New coupled microstrip SIR bandpass filters with transmission zeros

A new configuration of coupled half-wavelength microstrip stepped impedance resonators (SIR) is presented. This back-to-back configuration can be used alternatively with face-to-face configuration to form bandpass filters. Tapped-line input and output are used to create transmission zeros. The coupling configurations used in the filter and corresponding number and positions of zeros are summarized, so as to provide guidance for design of filters with specific requirements. A fourth-order bandpass filter with alternant face-to-face and back-to-back configurations is fabricated and measured, and the result agrees well with the theory.