In this paper， two millimeter-wave zero-bias Schottky detectors for the direct detection system of the CubeSat radiometer， with center frequencies of 89 GHz and 150 GHz， respectively， were designed and implemented. These designs were based on zero-bias Schottky diodes of ACST. A radial stub structure was adopted at the DC ground and output port with a tuning line for optimum impedance matching to achieve stable and high performance and broadband characteristics； this structure also makes the circuit easier to integrate with pre-level systems and more suitable for CubeSat radiometer miniaturization. Circuit structure and Schottky diode were analyzed， modeled， and optimized to obtain better performance. The results showed that the W-band detector has a typical sensitivity of about 2500 V/W in the range of 85 GHz to 95 GHz and a linearity of 0.9994 at 89 GHz. Moreover， the D-band detector has a typical sensitivity of about 1600 V/W in the range of 145 GHz to 155 GHz and a linearity of 0.9992 at 150 GHz. These results verified the advantages of the improved circuit structure in the detector and the feasibility of the direct detection system.