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Electrically Small Square Loop Antenna with a Capacitive SRR Cover Structure

In this paper, an electrically small square loop antenna with a capacitive SRR cover structure is built and tested. The size of the proposed antenna (ka 0.34) is much smaller than the corresponding Chu limit value. The experimental result shows that the resonant frequency and impedance bandwidth (VSWRles2) are 906 MHz and 5.8 MHz (901.7 - 907.5 MHz) respectively. The proposed antenna has maximum gain of -0.59dBi and radiation efficiency of 42.85% at 906 MHz. Although the proposed antenna has very small size, the measured maximum gain and radiation efficiency of the antenna show good performances. The proposed antenna is efficiently matched without additional matching network and designed by equivalent circuit model. A Teflon substrate (epsivr = 2.2) is used for the antenna fabrication. Therefore it has advantages of low cost, small size, and light weight and will be applied to wireless communication systems where small size antennas are required such as RFID (Radio Frequency Identification).