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A half-wave dipole antenna consists of two quarter-wavelength conductors placed end to end for a total length of approximately ℓ = 1 / 2 λ. The current distribution is that of a standing wave , approximately sinusoidal along the length of the dipole, with a node at each end and an antinode (peak current) at the center (feedpoint ...
The electric field strength at a specific point can be determined from the power delivered to the transmitting antenna, its geometry and radiation resistance. Consider the case of a center-fed half-wave dipole antenna in free space, where the total length L is equal to one half wavelength (λ/2). If constructed from thin conductors, the current ...
The difference between EIRP and ERP is that ERP compares the actual antenna to a half-wave dipole antenna, while EIRP compares it to a theoretical isotropic antenna. Since a half-wave dipole antenna has a gain of 1.64 (or 2.15 dB) compared to an isotropic radiator, if ERP and EIRP are expressed in watts their relation is = If they are expressed ...
[g] As can be seen in the above table, for linear antennas shorter than their fundamental resonant length (shorter than 1 / 2 λ for a dipole antenna, 1 / 4 λ for a monopole) the radiation resistance decreases with the square of their length; [24] for loop antennas the change is even more extreme, with sub-resonant loops ...
Antenna directivity is the ratio of maximum radiation intensity (power per unit surface) radiated by the antenna in the maximum direction divided by the intensity radiated by a hypothetical isotropic antenna radiating the same total power as that antenna. For example, a hypothetical antenna which had a radiated pattern of a hemisphere (1/2 ...
[1] [2] It was a popular antenna design during the middle of the 20th century, but fell out of common use during the latter part of the century with the growing popularity of upper HF and VHF frequencies, which needed dipoles with more feasible lengths – only ~16 feet (4.9 m) or smaller, as opposed to quarter-wave antennas ~70 feet (21 m ...
In general terms, at any given frequency the log-periodic design operates somewhat similar to a three-element Yagi antenna; the dipole element closest to resonant at the operating frequency acts as a driven element, with the two adjacent elements on either side as director and reflector to increase the gain, the shorter element in front acting ...
The Friis transmission formula is used in telecommunications engineering, equating the power at the terminals of a receive antenna as the product of power density of the incident wave and the effective aperture of the receiving antenna under idealized conditions given another antenna some distance away transmitting a known amount of power. [1]