# Feasibility Investigation of SIW Cavity-Backed Patch Antenna Array for Ku Band Applications
## 4 Antenna Fabrication and Characterization  
The single antenna prototype, manufactured by SOMACIS Spa, using a Rogers Duroid 5880 substrate with a dielectric constant \(\varepsilon_{\mathrm{rs}}\) = 2.2 and loss tangent \(\delta\) = 0.0009, is shown in Figure 7. The top view (Figure 7a) and the bottom view (Figure 7b) are depicted. To keep the electrical continuity between the top layer and the bottom layer, four external screws were used. Figure 8a illustrates the simulated (solid curve) and measured (dashed curve) modulus of the S\({}_{11}\) scattering parameter of the single SIW cavity backed antenna. The measured and simulated curves were in good agreement in the overall Ku bandwidth (10.7-12.7 GHz). The measured \(-\)10 dB bandwidth was about 2 GHz, as expected. Figure 8b illustrates the simulated (solid curve) and measured (dashed curve) gain G of the SIW cavity backed antenna versus the frequency. The gain of the antenna was higher than 6.8 dB in the frequency band 10.7-12.7 GHz. The maximum gain G = 8.6 dB occurred at the frequency f = 11.7 GHz. Figure 6: Layout of the base cell: patch antenna array of 2 \(\times\) 2 elements. Figure 7: Prototype of the dual layer, SIW cavity backed antenna: (**a**) top view; (**b**) bottom view. Figure 9 shows the prototype of the 2 \(\times\) 2 antenna array (base cell). Figure 10a illustrates the simulated (solid curve) and measured (dashed curve) modulus of the S\({}_{11}\) scattering parameter. Figure 10b shows the gain versus the frequency. The measured maximum gain is G = 13 dBi close to the frequency f = 12 GHz. The slight difference, less than 1.2 dBi, between the simulated and measured gain curves in the Ku band was due to both the power leakage of the feeding network and the substrate losses, which could be slightly different with respect to the values used in the simulation. As for the previous case, the good agreement between the simulated and the measured curve was apparent overall in the Ku bandwidth. The \(-\)10 dB bandwidth was about 2.5 GHz. For the prototype of the 2 \(\times\) 2 antenna array, Figure 11a,b show the simulated (solid curves) and measured (dashed curves) gain G, at the frequency f = 11.7 GHz, in azimuth y-z plane and in elevation x-z plane, respectively. The half power beam width HPBW = 37.8\({}^{\circ}\) was measured at the frequency  
Figure 8: Measured (dashed curve) and simulated (solid curve) \(|\)S\({}_{11}\)\(|\) scattering parameter (**a**) and gain G (**b**) for the SIW cavity backed antenna. Figure 10: Simulated (solid curve) and measured (dashed curve) \(|\)S\({}_{11}\)\(|\) scattering parameters (**a**) and gain G (**b**) versus the frequency of the 2 \(\times\) 2 antenna array. Figure 9: Prototype of the 2 \(\times\) 2 antenna array, dual layer SIW cavity backed, antenna: (**a**) top view; (**b**) bottom view. f = 11.7 GHz in the azimuth y-z plane. The radiation pattern and gain measurements were performed with StarLab Antenna Measurement Systems-SatimO. The 4 \(\times\) 4 array was constructed, see the prototype in Figure 12, by repeating the 2 \(\times\) 2 base cell in both the x and y directions; then characterized, see Figure 13, which illustrates the anechoic chamber. Figure 11: Radiation pattern of the 2 \(\times\) 2 antenna array at f = 11.7 GHz in the y–z plane (**a**) and the x–z plane (**b**). Figure 12: Prototype of the 4 \(\times\) 4, dual layer, SIW cavity backed antenna array: (**a**) top view; (**b**) bottom view. Figure 13: Radiated gain measurement of the 4 \(\times\) 4 array antenna made with StarLab Antenna Measurement Systems-SatimO. The measured (dashed curves) and simulated (solid curves) gain G pattern in the azimuth y-z plane and in the elevation x-z plane are reported in Figure 14a,b, respectively. In both cases, the figures show good agreement between the simulation and measurement. As expected, by increasing the number of the array elements, a narrower shape (pencil like) of the radiating main lobe occurred.