The Half-Wave Dipole Antenna

The half-wave dipole antenna is just a special case of the dipole antenna, but its important enough that it will have its own section. Note that the "half-wave" term means that the length of this dipole antenna is equal to a half-wavelength at the frequency of operation. To make it crystal clear, if the antenna is to radiate at 600 MHz, what size should the half-wavelength dipole be? One wavelength at 600 MHz is = c / f = 0.5 meters. Hence, the half-wavelength dipole antenna's length is 0.25 meters (or 9.85 inches if you don't like the metric system). The half-wave dipole antenna is as you may expect, a simple half-wavelength wire fed at the center as shown in Figure 1: Figure 1. Electric Current on a half-wave dipole antenna. The input impedance of the half-wavelength dipole antenna is given by Zin = 73 + j42.5 Ohms. The fields from the half-wave dipole antenna are given by: The directivity of a half-wave dipole antenna is 1.64 (2.15 dB). The HPBW is 78 degrees. In viewing the impedance as a function of the dipole length in the section on dipole antennas, it can be noted that by reducing the length slightly the antenna can become resonant. If the dipole's length is reduced to 0.48 , the input impedance of the antenna becomes Zin = 70 Ohms, with no reactive component. This is a desirable property since the antenna will be better matched to the radio (transmitter or receiver), and hence is often done in practice for thin dipoles. The radiation pattern remains virtually the same. The above resonant length (0.48 ) is valid if the dipole is very thin. In practice, dipoles are often made with fatter or thicker material, which tends to increase the bandwidth of the antenna. When this is the case, the resonant length reduces depending on the thickness of the dipole. Very fat dipoles can have the resonant length reduced to 0.45 and below. Video Analysis of Half-Wave Dipole Antennas In this video, we go over the short-dipole antenna, the half-wave dipole antenna and the general dipole antenna. The idea is to give an intuitive overview of the first 3 antennas we've discussed. This material is mostly a review; it is here to present the information in a different medium, which I hope most people will find helpful. Feel free to skip over this if it is not your cup of tea. Next: Broadband Dipole Antennas Top: Half-Wave Dipoles Antennas List Home: The Antenna Tutorial This page on half-wave dipole antennas (half-wavelength dipole antenna) is copyrighted, but can be reproduced without permission from the author as long as the source is cited. Copyright antenna-theory.com, 2009-2021, half-wave dipole antenna, half-wavelength dipole antenna.