In this paper, a novel near zero refractive index metamaterial is designed and used as a superstrate of a microstrip antenna. In order to decrease the return loss, particle swarm optimization (PSO) is used to optimize the metamaterial structure. One of the important factors in the antenna designing, which influences the radiation efficiency, is to determine the accurate position of the feed, and PSO is used to find a precise location of the feed with minimum return loss. The simulation and fabrication of the microstrip antenna using the optimized metamaterial structure is also presented. The performance of the antenna is improved, and the gain is increased up to 4.5 dB. The directivity and radiation efficiency are significantly enhanced. Moreover, a very good agreement is observed between simulation and measurement results.
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