In IPC-D-275 on p. 13 there are formulas for Zo and Co for
stripline and dual stripline PCB structures. Can anyone confirm
for me that these formulas are (approximately) correct, or 
have there been any revisions to them?

In particular, for the two Co formulas, if you plug in
identical values for the variables (letting C = H in
the dual stripline case) you get a higher value for Co in the
dual stripline configuration than you do in the basic
stripline one. This seems counterintuitive to me ---
why would unit capacitance be HIGHER in the dual stripline
configuration?

Thanks for any help you can give

Doug Brooks
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