Introduction to Waveguide Horn Antenna
Waveguide horn antenna is a kind of aperture antenna. Its internal metal wall gradually transitions to ensure the impedance matching between the waveguide port and the free space. In this way, the aperture and axial length of the waveguide horn antenna can be adjusted to obtain the gain and directivity required for a given application. The waveguide antenna can be a pyramid (rectangular) horn, a conical horn, a sector horn, a horn lens, a corrugated feed horn, a probe or an omnidirectional horn. In addition, the waveguide horn antenna can be designed with metal ridge or dielectric structure, which changes the impedance or bandwidth characteristics of the horn antenna. In general, Waveguide Horn Antennas exhibit high gain and high directional beam characteristics, which makes them very suitable for microwave / millimeter wave testing, sensing (radar) and satellite communication (often paired with truncated Paraboloid Antennas).
（2） Principle and characteristics
In the waveguide horn antenna, the plane electromagnetic wave conducted by the waveguide is gradually transformed into a curved wavefront propagating in free space. In a rectangular antenna, the waveguide mode is usually TE10 or TE01 with a curved wavefront. The sector horn antenna emits cylindrical wavefront, and the conical horn antenna emits spherical wavefront. The flare of the horn affects the gain, beam width and directivity of the antenna response. The wider the flare, the wider the beam width, and the lower the directivity and gain. Pyramidal / rectangular horn antennas often damage considerable sidelobes due to the phase error related to horn transition. Nonlinear flares of horns (soft horns), such as corrugations, dielectric wall linings, or strips perpendicular to the direction of electromagnetic field propagation, are sometimes used to correct this situation.
Various horn antennas exhibit different bandwidth characteristics, but generally "simple" horn structures tend to have narrow operating bandwidth caused by impedance matching transition. To increase this bandwidth, ridges or dielectric lenses / inserts can be added to allow wider bandwidth impedance matching and greater utility of the waveguide band. Dielectric lens can also be used to convert the curved wavefront at the output of horn antenna into plane wavefront. These are often called horn lens antenna.
Considering the high gain, directivity, power processing, etc. of Waveguide Horn, these antennas are often used to test other antennas, free space of electric characteristic medium, electromagnetic compatibility / electromagnetic interference (EMC / EMI), radar and other applications.