Compact wide-stopband quad-band bandpass filter with tunable transmission zeros

A quad-band bandpass filter using double-layered structure has been presented. The proposed filter is principally composed of four pairs of stepped impedance resonators on the top metal layer and middle metal layer. In comparison to the conventional quad-band bandpass filters, the proposed filter has the advantages of compact size and wide-stopband response. Besides, due to multi-path effect, transmission zeros beside the passbands are created to achieve sharp rejection. The full-wave simulator IE3D is used to design the quad-band bandpass filter and to calculate the loaded and unloaded coupling coefficients for each pair of resonators.