# Wide-Band Wide-Beam Circularly-Polarized Slot-Coupled Antenna for Wide-Angle Beam Scanning Arrays
## 6 Conclusions  
The design of a novel wide-band wide-beam circularly-polarized elementary radiator has been proposed for _WASAs_. Such a _WWCS_ structure leverages on a cross-shaped aperture-coupling feeding mechanism to achieve wide-band _LHCP/RHCP_ operation using a simple circular patch and a single microstrip line. Moreover, it takes advantage of the air coupling between the primary and secondary _EM_ sources to realize rotational-symmetric patterns with large elevation _HPBW_s and high polarization purity in the complete upper semi-sphere. The computationally-efficient synthesis of the layout of the _WWCS_ antenna, which supports the desired _CP_ operation, has been carried out with a customized implementation of the _SbD_ paradigm. Accordingly, the main advancements with respect to the state-of-the-art [20] include (_i_) the exploitation of an aperture feeding mechanism instead of a probe feeding to significantly widen the impedance bandwidth, mitigate spurious radiation, and enable an easier manufacturing, (_ii_) the formulation of the design problem as a global optimization one rather than a parametric _trial-and-error_ approach, enabling to better control the _AR_ and the _XPD_ in the complete radiating semi-sphere, (_iii_) the study over a wide-band of the radiation features of the resulting planar array, as well as (_iv_) the fabrication tolerance analysis on both single element and array performance. The numerical results, concerned with the representative design of a _WWCS_ radiator working at the central frequency of \(f_{0}=2.45\) [GHz], have demonstrated that the proposed radiating structure provides  
Figure 21: _Experimental Assessment_ —Comparison between the simulated and measured patterns at \(f=f_{0}=2.45\) [GHz] along the elevation cuts (**a**) \(\varphi=0\) [deg] and (**b**) \(\varphi=90\) [deg]. 1. wide-band fractional impedance bandwidth (\(FBW\simeq 15\%\)), which is 12.5 times larger than that in state-of-the-art solutions based on similar \(EM\) mechanisms [20];
2. wide-beam radiation pattern with \(HPBW(f_{0})\simeq 180\) [deg] in all elevation planes (versus \(HPBW(f_{0})=131\) [deg] of [20]);
3. high polarization purity with broadside \(AR(f_{0})=3.2\) [dB] and \(XPD(f_{0})=15\) [dB], together with a 3 [dB] \(AR\) bandwidth 12 times larger than [20]. As for the arising _WASA_, the numerical assessment has pointed out the potential of the proposed layout of the elementary radiator for the realization of wide-band circularly-polarized _WASA_s. Finally, the reliability and robustness on the fabrication tolerances of the proposed antenna layout have been verified for both the stand-alone and the array arrangement. Furthermore, the experimental assessment of a \(PCB\)-manufactured prototype has verified the \(FW\)-simulated outcomes, confirming both the wide-band and the wide-beam features of the designed _WWCS_ radiator (Figures 20 and 21). It should be pointed out that the proposed design concept and methodology are general since they can be applied to synthesize wide-band wide-beam \(CP\) radiators working in different operative bands. Indeed, the designer is given the freedom to choose the materials of the different layers as well as the desired target performance (i.e., bandwidth, \(HPBW\), \(AR\), and \(XPD\)) for the specific applicative scenario at hand. Future works, beyond the scope of the current manuscript, will be aimed at assessing the possibility to exploit the stripline technology to feed the antenna and at investigating the resulting advantages and drawbacks. Conceptualization, M.S., G.O., M.A.H., R.A. and A.M.; Methodology, M.S., G.O., M.A.H., R.A. and A.M.; Software, M.S., G.O., M.A.H., R.A. and A.M.; Validation, M.S., G.O., M.A.H., R.A. and A.M.; Writing-original draft, M.S., G.O., M.A.H., R.A. and A.M.; Writing-review and editing, M.S., G.O., M.A.H., R.A. and A.M. All authors have read and agreed to the published version of the manuscript.