Capacitively I/O coupling structure for magnetically coupled resonator filters

A novel capacitively I/O coupling structure for coupled resonator filters is presented, analyzed theoretically, and demonstrated experimentally. A novel I/O coupling structure, adds two transmission zeros to the filter response. The bandpass filter uses second order magnetically coupled resonators with two transmission zeros to obtain lower insertion loss than a conventional cross-coupled microstrip filter. The two zeros are close to the passband, such that the selectivity and out-of-band rejection of the filter are significantly increased. The design is verified by experimental results.