New-Tech Europe Magazine | Oct 2017 | Digital Edition

Figure 9: Measurement plots of S21 (black), S11 (red), and S22 (blue) for combined XHF-23+ and XLF-73+, exhibiting a bandpass response with roughly 138% bandwidth and good stopband rejection up to 40 GHz.

Figure 8: Test board for XHF- 23+ and XLF-73+

loss, input and output return loss for the two filters on the test board shown in figure 8. The same measurement method was used as in the previous cases. The measured response shows a 3 dB passband from roughly 1.7 to 9.3 GHz (5.5:1 or 138% bandwidth), with stopband rejection well above 15 dB up to 40 GHz. This result confirms that this technique can be used in UWB applications without unintentional emissions out of band due to re-entry. Case 4: Combining Reflectionless Filters and LTCC Filters to Sharpen Selectivity We’ve shown that reflectionless filters can be combined to achieve ultra-wide passbands and that this approach provides excellent stopband rejection up to 40 GHz without re-entry. To come closer to the real-world requirements of a UWB system under FCC specifications, it may be necessary to sharpen the transition to conform to the FCC spectral mask. The absorptive characteristic

Figure 4: Simulation of band pass response combining XHF-292M+ and LFCW-1062+ with FCC spectral mask for UWB indoor transmissions (dotted line and right axis).

of reflectionless filters means that they’re not only cascadable with other reflectionless filters, but also with all manner of conventional filters. This hybrid approach allows us to achieve the desired wideband response while incorporating the selectivity of another filter technology. In this case, we combine a two-section, high pass reflectionless filter (XHF- 292M+) with a low pass LTCC filter

(LFCW-1062+) to take advantage of the greater selectivity of the latter. Simulation results of this combination are shown in figure 10 along with the FCC spectral mask for indoor UWB transmissions (dotted line and right axis). This combination exhibits a passband from 2.4 to 10.9 GHz (4.5:1 or 128% bandwidth). The deep rejection at the lower stopband below 2.4 GHz keeps transmissions

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