Heatsinks as quasi-antennas and frog forming: frequency and feeding point effect

Abstract

High-speed switching capabilities of modern ICs cause generating more heat, and it must be ejected via metallic heat-sinks behaving as an antenna at certain frequencies. Having different radiation patterns(RP) at different frequencies may cause a malfunction on nearby electronics placed on the other part of PCB. In this study, 50W equivalent heat-sink is investigated at 2-8 GHz in terms of feeding point. RP measurements and simulation results at four different feeding points are discussed, and it is observed that point of feeding is the pre-dominant factor of RP. As expected, the feeding of the heat-sinks from the center is to be preferred for lower frequencies, but it causes critical emission/interference problems at higher frequencies. As the frequency increases, it metamorphoses like a frog forming. While it behaves as an omnidirectional antenna having gain at 2GHz, RP turns to one that includes 6 beams with 30-degree beam-widths and gain.