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APRIL 2019 I DESIGN007 MAGAZINE 69 ground-signal spacing of 4x the trace width, extra loss reduction of 0.25 dB is achieved. The experiment is repeated on differential microstrip with five models of 1" differential microstrip listed in Table 2. Simulation topol- ogy is depicted in Figure 4. For model 2A, microstrip traces (5-mil trace width, 7-mil intra- pair spacing, and 1 oz. in thickness) is laid out 3 mils above the reference plane insulated by low-loss dielectric substrate material. This differential pair is sandwiched between two ground traces on the same outer layer. The spacing between each adjacent ground Figure 4. Differential microstrip model. Table 2: List of models showing the effect of copper pour on differential microstrip. Figure 3a: TDR plots for models listed in Table 1. Figure 3b: Insertion loss plots for models listed in Table 1.