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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 ...
As frequency increases, the directivity of an antenna of a given physical size will increase. In order to keep receiver antenna directivity constant in the formula, the antenna size must be reduced, and a smaller size antenna results in less power being received as it is able to capture less power with a smaller area.
The Foltz drawing pin like antenna from 1998 size 0.62 and 22% bandwidth. The Rogers cone from 2001 is size 0.65 and right on the limit. Lina and Choo planar spirals in size ratios range from 0.2 to 0.5; The fractal Koch curve antenna approaches the limit. [5] A meander line antenna optimizes the size for narrower bandwidths of the order 10%. [11]
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 make assumptions 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 ...
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]
Exponentiation of both side leads to the formula for the equivalent radius. The formula for the equivalent radius provides consistent results. If the conductor cross-section dimensions are scaled by a factor , the equivalent radius is scaled by | |. Also, the equivalent radius of a cylindrical conductor is equal to the radius of the conductor.
In antenna terms, each of the conductors making up the antenna is known as an element. [9] To calculate the net result, NEC breaks the antenna's elements into a number of sampled points, called segments. It uses simple calculations based on the diameter of the conductor and the wavelength of the signal to determine the induced voltage and ...
The frequency range or bandwidth over which an antenna functions well can be very wide (as in a log-periodic antenna) or narrow (as in a small loop antenna); outside this range the antenna impedance becomes a poor match to the transmission line and transmitter (or receiver).