Abstract: A broadband turnstile waveguide junction has four rectangular side ports that lie in a common plane, symmetrically about and orthogonal to a longitudinal axis of a circular port. The turnstile waveguide junction comprises a circular to quad-ridged waveguide transition disposed between the circular port and the four rectangular side ports. Quad-ridged waveguide ridges are provided that transition to a single ridged waveguide in the four rectangular side ports. A transition is provided from the single ridged waveguide to rectangular waveguide in the side ports. A center matching post, or pedestal, extends from the rear of the junction a predetermined distance toward the circular port. Another embodiment may use a quad-ridged waveguide having a port at the input in lieu of a circular to quad-ridged transition. Another embodiment may use single ridged waveguides at each side port instead of transitioning from single ridged waveguide to rectangular waveguide.