# A 3-D Metal-Printed Dual-Polarized Ridged Waveguide Slot Array Antenna for X-Band Applications
## 4 Experimental Results and Discussion  
To verify the performance of the proposed dual-polarized array, a ridged waveguide array with 2 \(\times\) 8 radiation slot elements in the X-band was optimized and fabricated for experimental measurements. The prototype was manufactured using three-dimensional (3-D) metal-printing technology with the material used to print the antenna being aluminum (with electric conductivity of 3.6 \(\times\) 10\({}^{7}\) S/m). The 3-D printer software cuts the CAD drawing of the antenna structure into horizontal slices and translates each slice into a 2-D path for the nozzle head to follow. One  
Figure 8: Design of the feeding structure for the VP linear array. (**a**) T-junction power divider. (**b**) S-parameters of the power divider. (**c**) Coaxial-to-RWG transition. (**d**) S-parameters of the transition. (Design parameters: \(w1\) = 2.35, \(w2\) = 3.6, \(w3\) = 1, \(w4\) = 7.8, \(l1\) = 6.55, \(l2\) = 4.4, \(h1\) = 1.15, \(h2\) = 1, and \(p1\) = 2.9 (units: mm)). Figure 9: Design of the feeding structure for HP linear array. (**a**) Coaxial-to-RWG transition. (**b**) S-parameters of the transition. (Design parameters: \(w5\) = 2.75, \(p2\) = 3.425, and \(h3\) = 1 (units: mm)). of the advantages of 3-D metal printing in one block is that it minimizes the source of misalignment between parts, thus, achieving robustness and stability in the mechanical structure. A photograph of the fabricated dual-polarized antenna array is shown in Figure 10a with overall dimensions of 179.6 \(\times\) 23.2 \(\times\) 29.82 mm, which corresponds to 5.87\(\lambda_{0}\)\(\times\) 0.76\(\lambda_{0}\)\(\times\) 0.97\(\lambda_{0}\). To feed the fabricated antenna, two commercial SMA connectors (model number: PAF-S06-000) were used for each linear array. Figure 10b shows the experimental setup for the measurement process of the scattering parameters using the two-port vector network analyzer (VNA, Model: Anritsu MS46122B, frequency ranges from 1 MHz to 20 GHz). With Port 1 connected to the VP array and Port 2 connected to the HP array, the scattering parameters for reflection (\(S_{11}\) or \(S_{22}\)) and transmission (\(S_{12}\) or \(S_{21}\)) were recorded. Additionally, the gains and radiation patterns were examined inside an RF anechoic chamber with a far-field antenna measurement setup as shown in Figure 10c. The chamber had dimensions of 16 \(\times\) 11 \(\times\) 9.5 m and a measurable frequency bandwidth of 400-24.5 GHz, with a standard gain horn source and the antenna under test (AUT) installed 12 m apart. Figure 10: (**a**) Photograph of the fabricated dual-polarized antenna array. (**b**) Two-port vector network analyzer to measure the S-parameters. (**c**) Far-field measurement setup in an anechoic chamber. Figure 11 illustrates the measured and simulated results of the reflection coefficients versus frequency. The measured \(-\)10 dB impedance bandwidths were 9.24-10.44 GHz (12.2%) for the VP array and 9.26-10.36 GHz (11.2%) for the HP array, while the simulated results were 9.27-10.44 GHz (11.9%) and 9.26-10.33 GHz (10.9%) for the VP and HP arrays, respectively. The isolation in both the measured and simulated results between the input ports of the two polarization arrays is better than 40 dB in the operating bandwidth. The measured and simulated realized gains in the broadside direction versus the frequency are illustrated in Figure 12. Within the impedance bandwidth, the measured realized gain of VP was from 12.5 to 14.6 dBi and, of HP, was from 13.5 to 15.5 dBi, which is lower than the simulated gain from 0.5 to 1 dBi. There is a slight deviation between the simulation and measurement results, which is mainly due to manufacturing errors. As in the 3-D printing fabrication process, additional losses due to surface roughness and geometrical tolerances in T-junction and radiation slots cannot be avoided. Figure 11: The S-parameters and isolation of the dual-polarized antenna array. Figure 12: The measured realized gain of the dual-polarized antenna array.