3. Conclusions

Depending on the specific cases, the application of MTMs as the DGS of the antenna not only reduces the size but also increases the obtained bandwidth of the antenna. Figure 19 compares the sizes and bandwidths of two antennas before and after applying the MTMs with the same 2.413 GHz resonant frequency for WLAN system. The ratio of the decreased size and the

Antenna types Antenna size ratio, % Ratio of BW, % Type of radiation pattern

Without MTM 100 100 Directional With MTMs 78.7 141 Directional

Table 2. Comparison between parameters of two types of antennas for WLAN system.

The application of metamaterials in antenna design has enhanced its bandwidth. Depending on the technical requirements of the designed antenna, the different metamaterial structures and different application methods are selected to achieve the most appropriate antenna

From the need to integrate multiple functions (many communication systems operation) on single devices, multiband antennas are more interested. The use of metamaterials in antenna design is an attractive trend not only to reduce size, improve the power gain, enhance bandwidth, but also to design multifrequency-band antennas [46]. The unit cells of metamaterials can be used as radiation components, a part or loaded part of the ground plane of antenna. Because, MTMs can support negative refraction indexes at resonant frequencies and unit cell structures of symmetric pairs. This can be used to design multifrequency antennas with smaller dimensions than traditional one [46]. Metamaterial can be combined with a conventional or fractal microstrip antenna to create multiband antenna, in which the antenna size is determined by the lowest

Figure 20. The configuration of microstrip antenna for WLAN systems without loaded CSRR (a), fractal antenna with

increased bandwidth is shown in Table 2.

2.3.4. Use metamaterials to get multiband

loaded CSRR (b), and S11 parameters of them (c) [27, 48, 49].

bandwidth.

80 Metamaterials and Metasurfaces

In this chapter, the applications of metamaterials in design to enhance antenna parameters are presented. The metamaterials can be applied as an environment of the antenna or as part of the antenna. Depending on the parameters of the desired antenna to improve, the metamaterials can be applied in different methods. The metamaterials can be applied to improve bandwidth, power gain, or to create compact, multifrequency-band antennas. To apply metamaterials in an antenna, the first is to design their unit cells, which are considered as atoms, creating special properties of the metamaterial at the desired frequency. The size of the unit cells is calculated, simulated, and optimized, based on the HFSS software. Effectiveness of improving the parameters of the antenna depends on the structure, size, quantity, and method of use of the unit cell of the metamaterials. Application of metamaterials in antenna design can increase their power gain ≥2 dB, bandwidth ≥100%, reduce size ≥50% or to create additional frequency bands for multicommunication systems operated antennas.
