A miniaturized bandpass filter using double folded dual-mode cavity resonators in LTCC

This paper proposes a miniaturized bandpass filter using dual-mode double-folded laminated waveguide cavity resonators on a multilayer low temperature co-fired ceramic (LTCC) substrate. The double-folded cavity is constructed by inserting a metal plate with an L-shape slot at the vertical center of the cavity. By changing the extra metal plate size along the folded side, the frequency ratio of resonant modes TE201 and TE301 can be flexibly adjusted as a dual mode cavity. Two dual-mode cavities are then stacked vertically and fed with two microstrip lines to form a 4^th order Chebyshev Alter, where the coupling and feeding slots are designed according to the field distribution to achieve the desired coupling coefficients and external quality factors for different resonant modes. Designed at center frequency 73.5 GHz with 5.8% fractional bandwidth, the proposed filter has compact size and good frequency responses.