Meandered TWAS array for near-field UHF RFID applications

An array of 2 × 2 travelling wave antennas (TWAs) is proposed for near-field RFID applications in the UHF band (865-928 MHz). Each array element is characterised by a meandered line based on coplanar waveguide technology. All the TWAs end on a matched load, which allows for non-stationary current and field distributions as well as a low far-field gain. Thus, strong and uniform fields within a confined volume above the antenna surface have been obtained, with a field maximisation in the antenna central area, where tagged items are supposed to lie on. The meander geometry allows exciting all-field components, making the tag detection almost independent of tag location and orientation when it lies on the antenna surface. Since TWAs are not resonating structures, the proposed antenna results are scalable, allowing for an easy integration in commercial readers with arbitrary sizes. In particular, a 275 × 135 × 10 mm³ antenna has been designed to fit a particular commercial desktop reader size. Measured tests on the antenna read range were carried out, showing a field distribution maximised in the broadside direction within 10 cm from the antenna surface.