Multi-resonator bandpass filter

A multi-resonator bandpass filter, comprising:

• a block, that is a substantially rectangular solid shape, comprising an open surface, a short-circuited surface opposite to the open surface, a top surface connected between the open surface and the short-circuited surface, and a plurality of resonant holes;
• wherein the plurality of resonant holes are defined by the'block and extend in parallel from the open surface to the short-circuited surface;
• the open surface is provided with a first hollowed-out region which is disposed around each resonant holes;
• the top surface is provided with two second hollowed-out regions, each of the two second hollowed-out regions is extended to the open surface and in communication with the first hollowed-out region;
• an input electrode is disposed on one of the two second hollowed-out regions, and an output electrode is disposed on the other one of the two second hollowed-out regions;
• the block further comprises a ground metal layer and a resonant coating layer;
• the ground metal layer is coated on the outer surfaces of the block, but the first hollowed-out region and the second hollowed-out region;
• the resonant coating layer is coated inside the resonant holes and is coupled with the ground metal layer at the short-circuited surface to form a short-circuited end:
• each of the resonant holes is coaxially provided with a first groove and a second groove in a direction from the open surface to the short-circuited surface;
• a cross-section of the first in core viewed from the open surface is substantially rectangular, and a cross-section of the second groove viewed from the open surface is substantially round.