# A Compact Triple Band Antenna Based on Multiple Split-Ring Resonators for Wireless Applications
## 1 Introduction  
The rapid development of wireless communication systems requires multiband antennas that can serve multiple wireless standards and systems. These antennas are designed to operate in a large number of frequency bands that can support different applications as they transmit and receive in different bands. When small devices integrate multiband antennas, issues such as size limitations or antenna location can arise that affect the overall design or functionality. For these reasons, the use of miniaturized multiband antennas is critical. The characteristics of the factors such as their shape, the feeding techniques used and defective grounds can be modified, leading to a compact multiband antenna design that covers a wide frequency band and makes it easy to integrate into devices such as smartphones, tablets, Internet-of-Things devices and industrial equipment. Since size and performance are key in wireless applications, multiband functionality combined with a compact form factor size increases the potential for integration into various communicationsystems. In the literature, there are various approaches to realize a compact multiband antenna. One of the methods used includes the slots technique [1; 2; 3; 4]. This technique has attracted much attention recently because slots cut into an antenna act as resonators and enable the antenna to cover multiple frequency bands. In [5], a multiband triangular antenna with dimensions of 57 \(\times\) 57 \(\times\) 1.6 mm\({}^{3}\) on an FR 4 substrate was proposed to meet the requirements of WLAN and WiMAX. The results showed that the antenna achieved the frequency bands 3.45-3.75 GHz, 4.75-5.5 GHz and 5.95-6.2 GHz by integrating slots in the antenna. However, it is very important to know that this technique comes with its own problems and compromises. The designed antenna can be expensive, as the manufacturing of the additional slots requires high precision. Also, the operating bandwidth of the designed antenna is limited, as the resonant structure resulting from the changes in slot dimensions can cause unwanted resonances. Other approaches to multiband antenna designs include the use of parasitic elements. In [6], a fractal multiband antenna with parasitic elements on an FR4 substrate is proposed to increase the gain. Although the antenna covers the 1.96-2.22 GHz, 3.51-3.91 GHz and 4.78-5.26 GHz frequency bands with dimensions of 37 \(\times\) 28 \(\times\) 1.6 mm\({}^{3}\) and an acceptable gain of 5 dBi, the parasitic elements increase the size of the antenna because they create a coupling effect that leads to unwanted resonances and makes the design more complex. In addition, these elements cause the antennas to exhibit a narrow operating bandwidth. Another common technique is the use of a reduced ground plane. In [7], a miniaturized antenna is fabricated on both sides of an FR4 substrate. Although this antenna has good impedance matching in the operating band, the reduced ground plane reduces the gain even though the antenna has a size of 46 \(\times\) 12 \(\times\) 0.5 mm\({}^{3}\). To solve this problem, many researchers have changed the shape of the antenna to obtain more multiband antennas with a compact size that can cover additional applications [8]. In [9], three microstrip antennas with dimensions of 70 \(\times\) 50 mm\({}^{2}\), 60 \(\times\) 50 mm\({}^{2}\) and 50 \(\times\) 50 mm\({}^{2}\) are proposed to cover 1.87-2.66 GHz, 3.33-3.69 GHz and 4.71-5.80 GHz. In [10], a dipole antenna with an overall size of 46 \(\times\) 10 \(\times\) 0.8 mm\({}^{3}\) is proposed for a wireless local area network. In this technique, the parameters of the antenna are varied to achieve resonance at different frequencies. This can present complex problems and challenges in terms of size, manufacturing complexity and cost. In addition, the use of metamaterials [11] or artificial magnetic conductors in antenna design can extend the frequency band of the antenna.