A horn antenna is a metal waveguide shaped like a flaring horn that directs radio waves in a beam. It serves as a transition between a waveguide and free space, allowing waves from the waveguide to radiate efficiently into space with minimal reflection. The wide aperture of the horn projects the waves in a narrow beam. Common types of horn antennas include pyramidal, sectoral, conical, and septum horns, which can have different flare angles and expansion curves to produce various beam profiles. A horn antenna works similarly to an acoustic horn, providing impedance matching to efficiently transmit waves from the confined waveguide into open space.

1. HORN ANTENNAS
R.Ramalakshmi
Assistant Professor
Ramco Institute of Technology
Rajapalayam

2. What is Horn Antenna?
• A horn antenna or microwave horn is an antenna
that consists of a flaring (gradually become wider
at one end) metal waveguide shaped like a horn
to direct radio waves in a beam.
• Horns are widely used as antennas at UHF and
microwave frequencies, above 300 MHz.
• A horn antenna is used to transmit radio waves
from a waveguide ( a metal pipe used to carry
waves) out into space, or collect radio waves into
a waveguide for reception.

3. History
• One of the first horn antenna was constructed in
1897 by Indian radio researcher Jagadish Chandra
Bose in his pioneering experiments with
microwaves.
• In the 1930’s the first experimental research and
theoretical analysis of horns as antenna was
done.
• The development of RADAR in world war 2
stimulated horn research to design feed horns for
radar antennas.

4. Description
• It typically consists of a short length of
rectangular or cylindrical metal tube closed at
one end, flaring into an open-ended conical or
pyramidal shaped horn on the other hand.
• The radio waves are usually introduced into
the waveguide by a coaxial cable attached to
the side, with the central conductor projecting
into the waveguide to form a quarter-wave
monopole antenna.

5. • The waves then radiate out the horn end in a
narrow beam.
• In horns installed outdoors, such as the feed
horns of satellite dishes, the open mouth of
the horn is often covered by a plastic sheet
which is transparent to the radio waves, to
keep out moisture.

6. Diagram

7. How it works?
• A horn antenna serves the same function for
electromagnetic waves that an acoustical horn
does for sound waves in a musical instrument
such as trumpet .
• It provides a gradual transition structure to
match the impedance of a tube to the
impedance of the free space, enabling the
waves from the tube to radiate efficiently into
space.

8. • This acts like an impedance matching
transformer, allowing most of the wave
energy to radiate out the end of the horn into
space, with minimal reflection.
• The wide aperture of the horn projects the
waves in a narrow beam.

9. Radiation Pattern

10. Types of Horn Antennas
• The following are the common types of horn
antenna. Horns can have different flare angles as
well as different expansion curves (elliptic,
hyperbolic, etc..) in the E-field and H-field
directions, making possible a wide variety of
different beam profiles.
• Pyramidal Horn
• Sectoral Horn
• Conical Horn
• Septum Horn

11. Pyramidal Horn
• A horn antenna with the horn in the shape of
a four-sided pyramid, with a rectangular
waveguides, and radiate linearly polarized
radio waves.

12. Sectoral Horn
• A pyramidal horn with only one pair of sides
flared and the other pair parallel.
• It produces a fan-shaped beam, which is
narrow in the plane of the flared sides, but
wide in the plane of the narrow sides.

13. Types of Sectoral Horn
• E-plane Horn: A sectoral horn flared in the
direction of the electric E-field in the
waveguide.

14. • H-plane Horn: A sectoral horn flared in the
direction of the magnetic or H-field in the
waveguide.

15. Conical Horn
• A horn in the shape of a cone with a circular
cross section. They are used with cylindrical
waveguides.

16. Septum Horn
• A horn which is divided into several subhorns
by metal partitions (septums) inside, attached
to opposite walls.

22. REFERENCES
• John D Kraus,” Antennas for all Applications”,
3rd Edition, McGraw Hill, 2005.
• Edward C.Jordan and Keith G.Balmain”
Electromagnetic Waves and Radiating
Systems” PrenticeHall of India, 2006
• Constantine.A.Balanis “Antenna Theory
Analysis and Design”, Wiley Student Edition,
2006.

23. Thank You