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For a monopole antenna (a), the Earth acts as a ground plane to reflect radio waves directed downwards, making them seem to come from a virtual "image antenna" (b).In Telecommunications, a ground plane is a flat or nearly flat horizontal conducting surface that serves as part of an antenna, to reflect the radio waves from the other antenna elements.
If the ground plane is a good conductor larger in radius than the height of the element (which will be assumed in this section), it approximates a perfect infinite ground plane, and the current and radiation can be calculated by replacing the monopole and plane with a vertical dipole antenna of twice the height.
Whips mounted on vehicles use the metal skin of the vehicle as a ground plane. In hand-held devices usually no explicit ground plane is provided, and the ground side of the antenna's feed line is just connected to the ground (common) on the device's circuit board. [2] Therefore, the radio itself serves as a rudimentary ground plane.
Counterpoises are typically used in antenna systems for radio transmitters where a good earth ground connection cannot be constructed.. Monopole antennas used at low frequencies, below 3 MHz, such as the mast radiator antennas used for AM broadcasting, require the radio transmitter to be electrically connected to the Earth under the antenna; this is called a ground (or earth).
The vertical plane is used to plot an antenna's relative field strength perpendicular to the ground (which directly affects a station's coverage area) on a polar graph. Normally, the maximum of 1.000 or 0 dB is at the side (unless there is beam tilt ), which is labeled 0°, to 90° at the top and −90° at the bottom.
A choke ring antenna is a directional antenna designed for reception of GNSS signals from satellites. It consists of a number of concentric conductive cylinders around a central antenna. The first choke ring antennas were invented at JPL; [ 2 ] since 1989 they have been improved and extended by many companies.
A discone antenna is a monopole version of a biconical antenna, in which one of the cones is replaced by a disc. It is usually mounted vertically, with the disc at the top and the cone beneath. It is usually mounted vertically, with the disc at the top and the cone beneath.
The antenna is made of a narrow helix of wire like a spring, which functions as the needed inductor. The springy wire is flexible, making it less prone to damage than a stiff antenna. The spring antenna is further enclosed in a plastic or rubber-like covering to protect it. The technical name for this type of antenna is a normal-mode helix. [7]