This transmission line structure operates similarly to a flattened coaxial cable. The central cylindrical conductor carries the signal while the two parallel metallic slabs act as the return path and shield. It is often used in microwave engineering and test fixtures because it provides high power handling and easily calculable characteristic impedance while allowing physical access to the center conductor for tuning.
Heard on the job
We'll use a slab line for the directional coupler so we can mechanically adjust the coupling factor on the bench.