A novel compact microstrip dual-band bandpass filter with independently controlled center frequencies based on dual-mode resonators concept

This letter presents a novel ultra-compact microstrip dual-band bandpass filter (DBBPF) with independently controlled center frequencies, and high Q-factor. The recommended DBBPF is realized by combining two different microstrip dual-mode resonators. One is a short-end stub-loaded resonator used to produce the first passband and the other one is an open-end stub-loaded resonator operating at the second passband which serves as part of the feed lines for the lower passband. To validate the performance of the proposed configuration, a novel compact DBBPF with center passband frequencies of 2.4 and 3.55 GHz is designed, simulated, fabricated and tested. A good agreement has been found between the simulation and measurement results. The designed microstrip DBBPF occupies a small area which is only about 0.19 λg × 0.15 λg. The presented microstrip DBBPF has many advantages in terms of compact size, low insertion loss, good frequency selectivity, easy fabrication, and high selectivity.