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For a gain measured relative to a dipole, one says the antenna has a gain of " x dBd" (see Decibel). More often, gains are expressed relative to an isotropic radiator , making the gain seem higher. In consideration of the known gain of a half-wave dipole, 0 dBd is defined as 2.15 dBi; all gains in "dBi" are shifted 2.15 higher than gains in "dBd".
When considering an antenna's directional pattern, gain with respect to a dipole does not imply a comparison of that antenna's gain in each direction to a dipole's gain in that direction. Rather, it is a comparison between the antenna's gain in each direction to the peak gain of the dipole (1.64). In any direction, therefore, such numbers are 2 ...
The addition of parasitic elements gives a diminishing improvement in the antenna's gain. [2] Adding a reflector to a dipole, to make a 2 element Yagi, increases the gain by about 5 dB over the dipole. Adding a director to this, to give a 3 element Yagi, gives a gain of about 7 dB over a dipole.
A directive antenna with moderate gain of about 8 dBi often used at UHF frequencies. Consists of a dipole mounted in front of two reflective metal screens joined at an angle, usually 90°. Used as a rooftop UHF television antenna and for point-to-point data links. Parabolic The most widely used high gain antenna at microwave frequencies and above.
The difference between ERP and EIRP is that antenna gain has traditionally been measured in two different units, comparing the antenna to two different standard antennas; an isotropic antenna and a half-wave dipole antenna: Isotropic gain is the ratio of the power density (signal strength in watts per square meter) received at a point far from ...
An antenna array consisting of two such antennas, one above the other and driven in phase has a gain of up to 17 dBi. Being log-periodic, the antenna's main characteristics ( radiation pattern , gain, driving point impedance ) are almost constant over its entire frequency range, with the match to a 300 Ω feed line achieving a standing wave ...
Since electromagnetic radiation is dipole radiation, it is not possible to build an antenna that radiates coherently equally in all directions, although such a hypothetical isotropic antenna is used as a reference to calculate antenna gain. The simplest antennas, monopole and dipole antennas, consist of one or two straight metal rods along a ...
An antenna designer must take into account the application for the antenna when determining the gain. High-gain antennas have the advantage of longer range and better signal quality, but must be aimed carefully in a particular direction. Low-gain antennas have shorter range, but the orientation of the antenna is inconsequential.
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