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Multihole waveguide coupler is an
extension of a singlehole coupler designed with the intention of
increasing the operational bandwidth. The performance is based on size
of the coupling holes and distance between them as it is important to
achieve wave amplification in the through-direction and cancellation in
the opposite direction. Typically, this type of couplers demonstrates
frequency selectiveness in its directivity response while its coupling
response is less frequency-dependent. Waveguides used correspond to
standard X-band WR 90, with dimensions of 22.86 mm by 10.16 mm (Fig. 1).
Waveguides are coupled through a series of rectangular holes arranged in
zig-zag order (Fig. 2).
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Figure 1. Multihole waveguide
coupler |
Figure 2. Part of the coupler –
arrangement of holes |
WIPL-D Simulation
The model displayed in previous figures is easy to create in WIPL-D Pro
thanks to the possibility of copying and translating few basic building
blocks multiple times to form the coupler. Moreover, the entire model
can be parameterized so influence of parameter changes (such as the size
of the holes or their distance) on model performance can be easily
investigated or the performance of the coupler can be automatically
optimized.
Number of unknowns, memory usage and simulation time are given in Tab.
1.
Simulation is performed in 21 frequencies in the range from 8 to 12 GHz.
The results for the entire range are obtained in just 6.5 minutes, which
is excellent. Computer used for these calculations is Intel ® Core2 Quad at 2.5 GHz clock.
S-parameters are displayed in Fig. 3. We can see that we have a
relatively equal behavior of the device within the hole range of
interest, during which Input stays below -18 dB and Coupling is between
-13 and -11 dB.
Fields inside the coupler are displayed in Fig. 4. A strong standing
wave is present in the excited upper guide, while a part of the energy
is transferred into the lower guide through the holes. As a result, we
can notice a weaker standing wave in the lower guide.
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Table 1. Analysis characteristics
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No. of unknowns |
RAM used [MB] |
Time [sec] |
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2644 |
56 |
201 |
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Figure 3. S-parameters of the
coupler |
Figure 4. Electric field inside
the coupler |
Conclusion
Modeling this structure is easy thanks to the fact that a basic building
block consisting of several plates can be copied and translated in order
to form the coupler model. Simulation is fast and requires a small
amount of computer memory thanks to the application of advanced
numerical techniques such as higher order MoM. WIPL-D Pro provides very
fast and accurate simulation of waveguide structures, whether radiating
(such as slot arrays on waveguides) or closed-region (such as the
presented coupler).
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