URSI GASS 2020, Rome, Italy, 29 August - 5 September 2020 Feasibility Study of a Stretchable Antenna Conformed on an Expandable Cylindrical Surface Rakib Hasan, Reyhan Baktur* Department of Electrical and Computer Engineering Utah State University Logan Utah, U.S.A rakib.hasan@aggiemail.usu.edu, reyhan.baktur@usu.edu Abstract Stretchable antennas are valuable to a wide range of applications, from biomedical field to transportation or weather forecast. The objective of this paper is to present a feasibility study for designing a stretchable antenna that has a better tradeoff between the gain and stretchablity, compared to previous studies. As the antenna under study is conformed to a cylindrical surface, the potential applications include integration with tires or balloons. 1 Introduction Stretchable antennas are highly desirable in applications such as monitoring tire pressure, integration on balloons, or in biological and medical field such as integration with human or animal joints. Previous studies on stretchable antennas have been mainly focused on utilizing stretchable material such as composite conductor, liquid metal, stretchable ink, and thin film technology [1]-[4]. It has also been shown to achieve stretchablity through relative elastic material and antenna design that can withhold reshaping [5]. Those former studies, however yield either very low gain or limited strechability of no more than 10%. Recognizing the trade-off between the stretchability and antenna gain as a key design consideration, in a recent study, we reported a cost effective and realistic method to achieve an effective antenna with a high stretch ratio [6]. The study was on a planar stretchable antenna. The objective of this paper is to examine a stretchable antenna conformed to a cylindrical surface. The potential application is for balloon or tire integration where the antenna is placed on a curved surface. 2 Design Philosophy and Antenna Geometry Although there exist different stretchable conductors such as composite material, the elasticity of those conductors are not acceptable for applications such as balloons that needs much higher stretching ratio. The accessibility of the material is another challenge. In this study, the stretchable antenna is achieved through combing conductive rubber and copper to form a patch antenna. Such a combo-material design was chosen because a conductive rubber alone is normally very lossy and the efficiency of the antenna will not exceed 50% for lower GHz bands. The conductive rubber chosen in this study is Silver Plated Aluminum- filled Fluorosilicone conductive elastomer. It has conductivity of 50000 S/m, stretchability of 350% and the value of ϵ_r is 3.0. The design method in this study is to alternate conductive rubber and copper to form patch antenna. To keep it simple, the geometry of the rubber and copper has been kept rubber grids filled with small copper patches as illustrated in Figure 1. The geometry of the rubber-copper antenna is shown in Figure 1, where a patch antenna made with rubber grids and copper patches is placed on a cylindrical substrate. As an initial study, we kept the substrate properties the same as a Rogers RT/duroid 5880 (ϵ_r=2.20, loss tangent = 0.0009), and it can be replaced to a more realistic material such as rubber of latex. The rubber grids were made taller than coper and its height reduces when being stretched. Figure 1. Geometry of the rubber-copper antenna. The dimension of the antenna before stretching is listed in Table I. These parameters are also marked in Figure 1. The study only examines the effect of the stretch ratio of the patch antenna on the gain, and therefore the ground is assumed to be copper. Although in the study, we also