Abstract: A dual circular polarization waveguide (24) is described which has a septum (36) which divides the waveguide (24) into two separate compartments (38, 40) each with a probe (30A, 30B) passing through the end wall (32) of the waveguide (24) into the compartment (38, 40) to detect respective signals in each of the compartments (38, 40). The septum (36) is proportioned and dimensioned to convert the left and right circularly polarized signals, into substantially linearly polarized signals as the signals pass along the waveguide (24) past the septum (36) so as by the time the signals reach the probes (30A, 30B) they are linearly polarized. The probes (30A, 30B) which pass through the rear wall (32) of the waveguide (24) are oriented such that they couple into the magnetic field of the primary or fundamental waveguide mode.