Wide-Band RCS Measurement for Calibration of the Metallic Sphere for the MIMO Radars

Millimeter-wave radar imaging is used for security inspections to detect dangerous objects hidden under clothing. The detection capability is determined by the reflection strength of the radio waves emitted from the radar and reflected by the target object. To evaluate the detection performance, a standard reflector with a known radar cross-section is used for the system calibration to confirm the performance of the radars. Metal spheres are widely used as standard reflectors for calibration, and the RCS of a sphere is a constant value determined by the size of the metal sphere, and independent of the measured frequency. However, when calibrating a radar, the received signal increases or decreases significantly with a small change in distance, so when calibrating a MIMO (Multiple Input and Multiple Output) radar in which the transmitter and receiver are spatially arranged, the difference in distance is observed as a difference in amplitude. This causes many errors in radar calibration. In this paper, the RCS of a metal sphere is measured by wideband sweeping for the characterization of the reflected wave strength and phase. The deviation of the reflected signal is also discussed by the comparison to the placement of the rotating axis. The wider bandwidth measurement can be analyzed for the placement error on the rotation axis.