*Article* **A Negative Index Nonagonal CSRR Metamaterial-Based Compact Flexible Planar Monopole Antenna for Ultrawideband Applications Using Viscose-Wool Felt**

**Kabir Hossain 1,2, Thennarasan Sabapathy 1,2,\*, Muzammil Jusoh 1,2, Mahmoud A. Abdelghany 3,4,\*, Ping Jack Soh 1,5 , Mohamed Nasrun Osman 1,2, Mohd Najib Mohd Yasin 1,2, Hasliza A. Rahim 1,2 and Samir Salem Al-Bawri <sup>6</sup>**


**Abstract:** In this paper, a compact textile ultrawideband (UWB) planar monopole antenna loaded with a metamaterial unit cell array (MTMUCA) structure with epsilon-negative (ENG) and near-zero refractive index (NZRI) properties is proposed. The proposed MTMUCA was constructed based on a combination of a rectangular- and a nonagonal-shaped unit cell. The size of the antenna was 0.825 λ<sup>0</sup> × 0.75 λ<sup>0</sup> × 0.075 λ0, whereas each MTMUCA was sized at 0.312 λ<sup>0</sup> × 0.312 λ0, with respect to a free space wavelength of 7.5 GHz. The antenna was fabricated using viscose-wool felt due to its strong metal–polymer adhesion. A naturally available polymer, wool, and a human-made polymer, viscose, that was derived from regenerated cellulose fiber were used in the manufacturing of the adopted viscose-wool felt. The MTMUCA exhibits the characteristics of ENG, with a bandwidth (BW) of 11.68 GHz and an NZRI BW of 8.5 GHz. The MTMUCA was incorporated on the planar monopole to behave as a shunt *LC* resonator, and its working principles were described using an equivalent circuit. The results indicate a 10 dB impedance fractional bandwidth of 142% (from 2.55 to 15 GHz) in simulations, and 138.84% (from 2.63 to 14.57 GHz) in measurements obtained by the textile UWB antenna. A peak realized gain of 4.84 dBi and 4.4 dBi was achieved in simulations and measurements, respectively. A satisfactory agreement between simulations and experiments was achieved, indicating the potential of the proposed negative index metamaterial-based antenna for microwave applications.

**Keywords:** metamaterials; high-performance textiles; wearable antenna; textile antennas; polymer
