摘要： A 120 GHz step-profiled horn antenna integrated in low-temperature co-fired ceramic (LTCC) packages with a radome is presented in this paper. As an antenna-in-package (AiP) design, the proposed hollow horn structure is constructed by the cavities with several surrounding fences of vertical metallic vias in multilayer LTCC substrates. In consideration of the practical application, co-design with a thick cylindrical radome attached to the surface of the antenna is also studied. A planar soft surface structure in electromagnetics around the horn antenna is introduced so as to suppress the propagation of surface waves inside the radome and thus improve the gain performance. The simulated results indicate that more than 9 GHz bandwidth of -10 dB return loss and a gain of 12.56 dBi in the radiation direction at 0θ= ? are obtained.