An electrically small elliptic PIFA for RFID in harsh metallic environments

To remotely identify a metallic object with an RFID tag it is required that the tag´s antenna consists of more than one layer of conducting material, where one layer can comprise the metallic object itself, or alternatively one can use the object itself to make a slot antenna. Tag antennas are also seldom smaller than about ¼ of a wavelength. This paper presents a capacitively fed PIFA for passive UHF RFID where the radiating element has received elliptical geometry and is placed inside a circular metallic cup that constitutes the tag antenna´s boundary conditions and is protected by a top layer of an extremely hard plastic material that also works as a superstrate. The elliptic radiating patch has length of only 0.068 wavelengths and with its cup it has total antenna diameter of 0.084 wavelengths and total antenna height 0.016 wavelengths. The final RFID tag can be placed upon a metallic or non-metallic surface or immersed into the same to create an overall flat surface, as long as it is optimized for the specific situation.