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article influence of via stub length and antipad size on the insertion loss profile continues Figure 24: Raw data of SDD21 magnitude. Figure 25: Average data for magnitude of SDD21. Figure 26: Main effect plot for magnitude SDD21 at 5 GHz. tive data on the effects, the numerical ANOVA data is evaluated, showing the panel to have only a 0.7% variation and the antipad size to account for 3.5% of the variation. The stub length causes 91.3% of the variation, which therefore has by far the largest influence (Figure 27). 58 The PCB Design Magazine • January 2014 Cross-Section Evaluation After completing the TDR and VNA evaluation, actual stub length measurements of the launch vias have been made using cross sections. Figure 28 shows examples of the depths, between "SE01," which was virtually no stub at