# Dipole Antenna Length Calculator

Use this calculator to find the dimensions of a Dipole antenna  designed to operate at a specified wavelength or frequency.

A half-wave dipole antenna is comprised of two quarter-wavelength conductors placed end to end.

This calculator gives the length of a dipole antenna.

Enter

1. The Operating Frequency
2. The Dipole Length as a function of its wavelength (λ) – one of the following options:
• λ/2
• λ
• 5λ/4
• 3λ/2

The tool will compute the antenna length (L).

## Formula

The total length (L) of the dipole antenna in feet is calculated as:

L = 468 / f

where f is the frequency in MHz.

A dipole antenna is comprised of two arms of equal length

l = L/2

## How to Calculate the Dipole Length

Enter the antenna’s frequency of operation with the appropriate units Hz/kHz/MHz/GHz.

The default configuration in the calculator is a half-wave dipole. However other lengths can be selected as well. The table below from Wikipedia shows the antenna gain as a function of wavelength.

Antennas with length 2λ and higher are not used. As well, those with a length that’s less than λ/2 are not used either on account of poor efficiency. Calculate Antenna Efficiency.

Select the length as a function of wavelength.

Once these two parameters are entered, the physical length L of the dipole is provided.

*Antenna Gain is a function of Antenna Factor and wavelength.

## Example Calculations

To calculate the dimensions of a dipole antenna that operates at a certain frequency or wavelength.

If the frequency is specified then it can be entered directly into the calculator above. For example, at a frequency of operation equal to 1000 MHz, the dipole length (L) is 5.62 inches or 0.14 meters.

Instead we might want to specify the wavelength of the antenna in meters. A popular band of operation for amateur radio is the 2 meter (2m) band. Use this tool to convert from wavelength to frequency. In this case, the frequency is 150 MHz. The length of the half-wavelength dipole is 3.12 feet or 0.95 meters.

As the frequency of operation decreases, the physical length of the antenna increases.

In the above calculation for the 2 meter band antenna, we can see that the length of the antenna is 0.95 meters which is approximately half the wavelength. This is consistent with the fact that it is a half-wave dipole antenna.

The reason it’s not exactly half wavelength (1 meter in this case) is because of the end effect* and a resulting multiplication by 0.95.

The actual formula for length (L) in feet of the half wave dipole is:

L = 492 / f

where f is the frequency in MHz.

Taking the end effect into account 492 * 0.95 ≈ 468.

* A practical rectilinear conductor will resonate when it is slightly less than a half-wave in length due to the end effect. End effect is due to a decrease in inductance and an increase in capacitance near the end of the conductor, which effectively lengthens the antenna. This is from the book Fundamentals of Single Sideband via KB6NU’s Ham Radio Blog.

## Construction

The dipole antenna consists of two conductive elements. Hence the name dipole. The two elements are parallel to each other and separated by a gap. The current flows through both conductors and causes the antenna to radiate, creating an RF signal that is radiated outward from the antenna. The radiation pattern is maximum in the direction perpendicular to the dipole.

A half wave dipole operating in the UHF band (300 MHz – 3 GHz) is shown in the picture below ## Notes

Fesz has published a video on resonant dipoles where he discusses his simulations and practical measurements – via “The Dipole Antenna Isn’t As Simple As It Appears” on Hackaday.

Fesz demonstrates the influence of material thickness on the antenna bandwidth. Thinner the wire, the narrower the bandwidth.

## Table of Wavelength vs Dipole Antenna Length

The following table provides the physical antenna dimensions (length in feet) as a function of the wavelength for a half wave dipole. For example, an antenna for 2 meter applications is 3.1 feet in length.

## Table of Frequency vs Dipole Antenna Length

This table provides the length of a dipole antenna as a function of its frequency of operation. For example a 144 MHz dipole antenna is 3.3 feet in length.

## References

 Dipole Antennas on Wikipedia