Abstract: A capacitively coupled printed patch (3) as a high efficiency device to couple orthogonally polarized energy between a microstripline (5) and a waveguide (1). Coupling between the microstripline (5) and the patch (3) is achieved by the microstripline terminating in a narrow strip probe (4), the end of which lies close to, but not in contact with, an edge of the patch (3). Two separate probes (4) arranged mutually orthogonally are used to effect independent polarized couplings to produce independent linear orthogonal signals or independent left- and right-handed circularly polarized signals. The microstriplines (5) and patch (3) are supported on a common substrate (8) which extends transversely through the waveguide (1). The waveguide wall has a quarter-wavelength thickness (T) so that its inner edge (10) appears continuous to energy passing through the substrate (8).