# Bio-Inspired Dielectric Resonator Antenna for Wideband Sub-6 GHz Range
## 3 Spiral Shell DRA Analysis and Optimization  
In order to evaluate the SsDRA performance and proceed with the antenna optimization, numerical analyses have been carried out on the SsDRA geometrical parameters by means of the CST Microwave Studio. Influence of SsDRA Thickness, Pin Height and SsDRA Height on the Scattering Parameter S\({}_{11}\): Evaluation of the Bandwidth  
In order to optimize the SsDRA design in terms of bandwidth, the scattering parameter S\({}_{11}\) was evaluated by varying the central pin height, h\({}_{\text{PIN}}\), and the SsDRA shell thickness t, by fixing the SsDRA height h\({}_{\text{DRA}}\) = 29 mm. The pin height h\({}_{\text{PIN}}\) is changed between 14.5 and 18 mm, while keeping the DRA thickness equal to t = 2 mm. The trend of the scattering parameter S\({}_{11}\) as a function of h\({}_{\text{PIN}}\) is reported in Figure 3a, where it can be noticed that when the pin height increases, the impedance matching becomes wider. In particular, for a pin height h\({}_{\text{PIN}}\) = 17 mm (cyan curve), a good impedance matching can be achieved at 3.5 GHz and 5.5 GHz, leading to a bandwidth of about 2 GHz. Figure 3b depicts the trend of the scattering parameter S\({}_{11}\) when h\({}_{\text{PIN}}\) is fixed at 17 mm and the SsDRA thickness t is varied (t = 1, 1.5 and 2 mm). The plots show that as t increases, the scattering parameter S\({}_{11}\) values improve, especially at 5.2 GHz, and, when t = 2 mm (yellow curve), the bandwidth at \(-\)10 dB is equal to about 2 GHz. Effect of the SsDRA Thickness, Pin Height and DRA Height on the Scattering Parameter S\({}_{11}\) and Realized Gain  
Figure 4a shows the scattering parameter S\({}_{11}\) when both h\({}_{\text{PIN}}\) and t are varied, while h\({}_{\text{DRA}}\) is set equal to 29 mm; the behavior of the monopole antenna (blue curve) having a pin height h\({}_{\text{PIN}}\) equal to 17 mm is also reported for reference. The monopole exhibits a scattering parameter S\({}_{11}\) value of about -14 dB at about 5.7 GHz with a bandwidth of about 1 GHz (from 4 GHz to 5 GHz). When the SsDRA is considered and its thickness t is increased, a better impedance matching is accomplished: in particular, the antenna bandwidth at -10 dB increases from 1.5 GHz for t = 1 mm and h\({}_{\text{PIN}}\) = 19 mm (red curve), up to about 2 GHz for t = 2 mm and h\({}_{\text{PIN}}\) = 17 mm (purple curve), along with lower scattering parameter S\({}_{11}\) value (-16 dB), especially around 5.2 GHz. Figure 4b depicts the realized gain of the antenna that takes into account the losses due to the matching: as we can infer from the plot, as the SsDRA thickness is increased, gain values are equal to 3.3 dBi at 2.8 GHz (red curve), and increase up to 5 dBi at 5.5 GHz (purple curve). Generally, the gain values improve by about 0.2 dB up to about 2 dB with respect to the reference monopole in the overall frequency range of interest. Furthermore, the inspection of Figure 4b shows that SsDRA allows the additional coverage of the WiFi band, at 2.45 GHz. Figure 3: (**a**) Scattering parameter S\({}_{11}\) as a function of the pin height h\({}_{\text{PIN}}\), by considering the DRA thickness t = 2 mm and h\({}_{\text{DRA}}\) = 29 mm; (**b**) Scattering parameter S\({}_{11}\) as a function of the DRA thickness, considering the pin height h\({}_{\text{PIN}}\) = 17 mm and DRA height h\({}_{\text{DRA}}\) = 29 mm. Figure 5 reports the evaluation of the scattering parameter S\({}_{11}\) and gain as the SsDRA height h\({}_{\text{DRA}}\) is varied between 10 mm and 30 mm, while h\({}_{\text{PIN}}\) and t are fixed to 17 mm and 2 mm, respectively. As evident from Figure 5a, when the SsDRA height is increased from 10 mm and 20 mm, the bandwidth at -10 dB increases as well, covering a range from about 1.3 GHz to 1.8 GHz (red and yellow curves).