Investigations on Passive RFID Tag Antenna for UHF Band Applications

Abstract

The use of automatic identification technologies such as radio frequency identification (RFID) to identify, track, and sense the people, items, or objects have evolved significantly owing to its great advantages. RFID System is a real-time processor that helps in tracking the information stored on a tag and to exchange it with the remote device known as the RFID Reader or Interrogator. The essential benefits offered by these RFID systems are automatic and non-line of sight detection at a distance of several meters, portable database, and flexibility towards unfriendly environments result in reduced manual localization work and hence man-power. These advantages also make RFID to be recognized as a cornerstone of the future Internet of Things (IoT) technology. The overall performance of the Passive RFID System in terms of size, cost, and read range depends on the design of the tag antenna. The Passive RFID tag must have a reasonable antenna size with improved gain and radiation efficiency in addition to conjugate impedance matching. Also, as RFID tags are generally designed to operate in a specific region, this limits their practical utility and restricts intercountry operations. Therefore UHF-RFID systems having multiple bands/broadband operations with long read range are in more demand. As an RFID tag needs to be affixed onto different objects therefore, the tag must operate reliably in a changing environment. Hence in addition to have compact and planar geometry, the designed tag must be robust and platform tolerant. In this thesis, methods to develop passive RFID tags exhibiting high read range performance over a single, multiple, and broadband UHF-RFID operation are investigated. Further, the use of artificial magnetic conductor (AMC) structures has been explored to enhance the radiation efficiency and read range of platform-independent tags. In this present research work, we started with a single-band tag design and then extended it for dual/broadband tag designs. The first tag antenna is designed to operate in a major U.S./ North American UHF-RFID band ranging from 902 to 928 MHz. The designed tag makes use of a meandered radiating element to achieve a compact antenna size. Further, inductively coupled feed with a spiral loop is used to achieve conjugate impedance matching with connected Alien Higgs-4 chip (used to store tagged object information) impedance. The read range, tag power sensitivity, differential radar crosssection (Δ RCS), and radiation pattern performance of the designed tag is tested using tagformance setup. Also, the platform tolerance capability of the tag is examined by mounting the tag on various objects in a real outdoor scenario. The designed tag exhibits a long-read range of 13.56 m in the operating U.S. UHF RFID band. ii In the second tag design, the antenna employs a linearly tapered structure with nonuniform meandering and exhibits broadband operation to cover two major UHF-RFID bands i.e. North American (902-928 MHz) and European (865-867 MHz) RFID bands. The T-match feed network is utilized to achieve conjugate impedance matching with the integrated RFID chip. The proposed tag is experimentally characterized to evaluate its read range, realized gain, read pattern, and platform tolerance capability performance on different objects. Also, the tag’s read range is measured on various mounting objects to validate its platform tolerance. The measured read range of the tag is observed to be 10 m in the European band and 12 m in the North American band. The third designed tag is compact with dual-band operation covering European and Korean UHF-RFID bands. The designed tag employed folded dipole configuration with meandered arms to attain the small size and conjugate matching with the Higgs-4 RFID chip. The proposed tag exhibits a measured read range of 5.5 m and 5.8 m at 866 MHz and 912 MHz. Again, the platform tolerance capability of the designed tag on various objects is examined. Finally, the fourth tag design employed a microstrip patch antenna with a full ground plane for metal mounting applications. The novel asymmetric shunt stub feed network is employed to achieve conjugate matching with the Alien Higgs-4 chip. Also, the designed tag employs Artificial Magnetic Conductor (AMC) structure to enhance its radiation properties for platform tolerant applications. The designed tag covers dual UHF-RFID bands used in Europe (855-867 MHz) and Japan (950-955 MHz). Further, its platform-independent capability is validated as it exhibits steady gain response inside the desired resonating bands for different sized metallic sheets. The measured read range of the tag is found to be 7.3 m in the European band and 10.8 m in the Japanese band. On the whole, all the four tag antenna designs exhibit single band, broadband, and multiband operation in UHF-RFID bandwidth (860-960 MHz). Hence, the aim of the research work to achieve compact size, high read range, multi-band operations with platform tolerance is accomplished. All designed tags are simulated using CST Microwave Studio Suite V.16 to access their performance. Thereafter, all the tag antenna structures are fabricated and experimentally characterized to evaluate their read range performance and platform tolerance capability. The performance of the first two tag designs is evaluated using commercial tagformance set up from Voyantic labs in Taiwan. The impedance performance of the other two tags is measured using Vector Network Analyzer (VNA), available in Microwave and Antenna Research Laboratory of Thapar Institute of Engineering and Technology (TIET), Patiala to validate the simulated results.