Suppression of Mode Conversion by Using Tightly Coupled Asymmetrically Tapered Bend in Differential Lines

Yoshitaka TOYOTA  Shohei KAN  Kengo IOKIBE  

IEICE TRANSACTIONS on Communications   Vol.E98-B   No.7   pp.1188-1195
Publication Date: 2015/07/01
Online ISSN: 1745-1345
DOI: 10.1587/transcom.E98.B.1188
Type of Manuscript: Special Section PAPER (Special Section on Electromagnetic Compatibility Technology in Conjunction with Main Topics of EMC'14/Tokyo)
differential lines,  tightly coupled bend,  mode conversion,  asymmetric tapers,  

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In this paper, we propose a tightly coupled asymmetrically tapered bend to suppress differential-to-common mode conversion caused by bend discontinuity in a pair of differential lines. Tightly coupled symmetrically tapered bends have been so far proposed to suppress the mode conversion by decreasing the path difference in the bend. This approach makes the path difference shorter so that the differential lines are coupled more tightly but the path difference of twice the sum of the line width and the line separation still remains. To suppress the remaining path difference, this paper introduces the use of asymmetric tapers. In addition, two-section tapers are applied to reduce differential-mode reflection increased by the tapers and hence improve differential-mode propagation. A full-wave simulation of a right-angled bend demonstrates that the forward differential-to-common mode conversion is decreased by almost 30 dB compared to the symmetrically tapered bend and that the differential-mode reflection coefficient is reduced to the same amount as that of the classic bend. Also, the generality of the proposed bend structure is discussed.