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Mapping CO, PO, Domain, KI : CO2, CO3, PO3, P5

CO2: Analyze the parameters of antenna such as radiation pattern, impedance,

directivity, gain, polarization

CO3: Design and evaluate various antennas to meet application requirements

PO3: Identify, formulate and provide effective solution to engineering problem

L�� ���� O���m��: a) Model a horn antenna in CST Microwave Studio Software

b) Observe and analyze the radiation characteristic of a horn antenna parameters

using CST Microwave Studio Software.

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The horn antenna is used in the transmission and reception of RF microwave signals,

and the antenna is normally used in conjunction with waveguide feeds.

Physical Description

The horn antenna gains its name from its appearance. The waveguide can be

considered to open out or to be flared, launching the signal towards the receiving

antenna. Horn antennas are often used as gain standards, and as feeds for parabolic or

'dish' antennas, as well as being used as RF antennas in their own right. One particular

use of horn antennas themselves is for short range radar systems, such as those used

for automotive speed enforcement. When used as part of a parabolic reflector, the

horn is orientated towards the reflector surface, and is able to give a reasonably even

illumination of the surface without allowing radiation to miss the reflector. In this way

it is able to maximize the efficiency of the overall antenna. The use of the horn antenna

also minimizes the spurious responses of the parabolic reflector antenna to signals

that are not in the main lobe.

There are two basic types of horn antenna: pyramid and conical. The pyramid ones, as

the name suggests are rectangular whereas the corrugated ones are usually circular.

The corrugated horn provides a pattern that is nearly symmetrical, with the E and H

plane beam widths being nearly the same. Additionally it is possible to control the side

lobes better with a conical or corrugated horn antenna. The horn antenna is a

particularly useful form of antenna for use with RF microwave applications and

waveguide feeder. Although it is not used below RF microwave frequencies because

waveguides are not used at low frequencies as a result of the sizes needed, the horn

antenna is nevertheless a very useful form of RF antenna design for use at high

frequencies.

Figure 1: The Structure of a Horn Antenna

Operation Mechanism

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 the horn antenna is

formed and this enables the impedance to be matched. Although the waveguide will

radiate without a horn antenna, this provides a far more efficient match. In addition to

the improved match provided by the horn antenna, it also helps suppress signals

travelling via unwanted modes in the waveguide from being radiated. However the

main advantage of the horn antenna is that it provides a significant level of directivity

and gain. For greater levels of gain the horn antenna should have a large aperture.

Also to achieve the maximum gain for a given aperture size, the taper should be long

so that the phase of the wave-front is as nearly constant as possible across the

aperture. However there comes a point where to provide even small increases in gain,

the increase in length becomes too large to make it sensible. Thus gain levels are a

balance between aperture size and length. However gain levels for a horn antenna

may be up to 20 dB in some instances.

S�m������ �� CST M�� w�v� D����� S����

Good Habit

1. SAVE EARLY AND OFTEN

2. CST is notorious for crashing at the most inopportune times. Do yourself a

favor and save in your flash memory.

3. Make sure all components/structures are connected. Loose wires are a

frequent cause of problems.

4. Try your hand at debugging first before calling me ☺. You will learn a lot by

struggling through problems that seem hard at first.

5. Read all background behind the antenna and the lab instructions carefully

before starting the lab. Often, there will be a little detail that ends up being

very important.

CST Work Flow

6. Choose Project Template

7. Specify Units (� �q����� - GHz, T�m� – �� ��� D�m����� - �m)

8. Parameters + Geometry + Materials

9. Ports

10. Frequency-range + Boundaries / Symmetries

11. Monitor Definition

12. Quick Check Meshing

13. Run Simulation

Horn Antenna Modelling in CST Design Studio

1. Click “create project” and then select “Antennas”, then click “Next”

2. Select a Workflow

3. Select units

4. New template summary - verify

5. Background Material, Set Frequency

6. Construct Horn Antenna

7. Continue to construct Horn Antenna structure

8. Use function Shell

9. Define Port

10. Boundary Condition

11. Set 3D Monitors

12. Mesh View

13. Start Transient Solver

14. Analyze 1D results

15. Analyze 2D results

16. Electric Field at 10 GHz

17. Farfield at 10 GHz

18. Polar Plot at 10 GHz

19. Parameterization

20. Parameterization

21. Result Processing Template

22. Result Processing Template

23. Result Processing Template

24. Parameter Sweep setting

25. Parameter Sweep Results

�v������� L�b 2 (5%) Print this and present it to me when you demonstrate your work.

R�q�� �m��� �����

Complete the lab on time /1

Show horn antenna structure /2

Show simulation results 2D - polar plot /2

Show parameter sweep results /2

Answer correctly /3

Total /10

1. Describe the operating bandwidth of the horn antenna.

2. What are the parameters that influence the operating frequency of the

antenna?

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