A modular antenna for near-field UHF-RFID smart point readers

A novel configuration of a Modular Antenna proposed for NF UHF-RFID desktop reader applications is here described. Specifically, a spiral Travelling Wave Antenna (TWA) is used to generate a strong and uniform field in proximity of the antenna surface. Then, such a microstrip transmission line feeds four resonating curved slot antennas placed close to the spiral TWA and 90-degree rotated with respect to the desktop reader antenna center, through a series-feeding connection. In order to radiate a circularly polarized field, the four slots are fed with the same current amplitude and with a 90-degree phase-shift (sequential rotation feeding technique). To make the antenna scalable, the spiral TWA is extended beyond each slot antenna, so spreading the generated field in a large and arbitrarily shaped area.