Abstract: A three-port waveguide circulator has three waveguide arms which meet at a common junction. A transformer step in the form of a Y-shaped ridge is disposed symmetrically at the common junction. This waveguide ridge step preferably supports a quarterwave gyromagnetic element. The step may be formed by cutting slots from a standard transformer step to form the ridge. The resulting ridge structure is of reduced size including reduced length compared to a standard uniform transformer section which is advantageous for certain applications such as in constructing a four-port circulator as disclosed herein. A double ridge step may also be used.