In the diagram below (surface, or exposed, microstrip) the signal line is exposed (to air) and referenced to a power or ground plane. In the Si9000 structures are categorised according to the arrangement of the dielectric with respect to the trace (below or above the trace). The diagram below shows the surface microstrip structure using a single dielectric layer below the signal trace (designated 1B)
Surface microstrip with single dielectric below the trace
The diagram below shows the surface microstrip structure using two dielectric layers below the trace (designated 2B).
Surface microstrip with two dielectric layers below the trace