An antenna device includes a substrate including a front surface, a back surface, and via holes formed therein, a plurality of patch antenna elements formed in an array on the front surface of the substrate, a feed line formed on the back surface of the substrate to feed the plurality of patch antenna elements through the via holes formed in the substrate, and a metal chassis disposed opposite the substrate with an air layer therebetween on the back surface of the substrate. The metal chassis is electrically grounded.