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

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 (Ω). In 50Ω 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.