A report on Antenna (radio) and Gain (antenna)

A stack of "fishbone" and Yagi–Uda television antennas
Animation of a half-wave dipole antenna radiating radio waves, showing the electric field lines. The antenna in the center is two vertical metal rods connected to a radio transmitter (not shown). The transmitter applies an alternating electric current to the rods, which charges them alternately positive (+) and negative (−). Loops of electric field leave the antenna and travel away at the speed of light; these are the radio waves. In this animation the action is shown slowed down enormously.
Electronic symbol for an antenna
Antennas of the Atacama Large Millimeter/submillimeter Array.
An automobile's whip antenna, a common example of an omnidirectional antenna.
Half-wave dipole antenna
Diagram of the electric fields ( blue ) and magnetic fields ( red ) radiated by a dipole antenna ( black rods) during transmission.
Cell phone base station antennas
Standing waves on a half wave dipole driven at its resonant frequency. The waves are shown graphically by bars of color ( red for voltage, V and blue for current, I ) whose width is proportional to the amplitude of the quantity at that point on the antenna.
Typical center-loaded mobile CB antenna with loading coil
Polar plots of the horizontal cross sections of a (virtual) Yagi-Uda-antenna. Outline connects points with 3 dB field power compared to an ISO emitter.
The wave reflected by earth can be considered as emitted by the image antenna.
The currents in an antenna appear as an image in opposite phase when reflected at grazing angles. This causes a phase reversal for waves emitted by a horizontally polarized antenna (center) but not for a vertically polarized antenna (left).
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Partial gain is calculated as power gain, but for a particular polarization.

- Gain (antenna)

Since high directivity in an antenna depends on it being large compared to the wavelength, highly directional antennas (thus with high antenna gain) become more practical at higher frequencies (UHF and above).

- Antenna (radio)
A stack of "fishbone" and Yagi–Uda television antennas

2 related topics with Alpha

Overall

Aperture (antenna)

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In electromagnetics and antenna theory, the aperture of an antenna is defined as "A surface, near or on an antenna, on which it is convenient to makeassumptions regarding the field values for the purpose of computing fields at external points. The aperture is often taken as that portion of a plane surface near the antenna, perpendicular to the direction of maximum radiation, through which the major part of the radiation passes."

The directivity of an antenna, its ability to direct radio waves preferentially in one direction or receive preferentially from a given direction, is expressed by a parameter called antenna gain.

Examples of sound levels in decibels from various sound sources and activities, taken from the "How loud is too loud" screen of the NIOSH Sound Level Meter app

Decibel

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Relative unit of measurement equal to one tenth of a bel (B).

Relative unit of measurement equal to one tenth of a bel (B).

Examples of sound levels in decibels from various sound sources and activities, taken from the "How loud is too loud" screen of the NIOSH Sound Level Meter app
A schematic showing the relationship between dBu (the voltage source) and dBm (the power dissipated as heat by the 600 Ω resistor)

dBi: dB(isotropic) – the gain of an antenna compared with the gain of a theoretical isotropic antenna, which uniformly distributes energy in all directions. Linear polarization of the EM field is assumed unless noted otherwise.

dBd: dB(dipole) – the gain of an antenna compared with the gain a half-wave dipole antenna. 0 dBd = 2.15 dBi