Shielding Effectiveness, Coupling Path, and EMI Mitigation for QSFP Cages With Heatsink

Quad form-factor pluggable (QSFP) interconnections shielding cages with heatsinks are often optimized for thermal, mechanical, and volume manufacturing. In this paper, shielding effectiveness (SE) of QSFP cages, including two configurations of 1 × 1 and 1 × 6 with three cases of normal (i.e., rising) heatsink, without a heatsink, and with a modified heatsink, is measured for the frequency range of 1-40 GHz using a dual reverberation chamber. For each measurement, three different vendors of optical modules are utilized and averaged SE is achieved for each case, indicating that the rising heatsink degrades the SE around 5-10 dB compare to the no heatsink or modified heatsink. Further, energy parcels and their trajectory concept are applied to visualize the coupling paths in a rising heatsink. The rising heatsink creates a new coupling path for EM waves to leak to the cage and emit from the chassis faceplate. From the energy parcel results, an electromagnetic interference (EMI) mitigation technique is proposed for the newly created coupling path by the rising heatsink, and its performance is evaluated with SE measurements. Further, a measurement is performed with an active board using a 40-Gbps optical module with and without the EMI mitigation technique.