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Horn antennas are among the simplest and
most widely used antennas. Horns have been used for more than a hundred
years, and today they used in radio astronomy, satellite communications,
in communication dishes as feeders, in measurements, etc. There are two
basic categories of horn antennas:
• Rectangular horns
• Circular horns
Main characteristics of a horn antenna filled with dielectric is side
lobe suppression, decreasing beamwidth and thus increasing gain in
relation to antenna without dielectric. The most important parameters
for operation of this antenna are shown in Fig. 1 and Fig. 2. These
parameters are:
• Length of the antenna (designated as Lhorn)
• Width of the aperture (designated as radius R)
• Characteristics of both, coaxially placed dielectrics are
 and
 .
Figure 1. Circular horn |
Figure 2. Quarter of a circular
horn, interior is filled with dielectric |
WIPL-D Simulation
In WIPL-D Pro, horn antenna given in Fig. 1, can be modeled in a very
simple way, by using several parameterized geometrical objects as
building blocks. One can use the Symmetry feature in both electric and
magnetic plane, so only half or quarter of given antenna can be modeled
(Fig. 2). Antenna is considered to be surrounded by vacuum, i.e. it is
located in free-space. Antenna is filled with two dielectrics, one in a
conical shape along the entire length of the horn and the other in a
disk shape at the aperture.
Dimensions of the rectangular horn model are given in Tab. 1. Operating
frequency is 10 GHz.
For parameters given in Tab. 1, we will calculate gain and near field.
Computer used for these calculations is Pentium Core2 Quad with 2.83 GHz clock.
Radiation pattern in 3D is shown in Fig. 3 and its phi cut, where phi=0
(antenna is placed along x axis) is shown in Fig. 4. Please note that
the theta angle is measured with respect to the xOy plane.
Table 1.
Parameters of analysis
 |
Figure 3. Radiation pattern |
Figure 4. Radiation pattern,
phi-cut |
Calculated near field is shown in Fig. 5.
It illustrates the radiation mechanism of the horn.
Number of unknowns, memory required, and simulation time are given in
Tab. 2.
|
Figure 5. Near field |
Table 2.
Analysis characteristics
|
Model |
No. of unknowns (memory [MB]) |
Time @ 10 GHz [sec] |
|
quarter model |
3801 (115.6) |
75 |
|
Conclusion
The presented antenna is not one of the simplest antennas for EM
modeling and simulation but also not one of the most complex. WIPL-D Pro
provides simulation results in a matter of minutes, demonstrating
efficiency of higher order MoM for models of mid range complexity. The
difference in performance comparing to the rectangular horn model is
mainly due to the introduction of dielectrics which require twice the
number of unknowns (and 4 times more memory) per surface unit than
metals.
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