Design a Patch Antenna Array to an Optimum Near Field Distribution in the Near-Zone for RFID Applications

The popularity of RFID in recent years has boomed a variety of potential applica- tions in the commercial uses. Its successful applications rely strongly on the applicable scenario to implement the system, where the radiation from the antenna plays a key factor of successful operation. Good radiation characteristics may help to reduce the interferences from surrounding structures. A scenario of antenna design is thus developed, which makes the antenna to radiate ¯elds with optimum ¯eld distributions in the near-zone of antenna. In particular, the design is based on the optimization of excitation weighting for phased array antennas. The antenna array is realized microstrip patch elements, which have advantages of easy implementation. This array will radiate electromagnetic ¯elds that are relatively uniform in the near-zone of array aperture for RFID applications. To simplify the implementation cost, the array feeding network is simpli¯ed by using equal power dividers in one dimension. In another dimension, an open-end transmis- sion line is used to create standing wave, which in conjunction with feeding microstrips allows one to control the phases and amplitudes of a row array. A prototype has been implemented to demonstrate the validity of this near-¯eld focused array. This design allows one to de¯ne a target zone that can be used as detection area of RFID tags as interested in the department store management system. Antenna design, as well as the design procedure, is presented. Numeri- cal simulations and experimental measurement are conducted and also presented to validate the concept.