An antenna system includes a glass plate having a thickness of 1.1 mm or more and a dielectric loss tangent of 0.005 or more at 28 GHz, and an antenna located away from one of surfaces of the glass plate, wherein a ratio of electric power radiated from the antenna to electric power input into the antenna is defined as a radiation efficiency, and when an effective wavelength of an electromagnetic wave at a predetermined frequency is 10 GHz or more is denoted as λg and the radiation efficiency as η0 [dB] when the glass plate and the antenna are in contact, and is denoted as ηλg/2 [dB] when a distance between the one of the surfaces and the antenna is λg/2, the glass plate and the antenna are arranged to obtain the radiation efficiency of ηA [dB] that satisfies ηA≥η0+(ηλg/2−η0)×0.1.