Directive Beam of the Monopole Antenna Using Broadband Gradient Refractive Index Metamaterial for Ultra-Wideband Application

This paper introduces a novel technique to enhance the gain of the basic monopole antenna by using broadband gradient refractive index (GRIN) metamaterial. The proposed GRIN is designed by using a parallel-line unit cell metamaterial with different refractive index. A seven GRIN lens is placed on the omnidirectional printed basic monopole antenna, perpendicularly. Due to the non-resonant and subwavelength properties of the parallel-line elements, the proposed GRIN metamaterial lens has a broad bandwidth property with low loss. The simulation and measurement results confirmed that the beam is more directive with narrow beam width. The measured reflection coefficient of the GRIN antenna is below -10 dB over the frequency bandwidth of 3.4-11 GHz. Due to GRIN lens, the peak gain of the basic monopole antenna is increased by 5.3 dB at 8.8 GHz.