Application Note - Nuhertz Technologies, LLC

Application Note
Miniaturized Hairpin Filter Design with FilterSolutions®
and Sonnet Software’s em® Analysis Program
in Microwave Office®
(February, 2014)
Nuhertz Technologies
This application note illustrates the technique for creating a design for a miniaturized
microwave hairpin filter design. The paper follows the synthesized design created by
Nuhertz as it is optimized by using the Sonnet electromagnetic analysis program toolset.
Further processing for simulation and optimization of the circuit is made possible in AWR
Corporation’s Microwave Office® program, an important tool used in this study.
http://www.awrcorp.com/
FilterSolutions creates filter circuits based on user-entered response and design
requirements. The program is used for the design of both Distributed and Lumped
elements. Alternately, the program can also be used in the creation of Digital and Active
filter circuits.
Sonnet Software’s provides a full line of Electromagnetic (em) software products ideal for
high frequency analysis. View the entire suite of programs at:
http://www.sonnetsoftware.com/.
While FilterSolutions’ versatility makes it useful in many applications, the design of a
miniaturized hairpin best demonstrates the seamless tool flow of the FilterSolutions design
into Sonnet’s electromagnetic optimization. Both companys’ programs run on Windows®based PC’s with easy-to-use Graphical User Interfaces.
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Application Note
Tuning and Optimizing
Synthesized planar filters generally require multiple tuning attempts and/or optimizations to
achieve maximum performance. This tuning technique normally requires multiple manual
edits to the synthesized circuit values and repeated electromagnetic optimizations. The
optimization can take the form of using Sonnet’s em port tuning technique. Another
alternative is the use of a circuit simulator compatible with Sonnet’s em®, such as
Microwave Office from National Instruments’ AWR Corporation.
Minimizing Board Space
Traditional Hairpin designs will generally be inefficient in space utilization. There would be
a large amount of wasted space as illustrated in Figure 1.
In addition, Hairpin designs are all-pole designs. This design permits wide bandwidth.
Figure 1
When synthesized using FilterSolutions, the result is a more efficient used of board space
achieved by folding the hairpin ends as shown in Figure 2.
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Application Note
Figure 2
The cross coupling products produce sideband zeroes that result in a narrower passband.
Issues in Analysis
Closed-form circuit level analyses of folded Hairpin filters generally produce poor results
without accounting for the considerable cross-coupling of the folded elements. (Figure 3).
Figure 3
Manual Tuning in FilterSolutions using the Sonnet Export Control Panel
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Application Note
An illustration of the use of the export control panel is shown in Figure 4. Nuhertz
recommends that the ‘Snap-to-Grid’ and ‘Conformal Mesh’ options are utilized. Before the
em analysis is performed, select “Simulate after Launch” then “Save and Close.” (See
Figure 4).
Figure 4
The next step is to move the synthesized circuit into Sonnet by clicking on “Sonnet Direct.”
The resulting Sonnet rendition is as shown in Figure 5.
Figure 5
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Application Note
The circuit response can then be viewed and measured in Sonnet’s em (Figure 6),
Figure 6
and reimported into FilterSolutions with the substitution of the Sonnet generated geometry
as shown in See Figure 7.
Figure 7
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Application Note
The process may be iterated until the desired Sonnet electromagnetic
achieved, as shown in Figure 8.
response is
Figure 8
Co-Calibration
Sonnet has incorporated a technique known as co-calibrated internal ports in their em
program. These internal ports can be inserted into the resutant Sonnet filter before reimporting the design into FilterSolutions. The resultant circuit can then be used as the
target for simulation and optimization using tools such as AWR’s Microwave Office. See
figures 9 and 10, below:
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Application Note
Figure 9: Selecting Co-Calibrated Ports
Figure 10: Representation in Sonnet em
Port Tuning in Microwave Office
Importing the circuit into AWR’s Microwave Office is simple, with well-defined and explicit
directions. The schematic is automatically set up in Microwave Office, looking like the
screen shown as figure 11.
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Application Note
Figure 11
Filter with co-calibrated ports, imported into Microwave Office
The additional small transmission line components are connected into the filter so as to
complete the filter. These “tuning” transmission line components can then be optimized in
Microwave Office so as to realize the desired filter response. The small changes indicated
by the new tuning element values are used to modify the filter layout so as to realize the
tuned response. All of this optimization is done at full circuit theory speed. Since almost the
entire circuit response is due to the Sonnet electromagnetic simulation, the Microwave
Office calculated response has nearly full Sonnet accuracy.
Finally, figure 12 shows the resulting port tuned filter’s electromagnetic response:
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Application Note
Figure 12
Conclusion
A 1 GHz Hairpin resonator filter, with a desired response shape, has been synthesized in
FilterSolutions. The filter was then resynthesized with the substitution of folded hairpin
resonators in lieu of the unfolded topology.
The electromagnetic response, taking all cross-coupling products into account, was
determined using the Sonnet Software program ‘em” After several iterative tuning steps
the internal co-calibrated ports were introduced into the filter architecture.
The filter, now with internal tuning ports was optimized in AWR’s Microwave Office to
achieve best response results.
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Application Note
Sales Representatives and Distributors
Europe and South Africa
Israel
John Kitchen
SJ Technologie, Northants, UK
Tel: +0333 123 4640
Intl.: +44 (0) 333 123 4640
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Victor Sharir
Galormic, Qiryat Tivon
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Cell: +972 54 5616606
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North and South America
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Alan Egger
Nuhertz Technologies, Roseland, NJ
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Jeff Kahler
Nuhertz Technologies, Phoenix, AZ
Tel: +1 602-279-2448
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