Horn antenna project report

WOLLO UNIVERSITY, KOMBOLCHA INSTITUTE OF TECHNOLOGY (KIOT)
DEPARTMENT OF ELECTRICAL AND COMPUTER ENGINEERING
(STREAM: ELECTRONIC COMMUNICATION)
PROJECT TITLE: HORN ANTENNA
SUBMIT TO
INSTRUCTOR: AREBU D.
SUBMISSION DATE:MAY 15/2015

WOLLO UNIVERSITYKIOT PROJECTON HORN ANTENNA
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WOLLO UNIVERSITY, KOMBOLCHA INSTITUTE OF TECHNOLOGY (KIOT)
DEPARTMENT OF ELECTRICAL AND COMPUTER ENGINEERING
(STREAM: ELECTRONIC COMMUNICATION)
PROJECT TITLE: HORN ANTENNA
SUBMITTED BY:
STUDENT’S NAME ID.NO.
1. AMSALU SETEY KIOT/0150/04
2. BRHANU ABRHA KIOT/0301 /04
3. FRIEHIWOT BAYE KIOT/0451/04
4. GENET ADEME KIOT/1311/04

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TABLE OF CONTENTS
Chapter 1: Horn Antenna_____________________________________________________4
1.1 Introduction____________________________________________________________5
1.2 Background_____________________________________________________________7
Chapter 2: Antenna parameters________________________________________________7
2.1 Radiation Pattern_____________________________________________________7
2.2 Antenna Gain ________________________________________________________7
2.3 Radiation Intensity____________________________________________________8
2.4 Directivity___________________________________________________________9
2.5 Antenna Efficiency____________________________________________________9
2.6 Antenna Beam Width _________________________________________________10
2.7 Band Width_________________________________________________________12
2.8 Polarization_________________________________________________________12
2.9 Input Impedance_____________________________________________________13
Chapter 3: Design consideration______________________________________________14
A. Impedance consideration___________________________________________14
B. Aperture and slant length considerations_______________________________15
C. Frequency consideration____________________________________________16
D. Money consideration_______________________________________________17
3.1 Material selection_________________________________________________ 17
Chapter 4: Application area__________________________________________________18
Chapter 5: Conclusion______________________________________________________18
5.1 Recommendation____________________________________________________18
References_______________________________________________________________ 19

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Chapter 1 :HornAntenna
1.1 Introduction
A horn antenna is used to transmit radio waves from a waveguide (a metal pipe used
to carry radio waves) out into space, or collect radio waves into a waveguide for
reception. It typically consists of a short length of rectangular or cylindrical metal
tube (the waveguide), closed at one end, flaring into an open-ended conical or
pyramidal shaped horn on the other end. 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.
The waves then radiate out the horn end in a narrow beam. In some equipment the
radio waves are conducted between the transmitter or receiver and the antenna by
a waveguide; in this case the horn is attached to the end of the waveguide. In
outdoor horns, such as the feed horns of satellite dishes, the open mouth of the
horn is often covered by a plastic sheet transparent to radio waves, to exclude
moisture.
 Horn antennas are used for transmission and reception of microwave signal
 Horn antennas are very popular at UHF (300 MHz-3 GHz)
 Higher frequencies as high as 140 GHz.

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1.2 Background
Currently there are many companies developing microwave antennas and highly
sophisticated test systems that range in the millions of dollars. Our aimis to build an
affordable horn antenna, less than $20, and an inexpensive antenna test system
setup. Horn antennas are extremely popular in the microwave region (above 1 GHz).
Horns provide high gain, low VSWR (with waveguide feeds), relatively wide
bandwidth, and they are not difficult to make.
We tend to think about electromagnetic technology as a new or modern
development. The fact is that more than 100 years ago the early pioneers in
electromagnetism were experimenting with horn antennas. Sir Oliver Lodge (1851-
1940) demonstrated microwave waveguide transmission lines in 1894. From there
we just need to go one step further to get a horn antenna. The man that took the
step three years later in 1897 was Sir Jagadish Chandra Bose (1858-1937). Bose’s
horn operated in the millimetre wave range and was able to ring bells and ignite
powder at a distance during his experiments in Calcutta. His horn and waveguide
were circular. These experiments and use of horn antennas makes Bose the father of
this type of antenna and of millimetre wave technology. Incidentally, Bose
performed some of his experiments in the 60 GHz range which is becoming popular
nowadays with the advent of Wireless HD technologies and industry standards such
as IEEE 802.15.3c for Personal Area Networks (PAN).
There are three basic types of rectangular horns:

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Figure 1: Basic types of horn antennas
 H-plane horn (a) – A sectoral horn flared in the direction of the magnetic or H-field in
the waveguide.
 E-plane horn (b) – A sectoral horn flared in the direction of the electric or E-field in
the waveguide.
 Pyramidal horn (c) – a horn antenna with the horn in the shape of a four-sided
pyramid, with a rectangular cross section. They are a common type, used with
rectangular waveguides, and radiate linearly polarized radio waves. Combination of
the E-plane and H-plane horns and as such is flared in both directions
Other Horn Antenna types:
 Multimode Horns
 Corrugated Horns
 Hog Horns
 Biconical Horns
 Dielectric Loaded Horns etc.

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Chapter 2: Fundamental Parameters Of HornAntenna
2.1 Horn AntennaRadiationPattern
The waves travel down a horn as spherical wave fronts, with their origin at the apex
of the horn, a point called the phase center. The pattern of electric and magnetic fields
at the aperture plane at the mouth of the horn, which determines the radiation pattern,
is a scaled-up reproduction of the fields in the waveguide. Because the wave fronts
are spherical, the phase increases smoothly from the edges of the aperture plane to the
center, because of the difference in length of the center point and the edge points from
the apex point. The difference in phase between the center point and the edges is
called the phase error. This phase error, which increases with the flare angle, reduces
the gain and increases the beam width, giving horns wider beam widths than similar-
sized plane-wave antennas such as parabolic dishes.
At the flare angle, the radiation of the beam lobe is down about −20 dB from its
maximum value. As the size of a horn (expressed in wavelengths) is increased, the
phase error increases, giving the horn a wider radiation pattern. Keeping the beam
width narrow requires a longer horn (smaller flare angle) to keep the phase error
constant. The increasing phase error limits the aperture size of practical horns to about
15 wavelengths; larger apertures would require impractically long horns. This limits
the gain of practical horns to about 1000 (30 dBi) and the corresponding minimum
beam width to about 5 - 10°.
2.2 Horn AntennaGain
Horns have very little loss, so the directivity of a horn is roughly equal to its gain.[1] The
gain G of a pyramidal horn antenna (the ratio of the radiated power intensity along its beam
axis to the intensity of an isotropic antenna with the same input power) is:[14]
G = 4πA / λ2 eA eqn 2.1
For conical horns, the gain is:
G = (πd /λ )2 eA eqn 2.2
where
A is the area of the aperture,
d is the aperture diameter of a conical horn
λ is the wavelength,
eA is a dimensionless parameter between 0 and
1 called the aperture efficiency.

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Generally, The gain of horn antenna depends on the ration of horn aperture to the
operating frequency. The directional gain can be increased by enlarging the horn area.
G=6.4xaxb/λ^2
Gain(db)=10 log(G) eqn 2.3
2.3 HornAntennaRadiationIntensity
Radiation intensity in a given direction is defined as the power radiated from an antenna per
unit solid angle. The radiation intensity is a far-field parameter, and it can be obtained by
multiplying the radiation density by the square of the distance. In a mathematical form, it is
expressed
eqn 2.4
Where
U - radiation intensity (W/unit solid angle)
Wrad - radiation density (W/m2)
r - distance (m)
or U = Prad /4∏ eqn 2.5
where Prad =radiated power

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2.4 HornAntennaDirectivity
Horns have very little loss, so the directivity of a horn is roughly equal to its gain.
• low values for S11 or VSWR).
• VSWR: 1.5 Max.
• Port Isolation : -50 db Max
eqn 2.6
eqn 2.7
Where :
G – is represents gain of antenna
D – stands for directivity
ab - area
2.5 Horn AntennaEfficiency
Related with an antenna, there are a number of efficiencies. The total efficiency, takes into
account losses at the input terminals and with the structure of the antenna. Such losses may
be due to reflections because of the mismatch between the transmission line and the antenna,
and R losses (conduction and dielectric). The overall efficiency can be written as
eqn 2.8

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Where
eo = total efficiency (dimensionless)
er = reflection (mismatch) efficiency = (1 − |Γ|2) (dimensionless)e
ec= conduction efficiency (dimensionless)
ed = dielectric efficiency (dimensionless)
Γ= voltage reflection coefficient at the input terminals of the antenna
Γ= (Zin − Zo)/(Zin + Zo) eqn2.9
Where Zo= characteristic impedance of the transmitter line
Zin= antenna input impedance of the transmission line.
V SWR = Voltage Standing Wave Ratio =(1 + |Γ|)/(1 − |Γ|) eqn 2.10
2.6 Horn Antenna Beam Width
Beam-width of an antenna is defined as angular separation between the two
half power points on power density radiation pattern OR Angular separation
between two 3dB down points on the field strength of radiation pattern

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It is expressed in degrees

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2.7 Horn Antenna BandWidth
Horns have a wide impedance bandwidth , is defined as the range of frequencies
within which the performance of the antenna, with respect to some
characteristic, conforms to a specified standard. The bandwidth can be
considered to be the range of frequencies, on either side of a center frequency,
usually the resonance frequency. In this range, the antenna characteristics such
as input impedance, pattern, beam width, polarization, side lobe level, gain, and
radiation efficiency are within an acceptable value of those at the center
frequency.
2.8 Polarization
The polarization of an antenna is the orientation of the electric field (E-plane) of the radio
wave with respect to the Earth's surface and is determined by the physical structure of the
antenna and by its orientation.
A simple straight wire antenna will have one polarization when mounted vertically, and a
different polarization when mounted horizontally.
Reflections generally affect polarization. For radio waves the most important reflector is
the ionosphere - signals which reflect from it will have their polarization changed
LF,VLF and MF antennas are vertically polarized
Polarization of a radiated wave is defined as the property of an electromagnetic wave
describing the time-varying direction and relative magnitude of the electric-field vector. It is
described by the geometric figure traced by the electric field vector upon a stationary plane
perpendicular to the direction of propagation, as the wave travels through that plane. The
three different types of antenna polarizations are shown in figure1.3 Vertical, and horizontal
polarizations are the simplest forms of antenna polarization and they both fall into a category
known as linear polarization. It is also possible that antennas can have a circular polarization.
Circular polarization occurs when two or more linearly polarized waves add together, such
that the E-field of the net wave rotates. Circular polarization has a number of benefits for
areas such as satellite applications where it helps overcome the effects of propagation
anomalies, ground reflections and the effects of the spin that occur on many satellites .
Another form of polarization is known as elliptical polarization. It occurs when there is a mix
of linear and circular polarization. This can be visualized by the tip of the electric field vector

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tracing out an elliptically shaped corkscrew. It is possible for linearly polarized antennas to
receive circularly polarized signals and vice versa. But, there is a 3 dB polarization mismatch
between linearly and circularly polarized antennas .
Figure: elliptical polarization
figure: linear and circular polarization
2.9 Horn Antenna Input Impedance
Horns input impedance is slowly varying over a wide frequency range .
Antenna impedance is presented as the ratio of voltage to current at the antenna’s
terminals. In order to achieve maximum energy transfer the input impedance of the
antenna must identically match the characteristic impedance of the transmission line. If
the two impedances do not match, a reflected wave will be generated at the antenna
terminal and travel back towards the energy source. This reflection of energy results a
reduction in the overall antenna efficiency. The impedance of an antenna, with no load
attached, is defined as:
ZA = RA + jXA eqn 2.11
Where

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ZA= antenna impedance (ohms)
RA= antenna resistance (ohms)
XA=antenna reactance (ohms)
The resistive part
RA = Rr + RL eqn 2.12
Where
Rr= radiation resistance of the antenna
RL= loss resistance of the antenna
The input impedance of an antenna is generally a function of frequency. Thus, the antenna
will be matched to the interconnecting transmission line and other associated equipment only
within a bandwidth. In addition, the input impedance of the antenna depends on many factors
including its geometry, its method of excitation, and its proximity to surrounding objects.
Because of their complex geometries, only a limited number of practical antennas had been
investigated analytically. For many others, the input impedance has been determined
experimentally
Chapter 3: HornAntennaDesign
3.1 design Considerations
Horns are among the simplest and most widely used microwave antennas and they
find applications in the areas of wireless communications, electromagnetic
sensing RF heating and biomedicine . The horn antenna may be considered as an RF
transformer or impedance match between the waveguide feeder and free space
which has an impedance of 377 ohms by having a tapered or having a flared end to
the waveguide. Horn antenna offers several benefits when employed in that
besides matching the impedance of the guide to that of free space or vice versa, it
helps suppress signals travelling via unwanted modes in the waveguide from
being radiated and it provides significant level of directivity and gain . While it serves
as entry medium for signal interception for processing in the case of
receiving systems, it serves in the case of transmission to illuminate dish antenna
from its focal area estimated from the f/d parameters of the parabolic dish . Dual
mode feed horns often provide excellent performance over wide range of
microwave bands. Some design considerations of horn antennas are :
A) Impedance consideration
Impedance matching is very desirable with radio frequency transmission lines.
Standing waves lead to increased losses and frequently cause the transmitted to
malfunction [5].When one considers a waveguide without a horn in operation,
the sudden interface of the conductive walls or free air as the case may be for

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interception or transmission of microwaves cause an abrupt change in
impedance at the interface. This often results in reflections, losses and standing
waves. Also when the flare angle becomes too large as it tends to 90
degrees, the operation tends to assume that of a hornless antenna thereby
resulting in losses, reflections and standing waves. In design, there is an
Optimum flare angle for different horn types where all the aforementioned
problems remain very minimal. Such horn antenna designed with considerations
to the optimum flare angle is often referred to as the optimum horn.
B) APERTURE AND SLANT LENGTH CONSIDERATIONS
To realise an optimum pyramidal horn, the width of the aperture in either the E-
field or the H-field direction is dependent on the intended wavelength and the
slant length of the aperture in either direction as shown below.
AE = √2𝜆LE eqn 3.1
AH = √2𝜆 LH eqn 3.2
Where
AE = width of the aperture in the E – field Direction
LE = Slant length of the aperture in the E – field Direction
AH = width of the aperture in the H – field Direction
LH = Slant length of the aperture in the H – field Direction
𝜆 = wavelength
To realise an optimum conical horn, the diameter of the cylindrical horn aperture is
dependent on the slant length of the cone from the apex as shown below.
d = √3 L eqn 3.3
Where:
d = diameter of the cylindrical horn aperture
L = slant length of the cone from the apex
The bandwidth for practical horn antennas can be of the order of 20:1 for instance, operating
from 1 GHz-20 GHz and while optimum horns give maximum gain for a
given horn length, they do not give maximum gain for a given aperture size.
The gain G of a pyramidal horn antenna is the ratio of the power intensity along its beam axis
to the intensity of an isotropic antenna with the same input power.

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The gain (G) of pyramidal and conical horn are expressed below .
For Pyramidal horn:
G = 4πA / λ2 eA
For Conical horn:
G = (πd /λ )2 eA
Where:
A = area of the aperture
d = aperture diameter for conical
= wavelength
Ea = aperture efficiency, usually btw 0 and 1.
Dimensionless.
Aperture efficiency is a dimensionless factor that increases with the length of the horn.
In Practical horns its value ranges from 0.4 to 0.8 while in optimum pyramidal horns its value
is 0.511and in optimum conical horns it is 0.522. However, an approximate value of 0.5 is
generally used.
C) FREQUENCY CONSIDERATIONS
For any waveguide to be operational at an intended frequency, it must as a critical condition
pass the frequency cut – off tests for it to be operational. The horn low cut-off frequency is
the lowest frequency below which the horn would not function or where cut-off phenomenon
occurs while the horn high cut – off frequency is the highest frequency above which the horn
would not function. The horn low – cut frequency can be estimated from Eqn(6) below.
LC 3.412r eqn 3.4
Where:
LC is the low cut-off wavelength,
r is the radius of the cylinder.
For pyramidal horn with square waveguide, the constant is divided by two, hence we have:
LC (mm) =1.706 base length (mm)eqn
Using standard wavelength formula, low cut off frequency is therefore:
F(GHz) = c/LC eqn 3.6
The horn high – cut frequency can be estimated from
Eqn(3.7) below.
 HC1.3065 base length (mm) eqn 3.7

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Then, equation (3.6) for high cut – off becomes:
F(GHz) =HC eqn 3.8
The lower cut-off must be below the frequency on which you want to operate and the high
cut-off must be above the frequency on which you want to operate. So if the two are 1.54GHz
and 2.66GHz respectively, the horn antenna operates in the band of 1.55GHz to 2.65GHz and
we have to choose a design frequency within this critical frequency range that we intend to
operate the antenna. While the intended frequency F of use is chosen, the wavelength for this
intended frequency also known as free space wavelength can be estimated using the
equation (3.6) which gives:
’(mm)= 300/F’(GHz) eqn 3.9
At either ends of microwave communication system where horn antennas are employed, it is
clear that the integrity of signal intercepted or transmitted depends largely on the design
considerations of the horn antenna. In all, it is essential that while deciding on the intended
frequency of operation, one need to define critical parameters upon which such design would
be predicated such as the cut – off frequency, hence the bandwidth of the horn antenna, the
physical length dimensions, the dipole distance and depth and the hood size. For any
decent design, good judgements on these parameters are extremely essential to the realization
of any sound horn antenna with a decent beam pattern.
D) money
money is essential consideration to design any type of antenna used to buy
different equipments.
3.2 Material Selection
The materials used for building the waveguide and the pyramidal horn is pure copper
with thickness of 0.5486 mm. Copper has a very high electrical conductivity; its
conductivity is second only to silver and the cost is significantly cheaper. This insures the
radio wave transmitted in the waveguide is properly reflected and surface current on
the waveguide does not produce much Ohmic loss. To ensure the copper used in
construction is thick enough for 915 MHz electromagnetic wave to propagate with the
least amount of attenuation.

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Chapter 4: ApplicationArea
 Microwave Heating System
 wireless communication
 used as a feed element for large radio astronomy, satellite tracking and
communication dishes
 A common element of phased arrays
 used in the calibration, other high-gain antennas
 used for making electromagnetic interference measurements
 In Electromagnetic sensing RF heating and biomedicine
Chapter 5: Conclusion
The construction of the horn antennas was simple in terms of paper and
pencil. However, fabrication was far more difficult than anticipated before
we started the project, but we managed to construct the horn antennas and
reach our goal. The resulted measured radiation pattern of the E and H field
supports our expected radiation pattern and the calculation of the
dimensions of the antennas.
5.1 Recommendation
We like to recommend our, Institute kiot (kombolcha institute of
technology)
 There are enough books in library store which describes detail about
antenna, but these books are not available for students to read.
 There is no previous worked projects in the lab and library .
 There is enough full laboratory but we can’t enter inside to test our
project in lab.
 There is no fully completed computer lab for more information
gathering .
 We can’t get enough internet connection to communicate with
professionals who work project previously on antenna design.
Finally, we want to recommend our institute to completely correct or
rearrange problems stated above for students to do good and problem
solving projects.

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 References
1. Bevilaqua, Peter (2009). “Horn antenna - Intro”.
Antenna-theory.com website. Retrieved 2010-11-11.
2. Poole, Ian. “Horn antenna”. Radio-Electronics.com website. Adrio
Communications Ltd. Retrieved 2010-11-11
3. http://en.wikipedia.org/wiki/Horn%20antenna?oldid=662061406
4. Warren L. Stutzman, “Antenna Theory and Design”, John Wiley & Sons,
(1981)
5. Carr, Joseph J, “Practical Antenna Handbook”, TAB BOOKS, (1989)
6. J. Ramsay, “Highlights of Antenna History” IEEE
Antennas and Propagation Newsletter, December 1981.
7. V. Rodriguez, “A New Broadband Double Ridge
Guide Horn with Improved Radiation Pattern for
Electromagnetic Compatibility Testing,”
16th International Zurich Symposium on
Electromagnetic Compatibility, February 2005

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