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secondary passband and remains
well below the FCC mask.
The test board for this filter
combination is shown in figure 14,
and the measured data for insertion
loss, input and output return loss
is shown in figure 15. The filter
response exhibits a 3 dB passband
from 4.25 to 9.15 GHz (2.2:1 or
73%), and conforms nicely to the
FCC spectral mask. Again, the
reflectionless-LTCC hybrid approach
comes with some tradeoffs that
warrant mention. First, as expected
the filter exhibits reflective behavior
in the upper stopband as seen from
the S11 and S22 plots above 9 GHz.
Second, while the upper stopband
achieves excellent rejection up to 25
GHz, it suffers some unexpected re-
entry around the 30 to 35 GHz region.
A different low pass filter model may
suppress this re-entry at higher
frequencies, but nonetheless, this
example illustrates how reflectionless
filters can be successfully cascaded
with other filter designs to achieve
the desired passband shape for UWB
communications.
Conclusion
The experiments in this article show
how reflectionless filters provide a
Figure 14:
Test board for XHF-
53H+ and LFCN-8400+
Figure 15:
Measurement plots of S21 (black), S11 (red), and S22
(blue) for combined XHF-53H+ and LFCN-8400+, exhibiting a bandpass
response with roughly 73% bandwidth and good stopband rejection
up to 25 GHz. The FCC UWB spectral mask is shown as dotted line
corresponding to right axis
novel and highly viable approach
to filter design for UWB front end
applications. The examples shown
all employ standard, catalog models
available off the shelf from Mini-
Circuits. Mini-Circuits currently
offers over 50 reflectionless filter
models from stock, and custom
designs are available on request to
refine performance to meet exact
application requirements.
The approach demonstrated here
provides designers several practical
advantages
over
previously
studied approaches. In addition
to electrical properties that make
reflectionless filters ideal for the
requirements of UWB applications,
the filters are smaller, less costly,
and more repeatable relative to
competing technologies, making
them suitable candidates for use
in commercial applications where
volume manufacturability may be a
requirement.
While this article highlights the
specific suitability of reflectionless
filters for UWB applications, it
should also broaden the reader’s
appreciation for the flexibility of these
innovative products as building blocks
with many valuable advantages in RF
system design, many of which still
remain to be explored
References
[1] J. Wilson, Intel Corporation, “Ultra-
Wideband: A Disruptive RF Technology?”
Version 1.3, 2002
[2] C. Hsu, F. Hsu, and J. Kuo, “Microstrip
Bandpass Filters for Ultra-Wideband
(UWB) Wireless Communications,” 2005
IEEE MTT-S International Microwave
Symposium Digest, Oct. 2005
[3] J. Pan, “Medical Applications of Ultra-
Wideband (UWB),” Washington University
St. Louis, Apr. 2008, retrieved from http://
www.cse.wustl.edu/~jain/cse574-08/ftp/uwb/index.html
[4] L. Zhu, S. Sun and W. Menzel, “Ultra-
Wideband (UWB) Bandpass Filters Using
Multiple-Mode Resonator,” IEEE Microwave
and Wireless Components Letters, Vol. 15,
No. 11, pp. 796 – 798, Nov. 2005
[5] A. Sheta and I. Elshafley, “Microstrip
Ultra-Wide-Band
Filter,”
PIERS
Proceedings, Marrakesh Morocco, pp. 198
– 200, March 20-23, 2011
[6] C. Cansever, “Design of a Microstrip
Bandpass Filter for 3.1 to 10.6 GHz UWB
systems,” Syracuse University, 2013
New-Tech Magazine Europe l 37