Microstrip impedance

Er_eff = (Er + 1) / 2 + ((Er - 1) / 2) * (1 + 12 * H / W)^(-0.5). H and W must use the same length unit. mm or mil does not change Z0 when both change together.

Narrow uses W/H below 1. Wide uses the other equation. eta_0 = 376.73 ohm. If effective width is blank, Z0 uses the drawn width.