According to various embodiments, an electronic device includes a front cover; a rear cover facing away from the front cover; a side frame surrounding a space between the front cover and the rear cover and at least partially includes a first conductive portion; a first array antenna includes a first substrate disposed in the space and a plurality of first antenna elements disposed on the first substrate and configured to form a beam pattern toward the first conductive portion; and a wireless communication circuit configured to transmit and/or receive, via the first array antenna, a wireless signal in a first frequency range. The first conductive portion includes, in a portion corresponding to the first array antenna, a plurality of first slits provided to be spaced apart from each other and to have a length in a first direction perpendicular to a polarization of the first array antenna.