How to Calculate Wavelength of Antennas

By J.T. Barett
Dipole antennas
amateur radio aerials image by leafy from

The simplest antennas are straight, long pieces of wire. A dipole antenna takes the concept a little further, using two pieces of wire held together in the middle by an insulator. You can calculate the range of wavelengths for a dipole antenna with a simple formula. The antenna is sensitive to a base frequency and also will pick up odd-numbered multiples of this frequency.

Measure the overall length of the dipole antenna. This is the distance from one end to the other, including the central insulator.

Calculate the base wavelength by multiplying the antenna wavelength by 2: Lw = 2 x La Lw is the wave length, and La is the antenna length. For example, if the antenna length is 24 feet, the wavelength is 48 feet. Radio technicians call the dipole a half-wave antenna since it's half the length of the waves it sends and receives.

Calculate some related wavelengths the dipole can pick up. First, note that wavelength is inversely related to frequency, and the antenna will pick up frequencies that are odd harmonics, or odd whole-number multiples of the main one. Since the antenna will pick up frequencies that are 3, 5 and 7 times the main one, the wavelengths will be 1/3, 1/5 and 1/7 as long as the main wavelength. Using the example from Step 2, since the main wavelength is 48 feet, 48 x 1/3 = 16 feet, 48 x 1/5 = 9.6 feet, and 48 x 1/7 = 6.9 feet. These are the wavelengths for which the antenna will be the most sensitive. It will pick up other wavelengths, but they will be weaker.

About the Author

Chicago native J.T. Barett has a Bachelor of Science in physics from Northeastern Illinois University and has been writing since 1991. He has contributed to "Foresight Update," a nanotechnology newsletter from the Foresight Institute. He also contributed to the book, "Nanotechnology: Molecular Speculations on Global Abundance."