# 3D Printed High Gain Complementary Dipole/Slot Antenna Array
## 2 Design and Fabrication of a 16 \(\times\) 16 Complementary Dipole Antenna Array  
Figure 1 shows an expanded perspective view of the proposed 16 \(\times\) 16 complementary dipole antenna array (139.5 mm \(\times\) 139.3 mm \(\times\) 16.2 mm). To reduce the fabrication tolerance, the antenna array should minimize the number of layers to prevent the structure deteriorating. The cutting layer was determined using the weakness current at the surface of the structure using simulation software. It was then determined whether or not the top and bottom of the cutting layer can be easily sprayed. The final array was composed of three layers. The bottom layer is the feeding network, which is constructed using 90\({}^{\circ}\) waveguide H-bends to transfer energy from the bottom WR-28 (7.112 mm \(\times\) 3.556 mm) waveguide input layer. E-type waveguide T-junction splitters are used to divide the incoming signal with equal amplitude and 180\({}^{\circ}\) phase difference. Such a power-dividing operation is conducted in six stages. The impedance matching stubs not only provide the impedance matching capability, but also the polarization rotation effect of the E-field inside the waveguide structures. The final E-field polarizations at all of the output ports of the impedance matching stubs are focused in the same direction. The middle layer has the 64 rectangular cavities (14.85 mm \(\times\) 10.35 mm \(\times\) 2.7 mm) with coupling apertures (6.075 mm \(\times\) 2.25 mm) which force the 64 sets of the 2 \(\times\) 2 subarray to radiate unidirectional broadside patterns. The top layer has the 64 sets of the 2 \(\times\) 2 subarray, containing 256 slots (6.3 mm \(\times\) 0.9 mm \(\times\) 1.8 mm) and 512 metallic cuboids (3.6 mm \(\times\) 2.25 mm \(\times\) 2.7 mm). The four slots and eight cuboids form one 2 \(\times\) 2 subarray. Each metallic cuboid with length = 0.21\(\lambda\) and the two cuboids' separation width = 0.29\(\lambda\) work as an electric dipole, whereas the slot with length = 0.5\(\lambda\) is equivalent to a magnetic dipole. Combining these two radiators together, complementary dipole  
antenna element is obtained. The 16 \(\times\) 16 complementary dipole antenna array was simulated using ANSYS High Frequency Structure Simulator (HFSS) 18.0. To verify the simulation results, a prototype of the 16 \(\times\) 16 complementary dipole antenna array was fabricated by 3D printing each layer using a Stratasys Objet30 Scholar system with VeroBlue RGD240 printing material. Its permittivity, \(\varepsilon_{r}\) and loss tangent, tan8 were 2.9 and 0.01, respectively. The first layer had 256 slots, 512 metallic cuboids, and the upper half of 64 rectangular cavities. The second layer had the lower half of 64 rectangular cavities, 64 coupling apertures, and the upper half of the feeding network. Finally, the third layer had the lower half of the feeding network and the waveguide input port. After first spraying the 3D printed components with copper conductive paint, then electroplating with copper using a current of 1.8 A for an hour, the metallized structure was assembled by combining the three layers as shown in Figure 2. For seamless assembly of the array, cylindrical pegs (Figure 2d,f) and holes (Figure 2c,e) were printed at the top surface of Layers two and three and the bottom surface of Layers one and two, respectively. Four rectangular holes (6.54 mm \(\times\) 5.6 mm \(\times\) 2.5 mm) were used for the assembly of the four metallic nuts inside the waveguide flange as shown in Figure 2g. For comparison, an aluminum version of the 16 \(\times\) 16 complementary dipole antenna array was also fabricated and is displayed in Figure 3. This was also fabricated by milling three aluminum layers followed by electroplating with copper. The three layers were soldered together to form the array. The 3D printed, and aluminum antenna arrays, weighed 0.35 kg and 1.36 kg, respectively. The antenna performance of the two arrays is demonstrated in the following section.