Here are a some specialise stripline calculators where we orientate to high power use of stripline. Typical high power usage would be as a 3db hybrid combiner with stripline transmission lines.
If we run a circular conductor in a dielectric filled rectancular enclosure we get a SlabLine.
Running power along normal rectangular bar tends to run into arc and corona problems. So what do we do use hefty rounded bars. The dielectric is commonly air, though extra rigidity can be given by air foaming the void.
One form of a high power bandpass filter or directional coupler is to use parallel coupled slabline.