The invention relates to a microwave waveguide element for matching a standard waveguide input port to an enlarged waveguide output port. In the waveguide element, a plurality of intermediate waveguide segments is cascaded in the propagation direction of the microwave energy to first split the waveguide element into two symmetrical waveguide branches and then combine the branches at the output port. Thus, the width of the waveguide element is gradually enlarged and the input port is matched to the output port. The intermediate waveguide segments are preferably dimensioned such that respective characteristic impedances are approximately matched with each other for the fundamental mode.