Triband Filter Design Using Laminated Waveguide Cavity in LTCC

This paper demonstrates the flexibility and superiority of multilayer low-temperature cofired ceramic structures in realizing filters with multifunction features. A systematic synthesis technique is employed to develop triband laminated waveguide filters with minimum number of resonators and improved band allocation. By exploiting the multiple resonant modes inside a cavity, the coupling mechanisms and feeding design for different bands can be selectively controlled in accordance with the modal field distributions. Thus, the different passbands can be treated with different methodologies to achieve the multiband function with flexible band allocation. A triband filter operated at 30, 35, and 37 GHz with a fourth-order quasi-elliptic response for the first band and a split-type response for the last two bands is developed. It shows only four cavities are needed with the overall circuit size of 4.9 × 4.1 × 0.88 mm³. Experimental and simulated results are in good agreement, both validate the design concept.