A dipole antenna uses two conductive arms driven from a feed point between them. The familiar reference is a straight, center-fed half-wave dipole, with a total electrical length of about half a wavelength at its operating frequency.
“About” matters. Conductor diameter, insulation, end effects, nearby material, height and mounting change the physical length that produces resonance. A calculated length is a starting point; final tuning belongs in the real installation.
How does a dipole antenna work?
RF voltage drives current in opposite directions on the two arms. In the ideal half-wave case, current is highest near the center and falls toward the ends. The changing current produces an electromagnetic field around the conductors.
In free space, a straight dipole’s strongest radiation is broadside to the wire. It has nulls along the wire axis. The three-dimensional pattern is often described as doughnut-shaped around the conductor.
Real installations distort that pattern. Height above ground, mast material, nearby antennas, buildings, terrain and feedline routing can change impedance and send energy in different directions.
Half-wave dipole length
The free-space half-wavelength reference is:
total electrical length ≈ c / (2f)
where c is the speed of light and f is frequency. The two arms are each about one quarter wavelength electrically.
Do not cut a production antenna from this equation alone. The physical resonant length is usually adjusted for conductor size, construction and surroundings. Build slightly long where practical, measure the installed response, then trim or tune according to the design procedure.
A dipole is a balanced load
The two arms form a balanced antenna. Coaxial cable is unbalanced. Without a suitable feed transition or common-mode control, current can flow on the outside of the coax shield. The feedline then becomes part of the radiator, changing pattern, impedance and noise pickup.
A balun, choke or other feed arrangement may be used depending on frequency, power and construction. Its job and rating must match the antenna system; adding an arbitrary coil of coax is not a universal fix.
Common dipole antenna types
Straight half-wave dipole
The reference form uses two straight arms on one line. It is simple to analyze and useful for single-band applications when enough span is available.
Inverted-V dipole
The center is raised and the arms slope down. This reduces the required horizontal span and changes feed impedance and pattern. Angle, height and nearby ground matter.
Folded dipole
A folded dipole uses parallel conductors connected at their ends. Its impedance-transforming behavior and bandwidth depend on conductor spacing, diameter and geometry. It is common as a driven element and in VHF/UHF arrays.
Dipole arrays
Multiple dipole or folded-dipole elements can be combined to increase gain or shape azimuth and elevation coverage. Spacing, phasing, support structure and feed network determine whether the array is omnidirectional, directional or sectorized.
Verified folded-dipole array examples
The products below are multi-element VHF/UHF folded-dipole systems. They illustrate commercial array selection; they are not basic two-wire half-wave dipoles.
| Model | Published range | Published selection facts | Product page |
|---|---|---|---|
| GL-DY015Q9A | 134–174 MHz | 6–9 dBi, vertical polarization, 50 Ω, N female or 7/16 DIN female | View model |
| GL-DY150IIA | 134–173 MHz | Omni 12 / directional 15 dBi, vertical polarization, 50 Ω, UHF or N female | View model |
| GL-DY350IIA | 330–400 MHz | Omni 12 / directional 15 dBi, vertical polarization, 50 Ω, UHF or N female | View model |
Read each current product page and datasheet before selection. Gain configuration, vertical beamwidth, power rating, dimensions, wind loading and mounting are part of the array decision.
Dipole antenna selection checklist
- required frequency range and tuning margin;
- single element, folded element or array;
- desired azimuth and elevation coverage;
- polarization and mounting orientation;
- feed impedance, balun/choke and connector;
- transmitter power and cable loss;
- mast, height, spacing and nearby structures;
- wind, temperature and mechanical load;
- measurement, tuning and maintenance access.
When is a dipole a good choice?
A simple dipole is a strong reference when the project can provide the span, balanced feed treatment and suitable placement. A folded dipole or array is useful when impedance, bandwidth, gain or pattern needs require a more engineered structure.
Choose from the coverage and installation requirement first. A larger gain number can narrow the vertical beam and miss nearby users if the site geometry is wrong.
Request a folded-dipole antenna review
Prepared by the Rftech Technical Team from ARRL/RSGB educational references and current Global RF Tech model pages. Sources and product data checked July 15, 2026; verify the latest drawing and installed response before deployment.
