Editing Ground plane (section)

==<span class="anchor" id="radio_GP_anchor">Radio antenna theory</span>==
[[File:Monopole and image antenna.svg|thumb|For a monopole antenna&nbsp;(a), the Earth acts as a ground plane to reflect radio waves directed downwards, making them seem to come from a virtual "[[image antenna]]"&nbsp;(b).]]

In [[Telecommunications]], a ground plane is a flat or nearly flat horizontal conducting surface that serves as part of an [[antenna (radio)|antenna]], to reflect the [[radio wave]]s from the other antenna elements.  In [[monopole antenna]]s the ground plane is connected to one side of the antenna [[feedline]], usually the shield conductor of a [[coaxial cable]], and the other side is connected to the monopole element itself.<ref>{{Cite web |url=https://www.cisa.gov/sites/default/files/publications/COMT%2520Pre-Course%2520Study%2520Guide_v5_0.pdf |title=COMT Pre-Course Study Guide |access-date=2022-07-08 |archive-date=2021-07-04 |archive-url=https://web.archive.org/web/20210704211235/https://www.cisa.gov/sites/default/files/publications/COMT%20Pre-Course%20Study%20Guide_v5_0.pdf |url-status=dead }}</ref> Ground plane shape and size play major roles in determining its radiation characteristics including [[antenna gain|gain]].

To function as a ground plane, the conducting surface must be at least a quarter of the [[wavelength]] {{nobr|({{sfrac| 1 |4}} {{mvar|λ}})}} of the radio waves in radius. In lower [[frequency]] antennas, such as the [[mast radiator]]s 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 [[Very high frequency|VHF]] or [[Ultrahigh frequency|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 antenna]]s projecting from it. In [[microstrip antenna]]s and printed [[monopole antenna]]s an area of copper foil on the opposite side of a [[printed circuit board]] serves as a ground plane. The ground plane does not need to be a continuous surface. In the ''ground plane antenna'' style [[whip antenna]], the plane consists of several wires {{sfrac| 1 |4}}&nbsp;{{mvar|λ}} long radiating from the base of a quarter-wave whip antenna.

The radio waves from an antenna element that reflect off a ground plane appear to come from a mirror image of the antenna located on the other side of the ground plane. In a monopole antenna, the radiation pattern of the monopole plus the virtual [[image antenna]] make it appear as a two-element center-fed [[dipole antenna]]. So a monopole mounted over an ideal ground plane has a radiation pattern identical to a dipole antenna. The feedline from the transmitter or receiver is connected between the bottom end of the monopole element and the ground plane. The ground plane must have good conductivity; any resistance in the ground plane is in series with the antenna and serves to dissipate power from the transmitter.

Antennas usually need ground planes as they serves as a stabilizing factor for the signal, ensuring that antennas have a consistent baseline from which to transmit and receive information.<ref>{{Cite web |title=What is a Ground Plane and Its Importance in GNSS/GPS Antennas? |url=https://novotech.com/pages/ground-plane#:~:text=The%20ground%20plane%20serves%20as%20a%20stabilizing%20factor,baseline%20from%20which%20to%20transmit%20and%20receive%20information. |access-date=2025-01-14 |website=Novotech |language=en}}</ref> It also helps create a specific radiation pattern by reflecting radio waves, ensuring that the antenna radiates efficiently. There are also some cases that ground planes can improve the overall performance of the antenna by ensuring better signal propagation.<ref>{{Cite web |date=2022-12-01 |title=Do All Antennas Need a Ground Plane? |url=https://resources.altium.com/p/do-all-antennas-need-ground-plane?form=MG0AV3 |access-date=2025-01-14 |website=Altium |language=en}}</ref>