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 UNIVERSITY KIOT PROJECT ON HORN ANTENNA

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 :Horn Antenna

1.1 IntroductionA 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 aim is 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 directionsOther Horn Antenna types:

Multimode Horns Corrugated Horns Hog Horns Biconical Horns Dielectric Loaded Horns etc.

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Chapter 2: Fundamental Parameters Of Horn Antenna

2.1 Horn Antenna Radiation Pattern 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 Antenna Gain

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

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isotropic antenna with the same input power) is:[14]G = 4πA / λ2 eA eqn 2.1For conical horns, the gain is:

G = (πd /λ )2 eA eqn 2.2whereA is the area of the aperture,d is the aperture diameter of a conical hornλ is the wavelength,eA is a dimensionless parameter between 0 and1 called the aperture efficiency.

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 Horn Antenna Radiation Intensity

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 Horn Antenna Directivity

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 Antenna Efficiency

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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http://www.antenna-theory.com/definitions/vswr.php

http://www.antenna-theory.com/definitions/sparameters.php

http://www.antenna-theory.com/basics/directivity.php


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 lineZin= 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 Band Width

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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http://www.antenna-theory.com/basics/bandwidth.php


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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http://www.antenna-theory.com/basics/impedance.php


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: Horn Antenna Design3.1 design ConsiderationsHorns are among the simplest and most widely used microwave antennas and they find applications in the areas of wireless communications, electromagneticsensing 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 thatbesides 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 frombeing radiated and it provides significant level of directivity and gain . While it serves as entry medium for signal interception for processing in the case ofreceiving 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 . Dualmode 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 tomalfunction [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 90degrees, 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 CONSIDERATIONSTo 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 = √ 2λ LE 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 3.412r 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 fromEqn(3.7) below. HC1.3065 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: Application Area

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” IEEEAntennas and Propagation Newsletter, December 1981.

7. V. Rodriguez, “A New Broadband Double RidgeGuide Horn with Improved Radiation Pattern forElectromagnetic Compatibility Testing,”16th International Zurich Symposium onElectromagnetic Compatibility, February 2005

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Engineering

Horn antenna project report