The existing applications of seekers and distance sensors in projectiles and other weaponry typically involve separate installations, which requires complex design processes and fails to meet convenience requirements. There is an urgent need to integrate distance sensors into seekers for a unified design. However, integrating distance sensors within the confined space of a seeker presents significant challenges, particularly in miniaturizing and designing the sensors to ensure effective transmission and reception performance of antennas when covered by the radome. In this paper, we propose a design method for distance sensors integrated coaxially with seekers that can determine the installation position, shape, and size of the distance sensor. To mitigate the negative impact of radome coverage on antenna performance, a method for characterizing the near-field and far-field electromagnetic field intensity of antennas with the radome coverage is presented. Using this method, we can obtain the radiation pattern to optimize antenna parameters.