A novel microstrip antenna which is dedicated to UHF (Ultra High Frequency) semi-passive RFID (Radio Frequency IDentification) transponders with an energy harvester is presented in this paper. The antenna structure designed and simulated by using mentor graphics hyper-lynx 3D EM software is described in details. The modeling and simulation results along with comparison with experimental data are analyzed and concluded. This paper is the need to eliminate a traditional battery form the transponder structure. The energy harvesting block, which is used instead, converts ambient energy (electromagnetic energy of typical radio communication system) into electrical power for internal circuitry.