Compact microstrip dual-band bandpass filter using short-circuited stub-loaded open loop resonators

In this article, a compact dual-band microstrip bandpass filter is proposed using two short-circuited stub-loaded open loop resonators and two common open loop resonators. The short-circuited stub-loaded resonators can generate two resonant modes. Under odd mode, the short-circuited stub at the central does not affect the resonant frequencies, and four resonators tightly coupling with each other work at the same frequencies, a wideband passband is obtained. Whereas under the even mode, considering the influences from short-circuited stubs, the resonant frequencies are decided only by two short-circuited stub-loaded resonators, two common resonators are seen as parts of feedlines connected to 50 omega. A new transmission zero is created between two passbands to improve the selectivity. Good agreement is achieved between simulation and measurement. (c) 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:1651-1653, 2014