Half-Wave Dipole Antenna Calculator

What Is a Half-Wave Dipole Antenna?

A half-wave dipole is one of the simplest and most widely used antennas in radio. It consists of two equal conductors fed at the center, with total length equal to half the operating wavelength. Amateur radio operators, Wi-Fi engineers, and RF designers use this geometry for its predictable radiation pattern.

Half-Wave Dipole Formula

$$L = \frac{\lambda}{2} = \frac{c}{2f}$$

$L$ is total dipole length, $\lambda$ is wavelength, $c$ is the speed of light ($299{,}792{,}458\,\text{m/s}$), and $f$ is frequency. At 100 MHz the wavelength is about 3 m and the half-wave dipole length is about 1.5 m.

Frequency and Length Relationship

Higher frequency means shorter wavelength and a shorter antenna. A 2 m ham band dipole resonates near 75 MHz. Real wire antennas are often trimmed slightly shorter than the theoretical half wavelength due to end effects.

Frequently Asked Questions

Why is it called a half-wave dipole?

Each arm is a quarter wavelength long, so the total span from tip to tip is half a wavelength. At resonance the current distribution fits a half sine wave on the structure.

Should I cut the wire exactly to the calculated length?

Start slightly long and trim for lowest SWR at your target frequency. Wire diameter, insulation, and height above ground all shift the resonant point.

What frequency units does the calculator accept?

Hz, kHz, MHz, and GHz. Amateur bands are commonly entered in MHz, while microwave designs may use GHz.

Does the speed of light vary?

In vacuum and air the speed is essentially constant. Signals in coax or other media travel slower, so antenna formulas based on free-space wavelength are approximations for wire in air.

Can I calculate frequency from a known dipole length?

Yes. Switch to length mode, enter the measured span, and the calculator finds the resonant frequency using f = c / (2L).

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Dipole Calculator

What Is a Half-Wave Dipole Antenna?

Half-Wave Dipole Formula

Frequency and Length Relationship

Frequently Asked Questions

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