Numerical Analysis and Applications of Planar Series Feed Antennas for Near-Field UHF RFID, Sensing and Radiative WPT

Near-field antennas have recently attracted an increased attention for the variety of near-field communication and sensing applications. At the same time, the radio frequency identification (RFID) technology has come of age and became an indispensable tool in the numerous industrial applications in the retail tracking, security, counterfeit prevention, and healthcare. Several designs of the near-field reader antennas utilized for different UHF RFID applications have been introduced in [1]. For the so-called smart shelf antenna applications, item RFID tags are typically placed on the reader antenna surface and may occupy various interrogation volumes within the reactive and radiative near-field zones. The UHF $(916-920 \mathrm{MHz})$ RFID antenna design producing the circularly polarized (CP) radiation in the near field of planar antenna based on the periodic strips EM coupled to the microstrip feed line has been presented in [2]. To address the specific demands of the emerging near-field wireless applications, new concepts of the near-field antenna operation are required.