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A high-gain antenna (HGA) is a directional antenna with a focused, narrow beam width, permitting more precise targeting of the radio signals. [1] Most commonly referred to during space missions , [ 2 ] these antennas are also in use all over Earth , most successfully in flat, open areas where there are no mountains to disrupt radiowaves.
A modern high-gain UHF Yagi television antenna with 17 directors, and one reflector (made of four rods) shaped as a corner reflector Drawing of Yagi–Uda VHF television antenna from 1954, used for analog channels 2–4, 54–72 MHz (U.S. channels).
In electromagnetics, an antenna's gain is a key performance parameter which combines the antenna's directivity and radiation efficiency. The term power gain has been deprecated by IEEE. [1] In a transmitting antenna, the gain describes how well the antenna converts input power into radio waves headed in a specified direction. In a receiving ...
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The result is a higher gain, or gain/spillover ratio, at the cost of surfaces that are trickier to fabricate and test. [ 10 ] [ 11 ] Other dish illumination patterns can also be synthesized, such as patterns with high taper at the dish edge for ultra-low spillover sidelobes , and patterns with a central "hole" to reduce feed shadowing.
A Winegard 68 element VHF/UHF aerial antenna. This common multi-band antenna type uses a UHF Yagi at the front and a VHF log-periodic at the back coupled together. When a higher-gain antenna is needed to achieve adequate reception in suburban or fringe reception areas, an outdoor directional antenna is usually used.
High-gain antennas have the advantage of longer range and better signal quality, but must be aimed carefully at the other antenna. An example of a high-gain antenna is a parabolic dish such as a satellite television antenna. Low-gain antennas have shorter range, but the orientation of the antenna is relatively unimportant.
The advantage of high-altitude aerial photography is that it can record the information of a larger area by taking one photograph only. [5] However, high-altitude photographs cannot show as many details as low-altitude photographs since some objects, such as buildings, roads, and infrastructures, are of a very tiny in size in the image. [5]