Antenna duplexer

An antenna duplexer comprising:

• a first ladder-type acoustic wave filter connected between an antenna terminal and an input terminal and having a first passband in a first frequency band;
• and
• a second ladder-type acoustic wave filter connected between the antenna terminal and an output terminal, the second ladder-type acoustic wave filter having a second passband in a second frequency band higher than the first frequency band, the first and second frequency bands being non-overlapping, the second ladder-type acoustic wave filter including a plurality of series-arm resonators connected in series along a signal path between the antenna terminal and the output terminal, and a plurality of parallel-arm resonators connected between the signal path and a ground, the plurality of parallel-arm resonators including a first parallel-arm resonator and at least one other parallel-arm resonator connected at a position closer to the antenna terminal than the first parallel-arm resonator, the first parallel-arm resonator having an interdigital transducer (IDT) electrode that includes a pair of busbars and a plurality of electrode fingers that extend from the pair of busbars and that interdigitate with each other, the IDT electrode including a constant pitch section in which the plurality of electrode fingers are arranged at a substantially constant first pitch, and at least one narrow pitch section in which the plurality of electrode fingers are arranged at a varying pitch that varies between the substantially constant first pitch and a minimum pitch that is narrower than the substantially constant first pitch.

A communications device comprising:

• an antenna;
• a first ladder-type acoustic wave filter having a first passband in a first frequency band
• a transmission circuit configured to input a transmission signal to the antenna via the first ladder-type acoustic wave filter, the first ladder-type acoustic wave filter being connected in series between the transmission circuit and the antenna, the transmission signal having a frequency within the first frequency band;
• a reception circuit configured to receive a reception signal from the antenna;
• and
• a second ladder-type acoustic wave filter having a second passband in a second frequency band higher than the first frequency band, the first and second frequency bands being non-overlapping, the second ladder-type acoustic wave filter being connected in series between the antenna and the reception circuit and configured to pass the reception signal from the antenna to the reception circuit, the reception signal having a frequency within the second frequency band, the second ladder-type acoustic wave filter including a plurality of series-arm resonators connected in series along a signal path between the antenna and the reception circuit, and a plurality of parallel-arm resonators connected between the signal path and a ground, the plurality of parallel-arm resonators including a first parallel-arm resonator and at least one other parallel-arm resonator connected at a position closer to the antenna than the first parallel-arm resonator, the first parallel-arm resonator having an interdigital transducer (IDT) electrode that includes a pair of busbars and a plurality of electrode fingers that extend from the pair of busbars and that interdigitate with each other, the IDT electrode including a constant pitch section in which the plurality of electrode fingers are arranged at a substantially constant first pitch, and at least one narrow pitch section in which the plurality of electrode fingers are arranged at a varying pitch that varies between the substantially constant first pitch and a minimum pitch that is narrower than the substantially constant first pitch.