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Helix antennas are used in space
applications, satellite systems, radar systems, TV signal
transmission, etc. Usually, a helix is manufactured as a wire,
coiled around dielectric cylinder.
Main characteristics of helix antennas are
• Circular polarization,
• Broad-band,
• Two operation modes depending of used frequency,
• For unifilar helices, using a reflector is necessary.
Several models of helix antennas are created and simulated in
WIPL-D Pro and presented here. One model is made of wires;
another model is made of plates while the third model is made of
plates coiled around the dielectric. The wire model is shown in
Fig. 1, plate model is shown in Fig. 2 and plate model with
dielectric rod is shown in Fig. 3. Main dimensions of these
antenna models are the same. Some differences exist, because of
using wires and plates which are of different geometrical
shapes. Parameters of the dielectric are:
•
 ,
•
 . |
Figure 1. Wire helix model |
Analyzed helix antennas consist of
radiating elements and a reflector. Our aim is to compare simulation
times, numbers of unknowns and radiation patterns for simulated
antennas. We will assume that given antenna is used in I-band (NATO
bands classification).
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Figure 2. Plate helix model |
Figure 3. Plate helix model with
dielectric |
WIPL-D Simulation
In WIPL-D Pro, helix antennas can be designed using the built-in Helix
object. Antennas shown in Figs 1-3 can be also modeled “manually” (using
individual wires as building blocks) but that would make modeling
difficult. Here, metallic parts are considered to be perfectly
conducting. Central operating frequency is 9 GHz. All of the antennas
are used in axial mode.
Radiation pattern of the wire helix model
in 3D is shown in Fig. 4. Overlaid 2D radiation patterns for phi cuts
are shown in Fig. 5. Please note that the theta angle is measured with
respect to the xOy plane.
Near field of the wire model is given in Fig. 6. Number of unknowns and
simulation time of analysis are given in Tab. 1. Computer used for these calculations is Pentium® Core2 Quad CPU @ 2.83 GHz.
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Figure 4. Radiation pattern of
wire helix antenna |
Figure 5. Overlaid 2D radiation
patterns for a phi cut |
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Figure 6. Near field of helix
antenna made of wires |
Table 1. Analysis characteristics
|
Model |
No. of unknowns |
Memory
[MB] |
Time @ 9 GHz [sec] |
|
Wires |
401 |
1.2 |
<1 |
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Plates |
751 |
4.5 |
<1 |
|
Plates/dielectric |
2245 |
40.3 |
3 |
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Conclusion
Using WIPL-D Pro Helix object with the possibilities for
parameterization, we can easily create and manipulate helicoidal
structures. As we can see in Tab. 1, proper approximation of plate
helixes using wires can decrease number of unknowns and simulation time.
Gains from replacing plates by wires wherever possible can be much
higher for more complex structures.
We can see (Fig. 5) that helix antenna model with dielectric has
significantly different radiation pattern. Reason for this is dielectric
influence on antenna characteristics. Dielectric is used because of
antenna physical solidity, but it changes the operating band of antenna
and thus must be considered in the design process. The influence of
dielectric is successfully simulated in WIPL-D Pro.
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