In electrical engineering, a ground plane is an electrically conductive surface.
Radio antenna theory
In telecommunication, a ground plane structure or relationship exists between the antenna and another object, where the only structure of the object is a structure which permits the antenna to function as such (e.g., forms a reflector or director for an antenna). This sometimes serves as the near-field reflection point for an antenna, or as a reference ground in a circuit.
There are a variety of ground planes, including drooping ground planes, and flat circular ground plane antennas. A ground plane may consist of a natural surface, such as the Earth (or ocean) (or salt marsh) or an artificial surface of opportunity (such as the roof of a motor vehicle). A ground plane can also be a specially designed artificial surface (such as the radial elements of a quarter-wave ground plane antenna). Artificial (or substitute) grounds (e.g., ground planes) concerns the grounding structure for the antenna and includes the conductive structure used in place of the earth and which grounding structure is distinct from the earth.
Essentially, the ground plane acts as the "missing half" of a dipole two element, half wave long, center fed antenna. It can be thought of as the "return current" path for the radiating antenna. The efficiency of a ground plane can be measured in ohms as the loss component (i.e., fewer ohms are better) of an antenna's total input impedance. In VHF (30 to 300 MHz or wavelengths 10 to 1 meter) used in mobile communications, the metal of a car body begins to act as an efficient quarter-wavelength groundplane. By the upper VHF and UHF frequencies (300 to 3000 MHz), the car or truck body ground plane can be several wavelengths long, making an "ideal and lossless" groundplane.
Printed circuit boards
A ground plane in PCB assembly is a layer of copper that appears to most signals as an infinite ground potential. This helps reduce noise and helps ensure that all integrated circuits within a system compare different signals' voltages to the same reference potential.
It also serves to make the circuit design easier, allowing the designer to ground anything without having to run multiple tracks; the component needing grounding is routed directly to the ground plane on another layer.
Ground planes can also be placed on adjacent layers to power planes creating a large parallel plate capacitor that helps filter the power supply.
Ground planes are sometimes split and then connected by a thin trace. This allows the separation of analog and digital sections of a board or the inputs and outputs of amplifiers. The thin trace has low enough impedance to keep the two sides very close to the same potential while keeping the ground currents of one side from impacting the other.
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