# Waveguide Manufacturing Technologies for Next-Generation Millimeter-Wave Antennas
## 3 Direct Metal Laser Sintering (DMLS)
DMLS avoided these two issues as no metallization was required and the threaded holes for the TSs could be machined by conventional means after printing the device. Figure 5: Schematic used generally to represent the direct metal laser sintering (DMLS) technique. Before inserting the WRPS module in the waveguide array, the performance of its phase shifters was studied individually, measuring experimentally their scattering parameters. Figure 7 represents the phase shift between the input and output ports of one of these phase shifters for different values of the parameter \(\kappa\), which represents how much the TSs penetrate into the waveguide normalized to the waveguide height. It can be seen that screw penetration produces a change of the phase shift. Moreover, the phase response presents good linearity for the whole operation band (from 16 to 18 GHz). At the central frequency, the achieved phase shifting range is 270\({}^{\circ}\) which, as will be shown, is enough to scan the main lobe in the range \(-25^{\circ}\leq\theta_{0}\leq 25^{\circ}\). Figure 8 presents the return loss at the input of one of the WRPS, which is better than 20 dB across the whole operation band for the different TS configurations. This level matches the predictions of the simulation, as shown by Figure 8.  
Figure 6: Photographs of the reconfigurable phase-shifters block built using DMLS: (**a**) frontal view; (**b**) cut view that allows observing the internal parts of the device. Figure 7: Measured phase shift produced by one of the WRPS for different values of TS (tuning screw) penetration. To demonstrate that the phase shifter provides scanning capabilities to the array, an experimental characterization of the radiation pattern was performed, scanning the main lobe in the range of \(-25^{\circ}\leq\theta_{0}\leq 25^{\circ}\) with a step of \(5^{\circ}\). To obtain the scanning for each of these directions, it was necessary that each shifter of the WRPS module introduced the phase shift presented in the right columns of Table 2. This table also presents the measured phase at each of the phase shifter outputs and, as can be appreciated, the obtained values are very close to the desired ones, which serves as an initial validation of the phase shifting characteristics of the proposed device. Moreover, Figure 9 presents the measured radiation patterns of each scanning direction in comparison with the simulated values. The match between both sets of data is very high, which again serves as a validation of the presented WRPS. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline  & \multicolumn{4}{c}{**Measurements**} & \multicolumn{2}{c}{**Desired**} \\ \hline \(\theta_{0}\) & \(\beta\) & \(\beta_{2}-\beta_{1}\) & \(\beta_{3}-\beta_{1}\) & \(\beta_{4}-\beta_{1}\) & \(\beta_{2}-\beta_{1}\) & \(\beta_{3}-\beta_{1}\) & \(\beta_{4}-\beta_{1}\) \\
0 & 0 & 358.3 & 358.8 & 0.0 & 0 & 0 & 0 \\
5 & 25.1 & 26.0 & 48.0 & 74.3 & 25.1 & 50.2 & 75.3 \\
10 & 50.0 & 49.1 & 105.0 & 160.6 & 50.0 & 100.0 & 150.0 \\
15 & 74.5 & 77.9 & 153.3 & 224.0 & 74.5 & 149.0 & 223.6 \\
20 & 98.5 & 92.7 & 200.4 & 297.1 & 98.5 & 197.0 & 295.5 \\
25 & 121.7 & 115.9 & 246.1 & 5.5 & 121.7 & 243.4 & 5.14 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Measured and desired phase shift (in degrees) produced by each of the phase shifters in the WRPS to scan the main lobe of the array to different directions \(\theta_{0}\) (\(\beta\) is the necessary progressive phase shift for each scanning direction and \(\beta_{i},\ i=1,..,4\) is the phase shift that each phase shifter must introduce). Figure 8: Measured and simulated (Sim) magnitude of the reflection coefficient at the input of one of the WRPS (the phase-shifter marked as I in Figure 6) for different values of TS (tuning screw) penetration. Reconfigurable phased arrays have been traditionally based on the use of tunable electronics to implement reconfiguration capabilities.