Coupling of through-hole signal via to power/ground resonance and excitation of edge radiation in multi-layer PCB

Abstract

This paper describes the edge radiation of signal power at multi-layer PCB mostly depends on coupling of through-hole signal via to power/ground plane, and the coupling mechanism is the loading effects of power/ground plane impedance on signal return current. It is well known that the variation of power/ground impedance comes from power/ground resonance, and the variation range is up to several tens ohm (/spl Omega/). In 50/spl Omega/ system, this range impedance makes signal input matching worse. Moreover, the transmitted signal is divided into two parts, load and power/ground plane. Finally, the assimilated signal power by power/ground plane is emitted from PCB open edge, which is a good radiation structure. Above analysis is shown in this paper by Spice modeling of through-hole signal via and power/ground plane and measuring the near field strength at PCB edge with/without through-hole signal via cases. The loading effects are seen in S-parameters and input impedance of signal traces and PCB edge radiation in |S21| between signal trace and near field probe. The trace with through-hole signal via case has the larger radiated emission at PCB edge than without case by more than 20dB.