An Ultrawideband Bidirectional Absorptive Common-Mode Filter Based on λ/4 Coupled-Line and Resistive Defected Ground Structure

In this letter, an ultrawideband bidirectional absorptive common-mode suppression filter (A-CMF) integrating <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda $</tex-math> </inline-formula>/4 coupled line structure and defect-ground structure (DGS) on a two-layer printed circuit board (PCB) is designed. First, an A-CMF with DGS combing <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda $</tex-math> </inline-formula>/4 wide-side coupled line structure loaded with resistors is proposed. Then, an ultrawideband bidirectional A-CMF combining DGS and narrow- and broad-side coupled lines is developed. The experimental results show that the proposed A-CMF can achieve 90% absorption efficiency from 1.79 to 6.76 GHz, with a fractional bandwidth of 143%, while the high bandwidth of differential-mode (DM) signal is from dc to 6.8GHz. The employed narrow-side coupled line with resistors can be directly inserted into the middle of differential line, thereby effectively reducing the area occupation in the realization of the wideband common-mode (CM) noise rejection.