Reflectionless high-selective bandpass filter based on acoustic wave resonators

© 2018, Electromagnetics Academy. All rights reserved. Reflective filters are characterized by a frequency response with good matching at the band of interest and usually reactive impedance out of those frequencies which may adversely affect the system performance. On the other hand, reflectionless filters are characterized by good matching characteristic not only at the interest frequencies, but in the whole frequency spectrum which improves the overall linearity, efficiency, and reduces instability scenarios at the system level. Although several reflectionless structures can be found in the literature, the concatenation of different reflectionless sections, combined with the use of acoustic resonators has not been exploited yet. The particular electrical behavior of acoustic wave resonators, where two different resonant frequencies are found, allow to obtain a frequency response with high selectivity due to the presence of transmission zeros below and above the passband. A bandpass filter has been designed following the described procedure with a fractional bandwidth FBW = 2%, a pair of transmission zeros below and above the bandpass, and an improved out-of-band rejection with respect conventional topologies.