1. INTRODUCTION

1.1 PROJECT OVERVIEW:

A horn antenna or microwave horn is an antenna that consists of a flaring 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 They are used as feeders (called feed horns) for

larger antenna structures such as parabolic antennas, as standard calibration antennas to measure

the gain of other antennas, and as directive antennas for such devices as radar guns, automatic

door openers, and microwave radiometers. Their advantages are moderate directivity, low

standing wave ratio (SWR), broad bandwidth, and simple construction and adjustment.

One of the first horn antennas was constructed in 1897 by Indian radio researcher Jagadish

Chandra Bose in his pioneering experiments with microwaves. In the 1930s the first

experimental research (South worth and Barrow, 1936) and theoretical analysis (Barrow and

Chu, 1939) of horns as antennas was done. The development of radar in World War 2 stimulated

horn research to design feed horns for radar antennas. The corrugated horn invented by Kay in

1962 has become widely used as a feed horn for microwave antennas such as satellite dishes and

radio telescopes.

An advantage of horn antennas is that since they have no resonant elements, they can operate

over a wide range of frequencies, a wide bandwidth. The usable bandwidth of horn antennas is

typically of the order of 10:1, and can be up to 20:1 (for example allowing it to operate from

1 GHz to 20 GHz). The input impedance is slowly varying over this wide frequency range,

allowing low voltage standing wave ratio (VSWR) over the bandwidth. The gain of horn

antennas ranges up to 25 dBi, with 10 - 20 dBi being typical.

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1.2 TYPES of Horn Antenna:

These 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.

1. Pyramidal horn (a) – 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.

2. Sectorial 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. These types are often used as feed

horns for wide search radar antennas.

3. E-plane horn (b) – A sectorial horn flared in the direction of the electric or E-field in

the waveguide.

4. H-plane horn (c) – A sectorial horn flared in the direction of the magnetic or H-field

in the waveguide.

5. Conical horn (d) – A horn in the shape of a cone, with a circular cross section. They

are used with cylindrical waveguides.

6. Exponential horn (e) – A horn with curved sides, in which the separation of the sides

increases as an exponential function of length. Also called a scalar horn, they can

have pyramidal or conical cross sections. Exponential horns have minimum 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.

7. Corrugated horn – A horn with parallel slots or grooves, small compared with a

wavelength, covering the inside surface of the horn, transverse to the axis. Corrugated

horns have wider bandwidth and smaller side lobes and cross-polarization, and are

widely used as feed horns for satellite dishes and radio telescopes.

8. Ridged horn – A pyramidal horn with ridges or fins attached to the inside of the horn,

extending down the center of the sides. The fins lower the cutoff frequency, increasing

the antenna's bandwidth.

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9. Septum horn – A horn which is divided into several sub horns by metal partitions

(septum’s) inside, attached to opposite walls.

Fig. (1) Different type of Horn Antenna

10. Aperture-limited horn – a long narrow horn, long enough so the phase error is a

negligible fraction of a wavelength, so it essentially radiates a plane wave. It has an

aperture efficiency of 1.0 so it gives the maximum gain and minimum beam width for

a given aperture size. The gain is not affected by the length but only limited by

diffraction at the aperture. Used as feed horns in radio telescopes and other high-

resolution antennas.

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1.3 WORKING:

A horn antenna serves the same function for electromagnetic waves that an acoustical horn does

for sound waves in a musical instrument such as a trumpet. It provides a gradual transition

structure to match the impedance of a tube to the impedance of free space, enabling the waves

from the tube to radiate efficiently into space.

If a simple open-ended waveguide is used as an antenna, without the horn, the sudden end of the

conductive walls causes an abrupt impedance change at the aperture, from the wave impedance

in the waveguide to the impedance of free space, (about 377 ohms). When radio waves travelling

through the waveguide hit the opening, this impedance-step reflects a significant fraction of the

wave energy back down the guide toward the source, so that not all of the power is radiated. This

is similar to the reflection at an open-ended transmission line or a boundary between optical

mediums with a low and high index of refraction, like at a glass surface. The reflected waves

cause standing waves in the waveguide, increasing the SWR, wasting energy and possibly

overheating the transmitter. In addition, the small aperture of the waveguide (less than one

wavelength) causes significant diffraction of the waves issuing from it, resulting in a wide

radiation pattern without much directivity.

To improve these poor characteristics, the ends of the waveguide are flared out to form a horn.

The taper of the horn changes the impedance gradually along the horn's length. 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 taper functions similarly to a tapered transmission

line, or an optical medium with a smoothly varying refractive index. In addition, the wide

aperture of the horn projects the waves in a narrow beam

The horn shape that gives minimum reflected power is an exponential taper. Exponential horns

are used in special applications that require minimum signal loss, such as satellite antennas and

radio telescopes.

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However conical horn and pyramidal horns are most widely used, because they have straight

sides and are easier to design and fabricate.

1.4 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°.

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2. STUDY AND ANALYSIS:

2.1 OPTIMUM HORN:

For a given frequency and horn length, there is some flare angle that gives minimum reflection

and maximum gain. The internal reflections in straight-sided horns come from the two locations

along the wave path where the impedance changes abruptly; the mouth or aperture of the horn,

and the throat where the sides begin to flare out. The amount of reflection at these two sites

varies with the flare angle of the horn (the angle the sides make with the axis). In narrow horns

with small flare angles most of the reflection occurs at the mouth of the horn. The gain of the

antenna is low because the small mouth approximates an open-ended waveguide. As the angle is

increased, the reflection at the mouth decreases rapidly and the antenna's gain increases. In

contrast, in wide horns with flare angles approaching 90° most of the reflection is at the throat.

The horn's gain is again low because the throat approximates an open-ended waveguide.

This discussion shows that there is some flare angle between 0° and 90° which gives maximum

gain and minimum reflection. This is called the optimum horn. Most practical horn antennas are

designed as optimum horns. In a pyramidal horn, the dimensions that give an optimum horn are:

For a conical horn, the dimensions that give an optimum horn are:

WhereaE is the width of the aperture in the E-field direction

aH is the width of the aperture in the H-field direction

LE is the slant length of the side in the E-field direction

LH is the slant length of the side in the H-field direction.

d is the diameter of the cylindrical horn aperture

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L is the slant length of the cone from the apex.

λ is the wavelength

2.2 GAIN:

Horns have very little loss, so the directivity of a horn is roughly equal to its gain. The gainG 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:

For conical horns, the gain is:

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,

The aperture efficiency ranges from 0.4 to 0.8 in practical horn antennas. For optimum

pyramidal horns, eA = 0.511., while for optimum conical horns eA = 0.522. So an approximate

figure of 0.5 is often used. The aperture efficiency increases with the length of the horn, and for

aperture-limited horns is approximately unity.

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3. SOFTWARE SPECIFICATION:

3.1 CST- COMPUTER SIMULATION TECHNOLOGY:

The electromagnetic simulation software CST STUDIO SUITE is the culmination of

many years of research and development into the most accurate and efficient computational

solutions for electromagnetic designs. It comprises CST’s tools for the design and optimization

of devices operating in a wide range of frequencies - static to optical. Analyses may include

thermal and mechanical effects, as well as circuit simulation.

CST STUDIO SUITE benefits from an integrated design environment which gives access

to the entire range of solver technology. System assembly and modeling facilitates multi-physics

and co-simulation as well as the management of entire electromagnetic systems.

CST STUDIO SUITE can offer considerable product to market advantages such as

shorter development cycles, virtual prototyping before physical trials, and optimization instead

of experimentation.

CST STUDIO SUITE comprises the following Modules:

1. CST MICROWAVE STUDIO (CST MWS) is the leading edge tool for the fast and accurate

3D simulation of high frequency devices and market leader in Time Domain simulation. It

enables the fast and accurate analysis of antennas, filters, couplers, planar and multi-layer

structures and SI and EMC effects etc.

2. CST EM STUDIO (CST EMS) is an easy-to-use tool for the design and analysis of static and

low frequency EM applications such as motors, sensors, actuators, transformers, and

shielding enclosures.

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3. CST PARTICLE STUDIO (CST PS) has been developed for the fully consistent simulation

of free moving charged particles. Applications include electron guns, cathode ray tubes,

magnetrons, and wake fields.

4. CST CABLE STUDIO (CST CS) for the simulation of signal integrity and EMC/EMI

analysis of cable harnesses.

5. CST PCB STUDIO (CST PCBS) for the simulation of signal integrity and EMC/EMI EMI

on printed circuit boards.

6. CST MPHYSICS STUDIO (CST MPS) for thermal and mechanical stress analysis.

7. CST DESIGN STUDIO (CST DS) is a versatile tool that facilitates 3D EM/circuit co-

simulation and synthesis.

3.2 CST-MWS’ (CST- Microwave Studio):

CST MICROWAVE STUDIO (CST MWS) is a specialist tool for the 3D EM simulation

of high frequency components. CST MWS' unparalleled performance making it first choice in

technology leading R&D departments.

CST MWS enables the fast and accurate analysis of high frequency (HF) devices such as

antennas, filters, couplers, planar and multi-layer structures and SI and EMC effects.

Exceptionally user friendly, CST MWS quickly gives you an insight into the EM behavior of

your high frequency designs.

CST promotes Complete Technology for 3D EM. Users of our software are given great

flexibility in tackling a wide application range through the variety of available solver

technologies. Beside the flagship module, the broadly applicable Time Domain solver and

the Frequency Domain solver, CST MWS offers further solver modules for specific applications.

Filters for the import of specific CAD files and the extraction of SPICE parameters enhance

design possibilities and save time. In addition, CST MWS can be embedded in various industry

standard workflows through the CST user interface.

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CST MICROWAVE STUDIO is seen by an increasing number of engineers as an

industry standard development tool.

4. DESIGN

4.1 ANTENNA DESIGN AND SIMULATION USING CST:

Antennas are essential wherever wireless communication required. They are the indispensable

link between the contained signal and the “ether”. CST provides a variety of tools for each stage

of the antenna design flow to study and improve your design.

Antenna Magus is a software tool which allows the engineer to make an informed choice

of an appropriate antenna element to suit their requirements, and produces validated designs

which can be analyzed further in CST MICROWAVE STUDIO (CST MWS). Antennas are used

in a vast variety of applications, and thus take come in a vast variety of form factors and

radiation mechanisms. The range of simulation methods in CST MWS allows the engineer to

choose the best technique for each application. The transient solver could be best for wideband

or planar antennas, the frequency domain solver may be more suitable for electrically small

antennas, while the integral equation solver can efficiently simulate electrically large or wire

antennas.

Antennas never operate in isolation, but are attached to a feed network. CST DESIGN

STUDI (CST DS) allows the hybrid co-simulation of the effect of an attached circuit on the

antenna performance. Installation of an antenna in a device or on a platform makes its analysis

even more complex. The System Assembly and Modeling framework in CST DS allows the user

to set up coupled simulations which can combine different solvers automatically by making use

of field sources.

Finally, powerful automated post-processing allows you to extract every magnitude of

interest for an antenna designer – nearfield plots, SAR, phase center, directivity or farfield gain

for single antennas or arrays - and to process those data further for use in parameter sweeps or

optimizations in order to improve the performance of your design.

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4.2 SIMULATION OF CONICAL HORN ANTENNA USING CST

MICROWAVE STUDIO:

1. Select the appropriate Studio which is CST Microwave Studio. To select template for a horn

antenna, click Antenna [Horn, Waveguide].

Fig. (2)

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2. Set the antenna units by click the icon.

Fig. (3)

3. Click the icon, to define the frequency range of horn antenna at Fmin = 4GHz and Fmax =

6GHz.

It can be select by “Solve Frequency”.

Fig. (4)

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4. Select the create cylinder for making waveguide which dimension is given in the below

diagram, on clicking the “ok” button in the below diagram the cylinder is created. Here the PEC

(Perfectly Electrical Conductor) is the material is loaded from library.

Fig. (5)

5. An another cylinder is also making just above the small cylinder as shown in the below

diagram, the dimension of cylinder is also shown.

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Fig. (6)6. Now select the faces of both the cylinder by using “Object --> Pick --> Pick Face” or shortcut

key “f” as shown in below diagram.

Fig. (7)

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7. Now select the option loft by “Objects --> Loft” to join this two faces as shown n the diagram.

Fig. (8)

Here we seen that a horn of specific dimension is prepared according the above diagram but this

horn is solid so in below step we go for solid to the sheet conversion or make it hollow.

8. The total solid objects/structures are three. To combine all the structures, select all

components and click Boolean Add, and this will add all structures into one.

Fig. (9)

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9. Now for solid to sheet conversion, Select the upper and lower face of the Horn and then select

“Objects --> Shell Solid or Thicken Sheet. (0.07 Inside)”.

Fig. (10)

10. For Port definition, click Pick Face to Face 2 edges then move on to

waveguide ports.

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Fig. (11)

11. Mesh view and 3D Monitor:

Click Mesh View icon and set Lines per wavelength = 5, lower mesh limit = 5, and mesh line

ratio limit = 10. Such settings would make the simulation process very faster.

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Fig. (12)

12. For start the simulation process.

(I) Click Solve Field Monitor to ensure the E Field (Set Frequency = 10.58 GHz) is

clicked for the 3D Monitor.

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(II) Click Solve Field Monitor to ensure the Farfield/RCS (Set Frequency = 10.58 GHz)

is clicked for the 3D Monitor.

Fig. (13)

13. Start Transient Solver:

For start Transient Solver, click Solve Transient Solver. Then, set the accuracy at -30dB, by

clicking Accuracy -30dB, and then click Start.

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Fig. (14)

5. RESULTS:

1. When the simulation is completed, from the navigation tree, Find and analyze the result for:

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a) 1D results Port Signal

b) 1D results |S|dB

c) 1D results Smith chart

d) 1D results Energy

2. For find the VSWR, Click, Results S parameter Calculations Calculate VSWR.

The Result of “Calculating VSWR” is shown in the 1D result table in the graph format as shown in

the fig below.

Fig. (15)

3. With the same navigation tree, observe 2D/3D results for E-field at the port for the surface

current.

For electric field observation, click 2D/3D Results E-field Abs right click check

animate fields.

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Fig. (16)

4. CST Microwave Studio also can generate 3D view of farfield radiation pattern.

a) Get the 3D view by clicking Farfields farfield (f=10.58 GHz) Abs.

b) Then, Right click Plot properties farfield and structure view check show structure.

Then, click Apply Ok.

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Fig. (17)

5. 3D can be also plotted into 2D, by right clicking of plot properties and change plot type to

Polar.

Right click Plot properties Plot type Polar Apply Ok

Results for 2D should get same as figure below.

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Fig. (18)

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6. APPLICATIONS:

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.

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7. ADVANTAGES

Multi-band operation

Very low side lobes

Superb cross polarization discrimination (XPD)

Small aperture-limited horn, used as a feed horn in a radio telescope for millimeter

waves.

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8. FUTURE SCOPE:

In this Design the Back Lobe takes more energy so in the future stag we try to reduce the back

lobe and try to transmit the whole energy in the forward direction.

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9. CONCLUSION:

This report discusses the Design and Analysis of Conical Horn Antenna for X-Band

Applications of 8-12 GHz conical horn antenna with high gain, suppressed side lobes, good

VSWR. All requirements for space application have been tried to meet according to international

space Standards. This conical horn antenna can be used in space applications. The procedure is

straight forward, and determines the physical dimensions of a conical horn that determine the

performance of the antenna. To examine the accuracy of this design procedure, antenna was

designed over 8 to 12 GHz with specific electromagnetic features. The measurement results

showed that the antenna's gain of 19.52 dB, directivity is 19.73 dBi, VSWR <1.18,

These measurement confirmed the results of the simulations and satisfied the design

requirements.

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10. REFERENCES:

Horn antenna - Wikipedia, the free encyclopedia

Exp 4 - CST 2010.pdf - Scribd www.scribd.com/doc/147142615/Exp-4-CST-2010-

pdf

CST - Computer Simulation Technology https://www.cst.com/

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