# Two-Dimensional Scanning of Circularly Polarized Beams via Array-Fed Fabry-Perot Cavity Antennas
###### Abstract  
In this paper, we present an array-fed Fabry-Perot cavity antenna (FFCA) based on a partially reflecting sheet (PRS) capable of generating a circularly polarized (CP), highly directive, far-field radiation pattern in the 27-28.5 GHz frequency range. The PRS, the cavity, and the array of feeders serve to different purposes in this original structure. The PRS is engineered to produce a circular polarization from a linearly polarized source placed inside the cavity. The cavity is optimized to obtain a directive conical beam from the dipole-like pattern of the simple source, and allows for a frequency scan of the beam along the elevation plane. The array of feeders is designed to obtain a pencil beam whose azimuthal pointing direction can be controlled by properly phasing the sources. The radiation performance is studied with a specific application of the reciprocity theorem in a full-wave solver along with the pattern multiplication principle. A number of array-pattern configurations in terms of operation frequency and phase shift are investigated and presented to show the potential of the proposed solution in terms of design flexibility and radiation performance. F +
Footnote †: journal: applied sciences  
Article  
Two-Dimensional Scanning of Circularly Polarized Beams via Array-Fed Fabry-Perot Cavity Antennas [PERSON] this respect, Fabry-Perot cavity antennas (FPCAs) [21] offer a flexible and advantageous solution. As is well known [22], FPCAs can be modeled as 2-D LWAs, and are often designed to radiate either a linearly polarized (LP) pencil beam at the broadside, or an LP frequency-scannable (almost omnidirectional) conical beam [14]. Progress has recently been made in realizing CP beams, as well as in beam-shaping techniques. Independent excitation of both a TM and a TE leaky wave has been proven as an effective technique in [23]. A way to ensure the two required modes consists of employing two distinct sources. A vertical electric dipole (VED) is obtained by the insertion of a coaxial cable through the ground plane to excite a TM leaky wave, whereas the TE counterpart can be excited by an equivalent vertical magnetic dipole (VMD) or, more practically, by a circular array of slots etched in the ground plane [24]. Considering a resonant cavity formed by a ground plane and a homogenized partially reflective surface (PRS), the proposed approach enables polarization control, easily switching from LP to CP beams. This feature is achieved through an antenna biasing system that equalizes the magnitudes of the vertical and horizontal far-field components and provides the desired phase shift in quadrature [23]. The antenna design in [23] demonstrates the flexibility in obtaining CP beams, once two complementary feeders are provided in the cavity. To reduce the complexity of the feeding structure, different antenna architectures for producing CP beams were explored. Linear-to-circular polarization conversion has been investigated through different techniques. A self-polarizing FPCA architecture has been proposed in [25], employing a nonresonant frequency selective surface (FSS) to induce resonance and a further twisting surface to produce the desired feature of circular polarization. A simple LP feeder is employed to generate resonance inside the cavity, which enables partial power leakage towards a polarizing ground plane, producing the complementary field component. Accurate cavity optimization allows it to radiate a pure CP beam at the broadside. Synthetic materials, given to their artificially derived properties, have extensively reshaped applications, including the sector of guiding and radiating systems. Recent advancements in the development of metasurfaces inspired interesting designs that operate in both reflection and transmission modes, also including tunable properties [26, 27, 28, 29, 30, 31, 32, 33, 34]. The profitable use of a metasurface-based PRS has been further investigated to obtain compact planar geometries devoted to polarization conversion.