Frequency Reconfigurable Near-Zero Refractive Index Material for Antenna Gain Enhancement Applications

In this paper, a planar near-zero refractive index material (NZRIM) consisting of an outer loop with four symmetrical quarter-rings is proposed. The quarter-rings are connected to the outer loop by two symmetrical microstrip lines on the opposite side. The backside of the substrate has mutually central split microstrip lines. By loading adjustable capacitor between the split in the center of the backside of the substrate, the resonance frequencies of the proposed NZRIM can be controlled and thus the epsilon-near-zero (ENZ) frequency bands change correspondingly. According to the specific frequency bands of its metamaterial characteristics, the proposed NZRIM can be mounted above the surface of different antennas with different operation bands for 5G applications. Results show that the proposed NZRIM can enhance the forward radiation gain of antennas.