## 1 Introduction  
Recently, the development of metamaterial has received significant interest as a material for the creation of numerous novel structures with unconventional electromagnetic properties and noticeably enhanced performances [1, 2]. Several metamaterials have been created with negative real parts for both permittivity (\(\varepsilon\)) and permeability (\(\mu\))--so-called double-negative metamaterials (DNG). This is in addition to the single-negative metamaterials (SNM) where either \(\mu\) or \(\varepsilon\) is negative, called mu-negative metamaterial (MNG) and epsilon-negative metamaterial (ENG), respectively [3, 4]. The first DNG was theoretically described by [PERSON] in 1968 [5] and experimentally verified later in [6]. The DNG supports an electromagnetic wave where the phase and group velocities propagate in opposite directions. This allows new electromagnetic properties [7, 8] and applications in antenna design, biomedical, and wireless technologies [9]. However, near-zero refractive (NZRI), as well as epsilon-and-mu-near-zero (EMNZ) properties, have been investigated for many metamaterial structures in the state-of-the-art for specific applications such as S, C, X, and KU-bands [10, 11, 12, 13]. Today, the demand for designing multiband antennas with a low cost and minimal weight has become highly essential due to the presence of multiple communication standards. Today, antenna performance has been significantly improved using metamaterial, which offers improved size miniaturization, gain, bandwidth, as well as decreased cost [14, 15, 16]. Several types of metamaterial structures have been proposed: a split-ring resonator (SRR) [17, 18], complementary split-ring resonators (CSRRs) [19, 20], periodic array structures [21], and spiral resonators (SR) [22]. For instance, SRR unit cell structures have been investigated for antenna design miniaturization, creating multiband operation, and improving bandwidth and gain [23, 24]. Moreover, several multiband antennas loaded with metamaterial have been reported in [25, 26, 27, 28], where there are trade-off characteristics, including the number of operating bands, size, and gain. However, miniaturization of antenna size can be attained using substrates with high permittivity or small size radiating elements [29]. The antenna radiator size can be decreased through various methods, including applying metamaterial, creating slots, using defected ground structure, and adding parasitic element strips. In this paper, we propose a multiband CPW-fed antenna array covered with a planar investigated metamaterial (MTM) superstrate based on a near-zero refractive index (NZRI) and double-negative metamaterials (DNG) over a wide frequency range. The proposed MTM unit cell structure consists of several symmetric split-ring resonators (SSRRs) in order to exhibit real values of negative permeability and permittivity. The proposed antenna simultaneously operates within a GSM900 bandwidth at 0.9 GHz, WLAN at 2.3/2.4/5/5.2/5.8 GHz, 4 th generation LTE-A at 3.5 GHz, and 5G Wi-Fi in the frequency range of 5.15-5.875, while it has an overall size of \(78.6\times 42.5\) mm\({}^{2}\) (\(0.236\lambda_{0}\times 0.128\lambda_{0}\) with respect to its lowest operating frequency). Simulated and measured results (with and without MTM) are in good agreement with the simulation. An overview of the different multiband CPW antennas published in the literature is presented in Table 1 for comparison with the proposed design. It can be seen that the proposed antenna offers significantly increased bandwidth and gain over similar antennas.