A right angle waveguide junction for a microwave multiplexer is provided including a step in one of the waveguides for improved electrical response. A rectangular waveguide manifold (10) is coupled to a filter (12) which includes a coupling iris (14) and a circular cavity resonator (16). The circular cavity resonator is a circular waveguide with two ends closed by a metal wall. The structure of the waveguide multiplexer includes a step change (18) in the rectangular waveguide (10) height which controls the electrical response properties of the junction.