Square enclosed circle split ring resonator enabled epsilon negative (ENG) near zero index (NZI) metamaterial for gain enhancement of multiband satellite and radar antenna applications

In this article, a square enclosed circle split ring resonator (SEC-SRR) based metamaterial is described that shows negative permittivity (ENG) with near-zero-index (NZI) of refraction. The unit cell of this metamaterial is formed with two SRR rings, one with square in shape and another circular shaped. The inner circular SRR has related to the outer square SRR by the metal strip. The analyzed design is very simple, but the outcome of this recommended unit cell is high i.e., it covers the multiband S-, C-, and X- bands. Rogers is used as a substrate to design the proposed SEC-SRR that has a thickness of 1.524 mm. The unit cell has a dimension (electrical) of 0.070λ × 0.070λ. The simulation software CST microwave studio-2019 is used to identify transmission (S21) and reflection (S11) coefficient and from this knowledge relative permittivity, permeability and refractive index is obtained by using MATLAB code based on Nicolson-Ross-Wier (NRW) method. The simulated resonance frequencies are 2.61, 6.32 and 9.29 GHz with well-matched to the measured ones. The negative permittivity regions are obtained in 2.63–2.87 GHz, 6.39–7.45 GHz, and 9.37–9.52 GHz covering S-, C-and X-bands, respectively. The equivalent circuit is modeled in Advanced Design Software (ADS) and verified by comparing obtained S21 with CST output. The designed unit cell also exhibits NZI property, and high effective medium ratio (EMR) of 14.37 at lower resonance frequency. The applicability of NZI property of this ENG metamaterial has been investigated by applying for gain enhancement of LPDA antenna. Due to its near zero refractive index, negative permittivity, high EMR and simpler design, the proposed metamaterial can be utilized for S-, C-, and X-bands applications, especially for improving the gain of satellite and radar antennas with special features.