A UHF RFID reader antenna for searching tagged items

In this work, a mobile atenna of a UHF RFID reader for searching tagged items on the shelves is presented. The antenna consists of a microstrip array of alternating orthogonal double dipoles which are fed in series by a meander microstrip line. The individual dipoles are designed such as to provide high bandwidth. The distance between the double dipoles is adjusted in order to excite them in phase at 867MHz and create two orthogonal electric-field components. The number of dipoles and the inter-element distance create beams with direction diversity. Based on the analysis of the pattern and the radiated field in the near-field zone, it was found that a semicylindrical area around the axis of the antenna is sufficiently covered.