Miniaturization of BPF Based on Broad-Side Coupled Strip Resonators

Three types of resonators and filters are described that belong to the family of broad-side coupled metal strip structure. Strong coupling between strips due to large mutual capacitance naturally increases the intensity of stored electric energy, resulting in a high effective permittivity for artificial dielectrics and a low resonant frequency for multi-strip resonators. Both features are useful for miniaturization of the resonators made of those principles. Improvement of loss and/or spurious characteristics is attained by a proper choice of metal strip dimension, orientation and intensity. Broad-side coupling is also used for wide range of control of coupling coefficient. By insertion of metal shield between two resonators, the coupling coefficient is controlled from 0.001 to 1.0 (1000 times) without changing the resonator distance. This feature is another means to miniaturize BPFs.