A horn antenna is applied to the transmission and reception of microwave signals. It derives it from the characteristic labile appearance. A horn antenna must be a definite minimum size relative to the wavelength of the incoming or outgoing electromagnetic field. If the horn is too small or the wavelength is too large and the frequency is too low, the antenna will not work efficiently. Horn antennas are generally used as the active element in a dish antenna.
How To Work Horn Antenna
A horn antenna serves a similar function for electromagnetic waves that an acoustical horn does for sound waves in a musical instrument such as a trumpet.
When radio waves traveling via the waveguide hit the opening this impedance-step reflects a very important fraction of the wave power remise the guide unto the source, so that not all of the energy is radiated. This can be the same as the reflection at an open-ended cable between optical mediums with a low and high index of refraction, like a glass surface.
When a wave-guide is suitably excited at one end and opened at the other end a small portion of the energy will be radiated. The reason is a mismatch at the end of the wave-guide with space. If the mouth of the waveguide is opened out, the drawback of mismatch can be avoided. This opening of the wave-guide results in an electromagnetic horn.
When the waveguide is terminated by a horn, the abrupt discontinuity is replaced by a gradual transformation and impedance matching is correct. Hence all the energy travels forward and will be radiated. The shape of a radiated field depends on the flare angle of the horn.
The pyramidal horn and the conical horn give pencil-like beams that have pronounced directivity in both vertical and horizontal planes. Fan-shaped beams result in sectoral horns. The biconical horn produces a pom cake shaped beam in the vertical direction but uniform in the horizontal plane.
Types Of Horn Antenna
There are several types of horn antenna:
- Pyramid horn antenna As the name suggests, the pyramid horn antenna takes on a rectangular shape – the cross-section through the antenna is rectangular, as is the end of the antenna. It is normally used with the rectangular waveguide.
- Has flared on both sides.
- If flaring is done on both the E & H walls of a rectangular waveguide, then pyramidal horn antenna is produced.
- This antenna shape of a truncated pyramid.
- The most standard antenna within the microwave frequency ranges (from 1 GHz up to 18 GHz)
- Sectoral horn antenna: This form of horn antenna is one in which only one pair of sides flared until the other remains parallel. This form of configuration produces a fan-shaped beam, which is narrow in the plane of the flared sides, but wide in the plane of the narrow sides.
- E-plane horn antenna: This form of antenna is one that is flared in the direction of the electric or E-field in the waveguide.
- H plan horn antenna: This form of antenna is one that is flared in the direction of the electric or H-field in the waveguide.
- Conical horn antenna A horn in the shape of a cone, with a notice cross-section. They are used with cylindrical waveguides. It is normally used with circular waveguide and is seen less frequently than the rectangular version.
- Exponential horn antenna This form of horn antenna is known as scalar horn antenna and it is one that has curved sides. The breakage of the sides increases as an exponential function of length. The antenna can come as either pyramidal or conical cross-sections. The advantage of interpretative horns is that they have a minimum level of 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.
- Dual-mode conical 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.
- Corrugated horn: The wavy horn antenna has parallel slots or grooves along the inside surface of the horn, transverse to the axis. These corrugations are small when compared to the wavelength.
Corrugated horns have several advantages including a wider bandwidth and smaller side-lobes that other types. As a result, wavy horn antennas are widely used as feed horns for satellite dishes and radio telescopes.
- Diagonal horn – This simple dual-mode horn outward looks like a pyramidal horn with a square output aperture. On closer reconnoiter, whichever, the square output aperture is seen to be rotated 45° relative to the waveguide. These horns are typically machined into divide blocks and used at sub-mm wavelengths.
- Ridged horn –A pyramidal horn with fins attached to the inside of the horn, diffused down the center of the sides. The fins lower the cutoff frequency, rising the antenna’s bandwidth.
- Aperture-limited horn – a long narrow horn, long enough so the phase mistake is a negligible fraction of a wavelength, so it originally radiates a plane wave. It has an aperture efficiency of 1.0 so it provides the maximum gain and minimum beamwidth for a given aperture size. The gain is not attacked by the length but only limited by diffraction at the aperture. Used the feed horns in radio telecommunication and other high-resolution antennas.
- Septum horn – A horn which divided into several sub horns by metal partitions (septums) inside, attached to opposite walls.
- It is simple in construction.
- It offers a bandwidth of about 10%.
- Horn antenna along with parabolic reflector disc can deliver a high gain.
- Good directivity
- Adequate bandwidth
- Simple mechanical construction
- Convenience to employ with wave-guides
- They can operate over wide range of frequencies.
- Very extensive bandwidth, for example allowing it to operate from 1GHz to 20GHz 20:1
- High Directivity
- High gain
- Support for wide applications
- As primary radiator for paraboloid reflectors
- For satellite tracking purposes
- At communication stations
- Horn antenna emit rays energy in spherical wavefront shape, as a result, horn antenna does not provide a sharp/directive beam.
- Usually, the gain of horn antenna is limited to 20dB. This is due to the fact that in order to increase the gain when the horn opening is made larger, the length of the horn also becomes excessive.
- They are commonly used for higher antenna formation like as parabolic antennas, as directive antennas for like devices as radar guns, automatic doors openers, microwave radiometer, etc.
- The common element of the phased array.
- Satellite and microwave communications.
- Used in the calibration, other high gain antenna.
- Used for making electromagnetic interference measure.
Observations about Horn Antennas
Horn antennas have a high degree of directivity. However, its power is radiated out in a spherical wavefront shape. A conical wavy horn will create a pencil beam, while the pyramidal horn is an else more common, directional antenna. However, it isn’t as directive as something known as yagi or arrow antenna. In theory, a conical wavy horn would have a very low loss. So for any horn antenna, the directivity is almost equal to its gain.