Increase of common-mode radiation due to guard trace voltage and determination of effective via-location

Tohlu Matsushima, Tetsushi Watanabe, Yoshitaka Toyota, Ryuji Koga, Osami Wada

Research output: Contribution to journalArticlepeer-review

19 Citations (Scopus)


A guard trace placed near a signal line reduces common-mode radiation from a printed circuit board. The reduction effect is evaluated by the imbalance difference model, which was proposed by the authors, when the guard trace has exactly the same potential as the return plane. However, depending on interval of ground connection of the guard trace, the radiation can increase when the guard trace resonates. In this paper, the authors show that the increase of radiation is caused by the common mode, and extend the imbalance difference model to explain a mechanism of increase of common-mode radiation. Additionally, the effective via location of the guard trace is proposed to reduce the number of vias. The guard trace voltage due to the resonance excites the common mode at the interface where the cross-sectional structure of the transmission line changes since the common-mode excitation is expressed by the product of the voltage and the difference of current division factors. To suppress the common-mode excitation, the guard trace should be grounded at the point where the cross-sectional structure changes. As a result, the common-mode radiation decreases even when the guard trace resonates.

Original languageEnglish
Pages (from-to)1929-1936
Number of pages8
JournalIEICE Transactions on Communications
Issue number6
Publication statusPublished - Jun 2009


  • Common-mode radiation
  • Ground via
  • Guard trace
  • Imbalance difference model
  • Printed circuit board

ASJC Scopus subject areas

  • Software
  • Computer Networks and Communications
  • Electrical and Electronic Engineering


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