Wideband balanced combline filter with extended common-mode suppression

Abstract

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 3dB bandwidth of 74 from 0.88 to 1.9GHz. The common-mode suppression is larger than 29dB, even up to 5GHz. Furthermore, the filter core size (0.026λg 2) is substantially smaller than previously reported wideband balanced filters. © 2011 The Institution of Engineering and Technology.