Stopband-Extended Balanced Bandpass Filter Using Coupled Stepped-Impedance Resonators

A novel fourth-order balanced bandpass filter is proposed based on the half-wavelength (lambda/2) stepped-impedance resonators (SIRs). By properly adjusting the parameters of each SIR, the proposed filter may be made compact and its stopband may also be extended simultaneously. Specifically, a balanced filter with acceptable common-mode rejection is implemented with its differential-mode and common-mode stopbands extended up to 5.5 f
_o

^d
, where f
_o

^d
is the center frequency of differential-mode passband.