# Analysis of 3D Printed Dielectric Resonator Antenna Arrays for Millimeter-Wave 5G Applications
## 3 Millimeter-Wave DRA Array for 5G Systems  
In DRA arrays operating at mmWave frequencies, every single DRA element needs to be fabricated with sufficient accuracy for the array to perform well. To assess the quality and reliability of the FDM technology in producing the DRAs at such frequencies, a 2 \(\times\) 2 DRA array working at the mmWave band for beam scanning applications was designed, simulated, manufactured, and measured. The configuration is shown in Figure 7. The substrate applied in simulation and fabrication is Rogers RO4003 (\(\epsilon_{r}\) = 3.55, \(\tan\delta\) = 0.0027) with a height of 0.2 mm. The DRA elements have a cylindrical shape with a dimension of \(O3.2\) mm (\(r_{d}\)) \(\times\) 1.9 mm (\(h_{d}\)). These dimensional parameters are frequency-dependent and determine the resonant frequency of the DRA. As indicated by Equation (1), higher frequency bands result in smaller DRA dimensions. The parameters provided here have been optimized for both matching and radiation performance. The distance (\(d\)) between two adjacent DRA elements is 6 mm. Each DRA element is slot-fed by a microstrip line, allowing for variable excitation during the initial simulation process. The beam scanning performance of the DRA array can be preliminarily verified by varying the excitation amplitude and phase through the four lumped ports connected to the microstrip lines, as shown in Figure 7. The slot measures 1.8 mm in length (\(l_{1}\)) and 0.2 mm in width (\(w_{1}\)), providing an efficient coupling mechanism between the microstrip feed and the DRA element. The width (\(w_{2}\)) of the microstrip line is designed to be 0.45 mm, ensuring a 50-ohm impedance for optimal matching performance with the rest of the system, including the SMA connectors. A matching stub with a length (\(l_{2}\)) of 1.5 mm was introduced to improve impedance matching and enhance coupling. This configuration minimizes reflection and maximizes power transfer to the DRA, thereby enhancing overall efficiency.  
Figure 5: Fabricated DRA. (**a**) top view, (**b**) bottom view.  
Figure 6: Simulated and measured \(S_{11}\) of the microwave DRA design. Adjusted dimensional parameters and permittivity were also taken into account based on the measured values.  
Total efficiency, rather than single-ended S-parameters, was considered to evaluate the matching performance of the DRA array due to the insufficient representation of individual S-parameters in multi-port antenna arrays. Further details on the S-parameters are provided in the full array design in Section 3.3. As shown in Figure 8, the total efficiency could achieve over 90% in the frequency range of 23.15-26.43 GHz, and the maximum efficiency of 99% and realized gain of 11.8 dBi at broadside direction could be observed at 24.8 and 25.8 GHz, respectively. In addition, the beam scanning performance of the DRA array in two orthogonal planes is given in Figure 9. A \(-\)3 dB beam scanning angle of \(\pm\)42\({}^{\circ}/\pm\)46\({}^{\circ}\) at the xz-/yz-plane could be observed when varying the excitation phases of the DRA elements. The simulated matching and radiation performance prove a promising beam scanning capacity of the designed DRA array in the 5G mmWave band.  
Figure 8: Simulated efficiency and realized gain for mmWave DRA array.  
Figure 7: Configuration of the mmWave DRA array.