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An active phased array or active electronically scanned array (AESA) is a phased array in which each antenna element has an analog transmitter/receiver (T/R) module [13] which creates the phase shifting required to electronically steer the antenna beam. Active arrays are a more advanced, second-generation phased-array technology that are used ...
In a radio antennas, the main lobe or main beam is the region of the radiation pattern containing the highest power or exhibiting the greatest field strength.. The radiation pattern of most antennas shows a pattern of "lobes" at various directions, where the radiated signal strength reaches a local maximum, separated by "nulls", at which the radiation falls to zero.
Most antennas boresight axis is fixed by their shape and cannot be changed. However phased array antennas can electronically steer the beam, changing the angle of the boresight by shifting the relative phase of the radio waves emitted by different antenna elements, and even radiate beams in multiple directions (multiple boresights). [1]
is the distance between elements of the array, and is the angle of arrival of an incident plane wave, defined from end-fire, i.e., = is a signal from array broadside. It is common to perform a variable substitution to ψ {\displaystyle \psi } -space, where ψ = 2 π λ d c o s θ {\displaystyle \psi ={\frac {2\pi }{\lambda }}dcos\theta } , and ...
where dx and dy are the element spacings in the x and y dimensions and is the "illumination efficiency" of the array that accounts for tapering and spacing of the elements in the array. For an un-tapered array with elements at less than λ {\displaystyle \lambda } spacing, η = 1 {\displaystyle \eta =1} .
For discrete aperture antennas (such as phased arrays) in which the element spacing is greater than a half wavelength, the spatial aliasing effect causes some sidelobes to become substantially larger in amplitude, and approaching the level of the main lobe; these are called grating lobes, and they are either identical, or nearly identical as shown in the figure, copies of the main beams.
and is the phase shift introduced by th unit cell of reflect array to its reflected field relative to the incident field. For a feed horn located at ( 0 , 0 , F ) {\displaystyle (0,0,F)} , the formula for the optimal phase distribution on a conventional reflectarray for a beam in the boresight direction is given by:
An optical phased array (OPA) is the optical analog of a radio-wave phased array. [1] By dynamically controlling the optical properties of a surface on a microscopic scale, it is possible to steer the direction of light beams (in an OPA transmitter [ 2 ] ), or the view direction of sensors (in an OPA receiver [ 3 ] ), without any moving parts.