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1. CONICAL HORN December 24
ANTENNA WITH
PARABOLIC
REFLECTOR
DESIGN
2012
COURSEWORK C
RF DESIGN
ECM617
NAME: NORAZLIN BINTI MOHAMAD RAZALI
STUDENT ID: 2009297332
LECTURER: DR. MOHD. KHAIRUL BIN MOHD. SALLEH

2. In this third project assignment, we are required to design a parabola reflector antenna
using Computer Simulation Technology (CST) Studio Suite. CST has number of solvers in it both
frequency and time domain. However in this project only transient solver is used which is time
domain solver. CST is based on finite domain time difference method (FDTD). The antenna is
front-fed by a circular horn waveguide antenna with rectangular waveguide feed of a given
standard S as prescribed in the table below. The aperture angle of the conical horn is 60◦. The
antenna 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, S
WR-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 following
parameters in Table 2. The model of the antenna in CST is designed with Perfect Conductivity
Conductor (PEC) as the material. The horn antenna is the combination of a cone, followed by a
cylinder and then being connected to a rectangular waveguide.
Radius of Diameter of Length of cone, l New frequency Distance, Angle of
parabolic (mm) cone, d (mm) (mm) limit (GHz) a (mm) cone, 2
1000 108 d/(2*tan(pi/6)) 7.05 – 9.35 700 60
Table 2: Conical waveguide antenna with parabolic reflector dimension specifications.
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3. The horn antenna is placed adjacent to parabolic reflector as such that the wave is to be
transmitted parallel to conical horn aperture in order to be shifted 180 in phase and being
reflected back parallel to the main axis. The final antenna designed in CST is shown in the
following 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.
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4. The simulation takes up about 5 hours to complete with default mesh properties. Such
long period is taken because the CST uses time domain transient solver instead of frequency
domain solver in other software for example High Frequency Structure Simulator (HFSS) that
based on finite element method (FEM). Screenshots of simulation result was obtained and
shown 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 nearest
frequency to the operating frequency of this antenna which is 8.2 GHz. The graph shows that the
magnitude in dB of its return loss is -12.17. Generally, the preferred value is in the range of -10
to -20 dB. However, the value less than -10 dB proved that the antenna is transferring the
maximum power and thus almost no power is reflected back. Further adjustments can be made
to 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
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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 which
resembles correct signal radiation is much bigger than the side lobe level. This fact strongly
suggest this is a good result of directivity because the signal radiates straight at the centre and
less signals radiates on its side avoiding from signal loss. This is why horn must be designed so
in such a way that waves direction from antenna is perpendicular to horn aperture, as shown in
Figure 4. These causes outgoing waves resemble TEM waves. Therefore the gain increases
purity of waves modes increase and finally side lobe level decreases.
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6. In addition, the direction of the main lobe is at 180.0 degree which is true as the horn
antenna needs to radiate the signal straight to the parabolic reflector since it is being placed
perpendicularly to the axis. The angular width at 3 dB is 2.3 degree which is narrow enough as
the directivity of this antenna is quite high and hence the flare angle is small. Therefore, the gain
of the antenna should also be high. Having a high directivity is directly related with the fact of
having 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 currents
could be determined as shown in figure 9 and 10. We can see that the radiation aperture is
created inside the waveguide. From the figure also, it is important in a parabolic reflector that
the position of the feed phase centre exactly at the focus of the reflector. There are important
losses because of axial defocusing. Hence, the best feed-horns must present the same phase
centre position for E and H planes and as stable as possible in its usable band.
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7. Figure 11: Radiation pattern of the antenna.
From the screenshots earlier, a very narrow beam is obtained with side lobes created
outside the waveguide horn. The narrow beam formed is as expected since it is the
characteristic of a horn antenna with reflector. The side lobes can be treated as a loss if its size
is dominating the radiation pattern. In figure 9, 10, and 11, we can observe the value of
directivity of the antenna is 36.64 dBi. Since the value is greater than 30 dBi, we can say the
directivity 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 12
below. It is also a desired gain since the best value of gain falls in between the range of 30 to 40
dB. Theoretically, the value of the directivity and gain of the antenna is supposed to be the same
value and in comparison, we have the values differ in a very small value. Hence, the overall
performance of the antenna is very good and closer to what being expected theoretically.
Figure 12: 3D radiation pattern.
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8. Figure 13: Power delivered plot.
Other information obtained is the power delivered plot as in figure 13 where at the
frequency of 8.2 GHz, the total power delivered is 0.9344 Watt. In addition, the total radiated
power 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.
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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, a
perpendicular waves that resemble TEM waves formed at the rectangular feed of the horn that
necessary 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 is
1000 mm where a is the value of distance between the centre of the parabolic reflector to the
aperture of horn antenna. The previous value being used is 700 mm and now we are comparing
the 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 mm
Directivity 36.64 dBi 39.61 dBi
Gain 36.62 dB 39.56 dB
Return loss at S-Parameter -12.17 dB -25.7922 dB
Total radiated power 26.68 dBm Watt 26.93 dBm Watt
Power delivered at 8.2 GHz 0.9344 Watt 0.9974 Watt
The following figures show the result obtained after the simulation. From the
comparison, it is clearly shows that the performance of the antenna is the best at the distance, a
of 1000 mm. The farther distance of the horn being placed from the parabolic reflector ensures
the radiated signal being reflected by the reflector more efficiently since the side lobes formed
can still be reflected instead of losing the signal. The radiated power is at the maximum at
frequency of 8.2 GHz causing the antenna is much better than the previous antenna with smaller
distance of a.
Figure 16: S-Parameter of antenna with a = 1000 mm.
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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.
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11. CONCLUSION
The design of a conical horn antenna fed by rectangular waveguide with parabolic
reflector is very easy to be design using CST. However, the time domain transient solver used by
the software cause the simulation to take so much time to complete the simulation. HFSS
software is recommended to simulate such a complex design because it can simulate by
frequency domain solver in a sweep of time. The antenna is working at the given frequency of
8.2 GHz with necessary dimensions. The analysis of the overall results of the antenna strongly
suggests that the antenna has achieves its desired performance in terms of directivity and gain
with 36.64 dBi and 36.62 dB respectively. The radiation fields obtained was a narrow beam that
also 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 and
thus ensures the best performance of the antenna. In addition, polar plot formed shows that the
antenna has small side lobes compared to its main lobe. This is a desired performance since the
outgoing waves from the horn successfully propagate in the behaviour of TEM waves toward
the reflector. The comparison between two antennas with different distance from its reflector
shows that the farther distance performed the best achievement with maximum power transfer
at the required frequency of 8.2 GHz.
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