## 1 Introduction  
The demand for high data rates in reliable communication has driven advancements in RF and microwave engineering, particularly in the field of wireless communication, which is widely acknowledged as one of the most significant contributions to the technology world. This technological revolution has resulted in the widespread use of digital data. To meet these increasing expectations, Ultra-Wide-Band (UWB) technology was introduced, offering improved communication accuracy, speed, and efficiency of data transmissions. The appeal of UWB technology has grown over the past few decades due to its desirable features such as accuracy, high data rates, and cost-effectiveness. The Federal Communications Commission (FCC) defines UWB within the frequency range of 3.1-10.6 GHz [1; 2]. UWB technology finds applications in various wireless communication domains, including radar systems, medical applications, and personal communications [3; 4; 5]. The enhancement of antenna characteristics such as antenna gain, bandwidth, and radiation pattern has made UWB particularly suitable for Wireless Capsule Endoscopy (WCE) systems [6; 7]. Interference issues arise when UWB signals coexist with narrow bands like WiMax, C-bands, and WLAN. Notching techniques have been employed to mitigate interference between these frequency bands. Previous studies have proposed compact UWB trapezoidal antennas with dual-band notching characteristics [8; 9; 10; 11] and UWB antennas with triple notching [12; 13; 14; 15; 16] to address this issue. These techniques involve the insertion of comb slot shapes into the radiating patch to achieve notching, while the UWB characteristics are achieved through ground structure modifications in a staircase form [17; 18; 19; 20]. In addition, UWB uses a variety of techniques for notching [21; 22; 23; 24; 25; 26], and switches and stubs are embedded in the slot antenna [27; 28; 29; 30; 31]. Moreover, MIMO (Multiple-Input Multiple-Output) technology was developed to enhance data transmission efficiency, communication quality, and capacity. However, it introduced coupling effects between antennas. To overcome this challenge and improve the quality of RF signals while utilizing available bandwidth efficiently, different techniques have been introduced in MIMO systems. For instance, CSRR (Complementary Split-Ring Resonator) slots and J-shaped slots have been utilized for notching dual bands [32], while coupling reduction has been achieved through resonating slots on the ground or isolation elements placed between resonating elements [33; 34]. In a co and cross configuration, periodic S-shaped DGS units (PSDGS) have been placed between square patch elements to induce high isolation [35]. Dielectric Resonator Antenna (DRA) techniques, Complementary Split-Ring Resonators (CSRR), neutralization techniques, and stub and T-slot integration into the ground have been proposed to block surface current flow and improve isolation [36; 37; 38; 39]. The use of a varactor diode enables capacitive tuning for reconfigurable antennas. Various techniques such as varactor diode and biasing circuit, Electromagnetic Band Gap (EBG), and Substrate-Integrated Backed Cavity Slots (SIBCS) have been proposed to reduce mutual coupling in MIMO systems [40; 41; 42; 43; 44; 45]. Despite these advancements, challenges remain in terms of antenna size, multiple notching, and additional elements for coupling reduction. In this paper, we present a 4 \(\times\) 4 crescent-shaped monopole UWB-MIMO antenna system that addresses these size and notching challenges and reduces coupling without the need for additional elements. The proposed system achieves multiple notches for C-band, WLAN, and satellite networks through the etching of Complementary Split-Ring Resonators on the patch elements, ground side, and C-shaped structures. The MIMO antenna system is arranged in an orthogonal configuration to achieve pattern diversity and polarization diversity. The proposed design covers a bandwidth from 2 GHz to 13 GHz.