In a radar assembly, a first dielectric member includes a dielectric outermost structural member of a vehicle. A radar device includes an antenna module, and a substantially tubular or domed radome. The radome includes a transmissive portion, and is disposed to cover the antenna module such that the transmitted radar wave passes through the transmissive portion. The transmissive portion is disposed behind the back surface of the first dielectric member with space thereto. A second dielectric member includes at least the transmissive portion, and is disposed to face the first dielectric member. A frequency-selective substrate passes a radar wave within a frequency band therethrough, and block radar waves outside the frequency band. The frequency-selective substrate is disposed such that its first surface is directly abutted onto the first dielectric member, and its second surface is directly abutted onto the second dielectric member to constitute a sandwich structure.