Filters including loop circuits for phase cancellation

A filtering circuit comprising:

• a primary filter including a plurality of primary acoustic wave elements constructed and arranged to provide the primary filter with a passband and a stopband, the plurality of primary acoustic wave elements including a plurality of series-arm acoustic wave elements connected in series along a signal path between an input of the filtering circuit and an output of the filtering circuit, and a plurality of parallel-arm acoustic wave elements connected between the signal path and a ground;
• and
• a loop circuit including a first capacitor, a second capacitor, and an acoustic wave filter connected in series between the first capacitor and the second capacitor, the first capacitor being connected at an input of the primary filter, the second capacitor being connected at a node along the signal path of the primary filter, a first parallel-arm acoustic wave element of the plurality of parallel-arm acoustic wave elements being connected between the node and the ground, and at least one series-arm acoustic wave element of the plurality of series-arm acoustic wave elements being connected between the node and the output of the primary filter, the acoustic wave filter including a first and second secondary acoustic wave elements each having a signal electrode and a ground electrode and being arranged such that a direction from the signal electrode to the ground electrode is oriented the same in each of the first and second secondary acoustic wave elements, and the loop circuit being configured to attenuate a portion of a signal in the stopband of the primary filter by signal phase cancellation.