Loop antenna for UHF near-field RFID reader

A loop antenna with phase shifters is proposed for ultra-high frequency (UHF) near-field radio frequency identification (RFID) readers. Using stub phase shifters, the solid-line loop antenna is capable of generating strong and uniform magnetic field in a near-field zone even though the perimeter of the loop is electrically large. Based on this design concept, a square loop antenna with a perimeter of two wavelengths at 915 MHz is prototyped and exhibits 100% reading rate with the reading range up to 24 mm.