# A Ka-Band Cylindrical Paneled Reflectarray Antenna
## 1 Introduction  
Reflectarray antennas have been among the most popular research topics of the last decades. The motivations behind this great diffusion are due to the great flexibility of this type of structure that can be indeed designed to meet manifold requirements [1]. Originally, they were introduced as a planar alternative of reflector antennas, advantageously employable in scenarios where the planarity of the reflecting surface could lead to relevant benefits [2]. For example, in space applications the development of inflatable [3] or deployable [4] reflectarrays was widely studied to obtain large reflecting surfaces that can be easily stowed in a small volume during the launch phase. In these cases, the reflecting surface extends outside the satellite main body while the feed is integrated on the spacecraft. This configuration is usually favorable to obtain an optimal illumination of the reflectarray, as the ratio between the geometric size and the focal distance (\(f/D\)) can be large enough to reduce the illumination angle between the feed and the peripherals elements. Typically, reflectarrays are designed with \(f/D\) higher than 0.5, as smaller values determine a great efficiency reduction. As a result, the reflectarray compactness is compromised by the feed location. Although not essential in many applications, this limitation becomes relevant in satellite communications (SatCom) and, in particular, for transportable user terminals. This type of terminal should be easily deployable and transportable with reduced size and light weight. Moreover, the direct integration of the feed with the block up-converter (BUC) and with the low noise block converter (LNB), which are typically too bulky to be incorporated with the reflectarray feed, is of great importance. In view of that, only few examples of SatCom reflectarrays have been investigated so far. For instance, in [5] a transportable reflectarray with dual linear polarization at the Ku-band is presented. This configuration employs apassive sub-reflectarray with an \(f\)/\(D\) that exceeds the unity and a main-reflectarray with 1-bit phase control. An example of a K/Ka SatCom [6; 7] reflectarray with \(f\)/\(D\) equal to 0.75 is reported in [8], while Tx-only reconfigurable folded reflectarrays are presented in [9; 10].  
This paper introduces a novel paneled reflectarray configuration that is derived from a parabolic cylindrical reflector. The proposed architecture is conceived for portable K/Ka SatCom user terminals. Cylindrical reflector antennas are limited by the \(f\)/\(D\) factor [11; 12; 13]. In fact, once height and diameter of the antenna are given, \(f\)/\(D\) is fixed and a larger diameter would result in a higher antenna profile. In order to solve this problem and to have a larger aperture without increasing the antenna height, a novel approach is evaluated in which the parabolic reflector is replaced with a segmented reflectarray. The phase of each individual reflectarray element is; thus, adjusted to coherently focus the beam, allowing for a larger aperture without changing the feed position. As a result, the proposed reflectarray leads to a better radiation efficiency while the \(f\)/\(D\) can be kept below 0.34.