Phased array antenna systems with antenna elements having substrates with varying dielectric constants selected to reduce the self-return signal of corner elements in the array. In one example, a phase array antenna system includes a plurality of stacked-patch microstrip antenna elements arranged in a two-dimensional array, each stacked-patch microstrip antenna element of the plurality of stacked-patch microstrip antenna elements including a pair of conductive patches disposed above a ground plane on a dielectric substrate. The dielectric substrate of corner stacked-patch microstrip antenna elements in the array has a dielectric constant lower than a dielectric constant of the dielectric substrate of non-corner stacked-patch microstrip antenna elements in the array.