This study addresses the challenge of simulating ground scattering characteristics in equivalent irradiation tests for radio detectors. By combining electromagnetic modeling with experimental validation—including drone-carried detection and sliding rail tests—the scattering properties of bare soil surfaces in the K, Ka, and V bands and their effect on millimeter-wave detector performance are systematically analyzed. By employing Monte Carlo methods and Gaussian rough surface modeling, we compared the radar cross-section (RCS) and echo signals of corner reflectors of different sizes against real ground responses. Experimental results show that a corner reflector no smaller than 14 cm closely matches the RCS characteristics of actual ground across multiple bands and reliably triggers the detector, meeting equivalence requirements. This work provides practical guidance for selecting equivalent targets and supports calibration and performance evaluation of millimeter-wave detectors in complex terrain.