What is a collinear antenna?
A collinear antenna stacks several half-wave radiating sections along a common axis and feeds them in phase, so their fields add broadside. The azimuth pattern stays omnidirectional while the elevation beam narrows, giving gain that grows with the number of sections, roughly 3 dB per doubling of aperture in practice.[1][2]
How are sections kept in phase?
Successive half-wave sections would have opposite current phase. Quarter-wave phasing stubs, coils or coaxial sections reversing inner and outer conductors (the coaxial collinear) insert the needed 180° shift so all radiating segments carry currents in the same direction.[1][3]
What gain is achievable?
Two in-phase half-wave elements give about 5 dBi; four to eight sections reach roughly 7–10 dBi. Beam tilt, feed losses and practical phasing errors limit very long arrays, and narrow elevation beams can overshoot nearby users.[1]
Where are collinears used?
VHF/UHF base stations, repeaters, LoRa gateways, Wi-Fi outdoor omnis and marine radios. Electrical downtilt is sometimes added for coverage near the site.[4]
Frequently asked questions
Does a collinear have more gain in all directions?
No; gain on the horizon rises while high-elevation coverage falls.
Is it vertically polarized?
Yes, when mounted vertically.
What is a Franklin antenna?
An early collinear design with phase-reversing sections.
See also
References
Online sources accessed October 21, 2026; printed works cited by edition. See all sources.
- “Antennas for All Applications, 3rd ed.”. J. D. Kraus and R. J. Marhefka, McGraw-Hill. 2002.
- “Antenna Theory: Analysis and Design, 4th ed.”. C. A. Balanis, Wiley. 2016.
- “The ARRL Antenna Book for Radio Communications”. ARRL. multiple editions.
- “Antennas and Propagation for Wireless Communication Systems, 2nd ed.”. S. R. Saunders and A. Aragón-Zavala, Wiley. 2007.