| Radio frequency identification(RFID)is a wireless identification technology that employs radio frequency wave to transfer data between a reader and tag attached to an object for purpose of identification and tracking.RFID technology has been widely used in many applications,such as distributions logistics,supply chain management,goods tracking and logistics,manufacturing industries,access control system,electronic toll collection,and good flow system.The full frequency of UHF RFID ranges from 840 MHz to 960 MHz(13.3%fractional bandwidth).The UHF frequencies authorized for RFID applications are particular in different countries and regions,e.g.,840.5–844.5 MHz and 920.5–924.5 MHz in China,866–869 MHz in Europe,902–928 MHz in north America,852–855 MHz in Japan,920–926 MHz in Australia,865–867 MHz in India,and 908.5–914 MHz in Korea.The issue of designing a reader antenna with an operating band covering the entire UHF RFID frequencies from 840 to 960 MHz would be beneficial for system configuration and cost reduction.The main innovation of this research is designing and realization a novel compact wideband antennas for universal UHF RFID reader applications.Designing one antenna structure with wide operation bandwidth to cover the universal UHF RFID frequency range is considered a novel,desirable,and beneficial.The designed antennas in this study are simplifying the antenna size and reducing the fabrication cost.Toward this end,several reader antennas were designed,fabricated,and investigated comprehensively during this research.Firstly,we designed a universal UHF RFID handheld reader antenna with wide operation bandwidth.The first design comprised of an inverted Z-shaped used as feedline,square slot with four diagonal stubs inserted at the slot corners,and two inverted T-shaped stubs placed at the two middle sides of the square slot.This Z-shaped feedline has ability to generate a dual circular polarization by reversing the direction of the two arms of the feedline.This design has overall size of 120×120×1.6 mm~3,operating bandwidth(overlapped bandwidth)of 262 MHz(745 MHz to 1007 MHz),high gain of 4.8d Bi,and maximum long reading-range of 3.45 m.This design is compact and simple compared to many reader antennas presented in the literature.Then,we designed the second antenna structure which composed of square slot with an inverted L-shaped feedline inserted at the right side,vertical stub,and horizontal stub.This designed antenna has the same overall size of the first design along with wide operation bandwidth of 285 MHz(818–1103)covered the entire UHF RFID frequency band.The L-shaped feedline used in this structure and subsequent designs to generate more resonant frequencies which conduces to wide operation bandwidth,as clearly seen in the subsequent chapters.In the third structure,we proposed a wideband antenna comprised of square slot120×120 mm~2 with two rectangular stubs mounted at opposite corners,an L-shaped feedline,and small slit cut at middle of the left side stub to improve the impedance matching of this design.This structure has an overall size of 120×120×1.6 mm~3 wide operating bandwidth from 796 MHz to 1269 MHz(473 MHz),dual circular polarization,and measured gain of3.9 d Bi.This operation bandwidth covered the entire UHF RFID band(840-960 MHz).Finally,the fourth design composed of square slot(112×112 mm~2),an inverted L-shaped feedline at the slot center,and L-shaped metal strip inserted at right center of the square slot towards the slot center.The experimental results of this design illustrate that this designed antenna has wider operating bandwidth of 444 MHz(824–1268 MHz)which easily covered the entire UHF RFID band.This design possesses an overall size of 112×112×1.6 mm~3,dual circular polarization,and long reading range of 3.61 m.The maximum measured gain of this antenna is 3.8 d Bi throughout the global UHF RFID frequency range.It is worth noting that the fourth structure possess a compact size,simple structure,wider operation bandwidth,and long reading-range compared to previous three designed antennas and even compared to a lot of universal UHF RFID reader antennas designed to operate for this band in open literature. |
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