# Circularly Polarized High-Gain Fabry-Perot Cavity Antenna with High Sidelobe Suppression
## 1 Introduction  
Array antennas are widely used in long-range wireless communications such as satellite [1, 2] and mobile communications [3], as well as in applications like air and maritime vessel traffic control, defense tracking, vehicle speed detection, and weather monitoring [4]. These antennas are favored due to their high gain, directional beam power patterns, low-profile fabrication [5], and simple feeding structure. These characteristics make them suitable for mobile communication systems.  
Conventionally, linear polarized reflectarray [6, 7], transmitarray [8, 9], and resonance cavity antennas [10, 11, 12, 13, 14] are designed by utilizing configurable superstrates and non-configurable substrates. However, there are relatively few antennas of these types [15, 16, 17] that offer circular polarization, which is important for defense and space applications [18]. Moreover, these antennas often have poor performance in terms of gain, axial ratio (AR), and sidelobe suppression (SLS). Achieving all the desired performance characteristics at the same time is challenging.  
To overcome these problems, a polarization configurable resonance cavity with an electrical approach [19, 20], a single-layered polarization conversion metasurface [21], and a circular polarized folded transmitarray antenna [22, 23] have been proposed to produce highly directional power patterns with circularly polarized (CP) waves. Even with these high-profile and complex multilayer design approaches, AR and SLS performance have not been satisfactory.  
In [19], a polarization-reconfigurable CP superstrate (Rogers RO4003C) is proposed as a switchable polarizer with double-etched circular patches and PIN diodes (SMP1245-079 LF). However, its full resonance model has high sidelobe levels for each left-handed CP and right-handed CP. In [20], a low-radar-cross-section (RCS) polarizer is employed with an isotropic high-impedance surface (HIS) to construct the resonance cavity. However, this antenna also suffers poor gain and aperture efficiency, as well as high sidelobes in both planes.  
In [21], a C-gap etched slot PRS is proposed to form LHCP and RHCP waves, and by rotating it, a phase gradient is formed to manipulate the cavity phase response for high realized gain. However, this antenna has low bandwidth and major sidelobes. In [22; 23], folded transmitarray antennas are proposed, offering an excellent methodology to reduce the resonance cavity height by one third and convert the polarization conversion metasurfaces from linear to circular. However, the low-profile fabrication results in poor aperture efficiency of the sidelobe radiation power patterns.  
To solve these problems, we propose a novel FPCA with a circularly polarized partially reflective surface (CP-PRS) to improve the AR. The use of artificial magnetic conductor (AMC) cells instead of a reflective ground plane enhances the broadside gain and SLS through Trentini's beamforming condition in the resonance cavity by associating CP-PRS cells [24]. All simulations of the unit cell, feeder, and full FPCA model are computed with the CST Microwave Studio Suite [25] using two solvers, a time domain solver and a frequency domain solver, which use the finite integration technique (FIT) and finite element method (FEM), respectively.  
The rest of the paper is organized as follows: Section 2 depicts the design and operation of the circularly polarized FPC antenna (CP-FPCA) in respect to ray theory, and sketches the PRS and AMC unit cell design and feeding structure. Additionally, the mechanism of the circularly polarized PRS is briefly elaborated. Section 3 describes the simulated and experimental results of the present study. Section 4 concludes the paper.