Investigations of a New Design Concept for Wide-Band Hybrid Ladder Filters

In this paper, a new design concept for wide-band hybrid ladder filters is investigated. The concept enables manipulation of the fixed behavior and limited electromechanical coupling coefficient (keff2) of acoustic-wave resonators by additional lumped-element resonators. This hybrid approach allows for resonance spreading of single acoustic-wave resonators, which corresponds to an increased keff2. An illustration of the concept is given, as well as an example for the application to wide-band filter design. Measurements of one of two proposed basic structures show an effective increase of keff2 by a factor of more than 4, demonstrating that the concept is feasible in practice.