A mutual coupled spider net-shaped triple split ring resonator based epsilon-negative metamaterials with high effective medium ratio for quad-band microwave applications.

• A novel SNTSSR based ENG metamaterial has been designed for microwave applications. • It provides multiband resonances at S-, C-, X-, and Ku-bands with six resonances. • Metamaterial exhibits negative permittivity and near zero refractive index. • Performance of 1 × 2 and 2 × 2 array is investigated that shows similar quad band features. • It has been used to enhance the bandwidth and gain of a 3D cross-fed wideband antenna. This paper discusses a spider net-shaped triple split ring resonator (SNTSRR) based epsilon-negative metamaterial with a high effective medium ratio. The proposed SNTSRR unit cell structure is a modification of the general split ring resonator and consists of three octagonal-shaped split ring resonators (SRR). Two metal strips attach the split ring resonators to increase the electrical length of the proposed SNTSRR unit cell. The optimized size of the proposed SNTSRR unit cell, using Rogers RO4350B substrate material, is 10 × 10 × 1.524 mm³. The frequency ranges of the transmission of microwave applications are: 2.83–2.89 GHz for S-band, 4.24–4.31 GHz and 6.74–7.06 GHz for C-band, 9.17–9.26 GHz and 10.98–11.16 GHz for X-band, and 12.62–13.00 GHz for Ku-band. The unit cell achieves six resonant frequencies of 2.86 GHz, 4.28 GHz, 6.94 GHz, 9.22 GHz, 11.10 GHz, and 12.89 GHz for S-, C-, X-, and Ku-bands, respectively. A comprehensive investigation of effective medium parameters, scattering parameters, mutual coupling effect, and the unit cell properties with electromagnetic propagation were accomplished in this paper. The proposed SNTSRR unit cell revelations epsilon negative (ENG) properties in the frequency ranges of 2.87–3.05 GHz, 4.27–4.45 GHz, 6.94–7.39 GHz, 9.24–9.34 GHz, 11.12–11.26 GHz, and 12.90–13.24 GHz. For experimental validation, we fabricated the proposed SNTSRR unit cell along with its array construction. After that, we measured the scattering parameters, which showed better agreement between the simulated and the measured outcomes. Furthermore, the coupling effects between the 1 × 2 and the 2 × 2 array structures with different distances were analyzed, and they showed better performance with low impact. Additionally, the calculated effective medium ratio (EMR) is 10.48, which infers compactness and efficacy of the unit cell. It should be noted that the compact size, effective medium parameters, S-parameters, and high EMR make the proposed SNTSRR metamaterial appropriate for quad-band microwave applications. Finally, the proposed SNTSRR unit cell has been employed as an application in 3D cross-fed wideband antenna to enhance the bandwidth and gain of the antenna, which is appropriate for microwave head imaging applications. [ABSTRACT FROM AUTHOR]