# Wide-Band Wide-Beam Circularly-Polarized Slot-Coupled Antenna for Wide-Angle Beam Scanning Arrays
## 5 Experimental Assessment  
The experimental validation of the performance of the designed _WWCS_ has been carried out next (Figure 19). In order to exploit available off-the-shelf RO4350B _PCB_ boards, two (layers \(\ell_{2}\) and \(\ell_{3}\)--Figure 1) and three (layer \(\ell_{1}\)--Figure 1) substrates of thickness \(h=1.52\) [mm] have been stacked to realize the different layers of the antenna. The overall structure has been assembled using four nylon _M4_ threaded rods and sixteen nylon bolts, stacking together the _PCB_s and placing the parasitic ring at distance \(D=D^{(opt)}\) from the driven patch (Figure 19). An _RS 759-5252 SMA_ connector has been used to feed the antenna prototype. Figure 20 shows the measured reflection coefficient at the input port of the antenna under test (_AUT_) by employing a properly calibrated scalar network analyzer Rohde & Schwarz ZVH4 (100 [kHz]--3.6 [GHz]). As it can be seen, the fabricated _WWCS_ exhibits a suitable impedance matching in the complete target band,  
Figure 18: _Numerical Assessment_ (\([f_{\min},\,f_{\max}]=[2.3,\,2.6]\) [GHz]—\(N=(50\times 50)\))—\(SL\) performance versus frequency when steering the beam towards \(\theta_{s}\in[0,\,90]\) [deg] and (a) \(\varphi_{s}=0\) [deg] or (b) \(\varphi_{s}=90\) [deg] for different settings of the manufacturing tolerance \(\xi\) on the feeding line (\(W_{f}\)) and the parasitic ring (\(W_{r}\)) widths.  
being \(\left|S_{11}^{(dB)}(f=f_{\min})\right|_{meas}=-10\) [dB] and \(\left|S_{11}^{(dB)}(f=f_{\max})\right|_{meas}=-17.8\) [dB]. Moreover, a slightly larger bandwidth has been observed with respect to the _HFSS_ simulation (i.e., \(\left.FBW\right|_{meas}=16.7\%\)--Figure 20).  
As for the radiation features of the fabricated antenna, the far field patterns have been measured inside an anechoic chamber having dimensions \(9\times 6\times 6\) [m\({}^{3}\)]. The _AUT_ has been placed on a remotely controlled rotating frame and the electric field has been measured by means of a circularly polarized probe connected to a signal analyzer, both placed on a dielectric mast at a distance of 3 [m] from the _AUT_. In order to avoid field perturbations due to cablings, the _AUT_ has been connected with a short coaxial cable  
Figure 19: _Experimental Assessment_—Picture of the fabricated prototype: (**a**) top and (**b**) lateral views.  
Figure 20: _Experimental Assessment_—Comparison between the simulated and measured reflection coefficients at the antenna input port.  
to a small transmitter able to generate a constant amplitude and frequency signal at \(f=f_{0}=2.45\) [GHz]. The transmitter has been placed just behind the layer \(\ell_{1}\) of the _AUT_. Similarly, the presence of a long coaxial cable connected to the field probe has been avoided thanks to the use of the PMM 9060 EMI Receiver/Signal Analyzer (30 [MHz]-6 [GHz]) that can be remotely controlled by means of a fiber optic link. A good matching between the simulated and measured gain pattern has been obtained. As a matter of fact, both pattern cuts along the \(\varphi=0\) [deg] [Figure 20a] and the \(\varphi=90\) [deg] [Figure 21b] elevation planes closely match the outcomes of the numerical assessment. Moreover, it turns out that the measured _HPBW_ verifies the wide-beam behavior of the radiator on both planes, being \(\left.HPBW(f_{0},\,\varphi=0)\right|_{meas}=151\) [deg] [Figure 21a] and \(\left.HPBW(f_{0},\,\varphi=90)\right|_{meas}=172\) [deg] [Figure 21b], respectively. Finally, the measured gain, \(AR\), and \(XPD\) are equal to \(G(f_{0},\,\theta=0,\,\varphi=0)\right|_{meas}=2.8\left[\text{dB}\right]\), \(AR(f_{0},\,\theta=0,\,\varphi=0)\right|_{meas}=3.3\left[\text{dB}\right]\), and \(XPD(f_{0},\,\theta=0,\,\varphi=0)\right|_{meas}=14.8\left[\text{dB}\right]\), respectively, thus verifying a good matching with the simulated values.