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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

Figure 14: Test board for XHF- 53H+ and LFCN-8400+

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

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

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

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