An analysis is presented of the efficiency of a dual-polarized planar connected-array antenna, with particular reference to possible use in wideband focal-plane-array applications. The modeling approach is described, and the results of different numerical techniques are compared. The analysis includes the effects of transmission lines used to load the array at a groundplane. Different types of loading are compared including optimum single-ended loading and optimum differential-mode loading with short-circuit and open-circuit common-mode terminations. The results indicate that high efficiency over useful bandwidths should be possible. In the case of differential-mode loading, the efficiency may be reduced at certain frequencies due to resonances of common-mode currents on the transmission lines. The current distributions on the array are analysed, and observations are made which may be useful for modified designs.