Omnidirectional loop antenna for a 5.8 GHz microwave backscatter RFID tag

A novel miniaturized printed circular loop antenna with perimeter of nearly one wavelength is designed for operation with a radio-frequency identification (RFID) tag at 5.8 GHz. RFID tags and RFID-enabled sensors which operate at this frequency offer many benefits over traditional UHF and LF tags, such as smaller footprints and increased bandwidth. The loop is broken into conducting segments that alternate on either side of a substrate for capacitive loading needed to maintain a constant current and generate a near omni-directional radiation pattern. The performance of the loop antenna is measured in-situ with the tag and the reader configured as a microwave backscatter radio communication system at 5.8 GHz. An overview of the RFID tag design is presented along with measured backscattered pattern.