## 2 Materials and Methods  
Consumer electronics and communications advancements have been continuously demanding for an antenna with a more compact design, higher bandwidth, and other performance metric improvements. Numerous antenna miniaturization methods have been suggested to reduce the dimension and to enhance the bandwidth and radiation gain of the antenna. One of these techniques involves use of metamaterials in antennas. In this method, metamaterial structures made of periodic subwavelength unit cells are loaded onto the antenna [18; 19]. These metamaterial structures show unique properties, such as negative permittivity or permeability, which can provide lower resonant frequency at similar antenna dimensions and hence help with antenna miniaturization and enhancement of the antenna's bandwidth and gain. Several antenna bandwidth enhancement and miniaturization based on this method have been reported and demonstrated in the literature [20; 21].  
Another common antenna miniaturization techniques includes introducing space-filling curves to the antenna's structure, which is utilized in this paper to design the proposed antenna. The idea is to use the available space efficiently to fit a larger radiating structure based on special mathematical curves. With this technique, the current distribution of the antenna should be well managed to constructively add at selected frequencies and angular directions. Otherwise, the radiation characteristics of the antenna, such as impedance matching, bandwidth, and gain, will degrade by miniaturization. Fractal antennas are one of the examples in this group in which an inherent geometrical self-similarity is used to achieve space-filling structures [22]. The Antenna I design is based on fractal structures, which uses Hilbert curves. Meander antennas are another example in this miniaturization group in which the structure of the antenna is miniaturized by introducing bendings and curves to the antenna's geometry [22]. The Antenna II design is based on the meander structure. It can be seen in the Results section that meander structures are more successful in maintaining the radiation characteristics of the antenna compared to fractal antennas. Overall, adding more curves to the antenna's structure comes at the expense of reducing radiation efficiency and bandwidth because some currents in the opposite phase are usually introduced in the structure of the antenna. Hence, a novel method previously proposed in [23] for the miniaturization of dual-band antennas is used here in the design of Antenna III for the design of a triple-band antenna. It can be seen in the Results section that this design is superior to the other two designs in terms of better radiation characteristics and smaller dimensions. In the design of the antennas, the inverted F method was used for feeding the antennas and tuning the input impedance to match the coaxial cable impedance. The planar inverted F antenna (PIFA) is a quarter-wavelength patch antenna with a shorting pin at the end. Since the antenna is shorted at the end, the current at the end of the patch antenna is no longer zero, and it has a path to flow in. In the planar inverted F antenna, the feed point is placed between the open and the short ends to adjust the input impedance of the antenna, while maintaining its high radiation efficiency.