Dipole Antennas

Wireless technology in industrial environments is becoming more and more common, whether it is utilizing Wi-Fi or proprietary systems for long-distance communication. In order for wireless technology to be successful, the signal must be transferred between a transmitter and receiver, converting the RF electrical signal from the transmitter into an electromagnetic wave in free space, and then converting that wave back again at the receiver. The device that makes this possible is the antenna. 

In industrial environments, there may be elements that interfere with the reception of a signal at the receiver and the right type of antenna can provide the transmission path to suit the application’s needs. Antennas come in many shapes and sizes and each has its own specific design characteristics that determine the range and radiation pattern of the radio signal. The radiation pattern or shape of the radio signal is what is referred to as antenna gain. Antenna gain is measured in decibels. The higher the gain of the antenna, the more focused the signal. The transmitting radiation pattern is the same as the sensitivity pattern for receiving. Which means that the direction in which the antenna transmits the strongest signal is also the direction in which it is most sensitive for receiving signals. 

Dipole antennas are the simplest and most widely used type of antenna. A dipole consists of two identical conductive elements such as metal wires or rods. The wire or rod is split in the center and the two sections are separated by an insulator. The length of the metal wires is approximately half of the maximum wavelength in free space at the frequency of operation. The most popular dipole antenna used in radio receivers is the half-wave dipole. The length of this dipole matches with the electrical half wavelength and can easily function around the frequency range of 3kHz to 300 GHz. 

Two dipole antennas can be connected in parallel to from a thin wire loop which is called a folded dipole antenna. In the folded dipole antenna, two half-wave dipoles, one continuous and the other split at the center, are folded and joined together in parallel at the ends. The split dipole is fed at the center by a balanced transmission line. The two dipoles have the same voltages at their ends and two identical currents are generated. The folded dipole antenna has a wide bandwidth suitable for FM and TV broadcast as well as high gain and directivity making it easy to be used as a directional antenna for long distance communications.