# Enhanced Efficiency and Reduced Side Lobe Level Convex Conformal Reflectarray
## 4 Feed Manufacturing and Testing  
For fast prototyping of the horn, its realization through 3D printing was considered. In particular, the selective laser melting (SLM) process was exploited, using an EOSINT M270 Dual Mode machine that has a building volume of 250 mm \(\times\) 250 mm \(\times\) 215 mm. In comparison with corrugated feed horns, the smooth-wall architecture is particularly suitable for SLM manufacturing. Indeed, this feed horn architecture does not present overhanging surfaces when the building direction is oriented along the propagation axis. Moreover, supporting structures are reduced or not necessary also for the external surfaces. For the measurement of the antenna system, an adapter from rectangular (WR28) to circular waveguide was integrated in the horn. The overall feed dimensions are 52 mm \(\times\) 52 mm \(\times\) 53.7 mm.  
Although results are already available in the literature (see, for example, [31]), the manufacturing of SLM components in the Ka band is still challenging in terms of accuracy. A fine tuning of the process parameters was carried out: the effect of the part shrinkage related to the high temperature gradients in the melting process was taken into account by introducing scaling factors in the transversal directions. Moreover, laser beam offsets were applied to consider the melted powder outside the nominal antenna shape. The SLM antenna prototype in AlSi10 Mg alloy is shown on the right of Figure 4.  
The horn was first simulated with CST Microwave Studio, and then measured in an anechoic chamber; the gain at the central frequency is 17 dB. The plots in Figure 5 show the  
Figure 4: CAD model of the designed horn (**left**) and SLM prototype (**right**).  
Figure 3: Linear profile for the smooth horn design with the definition of the nodes, initial stepwise approximation and final optimized horn profile. Even if the three curves have the same starting and ending points, they are not plotted one over the other for clearness.  
comparison between measured and simulated radiation patterns in the \(\varphi\)-cuts \(0^{\circ}\) and \(90^{\circ}\) for the central, lower and upper frequencies of the band. The good agreement confirms the manufacturing quality of the horn. It is also worth noting that its performance is very stable with the frequency.  
In Figure 6, the simulated frequency behavior of the horn \(|S_{11}|\) and of its simulated and measured cross-polarization level are plotted. In the range of frequencies of interest, the amplitude of \(S_{11}\) is always below \(-34\) dB, confirming the excellent matching, while the cross-pol is lower than \(-37\) dB, confirming the effectiveness of the adopted design procedure. The values of the cross-pol obtained through the experimental characterization of the manufactured feed, in correspondence with seven frequency points in the interval [28.5, 31.5] GHz, are in good agreement with the simulations.  
Figure 5: Measured and simulated radiation patterns of the optimized horn in the E (**top**) and H (**bottom**) planes at three different frequencies in the considered band.