A wideband UHF RFID reader antenna array with bow-tie elements

This paper presents the design procedure of a wideband UHF RFID reader antenna with polarization diversity suitable for searching tagged items. The antenna consists of a microstrip array with alternating orthogonal bow-tie elements, which are fed in series by a pair of microstrip lines. The elements are designed to provide the required bandwidth. The inter-element distance is adjusted to be about 0.8λ at the center frequency, whereas the elements provide in-phase excitation and create two orthogonal electric field components that give beams with polarization diversity. Simulated results indicate that the bandwidth covers the frequency bands of ETSI and FCC (865-928 MHz) standards. Regarding the coverage, it was deduced that the antenna can identify tagged items in a semi-cylindrical volume around its axis. The radius of coverage depends on the input power and tag sensitivity. A case study of reading tagged items in front of a cabinet with shelves is presented.