Tri-band filter design using substrate integrated waveguide resonators in LTCC

This paper exploits the modal orthogonality to present a new design technique for tri-band filters with minimum number of resonators. Taking advantage of the multiple modes inside one substrate integrated cavity, the coupling mechanisms for different pass bands can be selectively controlled by the modal field distributions. Thus, a tri-band filter of four-pole quasi-elliptic response can be realized by four resonators only. Also, the design can facilitate the feeding design to meet the required external quality factor at the three bands simultaneously. In terms of low-loss co-fired ceramic (LTCC) technology, the cavities are vertically stacked, and the filter size can be miniaturized. The design concept has been verified by both the simulation and measured results.