A Novel Differential Bandpass Filter With Ultra-Wide Band Common-Mode Suppression

A compact differential filter with ultra-wide band common-mode (CM) suppression is proposed. Ultra-wide band property is achieved by the frequency-selecting coupling structure (FSCS), which generates three transmission zeros in the passband of differential-mode (DM) as well as in the stopband of CM. Moreover, the position of the transmission zeros, the CM insertion loss and the DM return loss can be customized by designing the parameters of the FSCS. To verify the concept, a filter has been designed, simulated and measured. The proposed filter shows the center frequency of 2.45 GHz with a DM 3 dB fractional bandwidth of 51% and a CM 20 dB fractional bandwidth of 108.6%.