Abstract: A high-isolation broadband polarization diverse circular waveguide feed apparatus capable of supporting any arbitrary linear, right-hand circular, left-hand circular or elliptically polarized electromagnetic wave with desirable performance over a broad range of frequencies and small size is disclosed. The waveguide feed employs the combination of a symmetrical shaped conical frustrum waveguide and circular waveguide segments together with a novel arrangement of orthogonal and nonplanar electric field probes and radio frequency impedance posts to achieve broad bandwidth, low cross-polarization when operating in arbitrary linear mode, and high-isolation for rejection of undesired cross-polarization components when operating in circular or elliptical polarization mode. Details of a 10.95-12.7 gigahertz embodiment of the waveguide feed including dimensions are provided.