# Analysis of 3D Printed Dielectric Resonator Antenna Arrays for Millimeter-Wave 5G Applications
## 3 Millimeter-Wave DRA Array for 5G Systems
### Other Possible Solutions and Future Work  
The cylindrical shape is very common in DRAs. However, other shapes can also be employed. In this section, we describe potential fabrication challenges associated with shapes that have sharper edges and corners, such as cuboids. The cuboid structure is presented as an array in RF simulations, and only the fabricated elements are discussed for potential issues in such designs.  
To provide more insight into FDM 3D-printed DRAs at 5G mmWave frequencies, a \(2\times 2\) cuboid DRA array featuring beam scanning performance was also simulated, as shown in Figure 20. The substrate used is also Rogers RO4003 (\(e_{r}=3.55\), tan \(\delta=0.0027\)) with a height of 0.2 mm. The DRA elements have a cuboid shape with dimensions of 2.5 mm \(\times\) 2.5 mm \(\times\) 2.0 mm. The total efficiency and gain at the broadside direction are shown in Figure 20b. A 90% efficiency frequency range of 25.38-29.66 GHz and a maximum realized gain of 11.5 dBi were observed. The beam scanning performance of the cuboid DRA array is shown in Figure 21. A \(-\)3 dB beam scanning angle of \(\pm 57^{\circ}/\pm 46^{\circ}\) in the xz-/yz-planes can be observed when varying the excitation phases of the DRA elements. The simulated matching and radiation performance also prove the promising beam scanning capacity of the designed cuboid DRA array in the 5G mmWave band.  
Figure 19: Simulated and measured realized gain at the broadside direction of the FDM 3D-printed DRA array.  
Figure 20: (**a**) Configuration of the DRA array, and (**b**) simulated efficiency and realized gain.  
Some cuboid DRA elements were fabricated using an FDM 3D printer. Initially, the accuracy of the cuboid elements was not satisfactory due to the use of a 0.2 mm sacrificial PLA support between the antenna and the printing plate. Such sacrificial layers are typically used to facilitate printing and make part removal easier. This can be particularly useful for small parts, like mmWave DRA elements, when printing with special materials, as it helps prevent breakage during removal. The sacrificial layer is generally printed with low infill, around 20%, to ensure it can be easily removed. However, the use of this layer resulted in a slightly uneven surface at the base of the cuboid, which caused further deformations throughout the structure. This issue was resolved by printing the cuboid directly on the plate without support and adjusting the print settings accordingly. After this process, the resolution and dimensional accuracy of the DRA elements improved significantly, as shown in Figures 22 and 23. In the initial prints, visible gaps and hollows were observed on the top and side surfaces of the cuboid DRA, leading to considerable errors in the final structure. After refining the printing process, these air gaps were eliminated, and the layer stacks became smoother and more uniform. Additionally, the 10 layers of filament in the print accurately indicated the target height of 2.0 mm for the cuboid DRA.  
Despite the improvements, it was clear from the fabricated cuboid samples that achieving sharp edges and corners is challenging with the current FDM technique. The limitations of this method may result in slightly rounded corners or less-defined edges, which would affect the overall performance of the DRA. Further refinements in the fabrication process, such as exploring alternative 3D printing methods or higher-resolution settings, may be required to achieve the precision needed for sharper geometries in future designs.  
Figure 21: Beam scanning performance of the cuboid DRA array in the (**a**) xz-, and (**b**) yz-planes.  
Figure 22: Top view of the FDM 3D-printed cuboid DRA element (**a**) before, and (**b**) after refining.