Compact rectangular waveguide 90° twist is studied. The twist transformer region is a square waveguide section with two stepped corner ridges. The twist can provide the 40‐dB return‐loss level over the rectangular waveguide operating band if the wide and narrow waveguide wall dimensions are in the ratio of 2:1. The twist lengths are less than the rectangular waveguide half‐wavelength at the central frequency of the chosen operating band. The design results are confirmed by the results of real device measurements. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 851–854, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24161