A cavity-backed patch phased array is proposed. The antenna configuration has some extra degrees of freedom not found in conventional microstrip patch antennas. These include the cavity dimensions and the slot size. It may be possible to exploit these features in order to further increase the bandwidth (e.g., by double-tuning) or to decrease the antenna mode scattering. The integral equation approach is used to analyze the structure considered. Through the use of the equivalence principle, solution of the problem is facilitated by dividing the analysis into two distinct (but coupled) problems: one for the cavity region below the ground plane, and one for the half-space above the ground plane. The input impedance and radar cross section of cavity-backed patch antennas have been investigated in both single-element and infinite phased-array environments.