SAW/BAW band reject filters embedded in impedance converter

This paper discusses SAW-BAW-based band reject filters. They are composed of the impedance converters, where capacitive elements are replaced with SAW/BAW resonators. First, basic properties of the unit cell are studied. It is shown how basic properties of a unit cell change with the design. It is also shown that when two notches caused by the resonators are placed in proximity, two synergy effects occur: (i) an extra matching point appears on one side of the transition band. This make the insertion loss at the point smaller and the transition band steeper, and (ii) the dip level becomes deeper, and the total rejection level becomes better. Then, the wide rejection band filter is designed by cascading multi-stages, and effectiveness of the device configurations is demonstrated.