# Bio-Inspired Dielectric Resonator Antenna for Wideband Sub-6 GHz Range
## 3 Spiral Shell DRA Analysis and Optimization
### Radiation Pattern, Realized Gain and Radiation Efficiency of the Optimized SsDRA  
The previous analyses allowed to define the geometrical parameters of the bio-inspired SsDRA which exhibits wider bandwidth and a satisfactory gain value at two frequencies, 3.5 GHz and 5.5 GHz: t = 2 mm, h\({}_{\text{DRA}}\) = 29 mm, h\({}_{\text{PIN}}\) = 17 mm and c\({}_{\text{theta}}\) = 0.2.  
Figure 7 shows the 3D radiation patterns of the optimized antenna, along with the polar cuts in the E and H planes, at 3.5 GHz and 5.5 GHz. In particular, when the frequency is equal to 3.5 GHz (Figure 7a-c), the maximum value of the gain is equal to 3.78 dBi. The main lobe magnitude in the E-plane (\(\varphi\) = 0 deg, Figure 7b) is equal to 0.727 dBi, the main lobe direction is equal to 53 deg and the angular width (3 dB) is equal to 82.7 deg. Conversely, when the H-plane is considered (\(\varphi\) = 90 deg, Figure 7c), the main lobe magnitude is equal to 1.05 dBi, while the main lobe direction is equal to 53 deg, with an angular width (3 dB) of 76.3 deg. Figure 7d-f plot the 3D radiation patterns and far-field radiation patterns of the optimized antenna at 5.5 GHz. In particular, in Figure 7e referring to E-plane, the maximum gain value is equal to 5.08 dBi, the main lobe magnitude at \(\varphi\) = 0 deg is equal to 3.91 dBi and the main lobe direction is equal to 61.0 deg with an angular width (3 dB) of 52.5 deg. In the H-plane (Figure 7f), for \(\varphi\) = 90 deg, the main lobe magnitude is equal to 4.22 dBi, the main lobe direction is equal to 61.0 deg and the angular width (3 dB) is equal to 50.4 deg.  
The electric field and the magnetic field intensities of the optimized SsDRA at 3.5 GHz and 5.5 GHz are displayed in Figure 8. The higher intensity is recorded at the coaxial cable pin, but larger part of it is distributed throughout the whole available SsDRA volume. As noticeable, at 3.5 GHz, both the electric field (Figure 8a) and the magnetic field (Figure 8b) intensities are symmetric with respect to the pin while, at 5.5 GHz, the electric field (Figure 8c) and the magnetic field (Figure 8d) intensities follow the dielectric resonator shape. In particular, in this last case, both intensities are located between the second and third loops of the shell. The analysis of the axial ratio reveals that the antenna shows a linear polarization as for the monopole over the frequency range of interest.  
Figure 6: (**a**) Scattering Parameter S\({}_{11}\) and (**b**) gain of the optimized SsDRA as the coefficient c\({}_{\text{theta}}\) is varied: 0.16, 0.18 and 0.20.  
The radiation efficiency calculated for the optimized SsDRA is reported in Figure 9: the antenna exhibits an efficiency of about 45% around 3.5 GHz, while it increases up to about 85% at 5.5 GHz.  
Figure 8: (**a**) Electric field and (**b**) magnetic field intensities at 3.5 GHz; (**c**) electric field and (**d**) magnetic field intensities at 5.5 GHz for the optimized SsDRA. The yellow lines define the SsDRA contour.  
Figure 7: (**a**) 3D radiation pattern of the optimized SsDRA at 3.5 GHz; (**b**) E-plane of the optimized SsDRA at 3.5 GHz; (**d**) 3D radiation pattern of the optimized SsDRA at 5.5 GHz; (**e**) E-plane of the optimized SsDRA at 5.5 GHz; (**f**) H-plane of the optimized SsDRA at 5.5 GHz.