This article has been accepted for inclusion in a future issue of this journal. Content is final as presented, with the exception of pagination. IEEE TRANSACTIONS ON ELECTROMAGNETIC COMPATIBILITY 1 Shielding Effectiveness, Coupling Path, and EMI Mitigation for QSFP Cages With Heatsink Atieh Talebzadeh , Member, IEEE, Philippe C. Sochoux, Jing Li, Qian Liu, Member, IEEE, Kaustav Ghosh, Student Member, IEEE, and David Pommerenke , Fellow, IEEE Abstract—Quad form-factor pluggable (QSFP) interconnections shielding cages with heatsinks are often optimized for thermal, me- chanical, and volume manufacturing. In this paper, shielding effec- tiveness (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 fre- quency 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 cou- pling 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. Index Terms—Coupling path, electromagnetic interference (EMI) mitigation, EMI/ electromagnetic compatibility (EMC), en- ergy parcel, heatsink, Quad form-factor pluggable (QSFP) inter- connect, reverberation chamber, shielding effectiveness, total radi- ated power. I. INTRODUCTION Q UAD form-factor pluggable (QSFP) interconnection is a compact transceiver used for telecommunication and data communication applications. Its features are four electrical lanes that operate at 10 Gbps to provide 4 × 10 Gbps Ethernet systems [1]. The throughput of QSFP interconnection is further raised from 4 × 10 Gbps to 4 × 28 Gbps, known as QSFP28, to address 100 Gbps network applications [2], [3]. Today, they have application in switches and routers, placed on the face- plate of the system chassis. From the electromagnetic inter- ference (EMI) point of view, however, the big challenge is to Manuscript received February 4, 2018; accepted February 27, 2018. (Corre- sponding author: Atieh Talebzadeh.) A. Talebzadeh, K. Ghosh, and D. Pommerenke are with the Electromag- netic Compatibility Laboratory, Missouri University of Science and Tech- nology, Rolla, MO 65401 USA (e-mail:, ath27@mst.edu; kgkb4@mst.edu; davidjp@mst.edu). P. C. Sochoux, J. Li, and Q. Liu are with the Juniper Networks, Inc., Sunnyvale, CA 94089 USA (e-mail:, psochoux@juniper.net; jingl@juniper.net; qianliu@juniper.net). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TEMC.2018.2813889 Fig. 1. Rising heatsink when optical module is inserted. maintain the radiation limit lower than a certain margin to meet electromagnetic compatibility (EMC) regulatory requirements. Approaching further higher data rate for network systems from 100 to 200/400 Gbps is currently under development based on doubling the density of QSFP interconnections, so-called QSFP-DD, in which eight lanes operating at up to 25 Gbps via NRZ modulation or 50 Gbps via PAM4 modulation providing 200 and 400 Gbps speed, respectively [4], [5]. The introduction of double-density technologies is expected to further increase radiation emission by a few decibels because of the doubled transmitted power in the QSFP-DD interconnections. Thus, it is required to revisit the design of the key components that are placed on the front-end of the system chassis faceplate consist- ing of the QSFP interconnection, QSFP shieling cage, and the optical module to make them more effective against emission. One of the components that is particularly investigated in this paper is the QSFP shielding cages possessing a heatsink. The heatsink is required to cool down the optical modules placed inside the QSFP shielding cage [6]. However, when the optical module is inserted, the heatsink rises as depicted in Fig. 1. The air gap created by a rising heatsink can degrade the shielding effectiveness (SE) of the cage. Extensive efforts have been made over the years to study the EMI associated with high-speed high-density interconnections including edge-coupled printed circuit board (PCB) backplane connectors [7]–[11], and board-to-board interconnections (i.e., SFP and QSFP) [12]–[14]. The interconnections often con- tribute to radiation emission and potentially increase the system noise. Some EMI mitigation techniques have been evaluated to reduce emission from interconnections [15], [16]. Furthermore, the EMI coupling paths and the resulting unintentional currents that lead to radiation in the optical link are described in 0018-9375 © 2018 IEEE. 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