## 3 Experimental Verification of the Monolithic Rotman Lens Design  
### Design for Manufacture Considerations  
For the prototype reported here, laser powder bed fusion (LPBF) AM was chosen [40]. LPBF involves the sequential deposition of metal powder layers, AlSi10 Mg aluminum alloy in this case, with each layer having a height range of approximately 20-30 \(\upmu\)m. The choice of material was driven here by the targeted space applications, with antenna systems often exposed to the harsh space environment, thus requiring components providing a good compromise between electrical and mechanical properties [40]. The uniform deposition of the metal powder on the printing bed is accomplished using a recoater. Selective melting of the metal powder is achieved using an energy source, a laser in this case. After melting the metal powder layer, a uniform layer is added again by the recoater, and the melting process is repeated until the final part is generated. While AM technologies provide some flexibility in the RF design by removing mechanical interfaces and simplifying the overall assembly, they do introduce some printing constraints, which require careful consideration [40]. The most important parameter to be defined is the printing direction, expected to provide a stable PPW thickness without requiring excessive supporting structures. It has been decided to print along the central focal axis of the lens (x-axis in Figure 1). This requires redesigning the ports on the top side of the PPW section to avoid overhangs and underhangs. To this end, starting from the feeding port design in Figure 2, an adaptation was made to introduce a roof with an inverted triangular shape, with angles at 45\({}^{\circ}\), compatible with the constraints of AM. The details of this design adaptation are highlighted in Figure 7. For what concerns dummy ports, the redesign effort would be quite significant with questionable impact on performance due to their orientation with respect to the printing direction. For this reason, it was decided to keep the sides of the PPW section open so absorbing material may be inserted in the cavity. For that purpose, ABS-MLSE samples from ABS Technics BV are used. ABS-MLSE is a thin and flexible silicon absorber with magnetic loading, providing a typical attenuation higher than 100 dB/cm in the K-band. The material is cut to produce a cavity shape in line with the full-wave model of Figure 3.  
Figure 7: Close-up view of the top (**left**) and bottom (**right**) feeding waveguides in the monolithic 10 \(\times\) 10 Rotman lens prototype. The Rotman lens prototype also required some adaptation for test purposes. To enable the use of available standard waveguide calibration kits, transitions from a double-ridged waveguide to a rectangular waveguide were added. The prototype was completed with alternating E-plane bends that enable inserting WR42 flanges without significantly increasing the length of the transitions. These require the addition of supporting structures in the final part of the waveguides, which are removed by drilling, as a part of the post-processing stage also required for the flanges. Moreover, the manufactured part was subjected to a sandblasting process, with glass micro-spheres, to uniformly reduce the surface roughness, \(Ra\), to 4-6 um. The manufactured prototype is shown in Figure 8. A prototype of the inner cavity, also shown in Figure 8, has been manufactured and facilitates the visualization of the final RF design, in particular, the alternating E-plane bend arrangement to accommodate the WR42 flanges. The multi jet fusion (MJF) AM technique was chosen in this case. MJF is a type of AM technology that uses a combination of inkjet printing and powder bed fusion. The process involves depositing a thin layer of powder material, usually a type of nylon, on a build platform. Then, using an inkjet array, a liquid agent is selectively applied to the powder layer, fusing the particles together in the desired pattern.