CONICAL HORN                December 24ANTENNA WITHPARABOLICREFLECTORDESIGN                            2012COURSEWORK C   ...
In this third project assignment, we are required to design a parabola reflector antennausing Computer Simulation Technolo...
The horn antenna is placed adjacent to parabolic reflector as such that the wave is to betransmitted parallel to conical h...
The simulation takes up about 5 hours to complete with default mesh properties. Suchlong period is taken because the CST u...
Figure 7: Energy plot.                        Figure 8: Far-field radiation pattern in polar plot.        Based on figure ...
In addition, the direction of the main lobe is at 180.0 degree which is true as the hornantenna needs to radiate the signa...
Figure 11: Radiation pattern of the antenna.        From the screenshots earlier, a very narrow beam is obtained with side...
Figure 13: Power delivered plot.       Other information obtained is the power delivered plot as in figure 13 where at the...
Based on figure 14 and 15, at zero degree, the E-field of magnetic charges is parallel to y-axis while H-field of electric...
Figure 17: Radiation pattern of the antenna with a = 1000 mm.Figure 18: Power delivered of the antenna with a = 1000 mm.  ...
CONCLUSION        The design of a conical horn antenna fed by rectangular waveguide with parabolicreflector is very easy t...
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Conical horn antenna with parabolic reflector using cst

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Conical horn antenna with parabolic reflector using cst

  1. 1. CONICAL HORN December 24ANTENNA WITHPARABOLICREFLECTORDESIGN 2012COURSEWORK C RF DESIGN ECM617NAME: NORAZLIN BINTI MOHAMAD RAZALISTUDENT ID: 2009297332LECTURER: DR. MOHD. KHAIRUL BIN MOHD. SALLEH
  2. 2. In this third project assignment, we are required to design a parabola reflector antennausing Computer Simulation Technology (CST) Studio Suite. CST has number of solvers in it bothfrequency and time domain. However in this project only transient solver is used which is timedomain solver. CST is based on finite domain time difference method (FDTD). The antenna isfront-fed by a circular horn waveguide antenna with rectangular waveguide feed of a givenstandard S as prescribed in the table below. The aperture angle of the conical horn is 60◦. Theantenna is working at 8.2 GHz. Table 1: Frequency bands & interior dimensions of waveguide antenna.Waveguide Frequency Band Freq. Limits (GHz) Inside Dimensions ( mm)Standard, SWR-112 H band 7.05 – 10.00 28.4988 12.6238 𝒍 𝒅 𝟐 𝒂 𝜽 𝒙 𝒅 𝒚 𝒍 𝟑 Figure 1: Conical Horn Waveguide Antenna with parabolic reflector specifications The above antenna design is simulated in CST Design Suite using the followingparameters in Table 2. The model of the antenna in CST is designed with Perfect ConductivityConductor (PEC) as the material. The horn antenna is the combination of a cone, followed by acylinder and then being connected to a rectangular waveguide.Radius of Diameter of Length of cone, l New frequency Distance, Angle ofparabolic (mm) cone, d (mm) (mm) limit (GHz) a (mm) cone, 21000 108 d/(2*tan(pi/6)) 7.05 – 9.35 700 60 Table 2: Conical waveguide antenna with parabolic reflector dimension specifications. 1
  3. 3. The horn antenna is placed adjacent to parabolic reflector as such that the wave is to betransmitted parallel to conical horn aperture in order to be shifted 180 in phase and beingreflected back parallel to the main axis. The final antenna designed in CST is shown in thefollowing figures. Figure 2: Conical horn antenna fed by rectangular waveguide. Figure 3: Back side of the horn antenna. Figure 4: Conical horn antenna with parabolic reflector from side view. 2
  4. 4. The simulation takes up about 5 hours to complete with default mesh properties. Suchlong period is taken because the CST uses time domain transient solver instead of frequencydomain solver in other software for example High Frequency Structure Simulator (HFSS) thatbased on finite element method (FEM). Screenshots of simulation result was obtained andshown below.RESULTS Figure 5: S-parameter S1,1 magnitude vs. frequency Figure 5 shows S-parameter 1D plot marked at frequency of 8.1968 GHz as the nearestfrequency to the operating frequency of this antenna which is 8.2 GHz. The graph shows that themagnitude in dB of its return loss is -12.17. Generally, the preferred value is in the range of -10to -20 dB. However, the value less than -10 dB proved that the antenna is transferring themaximum power and thus almost no power is reflected back. Further adjustments can be madeto achieve its desired performance by varying the distance of the horn antenna to the reflector,a, size of the antenna, and others. Figure 6: Port signal plot 3
  5. 5. Figure 7: Energy plot. Figure 8: Far-field radiation pattern in polar plot. Based on figure 8 shown above, the plot clearly indicates that the main lobe whichresembles correct signal radiation is much bigger than the side lobe level. This fact stronglysuggest this is a good result of directivity because the signal radiates straight at the centre andless signals radiates on its side avoiding from signal loss. This is why horn must be designed soin such a way that waves direction from antenna is perpendicular to horn aperture, as shown inFigure 4. These causes outgoing waves resemble TEM waves. Therefore the gain increasespurity of waves modes increase and finally side lobe level decreases. 4
  6. 6. In addition, the direction of the main lobe is at 180.0 degree which is true as the hornantenna needs to radiate the signal straight to the parabolic reflector since it is being placedperpendicularly to the axis. The angular width at 3 dB is 2.3 degree which is narrow enough asthe directivity of this antenna is quite high and hence the flare angle is small. Therefore, the gainof the antenna should also be high. Having a high directivity is directly related with the fact ofhaving a big aperture where the fields could be generated properly. Figure 9: 3D far-field radiation pattern. Figure 10: 3D far-field radiation pattern from top view. The simulation makes the radiated fields generated by the electric charges and currentscould be determined as shown in figure 9 and 10. We can see that the radiation aperture iscreated inside the waveguide. From the figure also, it is important in a parabolic reflector thatthe position of the feed phase centre exactly at the focus of the reflector. There are importantlosses because of axial defocusing. Hence, the best feed-horns must present the same phasecentre position for E and H planes and as stable as possible in its usable band. 5
  7. 7. Figure 11: Radiation pattern of the antenna. From the screenshots earlier, a very narrow beam is obtained with side lobes createdoutside the waveguide horn. The narrow beam formed is as expected since it is thecharacteristic of a horn antenna with reflector. The side lobes can be treated as a loss if its sizeis dominating the radiation pattern. In figure 9, 10, and 11, we can observe the value ofdirectivity of the antenna is 36.64 dBi. Since the value is greater than 30 dBi, we can say thedirectivity is very good and fulfilling the requirement of the antenna. On the other hand, we have the value of its gain which is 36.62 dB as stated in figure 12below. It is also a desired gain since the best value of gain falls in between the range of 30 to 40dB. Theoretically, the value of the directivity and gain of the antenna is supposed to be the samevalue and in comparison, we have the values differ in a very small value. Hence, the overallperformance of the antenna is very good and closer to what being expected theoretically. Figure 12: 3D radiation pattern. 6
  8. 8. Figure 13: Power delivered plot. Other information obtained is the power delivered plot as in figure 13 where at thefrequency of 8.2 GHz, the total power delivered is 0.9344 Watt. In addition, the total radiatedpower of the antenna is 26.68 dBmW which is high enough as required. Figure 14: E-field of the antenna. Figure 15: H-field of the antenna. 7
  9. 9. Based on figure 14 and 15, at zero degree, the E-field of magnetic charges is parallel to y-axis while H-field of electrical charges is parallel to x-axis. Hence, at the same time, aperpendicular waves that resemble TEM waves formed at the rectangular feed of the horn thatnecessary to generates radiated fields in a stable state.SIMULATION OF ANTENNA WITH a = 1000 mm. The same antenna is simulated at the same frequency with the other value of a which is1000 mm where a is the value of distance between the centre of the parabolic reflector to theaperture of horn antenna. The previous value being used is 700 mm and now we are comparingthe results obtained and summarized in the table as below. Table 3: Comparison of performances of antenna with different value of a. Characteristics being Horn antenna with a = 700 Horn antenna with a = 1000 measured mm mmDirectivity 36.64 dBi 39.61 dBiGain 36.62 dB 39.56 dBReturn loss at S-Parameter -12.17 dB -25.7922 dBTotal radiated power 26.68 dBm Watt 26.93 dBm WattPower delivered at 8.2 GHz 0.9344 Watt 0.9974 Watt The following figures show the result obtained after the simulation. From thecomparison, it is clearly shows that the performance of the antenna is the best at the distance, aof 1000 mm. The farther distance of the horn being placed from the parabolic reflector ensuresthe radiated signal being reflected by the reflector more efficiently since the side lobes formedcan still be reflected instead of losing the signal. The radiated power is at the maximum atfrequency of 8.2 GHz causing the antenna is much better than the previous antenna with smallerdistance of a. Figure 16: S-Parameter of antenna with a = 1000 mm. 8
  10. 10. Figure 17: Radiation pattern of the antenna with a = 1000 mm.Figure 18: Power delivered of the antenna with a = 1000 mm. Figure 19: Polar plot of the antenna with a = 1000 mm. 9
  11. 11. CONCLUSION The design of a conical horn antenna fed by rectangular waveguide with parabolicreflector is very easy to be design using CST. However, the time domain transient solver used bythe software cause the simulation to take so much time to complete the simulation. HFSSsoftware is recommended to simulate such a complex design because it can simulate byfrequency domain solver in a sweep of time. The antenna is working at the given frequency of8.2 GHz with necessary dimensions. The analysis of the overall results of the antenna stronglysuggests that the antenna has achieves its desired performance in terms of directivity and gainwith 36.64 dBi and 36.62 dB respectively. The radiation fields obtained was a narrow beam thatalso resembled a characteristic of a horn antenna with parabolic reflector. Return loss on the S-Parameter plot of less than -10 dB also proved that a maximum power transfer occurred andthus ensures the best performance of the antenna. In addition, polar plot formed shows that theantenna has small side lobes compared to its main lobe. This is a desired performance since theoutgoing waves from the horn successfully propagate in the behaviour of TEM waves towardthe reflector. The comparison between two antennas with different distance from its reflectorshows that the farther distance performed the best achievement with maximum power transferat the required frequency of 8.2 GHz. 10

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