Hybrid Bandpass-Absorptive-Bandstop Magnetically Coupled Acoustic-Wave-Lumped-Element-Resonator Filters

This letter presents a novel advancement in acoustic-wave-lumped-element-resonator (AWLR) filters, which improves transmission zero isolation by over 40 dB without adding any additional components. By spacing and orienting the AWLR-lumped inductors for intentional magnetic coupling, a hybrid bandpass-absorptive-bandstop filter is generated. The filter is demonstrated in three configurations using aluminum nitride contour-mode resonators and off-the-shelf lumped elements. Measured performance of as low as 3.2-dB insertion loss, bandwidth of 0.87%, and transmission zero notch depth greater than 60 dB is shown.