Investigation on Radiated Emission Characteristics of Multilayer Printed Circuit Boards

Takashi HARADA  Hideki SASAKI  Yoshio KAMI  

IEICE TRANSACTIONS on Communications   Vol.E80-B   No.11   pp.1645-1651
Publication Date: 1997/11/25
Online ISSN: 
Print ISSN: 0916-8516
Type of Manuscript: Special Section PAPER (Special Issue on EMC Implications of Densely Mounted Electronic Devices)
radiated emission,  multilayer printed circuit board,  power distribution,  decoupling,  

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This paper analyzes mechanisms of radiated emissions from multilayer printed circuit boards (PCBs) and presents a model to describe the characteristics of such radiation. The radiation mechanism from a four-layer PCB, including the internal power and ground planes, is investigated using a time-domain magnetic field measurement near the PCB. Measurement of the waveform indicates that the main source of radiation is in the power distribution planes. To investigate the characteristics of the radiation from the power distribution, the S21s of the board are measured; the board impedance and the transmission characteristics of the power distribution planes are found to be directly related to the S21 between the two points in the board. The results indicate that the power distribution acts as a transmission line at frequencies higher than 100 MHz. A model that can explain well the radiation properties of these planes treats them as a parallel-plate transmission line interconnected by decoupling circuit comprising a decoupling capacitor and interconnect inductance. From the transmission line theory it is deduced that the line resonance gives rise to strong radiated emissions. The interconnect inductance is an important factor in determining the radiation characteristics.