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The far-field range was the original antenna measurement technique, and the simplest; it consists of placing the antenna under test (AUT) a long distance away from the instrumentation antenna. Generally, the far-field distance or Fraunhofer distance , D F r n h , {\displaystyle \ D_{\mathsf {Frnh}}\ ,} is considered to be
Directivity is an important measure because many antennas and optical systems are designed to radiate electromagnetic waves in a single direction or over a narrow-angle. By the principle of reciprocity , the directivity of an antenna when receiving is equal to its directivity when transmitting.
Measurement [ edit ] Since the angular distance (or separation) is conceptually identical to an angle, it is measured in the same units , such as degrees or radians , using instruments such as goniometers or optical instruments specially designed to point in well-defined directions and record the corresponding angles (such as telescopes ).
Measurement of AoA can be done by determining the direction of propagation of a radio-frequency wave incident on an antenna array or determined from maximum signal strength during antenna rotation. The AoA can be calculated by measuring the time difference of arrival (TDOA) between individual elements of the array.
In China, Pei Xiu (224–271) identified "measuring right angles and acute angles" as the fifth of his six principles for accurate map-making, necessary to accurately establish distances, [5] while Liu Hui (c. 263) gives a version of the calculation above, for measuring perpendicular distances to inaccessible places. [6] [7]
And these systems of the mathematics convention may measure the azimuthal angle counterclockwise (i.e., from the south direction x-axis, or 180°, towards the east direction y-axis, or +90°)—rather than measure clockwise (i.e., from the north direction x-axis, or 0°, towards the east direction y-axis, or +90°), as done in the horizontal ...
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An inclinometer or clinometer is an instrument used for measuring angles of slope, elevation, or depression of an object with respect to gravity's direction. It is also known as a tilt indicator , tilt sensor , tilt meter , slope alert , slope gauge , gradient meter , gradiometer , level gauge , level meter , declinometer , and pitch & roll ...