page_title: Horn antenna
section_title: Types
hierarchical_section_title: Horn antenna / Types
caption_attribution_description: Deutsch: höhenwinkelgestaffelte Strahler (stacked-beam) eines Radargerätes English: Elevation angle graduated (stacked-beam) feed horns on a German airport surveillance radar. These radiate microwaves which are focused by the radar dish to form a narrow vertical fan-shaped radar beam, which is scanned 360° around the horizon by the rotating antenna. The separate horns allow the elevation angle and thus the altitude of the plane to be determined.
context_page_description: A horn antenna or microwave horn is an antenna that consists of a flaring metal waveguide shaped like a horn to direct radio waves in a beam. Horns are widely used as antennas at UHF and microwave frequencies, above 300 MHz. They are used as feed antennas for larger antenna structures such as parabolic antennas, as standard calibration antennas to measure the gain of other antennas, and as directive antennas for such devices as radar guns, automatic door openers, and microwave radiometers. Their advantages are moderate directivity, low standing wave ratio, broad bandwidth, and simple construction and adjustment.
  One of the first horn antennas was constructed in 1897 by Bengali-Indian radio researcher Jagadish Chandra Bose in his pioneering experiments with microwaves. The modern horn antenna was invented independently in 1938 by Wilmer Barrow and G. C. Southworth The development of radar in World War 2 stimulated horn research to design feed horns for radar antennas. The corrugated horn invented by Kay in 1962 has become widely used as a feed horn for microwave antennas such as satellite dishes and radio telescopes.
context_section_description: Below are the main types of horn antennas. Horns can have different flare angles as well as different expansion curves (elliptic, hyperbolic, etc.) in the E-field and H-field directions,  making possible a wide variety of different beam profiles.
  Pyramidal horn (a, right) – a horn antenna with the horn in the shape of a four-sided pyramid, with a rectangular cross section.  They are a common type, used with rectangular waveguides, and radiate linearly polarized radio waves.
  Sectoral horn – A pyramidal horn with only one pair of sides flared and the other pair parallel.  It produces a fan-shaped beam, which is narrow in the plane of the flared sides, but wide in the plane of the narrow sides.  These types are often used as feed horns for wide search radar antennas.
  E-plane horn (b) – A sectoral horn flared in the direction of the electric or E-field in the waveguide.
  H-plane horn (c) – A sectoral horn flared in the direction of the magnetic or H-field in the waveguide.
  Conical horn (d) – A horn in the shape of a cone, with a circular cross section.  They are used with cylindrical waveguides.
  Exponential horn (e) – A horn with curved sides, in which the separation of the sides increases as an exponential function of length.  Also called a scalar horn, they can have pyramidal or conical cross sections. Exponential horns have minimum internal reflections, and almost constant impedance and other characteristics over a wide frequency range.  They are used in applications requiring high performance, such as feed horns for communication satellite antennas and radio telescopes.
  Corrugated horn – A horn with parallel slots or grooves, small compared with a wavelength, covering the inside surface of the horn, transverse to the axis.  Corrugated horns have wider bandwidth and smaller sidelobes and cross-polarization, and are widely used as feed horns for satellite dishes and radio telescopes.
  Dual-mode conical horn – (The Potter horn ) This horn can be used to replace the corrugated horn for use at sub-mm wavelengths where the corrugated horn is lossy and difficult to fabricate.
  Diagonal horn – This simple dual-mode horn superficially looks like a pyramidal horn with a square output aperture. On closer inspection, however, the square output aperture is seen to be rotated 45° relative to the waveguide. These horns are typically machined into split blocks and used at sub-mm wavelengths.
  Ridged horn – A pyramidal horn with ridges or fins attached to the inside of the horn,  extending down the center of the sides.  The fins lower the cutoff frequency, increasing the antenna's bandwidth.
  Septum horn – A horn which is divided into several subhorns by metal partitions (septums) inside, attached to opposite walls.
  Aperture-limited horn – a long narrow horn, long enough so the phase error is a negligible fraction of a wavelength, so it essentially radiates a plane wave.  It has an aperture efficiency of 1.0 so it gives the maximum gain and minimum beamwidth for a given aperture size.    The gain is not affected by the length but only limited by diffraction at the aperture.  Used as feed horns in radio telescopes and other high-resolution antennas.
caption: Stack of sectoral feed horns for air search radar antenna
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