Issue link: https://iconnect007.uberflip.com/i/1028393
SEPTEMBER 2018 I DESIGN007 MAGAZINE 71 Figure 6: Power from the microstrip does not go all the way to the stripline in layer INNER1. Figure 7: A close-up of interaction between reference planes GND7 and GND8. vias about 30 mil from the signal via. The TDR correlation for this via is acceptable, so let's look at Figure 8 and Figure 9 to see how the power propagates along that structure at dif- ferent frequencies. What a difference two properly designed stitching vias make! The localization band- width of the single via is extended to 15-20 GHz. The localization degrades progressively starting from about 20 GHz in this case—it means that this via becomes coupled to the parallel plane structures with all the unpredict- ability consequences as we observed for the single via. What if we want to extend the fre- quency range to 50-60 GHz? That is very dif- ficult task for the single-ended through vias in general. Just take a closer look at an example of the single via launch localized up to about 60 GHz with 17 stitching vias as shown in Fig- ure 10. This via transition was designed by Scott McMorrow for one of our material model iden- tification projects reported in Design/Optimi- zation with 50 GHz Material Characterization (D. Dunham, J. Lee, S. McMorrow, Y. Shlepnev, DesignCon2011) [4] .