# Analysis of 3D Printed Dielectric Resonator Antenna Arrays for Millimeter-Wave 5G Applications
## 3 Millimeter-Wave DRA Array for 5G Systems
### Fabrication and Measurements  
For the purpose of verification, a 2 \(\times\) 2 DRA array with an in-phase feeding network was manufactured, fabricated, and measured. The spacing between each two adjacent  
Figure 11: Efficiency with different (**a**) radius, (**b**) height, (**c**) \(\varepsilon_{r}\), (**d**) tan \(\delta\) of DRA element. DRA elements was optimized for a compromising efficiency and realized gain performance. The simulation model and fabricated photographs are shown in Figures 12 and 13, respectively. Considering the space for mounting the SMA connector, the overall dimension of the array was slightly enlarged and set to 26 mm \(\times\) 26 mm \(\times\) 2.1 mm, equivalent to 2.2 \(\lambda_{0}\times\) 2.2 \(\lambda_{0}\times\) 2.2 \(\lambda_{0}\times\) 0.17 \(\lambda_{0}\). However, it could be observed from the photos in Figure 13 that the overall dimension of the DRA array could be further reduced to make the array more compact. An equivalent model of the SMA connector was also considered in the simulation. The results indicate that the SMA connector has a limited effect on the array's performance. The DRA elements were manufactured using the Raise E2 3D printer and PREPERM(r) ABS1000 filament. A positioning resin mold, matching the exact dimensions of the substrate and featuring positioning holes for the DRA elements, was also fabricated to assist in the assembly of the DRA array. A 3D surface profile was also conducted for the mmWave DRA using the KEYENCE portable microscope (KEYENCE (UK) Ltd., Milton Keynes, UK). Some 3D surface profiles, zoom-in view profiles, and 2D profile cuts of the manufactured DRAs are shown in Figures 14-16. The shape generally agrees with the simulation model and relatively smooth surfaces were observed in the photos in Figure 15. Upon inspection of the profile, the diameter appears to be 0.2 mm to 0.3 mm, or about 8% larger than the simulated model when viewed from the top. This discrepancy may contribute to the observed frequency shift. Side bumps and dents resulting from printing layers were not measurable, as they were not observable in the downward-facing microscope view. Furthermore, several imperfections, one of which measures 152 \(\upmu\)m, were observed, likely resulting from termination points in the printing process. A 3D side view and 2D cut surface profile of one of the mmWave DRA samples are shown in Figure 16. Protuberances with a maximum height (\(R_{\text{z}}\)) of 129.45 \(\upmu\)m and an arithmetic average roughness (\(R_{\text{d}}\)) of 20.81 \(\upmu\)m can be observed in the 3D side view and 2D cut surface profile shown in Figure 16. A total of nine layers, each 0.2 mm thick,  
Figure 12: Configuration of the DRA array with an in-phase feeding network. Figure 13: Photographs of the FDM 3D-printed DRA array with an in-phase feeding network. (**a**) top view, (**b**) bottom view. were necessary for constructing the microwave DRA model. However, the 3D design's required height of 1.9 mm is not a multiple of the typical FDM layer thickness (0.2 mm). This discrepancy arose from the measured height falling 0.1 mm short of the 3D simulated model. The imperfections created by the nine layers, along with other irregularities, became more conspicuous relative to the antenna's size at this frequency, compared to the microwave band. Taking this issue into account, a simulation was conducted with modified heights of the DRA elements. The \(S\)-parameters, far-field radiation patterns, and realized gain at the broadside direction of the FDM 3D-printed DRA array were then measured, and the results are given in Figures 17-19. As shown in Figure 17, the measured \(S\)-parameters indicate that the FDM 3D-printed DRA array could resonate within and cover the 5G mmWave frequency band. The simulated and measured Q factors are 21.43 and 57.27, respectively. Additionally, the modified simulation model with reduced height suggests that the possible cause of the frequency band shift is the change in element dimensions.