A novel RFID inverse synthetic aperture radar (ISAR)-synthetic aperture radar (SAR) localization method is proposed and demonstrated which exploits reference tags with known locations to estimate the trajectory of a mobile platform and locate target tags with unknown locations. A system that integrates a mobile robot with an integrated RFID reader and antenna is used to obtain phase measurements of both reference and target tags when the robot is moving along its trajectory. The ISAR algorithm estimates the antenna trajectory and a novel ISAR-SAR loop then adjusts the estimated trajectory. The estimated trajectory is combined with phase measurements of the target tags to determine their location. The performance is compared to SAR using a LiDAR measured antenna trajectory. Similar localization accuracy (15 cm MAE) is achieved using LiDAR-SAR or ISAR-SAR method with a straight-line trajectory and higher accuracy (6 cm) is achieved using ISAR-SAR method than LiDAR-SAR method (8 cm) with an L-shape trajectory.