A simple metamaterial resonator structure based efficiency electrically small semi-circular loop antenna (ESSCLA) is proposed. It is demonstrated numerically that capacitive offered by the simple metamaterial resonator structure can counteract inductive impedance of the ESSCLA at the resonance frequency. The overall structures of ESSCLA can be fabricated on one dielectric substrate, and match conjugate to a 50 Ohm coaxial transmission line source without additional matching network. The size of the proposed ESSCLA is ka = 0.6745 by Chu limit. The resonance frequency is 3.2239 GHz, and impedance bandwidth (S11<-10) is from 3.19 GHz to 3.26 GHz about 0.07 GHz, the relative bandwidth is about 2.2%. The measure results accord with the simulation results well. The peak gain is 4.58 dB. The radiation efficiency is 97.81%, the overall efficiency is 96.71% at the resonance frequency. The proposed antenna has advantages of efficiency, high gain, low cost, small size, and light weight and will be applied to wireless communication systems for required small antennas.
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