The Pros and Cons of Horn Antennas
Horn antennas generally use a flared metal waveguide to direct radio waves in a beam. They can both send and receive a wide range of frequencies. They were invented in the late 19th century and well established by the 1930s. They’re used today for radar guns, door sensors, and microwave radiometers.
Types of Horn Antennas
There are several types of horn antennas, many of which are named for the general shape of the horn.
Pyramid horn antennas have a rectangular shape, giving it a pyramidal ship. They’re usually used with a rectangular waveguide.
A sectoral horn antenna that has two sides flared and two that remain flat and parallel to each other. This creates a fan-shaped beam. E-plan horns are flared in the direction of the electric field of the waveguide; these are usually taller than they are wide. H-plan horns are flared in the H-field of the waveguide; this makes them wide but narrow.
Conical horn antennas have a circular cross-section. They resemble a cone. They’re rarely used but create a circular waveguide. This creates a pencil-like beam.
An exponential horn antenna or scalar horn antenna has curved sides. The curvature increases exponentially with the length. These antennas are notable for their constant impedance across a wide frequency range and very low internal reflections.
Corrugated horn antennas have slots or groves on the inside of the horn. The corrugations are a fraction of the size of the received wavelength. The corrugations give the horn a wider bandwidth and smaller side-lobes. Their radiation patterns are almost symmetrical.
The Pros of Horn Antennas
Horn antennas have a wide bandwidth. Horn antennas with a 10:1 ratio like 1 GHz to 10 GHz are common. Twenty to one ratios are possible.
They’re easy to build; that’s demonstrated by the fact they’ve literally been around for more than a century. They are also straightforward to connect to the waveguide and can be connected to a coaxial feeder.
They have a low standing wave ratio or SWR. In short, they minimize standing waves.
Performance for horn antennas is rather stable over its entire frequency range. Exponential horns have constant impedance over a wide frequency range.
Horn antennas, like Vivaldi antennas, have high gain. Combine it with a parabolic reflector disk to create a Hog-Horn or horn reflector, and you’ll achieve even better gain. Horn antennas used as feed antennas for large parabolic antennas are called “feed horns”. In this application, they have relatively little spillage over the edge of the reflector. The use of a horn antenna with the reflector reduces the spurious signals the antenna would otherwise receive.
The Cons of Horn Antennas
The gain of the horn depends on its aperture dimensions. The horn gain typically tops out at about 20 dB, though 25 dBi is possible. This is because the horn becomes unwieldy if you make it large enough to exceed that level of gain.
The antennas are rarely used below the microwave frequency range, because waveguides are rarely needed at lower frequencies.
The flare angle has a significant impact on the directivity; mess this up when adjusting the horn and you could get very different results than intended.
Observations about Horn Antennas
Horn antennas have a high degree of directivity. However, its energy is radiated out in a spherical wave front shape. A conical corrugated horn will create a pencil beam, while the pyramidal horn is a far more common, directional antenna. However, it isn’t as directive as something like a yagi or arrow antenna. In theory, a conical corrugated horn would have very low loss. For any horn antenna, the directivity is nearly equal to its gain.
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© 2018 Tamara Wilhite