Design of dual-passband cross-coupled filter using stub-loaded open-loop resonators

Compact open-loop resonators loaded by open stubs are used to design cross-coupled filters with a dual-passband response of Chebyshev function. The second passband of the proposed filter is obtained by tuning higher resonant modes of the open-loop resonator by changing the stub length and position. Proper couplings required for the two desired/designed frequencies are obtained by tuning the relative open position of open-loop resonator and the distance between the resonators. Required external coupling is obtained by adjusting the tapping position and dual-frequencies transformer. The S-parameter of the dua-passband filter has been measured. The results show good agreement with the simulation ones. Furthermore, the proposed filter has two transmission zeros and exhibits high skirt selectivity.