The beam antenna, also known as the Yagi-Uda antenna, Yagi, or directional antenna, was invented in 1920 by a two Japanese scientists, Doctors Yagi and Uda, while experimenting with dipole antennas. Dipole antennas are the simplest forms of antennas and use one piece of wire or a single element. Old-style television antennas that are mounted on rooftops are one example of a beam antenna.
A beam antenna uses several wires, also called elements, in specific yet different lengths that are placed in parallel with each other and spaced about .1 wavelength apart. The center element is called the driven element, and is where the antenna is connected to the feedline, a piece of wire or cable that is attached at the other end to the transmitter, receiver, or transceiver. The longer elements are called reflectors because they reflect any signal that goes past the center element. The shorter elements are called directors because they direct the direction the signal needs to go.
Beam antennas use a technique known as beamforming for signal transmitting and/or receiving. Beamforming takes a signal and guides the direction that it goes. Beamforming is often used in broadcast TV and radio, amateur (ham) radio, and on cell phone towers.
The side of the antenna with the smaller elements, the directors, is considered the front of the beam antenna, while the side with the longer elements, the reflectors, is the back. To receive a signal, the antenna is pointed in the direction of the signal, and the smaller elements pull the signal into the middle element. The longer elements reflect back any signal that would be lost back to the center element.
Using a beam antenna to transmit a signal works in the same way. The beam antenna is pointed in the direction that the transmitter wants the signal to go. The signal goes from the transmitter or transceiver, through the feedline, to the center element in the antenna. The directors send the signal in the direction it needs to go while the reflectors reflect back any signal that would be lost toward the smaller elements to be sent out.