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''For the ultrasonic and medical imaging application, see Phased Array Ultrasonics .''

In , leading to Physics Nobel Prizes for Antony Hewish and Martin Ryle after several large phased arrays were developed at Cambridge University . The design is also used in Radar , and is generalized in Interferometric radio antennas.

An antenna array is a multiple of active antennas coupled to a common source or load to produce a directive radiation pattern. Usually the spatial relationship also contributes to the directivity of the antenna. Use of the term "active antennas" is intended to describe elements whose energy output is modified due to the presence of a source of energy in the element (other than the mere signal energy which passes through the circuit) or an element in which the energy output from a source of energy is controlled by the signal input.


USAGE

The relative Amplitude s of — and constructive and destructive Interference effects among — the signals radiated by the individual antennas determine the effective Radiation Pattern of the array. A phased array may be used to point a fixed radiation pattern, or to Scan rapidly in Azimuth or elevation. When phased arrays are used in sonar, it is called Beamforming .

The phased array is used for instance in Optical Communication as a Wavelength -selective Splitter .

For information about active as well as passive phased array radars, see also Active Electronically Scanned Array .


Broadcasting

In Broadcast Engineering , phased arrays are required to be used by many AM Broadcast Radio Stations to enhance Signal Strength and therefore coverage in the city of license, while minimizing interference to other areas. Due to the differences between daytime and nighttime Ionospheric Propagation at Mediumwave frequencies, it is common for AM broadcast stations to change between day ( Groundwave ) and night ( Skywave ) radiation patterns by switching the Phase and power levels supplied to the individual antenna elements ( Mast Radiator s) daily at Sunrise and Sunset .

On VHF , phased arrays are used extensively for FM Broadcasting . These greatly increase the Antenna Gain , magnifying the emitted RF energy toward the Horizon , which in turn greatly increases a station's Broadcast Range . In these situations, the distance to each element from the transmitter is identical, or is one (or other Integer ) wavelength apart. Phasing the array such that the lower elements are slightly delayed (by making the distance to them longer) causes a downward Beam Tilt , which is very useful if the antenna is quite high on a Radio Tower .

Other phasing adjustments can increase the downward radiation in the Far Field without tiliting the main Lobe , creating Null Fill to compensate for extremely high Mountain top locations, or decrease it in the Near Field , to prevent excessive exposure to those workers or even nearby homeowners on the ground. The latter effect is also achieved by half-wave spacing – inserting additional elements halfway between existing elements with full-wave spacing. This phasing achieves roughly the same horizontal gain as the full-wave spacing; that is, a five-element full-wave-spaced array equals a nine- or ten-element half-wave-spaced array.


Naval usage

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Phased array radar systems are also used by Warships of several navies including the Chinese, Japanese, Norwegian, Spanish, Korean and United States' navies in the Aegis combat system. Phased array radars allow a warship to use one Radar system for surface detection and tracking (finding ships), air detection and tracking (finding aircraft and missiles) and missile uplink capabilities. Prior to using these systems, each Surface-to-air Missile in flight required a dedicated Fire-control Radar , which meant that ships could only engage a small number of simultaneous targets. Phased array systems can be used to control missiles during the mid-course phase of the missile's flight. During the terminal portion of the flight, Continuous-wave fire control directors provide the final guidance to the target. Because the radar beam is electronically steered, phased array systems can direct radar beams fast enough to maintain a Fire Control Quality track on many targets simultaneously while also controlling several in-flight missiles. The AN/SPY-1 phased array radar, part of the Aegis Combat System deployed on modern U.S. Cruisers and Destroyers , "is able to perform search, track and missile guidance functions simultaneously with a capability of over 100 targets."1. Likewise, the Thales Herakles phased array multi-function radar onboard the Formidable Class Frigate s of the Republic Of Singapore Navy has a track capacity of 200 targets and is able to achieve automatic target detection, confirmation and track intiation in a single scan, while simultaneously providing mid-course guidance updates to the MBDA Aster missiles launched from the ship.2

See also: Active Phased Array Radar , Aegis Combat System and AN/SPY-1



Space probe communication

The MESSENGER spacecraft is a mission to the planet Mercury (arrival 18 March 2011 ). This spacecraft is the first deep-space mission to use a phased-array antenna for Communication s. The radiating elements are Circularly-polarized , slotted Waveguide s. The antenna, which uses the I Band , can operate with 4 or 8 radiating elements.


Weather research usage

, Norman, OK.]]
The , 2006 .

Harris Corporation is a contributor to the technology.


Optics

Within the visible or infrared spectrum of electromagnetic waves it is also possible to construct Optical Phased Arrays . They are used in wavelength multiplexers and filters for telecommunication purposesP. D. Trinh, S. Yegnanarayanan, F. Coppinger and B. Jalali Silicon-on-Insulator (SOI) Phased-Array Wavelength Multi/Demultiplexer with Extremely Low-Polarization Sensitivity IEEE PHOTONICS TECHNOLOGY LETTERS, VOL. 9, NO. 7, JULY 1997, laser beam steering, and holography.


MATHEMATICAL PERSPECTIVE AND FORMULAE

A phased array is an example of ''N''-slit Diffraction . It may also be viewed as the coherent addition of ''N'' Line Source s. Since each individual antenna acts as a slit, emitting radio waves, their diffraction pattern can be calculated by adding the phase shift φ to the fringing term.

We will begin from the ''N''-slit diffraction pattern derived on the Diffraction page.

:
\psi ={\lambda }\sin heta ight)}{ rac{\lambda }\sin heta} ight]\left[ rac{\sin
\left( rac{N}{2}{kd}\sin heta ight)}{\sin \left( rac{2}\sin heta ight)} ight]


Now, adding a φ term to the \begin{matrix}kd\sin heta\,\end{matrix} fringe effect in the second term yields:

:\psi ={\lambda }\sin heta ight)}{ rac{\lambda }\sin heta} ight]\left[ rac{\sin
\left( rac{N}{2}\big( rac{\lambda }\sin heta + \phi \big) ight)}{\sin \left( rac{\lambda }\sin heta +\phi ight)} ight]


Taking the square of the wave function gives us the intensity of the wave.

:I = I_0{\lambda } \sin [ heta
]} ight]}^2}{\lambda
} \sin heta+\phi ight)} ight]}^2}


:
I =I_0{\lambda } \sin heta ight)}{ rac{\lambda }