DESIGN OF MICROSTRIP ANTENNA WITH VARIOUS SHAPE OF SLOT FOR SPECIFIC APPLICATION

Abstract

Novel asymmetric-circular shaped slotted microstrip patch antennas are proposed for circularly polarized (CP) radiation and radio frequency identification (RFID) reader applications. A single-feed configuration based asymmetric-circular shaped slotted square microstrip patches are adopted to realize the compact circularly polarized microstrip antennas. The asymmetric-circular shaped slot(s) along the diagonal directions are embedded symmetrically onto a square microstrip patch for CP radiation and small antenna size. The CP radiation can be achieved by slightly asymmetric (unbalanced) patch along the diagonal directions by slot areas. The reader antenna is one of the important components in the RFID system. Circularly polarized microstrip antennas (CPMAs) can reduce the loss caused by the multipath effects between the reader and the tag antenna. Frequencies specifically that have been reserved for the ISM (industrial, scientific, medical) bands can be used for the RFID applications. Due to the merits of high data transfer rate and broad readable range, passive RFID systems at the UHF band are preferred in many applications. The total frequency span of the UHF band used for RFID systems is 840–960 MHz. However ,there is not a UHF range accepted worldwide for the RFID applications. The system operates at the bands of 902–928 MHz in America, 865–867 MHz in Europe, and 840–955 MHz in Asia-Pacific region. In Asia-Pacific region, the UHF RFID frequency range is different in different countries: China (840.5–844.5 MHz, 920.5–924.5 MHz), Japan (952–955 MHz), India (865–867 MHz), Hong Kong (865–868 MHz, 920–925 MHz), Taiwan (920–928 MHz), Korea (908.5–910 MHz, 910–914 MHz), Singapore (866–869 MHz, 923–925 MHz),Australia (920–926 MHz), etc. As a result, except the America UHF RFID frequency-band, in other countries UHF RFID allocation bandwidths are between 3 to 6 MHz. The broadband CPMA designs to cover total frequency span of the UHF band for RFID applications have been reported. The sizes of the broadband CPMAs are bulky and not suitable for handheld or portable reader applications. The single-feed CPMAs are usually more compact as compared to the dual-feed CPMAs .The major consideration for the CP microstrip antenna design of handheld/portable RFID reader applications is overall compact size of the antenna.The antenna gain and bandwidth are not so critical. However, the antenna must cover at least one UHF RFID band with bandwidth of few MHz. The small size of the CPMA can be achieved at the cost of limited gain, narrow 3-dB AR bandwidth and impedance bandwidth. Various techniques have been published to generate the CP radiation of the single-feed microstrip antennas. The single-feed square patch was proposed by Sharma and Gupta for CP radiation using the symmetric truncated corners method . The single-feed CP annular-ring, square and circular patch antennas with perturbation elements (symmetric cross, inner stubs techniques etc.) . The study of the asymmetric-circular shaped slotted microstrip patches (ACSSMPs) for the CP radiation was not popular in open literature.