# Feasibility Investigation of SIW Cavity-Backed Patch Antenna Array for Ku Band Applications
## 4 Antenna Fabrication and Characterization
In fact, for the 4 \(\times\) 4 array, a half power beam width (HPBW) of 19.6\({}^{\circ}\) at the frequency f = 11.7 GHz was measured. The simulated (solid curve) and measured (dashed curve) gain for the 4 \(\times\) 4 array versus the frequency is illustrated in Figure 15. The highest measured gain was G = 18.7 dBi at a 12.5 GHz. The 8 \(\times\) 8 antenna array was constructed as seen in the prototype shown in Figure 6:0 Figure 17a shows the simulated (solid curve) and measured (dashed curve) modulus of the S\({}_{11}\) scattering parameter versus the frequency for the 8 \(\times\) 8 antenna array. A \(-\)10 dB bandwidth was about 3. A little ripple of the measured modulus of the S\({}_{11}\) scattering parameter occurred close to the frequency f = 10.55 GHz and is most likely due to the thin air gap between the two layers fixed with external screws. A similar ripple can be obtained via simulation by considering an air gap g = 0.068 mm. This problem can be avoided by integrating the two layers via a prepreg/press procedure. In Figure 17b, a difference of about 1.7 dBi between the simulated and measured gain occurred. The difference  
Figure 6:1 Radiation pattern of the 4 \(\times\) 4 antenna array gain at f = 11.7 GHz in the y–z plane (**a**) and x–z plane (**b**). Figure 6:2 Simulated and measured gain G of the 4 \(\times\) 4 antenna versus the frequency. between the simulated and measured gain was due to the manufacturing tolerance. For the 8 \(\times\) 8 antenna array, the measured maximum gain was G = 23.8 dBi at a 12.5 GHz. The gain G is practically coincident with the results reported in [26] while the bandwidth 9.5-12.7 GHz almost doubled with respect to the antenna reported in [26]. The radiation gain of the array 8 \(\times\) 8 in the y-z and x-z planes is shown in Figure 18a,b, respectively. The half power beam width in the azimuth y-z plane measured at a frequency of 11.7 GHz was HPBW = 9.5\({}^{\circ}\). The maximum gain of the main lobe at the frequency f = 11.7 GHz was G = 22.6 dBi, the first side lobe level was \(-\)12.9 dBi. Figure 6:3 Prototype of the 8 \(\times\) 8, dual layer, SIW cavity backed antenna array: (**a**) top view; (**b**) bottom view. Figure 6:4 Simulated (solid curve) and measured (dashed curve) \(\mid\)S\({}_{11}\)\(\mid\) scattering parameters (**a**) and gain G (**b**) versus the frequency for the 8 \(\times\) 8 antenna array. In actual satellite application, a gain of about G = 30 dBi and a band of at least 2 GHz is required. A wider bandwidth is welcome to increase the communication capacity. To definitively prove the practical interest toward this kind of antenna [18; 26; 28; 29] the investigation was further extended and an array with 256 elements (16 \(\times\) 16 array) was built (see the prototype of Figure 19). Figure 20 shows good agreement between the simulated and measured S\({}_{11}\) in a very wide range of frequencies (at \(-\)10 dB, the range was about 9.8-12.6 GHz). A flat behavior of the measured and simulated gain, with a difference of about 2.4 dBi between the two curves, is apparent in Figure 20b. The maximum gain value measured was obtained at a frequency of 12.6 GHz and it was close to G = 29.2 dBi. The simulated 3D radiated gain at a frequency of f = 11.8 GHz obtained with CST Microwave Studio(r) is shown in Figure 21, the maximum simulated gain was G = 30.59 dBi. The radiated gain measurement was made with a StarLab Antenna Measurement Systems-Satimo(r) anechoic chamber as shown in Figure 6:5 Figure 23a,b show the agreement between the simulated and measured gain G in azimuth y-z plane, and in elevation x-z, respectively, at a frequency of f = 11.8 GHz. A half power beam width (HPBW) of 4.8\({}^{\circ}\) was measured at a frequency of 11.8 GHz in the azimuth y-z plane. The measured gain at a frequency of f = 11.8 GHz was 26.8 dBi. Figure 24 shows the cross polarization of the 16 \(\times\) 16 array. The measured cross-polarization at a frequency of f = 11.8 GHz was \(-\)10 dB.