Sliding joints can be used instead of waveguide bellows if some mode conversion can be tolerated. In a sliding joint, a welded stainless-steel bellows provides the flexibility. The input and output waveguides overlap closely.
63.5-mm Waveguide Sliding Joint mounted in a transmission line for long high-power tests. The input and output waveguides are machined from copper alloy and have cooled flanges.
John Doane, GA-MFE Technologies