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The conventional Vivaldi antenna
typically has at least octave bandwidth and thus it can be used in many
applications. Vivaldi antenna is placed on dielectric substrate and
because of its complex shape and size, it is considered to be not so
easy for modeling and simulation.
Antenna shown here is a balanced antipodal antenna which consists of a
microstrip line and its ground plane which both gradually flare out.
Thus, the lower operating band limit is determined by the cut-off
mechanism of the flare. The skew in the electric field across the slot
makes poor cross-polar polarization performance which degrades with
frequency rising. Antenna is considered as triplate based structure.
That is done by adding additional dielectric and metallization layer,
which is provided for balancing the E-field distribution in the flared
slot. The configuration of antenna uses arcs and elliptically tapered
geometry what is serious test for some software in terms of providing
accurate meshing and far field results.
In November 2000, presented antenna was used for EM solver comparison,
when six software vendors took part in benchmarking. Although WIPL-D
didn’t take part in the benchmarking, we will show here that it the
software is capable for designing and simulating this Vivaldi antenna.
Main characteristics of Vivaldi antenna are
• Broad band,
• Dielectric substrate influence on signal transition.
The picture of Vivaldi antenna with flared slot aperture (taken from the
2000 benchmark) is shown in Fig. 1. Because of complex geometry, full
explanation of antenna model is appropriate here, so we add Figs 2-3 to
show dimensions and shape of the antenna from both sides.
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Figure 1. Vivaldi antenna |
Figure 2. Vivaldi antenna,
dimensions |
Our aim is to inspect S11 parameter from
1 GHz up to 20 GHz, radiation pattern and near field for two operating
frequencies. Also, we will see what is the simulation time, i.e. how
long do we need to simulate this model in entire frequency range. For
near field and radiation pattern, frequencies 3 GHz and 15 GHz will be
used.
WIPL-D Simulation
The model of Vivaldi antenna designed and simulated using WIPL-D Pro is
shown in Fig. 4. The antenna (blue) is printed on dielectric substrate
(red). Dielectric used has permittivity of 2.32 and height of 3.15 mm.
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Figure 3. Dimensions and
explanations of Vivaldi antenna |
Figure 4. Vivaldi antenna model
in WIPL-D Pro |
Computer used for these calculations is Intel® Core2 Quad CPU @ 2.83 GHz. Memory requirements and simulation
times are given in Tab. 1.
Parameter S11 is shown on Fig. 5.
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Figure 5. S11 parameter for
Vivaldi antenna |
Table 1. Simulation
characteristics
|
Model |
Number of unknowns |
Memory [MB] |
Time [sec] |
|
3 GHz |
3160 |
80 |
217 |
|
15 GHz |
17339 |
2400 |
1344 |
|
Radiation patterns and distribution of
near field for 3 GHz and 15 GHz are given on Figs 6-9.
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Figure 6. Radiation pattern at 3
GHz |
Figure 7. Radiation pattern at 15
GHz |
|
Figure 8. Near field at 3 GHz |
Figure 9. Near field at 15 GHz |
Conclusion
WIPL-D Pro offers very efficient simulation of a Vivaldi antenna.
Results given by WIPL-D Pro, presented here, coincide with theoretical
expectations, and agree well with the results presented by most other
software vendors in the software benchmark published in 2000.
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