An antenna array includes: an electrically conductive member having an electrically conductive surface in which a plurality of slots are open; a plurality of electrically-conductive ridge pairs on the electrically conductive surface, each pair protruding from edges of the central portion of a corresponding one of the plurality of slots. As viewed along a direction that the central portion of each slot extends, at least a portion of the first gap between the first ridge pair and at least a portion of the second gap between the second ridge pair overlap each other, with no other intervening electrically-conductive member therebetween; or at least a portion of the first ridge pair and at least a portion of the second ridge pair overlap each other, with no other intervening electrically-conductive member therebetween.