# A Circularly Polarized mmWave Dielectric-Resonator-Antenna Array for Off-Body Communications
## 2 Design Methodology
### Array Next to a Human Body  
To learn more about the effects of the human body on the array performance, the same procedure used for a single DRA element was followed, i.e., the DRA array was placed at distances of 1 cm and 5 cm away from the three-layer human-body model, as illustrated in Figure 10.  
Figure 11 presents the reflection coefficient when the array is placed in free space and at distances of 1 mm and 5 mm from the phantom. These results confirm that the attained impedance bandwidth is approximately 28% at the two considered distances, which is comparable to that of a DRA array operating in free space. Owing to the presence of a ground plane between the antenna and the simulated tissue layers, the effect of the human tissue on the impedance bandwidth was minimized.  
Figure 6: Configuration of the proposed DRA-array antenna (**a**) top view, (**b**) three-dimensional view and (**c**) feed network.  
Figure 8: Axial ratio of the DRA array using various separation distances (d\({}_{\rm s}\)) between the DRAs.  
Figure 7: 1S\({}_{11}\)  of the DRA arrays for various separation distances (d\({}_{\rm s}\)).  
Figure 9: Gain of the DRA array using various separation distances (d\({}_{\rm s}\)) between the DRAs.  
Similarly, the far-field characteristics are not affected by the presence of the human-tissue phantom layers, as demonstrated in Figures 12 and 13, where it is evident that the achieved axial ratio bandwidth of 13% and gain of 14 dBic when the array is located at free space, are comparable to those when the array operates close to the human-tissue model. As mentioned above, the chosen DRA element supports the following TE resonance modes across the considered frequency range of 24-31 GHz: TE\({}_{111}\), TE\({}_{113}\) and TE\({}_{133}\). The excitation of the higher-order modes provided a maximum gain of \(\sim\)14 dBic at 28 GHz, which is considerably higher than those reported in the literature for four-element DRA arrays. This was to be expected, since the gain of the designed single dielectric-resonator antenna is \(\sim\)9 dBic, compared to a typical gain of \(\sim\)6 dBi for a DRA that operates in a lower-order mode. In addition, all the excited modes support broadside radiation, which provided the required stability of the radiation patterns over the considered frequency range. Furthermore, merging the bandwidths of the excited adjacent resonance modes provided considerably wider impedance and CP bandwidths. In addition, the surface-current distribution at the resonant frequency of 28 GHz is depicted in Figure 14, where a clockwise rotation of the current vectors can be observed, which produces the left-hand circularly polarized radiation. It should be noted that the same current distribution was observed for the single circularly polarized DRA, which demonstrates the unnoticeable impact of the mutual coupling between the array elements on the current distribution.  
Figure 11: Reflection coefficient of a DRA array in free space and placed next to a phantom.  
Figure 10: Cross-section view of a DRA array next to the body phantom.