No / Abstract: Radio Frequency Identification (RFID) systems has gained increasing popularity with multiple deployments to existing wireless sensors in a view to achieve energy and overall operational efficiency at a much lower cost. This paper presents the design and analysis of a UHF (860-868MHZ) passive tag using HFSS (High Frequency Structural Simulator) platform. It explores specific tag geometry characteristics that affect overall tag antenna performance and presents the optimised result. The simulation results and parametric analysis are compared. Further simulations on HFSS platform is carried out to theoretically demonstrate the reflections of the tag when deployed as sensors to multiple levels of a cistern.