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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 ...
Specifically, the Gain or Power gain of an antenna is defined as the ratio of the intensity (power per unit surface) radiated by the antenna in a given direction at an arbitrary distance divided by the intensity radiated at the same distance by an hypothetical isotropic antenna:
This corresponds to the following non-logarithmic gain model: =, where = / is the average multiplicative gain at the reference distance from the transmitter. This gain depends on factors such as carrier frequency, antenna heights and antenna gain, for example due to directional antennas; and = / is a stochastic process that reflects flat fading.
Isotropic gain is the ratio of the power density (signal strength in watts per square meter) received at a point far from the antenna (in the far field) in the direction of its maximum radiation (main lobe), to the power , received at the same point from a hypothetical lossless isotropic antenna, which radiates equal power in all directions ...
Free-space loss increases with the square of distance between the antennas because the radio waves spread out by the inverse square law and decreases with the square of the wavelength of the radio waves. The FSPL is rarely used standalone, but rather as a part of the Friis transmission formula, which includes the gain of antennas. [3]
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]
A e = (λ 2 G)/4π : the antenna effective aperture; P D is the power density in watts per unit area; P r is the power delivered into the load resistance presented by the receiver (normally 50 ohms) G: the antenna gain; is the magnetic constant; is the electric constant
Because the antenna only radiates its power into half the space of a dipole antenna, its gain is twice (or in decibels, 3 dB greater than) the gain of an equivalent dipole. [ 69 ] The actual gain and radiation pattern is dependent on the size and conductivity of the ground plane. [ 24 ]
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