# Design of a Flat-Panel Metasurface Reflectarray C-Band Antenna
## 1 Introduction  
The concept of a reflectarray was proposed in the 1960s using a short-circuited waveguide array composed of different lengths [1]. Early reflectarray designs have not received much attention due to their impractical structures, but the development of a printed flat-panel microstrip reflectarray paved a new way in the late 1980s [2]. The breakthrough of printed microstrip circuit technology has contributed significantly to the innovation of reflectarray antennas, which have emerged as high-gain antennas for long-distance communications, such as nano-/cube-satellite communications. Dish-type parabolic reflector antennas are widely used in satellite communications for the space-Earth link because of their high-gain property. Small satellite platforms such as CubeSat have extremely limited payload, so it is challenging to mount bulky high-gain reflector antennas on them for the space-Earth link [3]. The advance of resonator-based metamaterial technology has expedited the progress of the metamaterial-based antennas. The metasurface consisting of resonator arrays is widely adopted for antenna, absorber, power-splitter and reflector designs [4; 5; 6; 7; 8]. It is because the negative constitutive parameters at desired frequency can be easily obtained by utilizing the planar resonator array structures. For the high gain antenna applications, a flat-panel metasurface reflectarray antenna is a good candidate for the high-gain foldable antenna of CubeSats because of their flat reflectors fabricated from a multi-layer PCB [9; 10; 11]. The operation principle and structure of a reflectarray are similar to those of a parabolic reflector antenna [12; 13; 14]. Both antennas reflect an incident wave from a source feedingantenna to focus or steer the wave's direction. The direction of the reflected wave is determined by the shape or phase response of the reflector. A conventional parabolic reflector antenna has a bulky curved metallic surface as a reflector, whereas a reflectarray has a flat planar antenna or resonator array, which results in a low profile, low mass, ease of fabrication and low cost. Reflectarrays are also different from conventional phased antenna arrays because they do not have a beamforming/steering network, such as a power dividing circuit and phase shifters. The phase response of each unit cell of a reflectarray works as a phase shifter, which results in high reliability due to the relatively simple feeding and passive phase shifting property. Unlike traditional active phased antenna arrays, designing large arrays of thousands of elements is much easier. This paper discusses a generalized design procedure for a planar reflectarray antenna design and presents a high-gain reflectarray in the C-band as a design example. It shows detailed simulation setup, design environment and automation of a reflectarray antenna. The detailed design procedure of a unit-cell and array analysis using a commercially available full-wave EM solver are discussed. The presented design procedure is demonstrated by a flat-panel reflectarray antenna consisting of a dual-ring resonator fed by a circular horn antenna. Measured experimental data agree well with the proposed design and analysis. It should be noted that the proposed design method is scalable to any EM solvers for numerical analysis. The measured antenna has a high co-pol gain value of 20.0-22.2 dBi with a cross-pol suppression level of 26-39 dB at the operation frequency. There was an error of 1-2\({}^{\circ}\) for the beam steering direction between the simulated data and the measured data. The size of the designed 16 \(\times\) 16 reflectarray is 400 \(\times\) 400 mm\({}^{2}\), whereas the distance between the source horn antenna and the reflectarray is 200 mm. The proposed design procedure is scalable to any frequency band. This article is organized as follows. Section 2 presents the detailed operation principle of the reflectarray antenna, its geometry, antenna design parameters and dimensions.