Waveguide Horn Antenna Primer

Waveguide Horn Antenna Primer

Waveguide Horn Antenna Primer

By: Peter McNeil

A waveguide horn antenna is a type of aperture antenna that is designed with a gradual transition of the inner metallic walls to ensure an impedance match between the waveguide port to free space. In this way, a waveguide horn antenna’s aperture and axial length can be adjusted to achieve the desired gain and directivity for a given application. Waveguide antennas may be pyramidal (rectangular) horn, conical horn, sectoral horn, horn lens, scalar feed horn, probe, or omnidirectional. Additionally, waveguide horn antennas may be designed with metallic ridges or dielectric structures that change the impedance or bandwidth properties of the horn antenna. Generally, waveguide horn antennas exhibit high gain and highly direction beam characteristics, which make them ideal for microwave/millimeter-wave testing, sensing (radar), and satellite communications (often paired with a parabolic dish).

Within the waveguide horn antenna, the planar EM wave conducted by the waveguide is gradually transformed into a curved wavefront for free space propagation. In a rectangular antenna the waveguide modes are generally TE10 or TE01 with a curved wavefront. Sectoral horn antennas emit a cylindrical wavefront where conical horn antennas emit a spherical wavefront. The flaring of the horn impacts the gain, beamwidth, and directivity of the antenna response, with wider flares leading to wider beamwidths with lower directivity and gain. Pyramidal/rectangular horn antennas tend to prejudice substantial sidelobes as a result of the phase error associated with the horn transition. Nonlinear flaring of a horn (soft horn), such as corrugation, dielectric wall liners, or strips transverse to the direction of propagation of the EM field are sometimes used to correct for this.

The various horn antennas exhibit different bandwidth behavior, but generally the “simple” horn structures tend to have a narrow bandwidth of operation caused by the impedance matching transition. In order to enhance this bandwidth, ridges or dielectric lens/inserts may be added to allow for wider bandwidth impedance matching and greater utility of the waveguide band. Dielectric lenses may also be used to convert the curved wavefront on the output of a horn antenna to a planar wavefront, and these are often referred to as horn lens antennas.

Given the high gain, directivity, power handling, etc. of waveguide horns, these antennas are often used in the testing of other antenna, dielectric free space characterization, electromagnetic compatibility/electromagnetic interference (EMC/EMI) testing, radar, and for other applications.

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