Many electronic components such as diodes and transistors exhibit certain degree of nonlinearity. In this paper, this nonlinearity is used for a radar target to generate intermodulation tones from incident waves with two fundamental frequencies, so that the radar detects only the target and rejects clutter reflections. In this paper, the intermodulation radar at 5.8 GHz ISM band and the passive tag were designed, fabricated and characterized. The motion and the intermodulation generated by the tag were measured, as compared with undesired fundamental reflections. This intermodulation-based nonlinear radar approach can overcome some drawbacks of harmonic radars. It has wide potential applications in clutter noise rejection and detection of unauthorized electronic devices.