After the detailed analysis of the diffusion characters of bridge cables, the principle of vibrating frequency-based cable tension estimation, and the principle of interferometric deformation measuring radar, a nano 77 GHz MMW (millimeter wave) radar was developed. A set of key parameters were achieved to control the maximum range, the deformation estimation precision, and the dynamic deformation measuring performance. Field experiments were conducted to compare the performances of the MMW radar with the 24 GHz K band radar. Results show that the new radar is a compact, light-weighted, low-power consumption,and the radar is of great value in cable tension measuring applications.