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UNIVERSITI MALAYSIA PERLIS SCHOOL OF COMPUTER & COMMUNICATIONS ENGINEERING
EKT 341 ANTENNA AND PROPAGATION LABORATORY MODULE
LAB 4
3D STRUCTURE ANTENNA SIMULATION
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3D Structure Antenna Simulation
– Computer Simulation Technology (CST) OBJECTIVES
Learn how to use and familiarize with CST Microwave Studio Software. Understanding the basic horn antenna simulation using CST Microwave Studio Software. Observing and analyzing horn antenna parameters using CST Microwave Studio Software.
THEORY OF HORN ANTENNA
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. The horn antenna gains its name from its appearance. The waveguide can be considered to o pen 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 o f the horn antenna also minimizes the spurious spur ious responses of the parabolic reflector antenna to signals that are not in the main main lobe.
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 LAB 4
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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. There are two basic types of horn antenna: a ntenna: pyramid and conical. The pyramid ones, o nes, 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 beamwidths 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 part icularly 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.
CST MICROWAVE STUDIO STANDARD WORKFLOW; a) Choose Project Template b) Specify Units (Frequency - GHz, Time – ns and Dimension - cm ) c) Parameters + Geometry Geo metry + Materials d) Ports e) Frequency-range + Boundaries / S ymmetries f) Monitor Definition g) Quick Check Meshing h) Run Simulation
HORN ANTENNA DESIGN Figure shows horn antenna with specifications and p arameters to be monitored.
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SIMULATION USING COMPUTER SIMULATION TECHNOLOGY TE CHNOLOGY (CST) SOFTWARE
1. Select the appropriate Studio (1) which is CST Microwave Studio. To select template for a horn antenna, c lick Antenna [Horn,Waveguide].
2. Set the antenna units by click the icon
, and and click the icon
, to define
the frequency range of horn antenna at Fmin = 4 GHz and Fmax = 6 GHz. [2] [1]
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3. Select the [1], for brick dimension is as follows, 4.0 x 2.0 x 3.0 . Then click [2], Pick Face for the brick , and click [3] to Extrude, with Height 10 and Taper 25 (deg) . [1]
[2]
[3]
4. The total solid objects/structures now are two. To combine bo th structures, select both components and click Boolean Add , and this will add two structures into one.
Boolean Add
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5. Click Pick Face on each side (front and rear faces). 6. Find Objects Shell Solid or Thicken Sheet. (0.1 Outside)
Face 2 Face 1
7. For Port definition, definition, click Pick Face to waveguide ports.
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Face 2 edges then move on to
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8. Boundary condition and Symmetry planes a) An antenna is normally being characterized (using network analyzer) with free space surrounding. Therefore, use Boundary Conditions Boundaries, open [add space] for all boundaries to s imulate this environment. b) By knowing that the E plane is YZ plane and H plane is XZ plane for horn antenna, please set YZ plane magnetic [Ht = 0], XZ plane electric [Et =0] and XY plane none
Boundary condition
Symmetry planes
9. 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 faster.
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Please click Solve
Field Monitors to ensure the E Field, H Field/Surface current and Farfield/RCS is clicked for the 3D Monitor.
10. Starts Simulation For Solver settings, click c lick Solve at -30dB, by clicking Accuracy
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Transient Solver. Then, set the accuracy c lick Start -30dB, and then click
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Analyze and explain the result from the question;
1. When the simulation is completed, from the navigation t ree, Find and analyze the result for; a) 1D results Port Signal b) 1D results |S|dB c) 1D results Smith chart d) 1D results Energy 2. Find the VSWR . C lick, Results VSWR.
S parameter Calculations
Calculate
3. With the same navigation tree, o bserve 2D/3D results for E-field and H-field at the port for the surface current. 4. For electric field observation, c lick 2D/3D Results on horn antenna check animate fields.
E-field
Y
right click
5. CST Microwave Studio also can generate generat e 3D view of farfield radiation pattern. a) Get the 3D view by clicking Farfields farfield (f=5) [1] Abs. b) Then, Right click Plot properties farfield and structure view check show structure. Then, click Apply Ok.
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6. 3D can be also a lso plotted into 2D, by right clicking of plot p lot properties and change plot type to Polar. Right click Plot properties Plot type Polar. Results for 2D should get same as figure below.
7. State your observation for question 3, 4, 5 and 6 in your report.
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