Bandpass Filter and Diplexer Based on Dual-Mode Dielectric Filled Waveguide Resonators

This paper presents the designs of a bandpass filter (BPF) and a diplexer based on the TM
₂₁₀
mode and the TM
₁₂₀
mode of the dielectric filled waveguide resonators (DFWRs). The DFWR is designed by integrating a dielectric main body and a printed circuit board (PCB) cover. The PCB cover is electrically connected with the top surface of the dielectric body. For each mode, metallized blind holes can be set at its maximum electric-field points to excite or extract it and the other mode will not be influenced. Microstrip lines on the PCB are utilized to connect different pairs of the metallized blind holes to form the internal and external coupling structures. For verification, a BPF and a diplexer are designed, fabricated and measured based on the DFWRs. In measurement, the BPF is with a frequency band of 2.515 GHz - 2.675 GHz, an insertion loss of 0.6 dB, and a return loss of 20 dB. The two frequency bands of the proposed diplexer are 3.3 GHz - 3.4 GHz and 3.7 GHz - 3.8 GHz. For the two frequency bands, the measured insertion losses are 0.9 dB/0.85 dB and the isolations are better than 40 dB/50 dB.