In broadcast engineering

Broadcast engineering

Broadcast engineering is the field of electrical engineering, and now to some extent computer engineering and information technology, which deals with radio and television broadcasting...

, directional array refers to an antenna array

Antenna array (electromagnetic)

An antenna array is a group of isotropic radiators such that the currents running through them are of different amplitudes and phases. These are radiators of electromagnetic frequency and energy. Antenna arrays are the solution to the problem defined as the limitations of operating a single antenna...

 arranged such that the superposition

Superposition principle

In physics and systems theory, the superposition principle , also known as superposition property, states that, for all linear systems, the net response at a given place and time caused by two or more stimuli is the sum of the responses which would have been caused by each stimulus individually...

 of the electromagnetic waves produce a predictable electromagnetic field

Electromagnetic field

An electromagnetic field is a physical field produced by moving electrically charged objects. It affects the behavior of charged objects in the vicinity of the field. The electromagnetic field extends indefinitely throughout space and describes the electromagnetic interaction...

. By spacing 2 or more antenna elements apart, changing the length of the transmission line from the transmitter

Transmitter

In electronics and telecommunications a transmitter or radio transmitter is an electronic device which, with the aid of an antenna, produces radio waves. The transmitter itself generates a radio frequency alternating current, which is applied to the antenna. When excited by this alternating...

, varying the power output, and shifting the 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:...

, radio

Radio

Radio is the transmission of signals through free space by modulation of electromagnetic waves with frequencies below those of visible light. Electromagnetic radiation travels by means of oscillating electromagnetic fields that pass through the air and the vacuum of space...

 broadcasters

Broadcasting

Broadcasting is the distribution of audio and video content to a dispersed audience via any audio visual medium. Receiving parties may include the general public or a relatively large subset of thereof...

 can "shape" the area of signal coverage.

Geographically close co-channel

Co-channel interference

Co-channel interference or CCI is crosstalk from two different radio transmitters using the same frequency. There can be several causes of co-channel radio interference; four examples are listed here....

 or adjacent channel

Adjacent channel

In broadcasting an adjacent channel is an AM, FM, or TV channel that is next to another channel. First-adjacent is immediately next to another channel, second-adjacent is two channels away, and so forth. Information on adjacent channels is used in keeping stations from interfering with one...

 stations employ directional arrays (or a single directional antenna

Directional antenna

A directional antenna or beam antenna is an antenna which radiates greater power in one or more directions allowing for increased performance on transmit and receive and reduced interference from unwanted sources....

) so that other broadcasters may utilize the same or adjacent frequency

Frequency

Frequency is the number of occurrences of a repeating event per unit time. It is also referred to as temporal frequency.The period is the duration of one cycle in a repeating event, so the period is the reciprocal of the frequency...

. In the United States

United States

The United States of America is a federal constitutional republic comprising fifty states and a federal district...

, the Federal Communications Commission

Federal Communications Commission

The Federal Communications Commission is an independent agency of the United States government, created, Congressional statute , and with the majority of its commissioners appointed by the current President. The FCC works towards six goals in the areas of broadband, competition, the spectrum, the...

 offers a first-come, first-served

First-come, first-served

First-come, first-served – sometimes first-in, first-served and first-come, first choice – is a service policy whereby the requests of customers or clients are attended to in the order that they arrived, without other biases or preferences. The policy can be employed when processing sales orders,...

 approach, meaning licenses granted on co-channel or adjacent channels must protect the service contour

Service contour

In US broadcasting, service contour refers to the area in which the Federal Communications Commission predicts and allows coverage....

of the previously licensed facility, thus, a directional array may be used to "shape" the station around existing facilities.