New-Tech Europe Magazine | Oct 2017 | Digital Edition

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 11: Test board for XHF- 292M+ and LFCW-1062+

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.

Figure 13: Simulation of band pass response combining XHF-53H+ and LFCN-8400+ with FCC spectral mask for UWB indoor transmissions.

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

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