Sensing passive object existence within an antenna near field based on return loss

Measuring RF signal strength is crucial in many wireless applications such as spectrum sensing and localization. However signal strength is highly affected by the existence of nearby object and particularly metallic object. This paper suggests the use of change in antenna return loss caused by electromagnetic coupling with nearby object as an indicator for object existence. The antenna itself will act as sensor for nearby metallic object, therefore any distortion in received signal strength due to the object can be identified. Experiments with 2.4GHz dipole antenna is presented and verified with simulation.