Abstract: An antenna device includes subarray antennas including antenna elements and feeding interfaces. Each feeding interface is connected to each of subarray antennas. The subarray antennas are arranged parallel to each other with an interval on a plane to be symmetrical about a central axis. The interval is less or equal than a free-space wavelength. The central axis is along with the center of two adjacent subarray antennas arranged at middle of the subarray antennas when the number of the subarray antennas is even. Moreover, the central axis is along with one subarray antenna arranged at the middle of the subarray antennas when the number of the subarray antennas is odd.

Abstract: A short slot directional coupler includes a dielectric substrate having both surfaces each covered by a metal film, a first via-hole string and a second via-hole string, each of which has via-holes penetrating through the substrate, and formed so that a distance between the first via-hole string and the second via-hole string is narrow at a center of a length direction of the string and wider along directions of both ends of the string, and a pair of third via-hole strings each having via-holes penetrating through the substrate, and formed between parts adjacent to both ends of the first via-hole string and parts adjacent to both ends of the second via-hole string to form a first post-wall waveguide along with the first via-hole string and a second post-wall waveguide along with the second via-hole string.