Waveguide antennas are a type of antenna that guides RF energy from the air medium into the waveguide. The RF energy is conducted through waveguide interconnections or picked up by coaxial interfaces and then transmitted through coaxial components.Waveguide antennas come in several different types, each with its specific advantages. Today, let's take a closer look at the waveguide horn antenna.
Waveguide horn antenna is a type of aperture antenna, which uses the conductive inner wall of the waveguide to the gradient transition at the end of the horn, causing the waveguide port to undergo an impedance transition matched to free space. This is, of course, frequency dependent, and the gradient of the waveguide horn antenna affects antenna performance. Waveguide horn antennas can be used with any type of waveguide, whether square, circular, or elliptical.
The shape of the horn of a waveguide antenna can also vary according to the desired performance, such as directivity, gain, and antenna radiation pattern. The purpose of the horn is to convert the plane electromagnetic waves (EM) inside the waveguide into a curved wavefront more suitable for propagation in free space. The way the horn flares affects the waveguide horn antenna's directivity/gain, radiation pattern, and bandwidth. Horns can flare in a single slope, curve, or even be nonlinear with ridges or other features (soft horns). Generally, a wider horn will have a broader beamwidth but will sacrifice gain/directivity to achieve this.
Modifications to the horn flare are made to correct undesirable antenna performance, such as significant sidelobes due to phase errors associated with the horn transition in conical/rectangular horns. Additional dielectric structures or conductive features can be added to the waveguide horn antenna shape to alter the horn's impedance and bandwidth characteristics. An example in this regard is the broadband waveguide horn antenna, which can have much higher bandwidth than typical conical or pyramidal horn antennas.
In a waveguide horn antenna, the plane electromagnetic wave conducted through the waveguide gradually transitions into a curved wavefront propagating in free space. In rectangular antennas, the waveguide mode is usually TE10 or TE01 with a curved wavefront. Sectoral horn antennas emit cylindrical wavefronts, while conical horn antennas emit spherical wavefronts. The flare of the horn influences the antenna's gain, beamwidth, and directivity; the wider the flare, the wider the beamwidth, and the lower the directivity and gain. Pyramidal/rectangular horn antennas tend to suffer from significant sidelobes due to phase errors associated with the horn transition. Non-linear flares in horns (soft horns), such as corrugations, dielectric linings, or strips perpendicular to the direction of electromagnetic field propagation, are sometimes used to correct this.
Dielectric lenses can also be added to the end of the waveguide to convert the plane wavefront into a curved wavefront. These horn lens antennas can exhibit higher gain/directivity compared to typical horn designs.
Waveguide horn antennas exhibit high gain and directivity, as well as high power handling and relatively high efficiency. This is why waveguide horn antennas are often used in high-power applications and very high frequencies. Waveguide horn antennas are commonly found in test and measurement facilities and are also deployed in sensing and satellite communication applications. Waveguide horn antennas examples include free-space characterization, electromagnetic compatibility/electromagnetic interference (EMC/EMI) compliance testing, over-the-air (OTA) antenna testing, etc.