Orthogonally-Coupled Dielectric Waveguide Filter with Tunable Transmission Zeros

This paper proposes a compact dielectric waveguide bandpass filter (DWBPF) that uses orthogonally coupled resonators to achieve improved performance, tunable transmission zeros (TZs), and wide out-of-band rejection. In an in-line configuration, cross coupling between non-adjacent resonators is achieved by rotating the resonator between them 90 degrees, making all the resonators perpendicular to each other. Rotating one of the non-adjacent resonators alters the sign of the cross-coupling coefficient, which provides flexibility in controlling the TZs. A third-order bandpass filter with three transmission zeros was designed at 3.5 GHz with 5.4% fractional bandwidth (FBW). The proposed DWBPF is compact in size (6.2×12×6.2 mm3), has low insertion loss and flexibly controllable TZs.