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30 The PCB Design Magazine • October 2017 PRACTICAL MODELING OF HIGH-SPEED BACKPLANE CHANNELS with different roughness parameters, we must calculate the sphere radius for each side sepa- rately. But most Huray models in EDA tools, in- cluding Polar Si900e, only allow one input for radius so I just take the average of the two for an effective radius (r eff ). Once we have that then it is easy to get the area (A flat ) of the flat tile base. For each length of transmission line of the topology shown in Figure 3, we would create and save a separate Polar file by following steps for each file: 1. The first step for modeling each transmis- sion line segment is to select the "Lossless Cal- Figure 3: Amphenol-FCI Examax demo platform and channel topology summary used for case study. Figure 4: Effective D k due to roughness summary of cores and prepregs used on the daughter cards and backplane. Table 1: Design parameters and data sheet summary.