# Wide-Band Wide-Beam Circularly-Polarized Slot-Coupled Antenna for Wide-Angle Beam Scanning Arrays
## 1 Introduction
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Ref.** & **Technology** & \(f_{0}\) **[GHz]** & **FBW (\%)** & **Pol.** & **HPBW [deg]** & **Size [\(\lambda_{0}\)]** \\ \hline
[11] & Magnetoelectric dipole with parasitic patches and metallic vias & 9.0 & 40 & \(LP\) & \(156\div 360\) & \(0.45\times 0.27\times 0.11\) \\ \hline
[19] & Probe-fed circular patch with rectangular parastic patches & 4.46 & 0.9 & \(LP\) & \(156\) & \(0.84\times 0.84\times 0.03\) \\ \hline
[20] & Probe-fed circular patch with rectangular parastic patches & 2.49 & 1.2 & \(CP\) & \(131\) & \(0.56\times 0.56\times 0.11\) \\ \hline
[21] & Comb-slot-loaded patch & 8.25 \(\div\) 11.5 & 7.6 \(\div\) 9.1 & \(LP\) & \(83\div 103\) & \(0.55\times 0.55\times 0.16\) \\ \hline
[22] & Probe-fed u-slotted patch with electric walls & 3.5 & 39 & \(LP\) & \(112\div 174\) & \(0.35\times 0.35\times 0.21\) \\ \hline
[23] & Aperture-fed patch with dielectric sheet and electric walls & 3.5 & 19.7 & \(LP\) & \(158\div 240\) & \(0.40\times 0.40\times 0.21\) \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Comparison in terms of central frequency (\(f_{0}\)), fractional bandwidth (\(FBW\)), polarization, elevation \(HPBW\) at the central frequency, and overall size (in wavelengths at \(f_{0}\), \(\lambda_{0}\)), between the proposed _WWCS_ antenna and wide-beam designs recently appeared in the scientific literature. Some interesting approaches implement the wide-beam behavior by adding parasitic elements (e.g., vertical electric walls [22; 23], patches [11; 19], or rings [20]--Table 1) where additional current components are induced to radiate end-fire patterns that constructively sum with those radiated by the main radiator. Following this guideline, both linearly (_LP_) [11; 21; 22; 23] and circularly (_CP_) polarized [20; 25; 28] (Table 1) and [11; 21; 22; 23] and circularly (_CP_) polarized [20; 25; 28] (Table 1) wide-beam radiators were synthesized even though the _CP_ ones have several advantages with respect to those with _LP_. For instance, there is an improved immunity to the multi-path distortion, polarization mismatch losses, and Faraday rotation effects caused by the ionosphere in satellite communications [26; 27; 31]. Thus, _CP_ wide-beam radiators are a very promising technological asset for many wireless systems including global positioning and navigation systems (_GPS_ and _GNSS_), radars, satellite communications, radio frequency identification, mobile communications, and wireless local area networks [26; 27; 28]. Accordingly, this paper proposes a novel wide-band wide-beam _CP_ slot-coupled (_WWCS_) antenna based on the combination of a _primary_ (driven) and a _secondary_ (passive) element to generate large-_HPBW_ patterns with rotational symmetry and high polarization purity. More specifically, a 3D microstrip layout is obtained by placing a dielectric layer hosting a metallic ring at a proper distance from a circular patch. By properly exciting a _CP_ current within such a parasitic element, a torus-shaped pattern with maximum gain on the azimuth plane is radiated, thus triggering an increased end-fire gain which, combining to the broadside radiation of the underlying patch, results in a wide beam along every elevation plane. Unlike the narrowband design in [20] (having a fractional bandwidth of \(FBW=1.2\%\)--Table 1), the proposed radiating element is characterized by (_i_) a wide-band impedance matching (i.e., \(FBW=15\%\)--Table 1), (_ii_) a wider beamwidth (i.e., \(HPBW\simeq 180\) [deg] versus \(HPBW=131\) [deg] of [20] --Table 1) as well as (_iii_) a simpler feeding mechanism for _CP_ (i.e., slot-coupling versus probe feeding) [7]. Moreover, unlike the single-element design in [20], the possibility to exploit such an element in a _WASA_ is addressed, as well.