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Introduction
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WIPL-D Pro is a Method of Moments
(MoM) tool which is using bilinear quads and wire segments as
mesh elements. Higher order basis functions are used on both
plates and wires, meaning that wire segments can be up to 2
wavelengths long. Using wires gives a significant advantage for
modeling wire-like structures since wire numerical models are
much more simple than plate models. Very large wire structures
can be simulated in a matter of seconds or minutes on an
ordinary PC.
Wires are often used to model
simple antennas like monopoles and dipoles placed on large
platforms, a situation in which higher order MoM used in WIPL-D
Pro excels. Wires are also used to build
helix
antennas, which are displayed here in a separate
chapter.
Wires are not meant to be a
replacement for plates in surface modeling (although this is
possible) and that's where WIPL-D Pro differs from wire-grid
tools like the well-known NEC. Using plates for surfaces is a
much more efficient approach. |
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Example: Yagi-Uda Antenna
Yagi-Uda (further Yagi) antenna is array
of dipoles. Radiation of all elements is summed in forward direction.
Yagi antennas are used in radio links for computer networks (Wi-Fi).
Some kinds of Yagi are used for receiving TV and FM radio signals.
Main characteristics of Yagi antennas are
• Gain 5-16 dBi,
• Narrow-band (relative bandwidth is ~10%).
WIPL-D Simulation
Models of Yagi antennas simulated in WIPL-D Pro are presented here.
Simulated Yagi antenna consists of one reflector, one fed dipole and ten
directors. One model is made of wires, while the other model is made of
plates. Wire antenna is shown in Fig. 1, while the plate antenna is
shown in Fig. 2 and the feeding area is zoomed-in in Fig. 3. Dimensions
of both models are the same. That means that every wire in wire model is
replaced by body of rotation and terminated using circle object in the
plate model. We will assume that given antenna is used in B-band (NATO
band classification).
Our aim is to compare simulation times for wire and plate antenna models
and show that wires are viable building blocks for many antenna types
for which they can speed-up the simulation significantly.
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Figure 1. Yagi antenna modeled
with wires |
Figure 2. Yagi antenna modeled
with plates |
In WIPL-D Pro, iterated structures can be
designed using convenient built in features. Antennas shown on Fig. 1
and Fig. 2 can be modeled in several ways but the optimum way is to use
(Anti-) Symmetry feature and Copy/Move manipulations to facilitate
modeling. Metallic parts are considered to be perfectly conducting.
Operating frequency is 266 MHz (B-band).
Radiation pattern in 3D is shown in Fig.
4. Overlaid 2D radiation patterns for a theta-cut are shown in Fig. 5.
As can be seen, there is no difference in calculated radiation pattern
regardless of what type of geometrical entity (wires /plates) is used in
the model.
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 @ 2.83 GHz.
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Figure 3. Yagi antenna modeled
with plates – feeding area and plate approximation |
Figure 4. Radiation pattern of
Yagi antenna made of wires |
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Figure 5. Overlaid 2D radiation
patterns for theta cut |
Figure 6. Radiation pattern of
Yagi antenna made of wires |
Table 1. Analysis characteristics
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Model |
No. of unknowns |
Time @ 266 MHz [sec] |
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Wires |
36 |
1 |
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Plates |
1560 |
24 |
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Conclusion
We conclude that using wires to model a Yagi antenna leads to great
diminishing of simulation time and number of unknowns. Various types of
structures can similarly be simulated using wire models, and not plate
models. Wires can be used to model cylinders whose radius is up to
and whose length is much larger than the radius. In those cases,
simulation is faster hundreds of times, and memory usage can even be
thousands of times lower.
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