Novel Ultra-Wideband and Multi-Mode LTCC Common-Mode Filter Based on the Dual Vertical Coupling Paths

A novel ultrawideband and miniaturized common-mode filter (CMF) is proposed for suppressing the CM noise based on the dual vertical coupling paths. In the proposed CMF, a modified quarter-wavelength transmission line resonator and a modified half-wavelength transmission line resonator are utilized to introduce three CM transmission zeros. Moreover, another CM transmission zero is produced by the dual vertical path coupling. An ultrawide CM stopband is achieved by the four CM transmission zeros. Subsequently, equivalent circuit models have been established to give physical insight into the CMF operating mechanism, and the design procedures are also provided. By using the low-temperature cofired ceramic technology, a surface-mounted device prototype is fabricated and measured. The measured results show that the CM noise can be suppressed over 10 dB from 2.45 to 9.85 GHz with 120.3% fractional bandwidth. Meanwhile, the low insertion loss and the relatively constant group delay for differential mode ensure that the proposed CMF can maintain the signal integrity of differential signals below 10 GHz.