A Ka-band multilayer LTCC 4-pole bandpass filter using dual-mode cavity resonators

This paper proposes a Ka-band 4-pole bandpass filter that uses dual-mode substrate integrated cavity resonator in a multilayer low-temperature co-fired ceramic (LTCC) structure. Circular-shaped dual-mode cavity resonator comprises metallic via arrays in substrate layer, a coupling via in the cavity, and external input and output feeding slots. Size of cavity and feeding slots determine the resonant frequency and quality factor of the resonator. The position of coupling via can control the coupling amount between two degenerate modes in a single cavity structure. Two dual-mode cavities are vertically laminated for fourth-order filter. Cross-shaped slot is used for coupling between the two laminated dual-mode cavity resonators. The cross-shaped slot can cause a coupling between non-adjacent resonators. Therefore the filter can have quasi-elliptic frequency response and high frequency selectivity. Example filter at Ka-band is designed and presented to demonstrate the validity of the new proposed structure.