the electromagnetic field generated by an antenna, normally the far-field power or field strength versus direction.[1] Patterns are plotted as 3D surfaces or as 2D cuts, usually the E-plane (containing the electric field and direction of maximum radiation) and the H-plane (containing the magnetic field), normalized to the peak in dB.[2]
What are the lobes of a pattern?
The main lobe contains the direction of maximum radiation; side lobes are any other lobes; the back lobe is roughly opposite the main lobe. Nulls separate them. Key figures are half-power beamwidth, first-null beamwidth, side-lobe level and front-to-back ratio.[2]
What shapes do patterns take?
- Isotropic: equal in all directions; a hypothetical reference.
- Omnidirectional: uniform in one plane (e.g., a vertical dipole’s azimuth plane), directional in the orthogonal plane.
- Directional: concentrates energy in one direction, e.g., Yagi, horn, dish.
- Shaped beams: cosecant-squared, sector or contoured coverage from reflectors and arrays.
How are patterns measured and plotted?
Patterns are measured on far-field ranges, in anechoic chambers or by near-field transformation, using spherical coordinates (θ, φ) and co-/cross-polar components as defined by Ludwig.[3][4] Linear-dB polar plots emphasize sidelobes; linear-power plots emphasize the main beam.
Does the pattern change with frequency?
Yes. Resonant antennas keep a stable pattern only over their impedance bandwidth, and a dipole longer than about 1.25λ develops multiple lobes. Log-periodic and spiral antennas are designed so that the pattern stays nearly constant over a wide band.[5]
Frequently asked questions
What is the E-plane?
The plane containing the electric-field vector and the direction of maximum radiation.
Is an omnidirectional antenna isotropic?
No; it is uniform only in one plane, with nulls or reduced gain elsewhere.
Why plot patterns in dB?
dB scales reveal sidelobes and nulls tens of dB below the peak.
See also
References
Online sources accessed October 21, 2026; printed works cited by edition. See all sources.
- “IEEE Standard for Definitions of Terms for Antennas (IEEE Std 145-2013)”. IEEE Antennas and Propagation Society. 2014.
- “Antenna Theory: Analysis and Design, 4th ed.”. C. A. Balanis, Wiley. 2016.
- “The Definition of Cross Polarization”. A. C. Ludwig, IEEE Transactions on Antennas and Propagation, vol. 21, no. 1, pp. 116-119. January 1973.
- “IEEE Recommended Practice for Antenna Measurements (IEEE Std 149-2021)”. IEEE Antennas and Propagation Society. 2022.
- “Frequency Independent Antennas”. V. H. Rumsey, Academic Press. 1966.