Bandpass filter having resonant holes formed in a block, where the resonant holes include hollowed-out sub regions

Abstract

Provided is a multi-resonator bandpass filter, which comprises a block, an input electrode, and an output electrode. The block comprises an open surface, a short-circuited surface, and a top surface. Multiple of resonant holes are penetrated through the block. The open surface is provided with a first hollowed-out region; the top surface is provided with two second hollowed-out region; the input electrode and the output electrode are disposed on the two second hollowed-out region, respectively. The block further comprises a ground metal layer and a resonant coating layer. Each of the resonant holes is coaxially provided with a first groove and a second groove in the direction from the open surface to the short-circuited surface. The first groove is a rectangular shape in the cross-section parallel to the open surface, and the second groove is substantially a round shape in the cross-section parallel to the open surface.