Can someone tell me if I have correctly defined a substrate for an air dielectric design incorporating a .212" Diameter coaxial resonator within a .625" 'slabline' ground plane?
Er=1
Ur=1
Tand=0
Rho=1
Thick=1.42
Sr=0.094
Height=625
Er=1
Ur=1
Tand=0
Rho=1
Thick=1.42
Sr=0.094
Height=625
You need using 3D EM simulator, as ADS EMDS to simulate the slab line with circular conductor.
In planar simulators it may be simulated the only after replacing round rod by rectangular only. In this case the substrate stack must consist of 2 air dielectric layers and thick metal layer for the central conductor having constant width. The top and bottom air layers must take into account the central metal height, which depends on what expansion for the thick metal do you use.
So for "UP" thick metal expansion:
Top air: Height=625/2-212/2=312.5-106=206.5 mil
Bottom air: Height=625/2+212/2=312.5+106=418.5 mil
For alternative "Down" thick metal expansion the Top and  Bottom air layer heights will be swapped.