# Wide-Band Wide-Beam Circularly-Polarized Slot-Coupled Antenna for Wide-Angle Beam Scanning Arrays
## 2 _WWCS Antenna Layout_  
Figure 1 shows a geometric sketch of the layout of the proposed _WWCS_ radiator. The antenna lies on the (\(x\), \(y\)) plane and it comprises \(\mathcal{L}=3\) square dielectric layers \(\ell_{l}\), \(l=1,\ldots,\mathcal{L}\) of side \(L_{a}\). The thickness, the relative permittivity, and the loss tangent of the \(l\)-th (\(l=1,\ldots,\mathcal{L}\)) layer are denoted with \(H_{l}\), \(\varepsilon_{rl}\), and \(\tan\delta_{l}\), respectively. The two stacked bottom layers (i.e., \(\ell_{1}\) and \(\ell_{2}\)) are relative to the _primary_ antenna element, which consists of a circular microstrip patch of radius \(R_{p}\), printed on the layer \(\ell_{2}\) [Figures 1 and 2b]. Such a patch is fed with an aperture-coupling mechanism. Towards this end, a cross-shaped slot is etched in the ground plane that separates the layers \(\ell_{1}\) and \(\ell_{2}\) [Figures 1 and 2a], which is in turn excited with a microstrip feeding line of width \(W_{f}\) and characteristic impedance \(Z_{0}\). This latter is printed on the bottom face of \(\ell_{1}\) [Figures 1 and 2a]. To maximize the _EM_ coupling, the microstrip line, the slot, and the patch are aligned with respect to the (\(x\), \(y\)) plane (Figure 1). Moreover, the feeding line is terminated into an open-circuited stub whose length \(L_{f}\) [Figure 2a] is properly tuned so that the standing-wave current, induced within the microstrip, is maximum at the slot barycenter [6]. It is worth pointing out that, even though a multiple-layer etching manufacturing process is required, the adopted aperture feeding enables some advantages with respect to a  
Figure 1: _WWCS Antenna Layout_—Geometry sketch of the proposed _WWCS_ radiator: (**a**) \(3D\) and (**b**) lateral view. Figure 2: _WWCS Antenna Layout_—top-view geometry sketches of layers (**a**) \(\ell_{1}\), (**b**) \(\ell_{2}\), and (**c**) \(\ell_{3}\). probe/pin-based choice [6]. For instance, (_a_) is a wide-band impedance matching, (_b_) is a an easier construction, since it avoids the vertical pin that would require additional drilling and soldering processes, and (_c_) is the higher polarization purity and pattern symmetry since the vertical pin would behave as an additional monopole degrading the overall axial ratio (_AR_) and cross-polar discrimination (_XPD_). Moreover, the use of independent substrates for both the circular patch (i.e., \(\ell_{2}\)) and the feeding line (i.e., \(\ell_{1}\)) gives the designer more flexibility in selecting the optimum dielectric support for each antenna \"building block\" with respect to a solution with coplanar edge feeding (either direct or inset-based) [6]. As for the shape of the slot, a 45-degrees rotated cross, with unequal arms of width \(W_{1}\) (\(W_{2}\)) and length \(L_{1}\) (\(L_{2}\)) [Figures 1 and 2a], was adopted to realize the desired circular polarization (_CP_). As a matter of fact, the introduced asymmetry allows one to excite, by injecting a current into the feeding line and exploiting the aperture coupling mechanism, two orthogonal current components having a phase difference of 90 [deg] onto the patch. As a result of the combination of such excited modes, a _CP_ current is yielded, which in turns radiates a _CP_ field. More specifically, left-hand (_LHCP_) or right-hand (_RHCP_) _CP_s are obtained by simply letting \(L_{1}<L_{2}\) or \(L_{1}>L_{2}\), respectively [7]. Otherwise, the polarization switching (_LHCP_\(\Leftrightarrow\)_RHCP_) could be yielded by simply mirroring the cross aperture with respect to the \(y\)-axis. Thanks to such a modeling, it is possible to enforce a _CP_ by means of a simple design and manufacturing process, since there is no need for two separate orthogonal microstrip lines. Moreover, a simple circular patch can be used by avoiding more complex solutions such as, for instance, a primary element with elliptic-shape (that would imply the tuning of the two semi-axes) or electrically-small perturbations of the external border of the patch (e.g., stubs or notches) to yield an _AR_ close to one [7].