Flexible Dual-Band Dielectric Waveguide Filter Based on Degenerate Modes

In this design, a novel flexible dual-band dielectric waveguide filter (DWF) based on degenerate modes is presented. The TM111 mode and TE (111) mode are separated by cutting corners, and they form two distinct passbands. The TE101 mode interacts with the two transmission modes (TMs) as the nonresonating mode. The topology of the filter contains two singlets to generate two transmission zeros (TZs), which improves the isolation between the bands and out-of-band suppression performance. By introducing blind holes in the resonator to modify the electric field distribution of the TMs, independent control of the resonant frequencies of the two TMs is achieved. The center frequencies of the two passbands are regulated from 3.66 to 4.02 GHz and 4.17 to 4.35 GHz, respectively. For demonstration, a dual-band DWF is fabricated and measured, with experimental results exhibiting good filtering characteristics.