Business-Card Sized UHF RFID Tag Antennas

The Radio Frequency Identification (RFID) is a technology that allows the information to be transferred wirelessly between the interrogator (reader) and the transponder (tag) [1]. In recent years, the RFID in ultra-high frequency (UHF) band, which operates through the radiative coupling mechanism, is attractive to the users due to its longer read range comparing to the RFID in low frequency (LF) or high frequency (HF) band, which operate through the inductive coupling mechanism [2]. In the passive UHF RFID tag, the antenna plays a key role in the overall system performance. Several works have discussed about the antenna design and how to measure the performance [3], [4]. In the application such as conference registration and tracking system, the size of RFID tag can be as large, but limited to the size of the nametag, which is approximately the size of business card. Even though the nametag is commonly used in horizontal direction, we also can find some use in vertical direction. Most of the passive tag antenna is a printed dipole which is typically a linearly polarized antenna, where the read range is maximized when the orientation of the tag antenna is matched with that of the reader antenna and is minimized when it is 90 rotated. In order to eliminate the read-orientation sensitivity, various antennas have been proposed [5], [6]. However, a 2-port IC chip is required in [4] and the overall size is comparatively large in both [5] and [6]. In this paper, we proposed the UHF RFID tag antenna that can be fit within the size of business card. The read range of this tag antenna is maximized when the tag antenna is placed at 0 orientation. We also modify the antenna to rotate the angle of the maximum read range to -45 and 45 so that we can obtain the same level of read range when the tag antenna is placed at 0 and 90 orientation which is slightly lower than the maximum one. The read range of these antennas at different orientation is measured and compared with that obtained from the calculation.