Wideband balanced combline filter with extended common-mode suppression

A wideband differential-mode combline filter with a tapped-line input is presented. High suppression of the common-mode and a small size are two important features of the proposed filter. The filter combines two conventional combline filters connected together through discrete capacitors. The realised sixth-order balanced combline filter has a 3 dB bandwidth of 74% from 0.88 to 1.9 GHz. The common-mode suppression is larger than 29 dB, even up to 5 GHz. Furthermore, the filter core size (0.026λ_g²) is substantially smaller than previously reported wide band balanced filters.