Here are a number of single line microstrip calculators that have been used, both at microwave and RF. There is the "normal" single substrate, suspended over an air dielectric and inverted over an air dielectric.
A simple calculator for the characteristic parameters of a Quasi-Static TEM mode microstrip line with up to two ground planes and three dielectrics. Add a real substrate from the catalog.
Introduce an air gap below the substrate and the characteristics change for the new structure.
Turn a suspended microstrip on it's head and we have an inverted microstrip structure.
