Two compact configurations for implementing transmission zeros in microstrip filters

This contribution presents compact structures for the implementation of transmission zeros using the zero shifting property. First, two open-loop resonators operating at different resonances are employed. Then, one of the open-loop resonators is substituted by a (λ/4) short-circuited transmission line, thus resulting into a more compact structure. Properties of these configurations are discussed, and two manufactured prototypes have been successfully tested. The results show the usefulness and validity of the new structures with high rejection capabilities.