Multiband Dielectric Waveguide Bandpass Filters Based on Frequency Mapping Technique

This article proposes a straightforward design approach for the multiband dielectric waveguide bandpass filters (BPFs) by adopting the frequency mapping technique. This technique can transform a single passband of a low-pass prototype into multiple passbands and out-of-band transmission zeros (TZs) can be predefined precisely. A universal coupling topology is proposed for multiband BPFs. The normalized coupling matrix of the proposed coupling topology is constructed only by simple calculations, which makes the design process convenient and straightforward. To verify the universality of the frequency mapping technique in the design of the dielectric waveguide multiband BPFs, four different prototypes are designed, fabricated, and measured. In the designs, the cascaded trisection (CT) or the cascaded quadruplet (CQ) coupling topologies are adopted to introduce TZs aside the passbands so as to improve the frequency selectivity. The four prototypes are a dual-band BPF with one CT, a dual-band BPF with two CTs, a triple-band BPF with one CT, and a dual-band BPF with one CQ. A good matching level between the simulated and measured results has been achieved, indicating that the proposed multiband dielectric waveguide BPFs own the advantages of convenient design process, low insertion loss, and high-frequency selectivity simultaneously.