In telecommunication

Telecommunication

Telecommunication is the transmission of information over significant distances to communicate. In earlier times, telecommunications involved the use of visual signals, such as beacons, smoke signals, semaphore telegraphs, signal flags, and optical heliographs, or audio messages via coded...

s and radar

Radar

Radar is an object-detection system which uses radio waves to determine the range, altitude, direction, or speed of objects. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, weather formations, and terrain. The radar dish or antenna transmits pulses of radio...

, a planar array is an antenna in which all of the elements, both active

Driven element

In a multielement antenna array , the driven element or active element is the element in the antenna which is electrically connected to the receiver or transmitter. In a transmitting antenna it is driven or excited by the RF current from the transmitter, and is the source of the radio waves...

 and parasitic

Passive radiator

In a radio antenna, a passive radiator or parasitic element is a conductive element, typically a metal rod, which is not electrically connected to anything else. Multielement antennas such as the Yagi-Uda antenna typically consist of a "driven element" which is connected to the radio receiver...

, are in one plane. A planar array provides a large aperture and may be used for directional beam

Beam

Beam may refer to:*Beam , a construction element*Beam , the most extreme width of a nautical vessel, or a point alongside the ship at the mid-point of its length*A narrow, propagating stream of particles or energy:...

 control by varying the relative phase

Phase (waves)

Phase in waves is the fraction of a wave cycle which has elapsed relative to an arbitrary point.-Formula:The phase of an oscillation or wave refers to a sinusoidal function such as the following:...

 of each element. A planar array may be used with a reflecting screen behind the active plane.

A planar array with a reflecting screen is related to a radar absorber

Radar absorbent material

Radar-absorbent material, or RAM, is a class of materials used in stealth technology to disguise a vehicle or structure from radar detection. A material's absorbency at a given frequency of radar wave depends upon its composition...

. Both are supposed not to reflect incoming radiation of the desired wavelength. Radar absorbers have the advantage that they can use magnetic materials to avoid reflections at the interface to air at least for some frequencies. For antennas to be broadband, the transition from air (vacuum) to the metal of the screen has to be a gradual one. Radar absorbers have the advantage that they do not have to collect the received energy. The antenna needs a 3D

Three-dimensional space

Three-dimensional space is a geometric 3-parameters model of the physical universe in which we live. These three dimensions are commonly called length, width, and depth , although any three directions can be chosen, provided that they do not lie in the same plane.In physics and mathematics, a...

 tree of twin-lead

Twin-lead

Twin-lead cable is a two-conductor ribbon cable used as a transmission line to carry radio frequency signals.- Characteristics and uses:...

s and chokes

Choke (electronics)

A choke is a coil of insulated wire, often wound on a magnetic core, used as a passive inductor which blocks higher-frequency alternating current in an electrical circuit while passing signals of much lower frequency and direct current by having an impedance largely determined by reactance, which...

to connect a single cable to a large number of micro antennas.
Micro dipole antennas are only resonant at a single high frequency, to be broadband the arms of adjoining antennas have to be connected.