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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.
[17] [8] A common type for mounting on masts or stationary structures is the ground plane antenna, consisting of a quarter-wave whip antenna with a ground plane of 3 or 4 wires or rods a quarter-wavelength long radiating horizontally or diagonally from its base, connected to the ground side of the feedline. [18]
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).
When an actual ground is not available (such as in a vehicle) other metallic surfaces can serve as a ground plane (typically the vehicle's roof). Alternatively, radial wires placed at the base of the antenna can form a ground plane. For VHF and UHF bands, the radiating and ground plane elements can be constructed from rigid rods or tubes.
In telecommunications and antenna design, an image antenna is an electrical mirror-image of an antenna element formed by the radio waves reflecting from a conductive surface called a ground plane, such as the surface of the earth. It is used as a geometrical technique in calculating the radiation pattern of the antenna.
During construction the proper attachment point for the feed-line is found by sliding the connection of the feedline back and forth along the stub while monitoring the SWR until an impedance match (minimum SWR) is obtained. [1] [6] Being a half-wave antenna, it provides a small gain of just under 1 dB over a quarter-wave ground-plane antenna. [7]
Although they provide an electrical "ground", they do not require any actual contact with the surrounding earth, even though advisable. A ground plane antenna. The white, downward sloping arms are radials. When the radials are mechanically incorporated into the structure of a small antenna it is called a ground plane antenna.
A patch antenna is a type of antenna with a low profile, usually consisting of a printed circuit board. It consists of a planar rectangular or circular sheet or "patch" of metal, mounted over a larger sheet of metal called a ground plane. It is the original type of microstrip antenna described by Howell in 1972. [1]