Dipole Antenna Calculator
Calculate dipole antenna dimensions, wavelength, and electrical properties for optimal performance.
Design and optimize dipole antennas by calculating the correct length, wavelength, impedance, and radiation resistance for your desired frequency.
Dipole Antenna Calculator
Calculate dipole antenna dimensions, wavelength, and electrical properties for optimal performance.
About the Dipole Antenna Calculator
A dipole antenna is the most fundamental type of radio antenna, consisting of two conductive elements extending in opposite directions from a central feedpoint. In its simplest form — the half-wave dipole — the total length equals one half of the operating wavelength. The half-wave dipole is a reference standard against which all other antennas are compared, and it is widely used at every frequency from HF (shortwave) through VHF and UHF by amateur radio operators, broadcast stations, and wireless equipment manufacturers.
The free-space wavelength λ is determined by the speed of light and the operating frequency: λ = c / f, where c ≈ 299.792458 m/s and f is in MHz, giving λ in metres. At 146.52 MHz (2-metre amateur band), λ ≈ 2.047 m. A free-space half-wave dipole would be about 1.024 m long from tip to tip, with each arm measuring approximately 0.512 m.
In practice, antennas are made from physical conductors that have finite diameter, insulation, or proximity to ground and other objects. These effects cause the effective electrical length of the antenna to differ from the physical length. The velocity factor (vf) accounts for this: it is the ratio of the wave propagation speed in the actual conductor to the speed of light in free space. For bare wire in free space, vf ≈ 0.97–0.99; for insulated wire, vf drops to 0.88–0.95 depending on the insulation dielectric constant.
The feedpoint impedance of a half-wave dipole in free space is approximately 73 Ω (purely resistive at resonance), which matches well with 75 Ω coaxial cable. A quarter-wave monopole over a perfect ground plane has an impedance of about 36 Ω (half of the dipole value), making it a good match for 50 Ω coaxial feed via a matching section. These are theoretical values; actual impedance depends on height above ground, conductor diameter, and nearby structures.
Dipoles are used in yagi-uda directional arrays, folded dipoles for higher impedance matching, sleeve dipoles for coaxial feed, and as reference elements in antenna gain calculations. Knowing the correct physical length for a given frequency and velocity factor ensures the antenna resonates at the desired frequency, providing maximum radiation efficiency and minimum reflected power on the feedline. This calculator gives you the key dimensions instantly so you can cut your elements to the right length before assembly.
Dipole Antenna Examples
Click any example button below the calculator to load a real amateur-radio antenna scenario.
| Frequency / Vf / Type | Total Length | Application |
|---|---|---|
| f = 146.52 MHz, vf = 0.95, Half-Wave | λ ≈ 2.047 m, L ≈ 0.972 m, arm ≈ 0.486 m | Standard 2-metre VHF half-wave dipole. Each arm is about 48.6 cm; ideal for portable operation or as an emergency antenna. |
| f = 446.0 MHz, vf = 0.95, Half-Wave | λ ≈ 0.672 m, L ≈ 0.319 m, arm ≈ 0.159 m | 70 cm UHF dipole for the amateur PMR446 band. Compact at 15.9 cm per arm, suitable for handheld or base-station use. |
| f = 7.074 MHz, vf = 0.95, Half-Wave | λ ≈ 42.36 m, L ≈ 20.12 m, arm ≈ 10.06 m | 40-metre HF dipole for FT8 digital mode at 7.074 MHz. Each arm spans just over 10 metres, requiring space but providing excellent low-band performance. |
| f = 146.52 MHz, vf = 0.85, Quarter-Wave | λ ≈ 2.047 m, L ≈ 0.435 m | Quarter-wave monopole for 2 metres using insulated wire (vf = 0.85). Mounted vertically over a ground plane, this creates an omnidirectional radiation pattern. |
How to Use the Dipole Antenna Calculator
- Enter the operating frequency in megahertz (MHz). For the 2-metre band, use 146 MHz; for 40 metres, use 7.1 MHz.
- Enter the velocity factor of the conductor material — use 0.95 for typical bare copper wire, or 0.85–0.92 for insulated wire.
- Select the dipole type: Half-Wave for the standard dipole used in most applications, or Quarter-Wave for monopole antennas over a ground plane.
- Click Calculate to see the free-space wavelength, total antenna length, and individual arm length in metres, centimetres, and feet.
- Use the example buttons to load common amateur-radio scenarios and verify your calculations.
Dipole Antenna FAQ
What is a half-wave dipole?
A half-wave dipole is a straight antenna whose total physical length equals approximately half the operating wavelength, adjusted by the velocity factor. It is the most common dipole type and serves as the 0 dBd reference for antenna gain. Its feedpoint impedance in free space is about 73 Ω, close to the 75 Ω of standard coaxial cable.
What is velocity factor and why does it matter?
Velocity factor (vf) is the ratio of electromagnetic wave speed in a conductor to the speed of light in free space. Because the wave slows down inside real conductors and insulators, the physical antenna must be shorter than the free-space wavelength. A vf of 0.95 means the wave travels at 95% of light speed, so the antenna is 95% of the theoretical free-space length.
What is the feedpoint impedance of a dipole?
A half-wave dipole in free space has a feedpoint impedance of approximately 73 Ω at resonance. A quarter-wave monopole over a perfect ground plane has about 36 Ω. Real-world values depend on height above ground, conductor diameter, and surrounding structures, so in practice the impedance may range from 50–100 Ω.
How do I cut a dipole to the right length?
Calculate the total length using this calculator, then cut each arm to half that length. Start slightly long (add 5%) to account for end effects, then trim and test with an antenna analyser or SWR meter, shortening each arm by equal amounts until you reach minimum SWR at the target frequency.
Can I use a dipole indoors?
Yes. Indoor dipoles work for HF and VHF bands, though proximity to walls, floors, and wiring affects impedance and radiation pattern. Efficiency is reduced by nearby lossy materials, but an indoor dipole is still far better than no antenna. Keep the antenna as far as possible from metal objects and power wiring.
What frequency bands can I use a dipole for?
Dipoles work at any radio frequency, but practical physical length limits their use. At AM broadcast frequencies (530–1700 kHz), a half-wave dipole would be hundreds of metres long. At VHF (145 MHz), a 2-metre dipole is about 1 metre total, making it very practical. At UHF (440 MHz), the antenna is only about 33 cm, suitable for compact installations.