A Broadband Near-Field UHF RFID Reader Antenna With Low Far-Field Gain

A broadband magnetic coupling antenna with low far-field gain for ultrahigh frequency radio frequency identification near-field applications is presented in this communication. The proposed antenna is consisted of a number of loop units and each unit has in-phase current along the loop. It generates a strong uniformly distributed magnetic field over a large interrogation. To meet different scenarios, the interrogated area can be adjusted by changing the number of units. The proposed antenna has low far-field gain and broadband characteristics. Mechanism analysis is carried out to provide the guidelines for the antenna design. As an example, a 10-unit antenna has been fabricated and measured. The experimental results show that the antenna achieves the impedance matching over the frequency range from 740 to 4600 MHz. And the proposed antenna achieves 100% reading rate with 140 button tags in the region of 100 mm <inline-formula> <tex-math notation="LaTeX">$\times750$ </tex-math></inline-formula> mm <inline-formula> <tex-math notation="LaTeX">$\times12$ </tex-math></inline-formula> mm.