Dual-band Passband Filter Based On Dual-short-stubloaded Tri-Mode Resonator

Two dual-band passband filters (DBPFs) using a dual-short-stub-loaded resonator (DSSLR) are proposed. The DSSLR is formed by loading two shunt short stubs, having compact size compared to open-loaded resonator. By properly adjusting the length of the resonator, the three resonant frequencies can form one group, two or three groups. The first filter uses two parallel DSSLRs having three resonant frequencies in one group. A three-pole filter with five transmission zeros (TZs), as well as high out-of-band rejection skirts, is initially analyzed and designed. Afterwards, the first two resonant frequencies form the first passband and the third frequency create another passband in one DSSLR. A symmetrical situation is used in another resonator. Then, a three pole filter having high isolation between adjacent passbands is constituted. Finally, two DBPFs are simulated, fabricated and measured, showing good agreement with the design.