Single and Multiband Bandstop Filters With Hybrid Transmission-Line/SAW-Resonator Transversal Filtering Sections

In this paper, new types of hybrid surface-acoustic-wave (SAW) resonator/transmission-line single and multiband bandstop filters(BSFs) are reported. The bandstop filters are based on acoustic-wave-distributed-element-resonators (AWDRs) formed by parallel grounding of transmission lines and SAW resonators, which are cascaded through transmission lines. Through this method, BFS maintains the high Q characteristics of SAW components, and the stopband of BSF can be widened without being constrained by the electromechanical coupling coefficient (k
²
t ) of its SAW resonator. As a theoretical model validation, a single band BSF prototype of 916.5 MHz and a dual-band BSF with two stopbands located at 868.95 and 916.5 MHz were derived, constructed, and tested. The single-band BSF exhibits a stopband 3-dB BW of 1.2 MHz (FBW: 1.0 k
²
t), and the dual-band BSF demonstrates a stopband 3-dB BW of 1.2 MHz (FBW = 1.2 k
²
t) at 868.95 MHz, 1.2 MHz (FBW = 1.0 k
²
t) at 916.5 MHz.