Synthesis and Design of a Dual-Band Diplexer Based on Coaxial Monoblock Dielectric Resonators for 5G Base Stations

This article presents a synthesis and design method for a dual-band diplexer based on coaxial monoblock dielectric resonators (CMDRs) applied in the fifth-generation (5G) base stations. First, a comprehensive synthesis process is analyzed in detail, which starts from the design specifications and ends with the coupling matrix of the entire dual-band diplexer. Then, a CMDR bandpass filter (BPF) with flexible near- passband transmission zeros (TZs) is investigated, which can be used as a general model for the channel BPF of the presented dual-band diplexer. Also, a novel strong feeding structure for multiband CMDR filtering circuits is introduced, which overcomes the limited values of external quality factor
${Q} _{\mathbf {e}}$
. Finally, an example of a dual-band CMDR diplexer is fabricated and measured for demonstration. It realizes four passbands with center frequencies at 1.660, 1.755, 1.847, and 2.037 GHz, respectively. The insertion loss of each channel BPF is less than 1.5 dB, and the corresponding return loss is better than 17 dB. The isolation of over 68 dB can be achieved for the whole frequency band from 1.5 to 2.2 GHz.