What is Horn Antenna : Working & Its Applications

The first horn antenna was designed with pioneering experiments through microwaves by a radio researcher namely Jagadish Chandra Bose in 1897. The current horn antenna was invented separately in 1938 by G. C. Southworth & Wilmer Barrow. After that frequent research was done to explain the design of horn-antenna, discover the radiation pattern & its applications in several fields. These antennas are very famous in the domains of waveguide transmission & microwave. So, these antennas are frequently called microwave antennas. So, this article gives talk about horn antenna, working, and its applications.

What is Horn Antenna?

A Horn antenna is a type of aperture antenna which is specially designed for microwave frequencies. The end of the antenna is widened or in the horn shape. Because of this structure, there is larger directivity so that the emitted signal can be easily transmitted to long distances. Horn antennas operate in microwave frequency, so the frequency range of these antennas is super high or ultra-high which ranges from 300 MHz – 30 GHz.

These antennas are used as feed horns for big antennas like parabolic antennas directive antennas, etc. The benefits of using these antennas are simple design & adjustment, low SWR (standing wave ratio), moderate directivity, and broad bandwidth.

Horn Antenna Design & Working

Horn antenna design can be done with a flared waveguide which is formed as a horn. These are used to transmit and receive RF microwave signals. Usually, these are used in combination with waveguide feeds & direct radio waves within a narrow beam. Here, the flared portion can be in any shape like square, conical or rectangular. For proper working, this antenna should be in minimum size. If the wavelength is very large or the horn size is very small then the antenna will not work properly.

In this antenna, the fraction of incident energy can be radiated from the entry of the waveguide and the rest of the energy will be reflected back from the same entry because of the open entry, the poor impedance matching will exist in between the space & waveguide. Also, at the edges of the waveguide, diffraction affects the poor radiating capacity of the waveguide.

So to overcome the drawbacks of the waveguide, its end is opened in an electromagnetic horn form. So that a smooth transition can be allowed in between the space & waveguide thus offering better directivity toward the radio wave.

By changing the waveguide like a horn structure, the existing discontinuity in between the space & waveguide, 377 ohms impedance is eliminated. So this provides the incident energy to be emitted in the forwarding direction by decreasing the diffraction on the edges. Therefore the transmitting antenna’s directivity can be enhanced with superior gain.

The working of the horn antenna is as follows, once the waveguide’s one end is excited then the field can be generated. In general, the fields within the waveguide & free space will transmit in a similar way. But, in the case of propagation with the waveguide, the pnm,ropagating field can be controlled through the waveguide walls so the field will not pass spherically as this is not the case through free-space propagation.

Once the traversing field arrives at the waveguide end then it transmits in the same way as the free space. So, at the waveguide end, spherical wavefronts can be attained.

Types of Horn Antenna

Horn antennas are classified into different types pyramidal, conical and exponential.

Pyramidal Horn Antenna

As the name suggests, this antenna is in a pyramid shape through a rectangular cross-section. This antenna can be formed by flaring both the waveguide walls. In this antenna, a rectangular waveguide is utilized & the flaring can be done within both the direction of magnetic and electric field vectors. These antennas are simply used to radiate linearly polarized radio waves & used with rectangular waveguides.

Sectoral Horn Antenna

It  is a  type of antenna where only one pair of faces are flared whereas the other pair is in parallel.  It generates a fan-shaped thin beam in the flared side’s plane, however broad in the narrow side’s plane. These types of antennas are frequently used as feed horns, especially for wide search radar antennas.

So in this antenna, flaring can be performed simply through one of the waveguide walls. Further, these are classified into two types E-plane and H-plane.

E-plane

Once one of the waveguide walls in an antenna is flared with the electric field vector direction is called an E-plane antenna.

H-plane

Once the waveguide walls in an antenna are flared with the magnetic field vector direction then it is called an H-plane antenna.

Conical Horn Antenna

When an antenna horn is in a cone shape with a circular cross-section is known as a conical horn antenna. These antennas are simply used through cylindrical waveguides. A conical antenna formation is an effect of a circular waveguide flaring. A circular horn antenna can be either biconical or conical within nature.

Exponential Horn Antenna

These antennas are sometimes called scalar horn antennas. As compared to another horn antenna, this antenna is an alternative that has an exponentially tapered face that forms a curved plane from the antenna opening to the termination of the waveguide.

This antenna is known as an exponential horn antenna because the separating space among the sides increases exponentially like a function of length. These types of antennas provide a constant impedance to a huge frequency so there is less possibility of internal reflections. This type of design will reduce the number of internal reflections, permit a constant impedance & electrical performance over an extremely broad bandwidth.

Corrugated Horn Antenna

This type of antenna includes grooves or parallel slots along t and is transverse toward the axis of the antenna. As compared to the wavelength of operation, these designs features are small, allowing extremely low sidelobes & cross-polarization levels above the bandwidth.

These antennas have many benefits like small side lobes and wider bandwidth. The corrugated horn provides a nearly symmetrical design including the E & H plane beam-widths being almost identical. So, these antennas are used as feed horns in radio telescopes & satellite dishes.

Gain of Horn Antenna

The gain of horn antenna can be calculated very easily through design parameters of horn antenna like axial length, path difference, flare angle, and aperture dimension. Generally, Pyramidal horns are designed to give optimal gain. So the gain of this antenna over an isotropic source that equally emits in all directions can be simply derived from the following formula:

Gain = 4πAeA/λ^2

The gain formula for a conical horn antenna can be expressed as

Gain = (π dλ^)2 eA

Where

‘A’ is the physical region of the aperture

‘d’ is the diameter of an antenna aperture

‘λ’ is the wavelength

‘eA’ is the aperture efficiency

The operating of this antenna can be done very efficiently. So the flare of this antenna gives a flat match among the free space & waveguide. Its angle will affect many properties like gain & directivity.

Horn Antenna Radiation Pattern

The horn antenna radiation pattern is a Spherical Wavefront which is shown in the following figure. In this antenna, the waves move as spherical wavefronts to downward of a horn through their source at the top of the horn known as the phase center.

The electric & magnetic fields pattern at the aperture plane at the entrance of the horn will determine the radiation pattern. As the wavefronts are spherical, then phase will be increased smoothly from the aperture plane edges to the center, due to the dissimilarity within the center point length & the edge points from the apex point which is known as the phase error.

This error will be increased through the flare angle, so increases the beamwidth & decreases the gain by providing wider beamwidths horns than parabolic dishes. Once the horn size is increased, then phase error will be increased and provide a wider radiation pattern to the horn.

Maintaining the beamwidth narrow needs a longer horn to maintain the phase error stable. The rising phase error restricts the size of aperture for practical horns to 15 wavelengths because larger apertures need long horns impractically. So this restricts the practical horns gain to 30 dBi & the equivalent smallest beam width to 5 to 10°.

Advantages

The advantages of a horn antenna include the following.

• These antennas can operate over a wide bandwidth, wide range of frequencies since they don’t have resonant elements.
• The beamwidth of the horn antenna is 10:1 ratio (1 GHz – 10 GHz) which is common and 20:1 is possible.
• Designing is simple.
• They are also simple to connect to the waveguide & a coaxial feeder.
• These antennas have a low SWR (standing wave ratio that means they reduce standing waves.
• Good impedance matching.
• Its performance is stable for the entire range of frequencies.
• Small minor lobes can be formed.
• These antennas are used as feed horns for large parabolic antennas.
• Better directivity.
• Avoided standing waves.
• The nonexistence of a resonance element within the construction allows it to work over a wide bandwidth.
• It is extremely directional within nature thus providing higher directivity.
• It provides fewer reflections.

Disadvantages

The disadvantages of horn antennae include the following.

• These antennas will radiate energy in spherical wavefront shape, thus this antenna does not provide a directive or sharp beam.
• They have limited gain like 20 dB, so in order to enhance the antenna gain, the opening of the horn should be made larger so that the length of the horn will become excessive.
• Flare angle design will decide the directivity.
• The length of the flare & Flare angle should not be extremely small.
• The antenna’s directivity depends on the flare angle.
• The flare dimensions must be adequately large otherwise it will make the antenna bulky sometimes.

Applications

The applications of horn antennae include the following.

• These are used mainly for astronomical studies.
• These are used in microwave-based applications.
• These can be used as feed elements.
• These are used in laboratories to measure different antenna parameters.
• At microwave frequencies, these are used wherever moderate gains are adequate.
• The horn dimensions must be high for high gain to use in moderate gain operations.
• These types of antennas are applicable in speed enforcement cameras to keep away from reflections that interrupt the desired response.
• Parabolic reflectors can be excited by feeding elements like horn antennas. So the higher directivity provided through this antenna permits it to light up the reflector.

Thus, this is all about an overview of horn antenna, types, and their applications. These antennas are very popular in the microwave region which provides less VSWR, high gain, fairly wide bandwidth, etc. Here is a question for you, what is an aperture antenna?