Resonator, filter, duplexer, and multiplexer

A filter comprising:

• at least one resonator, the at least one resonator comprising:
• a resonant cavity casing including a resonant cavity and an open end;
• a cover covering the open end and being connected to the resonant cavity casing;
• a resonance tube located inside the resonant cavity;
• a tuning rod disposed inside the resonance tube;
• and
• a dielectric material located in the resonant cavity, wherein the dielectric material is located in a capacitance area formed between a top of the resonance tube and the cover, wherein the dielectric material comprises a dielectric constant greater than 1,
• wherein the tuning rod is rotatable relative to the dielectric material, and
• wherein surfaces of the tuning rod and the dielectric material face each other and comprise non-circular structures so that an overlapping of the surfaces is changeable to adjust a frequency when the tuning rod is rotated relative to the dielectric material.

A duplexer comprising:

• a transmitter channel filter;
• and
• a receiver channel filter, wherein the transmitter channel filter and the receiver channel filter perform filtering by using a filter including at least one resonator, the at least one resonator comprising:
• a resonant cavity casing comprising a resonant cavity and an open end;
• a cover covering the open end and being connected to the resonant cavity casing;
• a resonance tube located inside the resonant cavity;
• a tuning rod disposed inside the resonance tube;
• and
• a dielectric material located in the resonant cavity, wherein the dielectric material is located in a capacitance area formed between a top of the resonance tube and the cover, wherein the dielectric material comprises a dielectric constant greater than 1,
• wherein the tuning rod is rotatable relative to the dielectric material, and
• wherein surfaces of the tuning rod and the dielectric material face each other and comprise non-circular structures so that an overlapping of the surfaces is changeable to adjust a frequency when the tuning rod is rotated relative to the dielectric material.