- The optical parameters of millimeter wavelength (MMW) imaging system are under investigation in this study. The Optical Transfer Function (OTF) was measured and simulated in this study. The performance and quality of the MMW imaging system were tested using point source objects and Point Spread Function (PSF) was obtained. The MMW imaging system is composed of large aperture 500 mm spherical mirror, CW MMW source and 8×8 Glow Discharge Detector (GDD) Focal Plane Array (FPA). In order to investigate the above optical parameters a diagonal mirror was used in order to allow vertically placing of objects rather than horizontally. In order to avoid stray light, absorber materials were placed around the quasi-optic set-up. Special metal resolution charts and point source objects were manufactured and imaged. The influence of the diffraction has been taken care in the calculations and simulations. The experimental results showed very good agreement with the simulations and calculations results.