Types
The ground plane used with a monopole may be the actual earth; in this case the antenna is mounted on the ground and one side of the feedline is connected to an earth ground at the base of the antenna. This design is used for the mast radiator antennas employed in radio broadcasting at low frequencies, as well as other low frequency antennas such as the T-antenna and umbrella antenna. At VHF and UHF frequencies the size of the ground plane needed is smaller, so artificial ground planes are used to allow the antenna to be mounted above the ground. A common type of monopole antenna at these frequencies consists of a quarter-wave whip antenna with a ground plane consisting of several wires or rods radiating horizontally from its base; this is called a ground-plane antenna. At gigahertz frequencies the metal surface of a car roof or airplane body makes a good ground plane, so car cell phone antennas consist of short whips mounted on the roof, and aircraft communication antennas frequently consist of a short conductor in an aerodynamic fairing projecting from the fuselage; this is called a blade antenna. The quarter-wave whip and "Rubber Ducky" antennas used with handheld radios such as walkie-talkies and cell phones are also monopole antennas. These don't use a ground plane, and the ground side of the transmitter is just connected to the ground connection on its circuit board. The hand and body of the person holding them may function as a rudimentary ground plane.
Read more about this topic: Monopole Antenna
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