Radio Frequency Identification systems are proposed for various applications such as warehouse inventories and supply chain management. A typical RFID system includes two parts: the Reader and the Tags. This paper is concerned with Tag simulation. Tags are components that are physically placed upon each item and consist of an antenna and a chip. The information on the chip includes all the item data. Upon interrogation by the Reader, the Tag transmits its stored information to the Reader's antenna. The EPC-Class 1-Generation2 UHF-RFID standard is used. An operational distance between 0.5 and 9 m is assumed here. The paper presents an electrical model for UHF-RFID Tags. Performance of the RFID system is evaluated as function of the operational distance. The model is validated by code recovery.