A compact dual-band filter based on dual-mode resonators

A dual-band filter has been designed and fabricated using two dual-mode resonators. Current distributions of four modes of this filter are investigated using full-wave electromagnetic simulations. It shows that the folded canonical topology can be realized using the proposed dual-mode filter structure. A dual-band filter is optimized using an analytical procedure and the corresponding coupling matrix with folded topology structure is synthesized. The designed topology exhibits a dual-band response with center frequencies of 3.05 GHz and 3.21 GHz and in between isolation of 20 dB created by two in-band transmission zeros. The designed dual-band filter shows insertion losses better than 3.4 dB for low-band and 2.6 dB for high-band, and narrow fractional bandwidths of 2.24%.