Compact Mobile RFID Antenna Design and Analysis Using Photonic-assisted Vector Near-field Characterization

We present the design and analysis of a small planar loop antenna for applications in mobile RFID readers within the cell phone band. Compactness of the loop antenna, crucial to size reduction in antennas designed for mobile handsets, is realized by bending a folded-dipole in a circular fashion. Furthermore, capacitive loading, through a parasitic patch, is created inside the loop antenna and has an effect of increasing the electrical length of the structure. This enhanced length provides tunability of the resonance frequencies and a secondary dominant radiation port in the center of the antenna. A short planar dipole is transformed to a twice folded dipole and a loop antenna to produce a larger input resistance. We also analyze the performance of the RFID antenna by exploring the current-induced near field radiation patterns using a non-invasive photonic- assisted dielectric field mapping system. The evolution from the near to the far field is also discussed.