36 / 84
Figure 11:
Test board for XHF-
292M+ and LFCW-1062+
Figure 12:
Measurement plots of S21 (black), S11 (red), and S22
(blue) for combined XHF-292M+ and LFCW-1062+, exhibiting a
bandpass response with roughly 127% bandwidth and good stopband
rejection up to 40 GHz. The FCC UWB spectral mask is shown as dotted
line corresponding to right
axis.
Figure 13:
Simulation of band pass response combining XHF-53H+ and
LFCN-8400+
with FCC spectral mask for UWB indoor transmissions.
at neighboring frequencies like
GPS at 1.6 GHz clean of emissions.
Note that while the data for the
LTCC filter stops at 15 GHz, it’s
clearly approaching some re-entry
at that point. This is a trade-off
of incorporating a different filter
technology.
The test board for this filter
combination is shown in figure 11,
and the measured data for insertion
loss, input and output return loss
shown in figure 12. This filter has
a measured 3 dB passband from
roughly 2.45 to 10.9 GHz (4.5:1 or
127% bandwidth), very consistent
with the simulation. Combination
with the LTCC filter introduces a few
noteworthy differences from the
previous cases. First, the insertion
loss suffers some re-entry around 25
GHz, enough to just cross the FCC
limit. Also, the return loss in the upper
stopband clearly degrades because
the LTCC filter is fully reflective in its
stopband.
Overall, the filter approaches the
desired response for real-world UWB
transmission, but is still a little wider
than ideal. A similar approach with
the right combination of filters may
come closer to the ideal filter behavior.
Case 5: UWB Filter Meeting
the FCC Emission Mask for
Indoor UWB Transmission
To realize filter response closer
to the ideal for real-world UWB
transmission, carefulmodel selection
led to a combination of three-
section, high pass reflectionless
filter, XHF-53H+ and low-pass LTCC
filter LFCN-8400+. A simulation of
these filters is shown in figure 13
with the FCC mask for indoor UWB
transmission (dotted line and right
axis). The simulated 3 dB passband
is from 3.9 to 9.4 GHz (2.4:1 or
83% bandwidth). Although the
LTCC filter does show some re-
entry in the upper stopband, it isn’t
significant enough as to become a
36 l New-Tech Magazine Europe