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Since a parabolic antenna's cost and wind load increase with the physical aperture size, there may be a strong motivation to reduce these (while achieving a specified antenna gain) by maximizing the aperture efficiency. Aperture efficiencies of typical aperture antennas vary from 0.35 [citation needed] to well over 0.70.
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 ...
Aperture efficiency e A is a catchall variable which accounts for various losses that reduce the gain of the antenna from the maximum that could be achieved with the given aperture. The major factors reducing the aperture efficiency in parabolic antennas are: [13]
The gain of horn antennas ranges up to 25 dBi, with 10–20 dBi being typical. [1] ... An optimum horn does not yield maximum gain for a given aperture size.
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.
Placing two high gain antennas very close to each other (less than a wavelength) does not buy twice the gain, for example. Conversely, if the antenna are more than a wavelength apart, there are photons that fall between the elements and are not collected at all. This is why the physical aperture size must be taken into account.
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
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.