Ground plane

In electrical engineering, a ground plane is an electrically conductive surface, usually connected to electrical ground. The term has two different meanings in separate areas of electrical engineering. In antenna theory, a ground plane is a conducting surface large in comparison to the wavelength, such as the Earth, which is connected to the transmitter's ground wire and serves as a reflecting surface for radio waves. In printed circuit boards, a ground plane is a large area of copper foil on the board which is connected to the power supply ground terminal and serves as a return path for current from different components on the board.

In telecommunication, 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. The plane does not necessarily have to be connected to ground. Ground plane shape and size play major roles in determining its radiation characteristics including gain.

To function as a ground plane, the conducting surface must be at least a quarter of the wavelength (λ/4) of the radio waves in size. In lower frequency antennas, such as the mast radiators used for broadcast antennas, the Earth itself (or a body of water such as a salt marsh or ocean) is used as a ground plane. For higher frequency antennas, in the VHF or UHF range, the ground plane can be smaller, and metal disks, screens and wires are used as ground planes. At upper VHF and UHF, the metal skin of a car or aircraft can serve as a ground plane for whip antennas projecting from it. In microstrip antennas and printed monopole antennas an area of copper foil on the opposite side of a printed circuit board serves as a ground plane. The ground plane doesn't have to be a continuous surface. In the ground plane antenna style whip antenna, the "plane" consists of several wires λ/4 long radiating from the base of a quarter-wave whip antenna.

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