High selective wideband bandpass filter with mixed-coupled resonators

Novel electric and magnetic mixed-coupled resonators and a general design method for high selective wideband bandpass filters are presented in this paper. Transmission zeros are introduced in the filters for high selectivity, and the location of the transmission zeros can be adjusted without passband characters changing. To verify the design method, an eighth-order mixed-coupled filter is designed, fabricated and measured; the measured results show higher rejection compared with the conventional interdigital filters. Good agreements are obtained between simulated and measured results.