Radar sensors play a key role in today's industrial automation. Being an alternative to frequency modulated continuous wave radar, Six-Port based radar sensors recently attracted the interest of the community as well as of the industry. This paper presents a 61 GHz Six-Port radar sensor for ultra-short range applications and a dedicated substrate integrate waveguide fed tapered slot antenna design. Due to an optimized design, the antenna allows for measurements in the direct near-zone of 0mm to 10mm without ambiguity effects. Making use of a spiral fitting operation, the presented measurement results show an absolute distance error of less than 100 μm.