A modular antenna for UHF RFID near-field desktop reader

The combination of a near-field coupling antenna placed in the central area of a UHF RFID desktop reader with a low-gain resonating antenna allocated at the reader border is here proposed to obtain a confined detection volume within the antenna near-field region (including both the reactive and radiative near field regions). The antenna layout consists of a spiral Travelling Wave Antenna (TWA) which series-feeds an array of two circularly-polarized miniaturized patches. The spiral TWA geometry allows for exciting an almost homogeneous field on the antenna surface, making the tag detection on the reader antenna (near-field reactive region) almost independent on tag location and orientation. The low-gain patch array is used to extend the read range up to the radiative near-field region. Good results in terms of read range and RSSI (Received Signal Strength Indicator) distribution have been checked experimentally, also for a stacked tag configuration.