Antenna arrays and signal processing for rfid tag readers

Abstract

Radio-frequency identification (RFID) systems use readers to query and locate passive RFID tags in stores, warehouses, and other environments. An interrogation signal emitted by an antenna array from a reader powers up the tag, which replies by modulating and backscattering incident radiation toward the reader. The antenna array in the reader detects the modulated and backscattered radiation, which is usually several of orders of magnitude weaker than the interrogation signal, as the tag's reply. Unfortunately, crosstalk between the antenna elements in the antenna array limits the reader's sensitivity, which in turn limits the range at which the reader can detect and locate tags. Increasing the pitch of the antenna array to greater than half the wavelength of the interrogation signal reduces crosstalk but introduces grating lobes that produce spurious replies. Fortunately, filtering these spurious replies yields sensitive measurements from an antenna array with a pitch large enough to suppress crosstalk.