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The most commonly used is the center-fed half-wave dipole which is just under a half-wavelength long. The radiation pattern of the half-wave dipole is maximum perpendicular to the conductor, falling to zero in the axial direction, thus implementing an omnidirectional antenna if installed vertically, or (more commonly) a weakly directional ...
Folded dipole A typical folded dipole is two half-wave dipoles mounted parallel to each other, a few inches apart, with the far ends connected. Only one of the dipoles is fed, and the second dipole connects straight through the center where the first has the usual feedpoint.
When the antenna is fed at a point of maximum current, as in the common center-fed half-wave dipole or base-fed quarter-wave monopole, that value is mostly the radiation resistance. However, if the antenna is fed at some other point, the equivalent radiation resistance at that point R r a d 1 {\displaystyle \ R_{\mathsf {rad\ 1}}\ } can easily ...
Antenna measurement techniques refers to the testing of antennas in order to ensure that the antenna meets specifications or simply to characterize it. Typical antenna parameters are gain, bandwidth, radiation pattern, beamwidth, polarization, impedance; These are imperative communicative means.
Animated diagram of a half-wave dipole antenna receiving a radio wave. The antenna consists of two metal rods connected to a receiver R. The electric field (E, green arrows) of the incoming wave results in oscillation of the electrons in the rods, charging the ends alternately positive (+) and negative (−).
Dipole field strength in free space, in telecommunications, is the electric field strength caused by a half wave dipole under ideal conditions. The actual field strength in terrestrial environments is calculated by empirical formulas based on this field strength.
An alternative definition compares the received power to the power received by a lossless half-wave dipole antenna, in which case the units are written as dBd. Since a lossless dipole antenna has a gain of 2.15 dBi, the relation between these units is G a i n ( d B d ) ≈ G a i n ( d B i ) − 2.15 {\displaystyle \mathrm {Gain(dBd)} \approx ...
Two element dipole array in front of a one wavelength square reflector used as gain standard. The gain of practical array antennas is limited to about 25–30 dB. Two half wave elements spaced a half wave apart and a quarter wave from a reflecting screen have been used as a standard gain antenna with about 9.8 dBi at its design frequency. [4]