{{Short description, Directional antenna Fan1p

A fan-beam antenna is a

directional antenna A directional antenna or beam antenna is an antenna that radiates or receives greater radio wave power in specific directions. Directional antennas can radiate radio waves in beams, when greater concentration of radiation in a certain directio ...

producing a main beam having a narrow

beamwidth The beam diameter or beam width of an electromagnetic beam is the diameter along any specified line that is perpendicular to the beam axis and intersects it. Since beams typically do not have sharp edges, the diameter can be defined in many differ ...

in one dimension and a wider beamwidth in the other dimension. This pattern will be achieved by a truncated

paraboloid In geometry, a paraboloid is a quadric surface that has exactly one axial symmetry, axis of symmetry and no central symmetry, center of symmetry. The term "paraboloid" is derived from parabola, which refers to a conic section that has a similar p ...

reflector or a circular paraboloid reflector. Since the reflector is narrow in the vertical plane and wide in the horizontal, it produces a beam that is wide in the vertical plane and narrow in the horizontal. (The larger the antenna dimension, the narrower the beam.)

Principle

In a

parabolic antenna A parabolic antenna is an antenna that uses a parabolic reflector, a curved surface with the cross-sectional shape of a parabola, to direct the radio waves. The most common form is shaped like a dish and is popularly called a dish antenna or p ...

, the

feed horn A feed horn (or feedhorn) is a small horn antenna used to couple a waveguide to e.g. a parabolic dish antenna or offset dish antenna for reception or transmission of microwaves. A typical application is the use for satellite television rec ...

is placed at the focal point and irradiate the reflector. The latter send back in space a highly focused parallel beam that one can describe as pencil shape. When one removes a section of the

, rays coming from that section are lost. In keeping the antenna only in the horizontal or the vertical, only the rays at right angle to the remaining antenna section will be focused and thus create a narrow beam in that direction while being wide in the other direction.

Usage

Fan beam antennas are used in

radar Radar is a system that uses radio waves to determine the distance ('' ranging''), direction ( azimuth and elevation angles), and radial velocity of objects relative to the site. It is a radiodetermination method used to detect and track ...

sets. Primary radar in airport have often fan-beam with the section of antenna oriented horizontally to give a narrow beam in

azimuth An azimuth (; from ) is the horizontal angle from a cardinal direction, most commonly north, in a local or observer-centric spherical coordinate system. Mathematically, the relative position vector from an observer ( origin) to a point ...

. They must then be complemented with a

height finder A height finder is a ground-based aircraft altitude measuring device. Early height finders were optical range finder devices combined with simple mechanical computers, while later systems migrated to radar devices. The unique vertical oscillating ...

s have the beam oriented horizontally because they cannot locate the altitude. Those have their reflector rotated 90 degrees and produce a beam that is wide in the horizontal plane but narrow in the vertical.

References

Radartutorial
Radar Radio frequency antenna types Antennas (radio) fr:Antenne parabolique#Faisceau plat