Dual-band coupling and feed structure for microstrip filter design

A new configuration of dual-band filter design is presented in this paper. Stepped-impedance transmission-line sections are used as the tunable dual-band resonators. New coupling structures and matching networks at input and output are also proposed to achieve a dual-band characteristics. Three filters with their second passband at 1.5, 2, and 2.5 times the fundamental frequency are designed as examples, and they are all verified by experimental results.