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The analysis of ring-slot elements backed by the ground plane via cavities is performed using a hybrid matrix formulation. The cavity region of the structure is modeled as a two-port network and the network parameters are determined using current and voltage sources at the two ports, respectively. These dissimilar port-excitations result in hybrid matrices' representation for the network. The aperture radiation is incorporated through the aperture admittance matrix. The numerical results are validated with a finite integration method of analysis. Radiation characteristics of ring-slot elements in an array environment are presented. The design of a wideband element with about 30% bandwidth is shown. Circular polarization using degenerate modes is achieved by incorporating offset vias, and the radiation characteristics of such configurations are explored. For millimeter-wave applications, such an “aperture type” of element is desirable because of its high-pass characteristic that helps reduce interference with the lower bands. Furthermore, the radiation efficiency is reasonably good because the loss is found to be less than 0.6 dB. Monte-Carlo simulation suggests that the performance is acceptable with respect to the fabrication tolerance.