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A new approach to integrate high-quality (Q)-factor three-dimensional vertical cavity filters with patch antennas into a single unit is presented. This integrated filter/antenna system exhibits small footprint, high efficiency and enhanced bandwidth. The patch antenna is designed to provide an additional transmission pole for the filtering function and works as a highly efficient radiator. In addition, this integrated patch antenna with a filter can achieve a bandwidth larger than that of a standalone patch antenna with the same geometry. A prototype three-pole Chebyshev filter/antenna is demonstrated at X band. The centre frequency and fractional bandwidth of the filter/antenna system are 10.27 GHz and 8.7%, respectively. Owing to the high Q factor ( ~650) of the cavity resonator and near loss-less transition between the antenna and filter, the overall efficiency of the filter/antenna system is simulated to be as high as 91.8%. The reduced footprint, enhanced bandwidth and low-loss performance of these integrated filter/antenna systems make them particularly useful for phased array applications. Prototypes of the filter/antenna systems as well as a filter/antenna array are fabricated and measured. An excellent agreement between the simulated and measured results is observed.