Analysis and procedure to design differential wideband filters with high-selectivity and high common-mode suppression

Abstract This paper proposes a new structure to design differential wideband bandpass filters by cascading two different types of wideband bandpass filters. Detailed analysis to obtain the equations for designing differential filters with high selectivity and fractional bandwidths between 20 and 55% is presented. To complement the equations a design methodology is proposed and two prototypes with different bandwidth are designed, simulated, and fabricated. The measurement results under differential mode show that the designed filters present two transmission zeros, constant insertion losses, return losses greater than dB and a stop band of at least 2.5. On the other hand, the common-mode signals are suppressed below dB in the whole passband.

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