0018-926X (c) 2019 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information. This article has been accepted for publication in a future issue of this journal, but has not been fully edited. Content may change prior to final publication. Citation information: DOI 10.1109/TAP.2020.2963922, IEEE Transactions on Antennas and Propagation IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION 1 A Thick Origami Reconfigurable and Packable Patch Array with Enhanced Beam Steering Muhammad Hamza, Student Member, IEEE, Constantinos L. Zekios, Member, IEEE, and Stavros V. Georgakopoulos, Senior Member, IEEE Abstract—This paper presents the first foldable thick-origami based antenna array made of a single non-flexible (rigid) printed circuit board (PCB), which can be easily fabricated using a stan- dard milling machine. The foldability of the design is achieved using a surrogate hinge architecture that allows the array to fold in a range of almost 360 ◦ , without showing any mechanical or electromagnetic (EM) failure even after 5,000 folding cycles of complete angular deflection (±180 ◦ ). The proposed physically reconfigurable antenna array consists of four patches that are differentially fed and a surrogate hinge at its center. As the array changes from its planar to its non-planar state it shows improved beam steering capabilities for scan angles greater than 35 ◦ . The array is designed on a 1.5 mm thick, low-cost FR4 substrate with overall dimensions of 250 × 102 mm and operating frequency of 2.45 GHz. Index Terms—Thick origami, antenna arrays, surrogate hinge, differential feeding, pattern reconfiguration. I. I NTRODUCTION R ECONFIGURABLE antennas and antenna arrays have been studied intensively in recent years providing mul- tiple functionalities in a system, [1]. Based on the properties of reconfiguration they can be organized in: a) Frequency reconfigurable, which are mainly used for cognitive radio applications, [2], [3]. b) Radiation pattern reconfigurable, which are exten- sively used for mobile antennas, [4], [5]. c) Polarization reconfigurable, which are mainly used in portable devices, [6], [7]. d) Hybrid reconfigurable, which are very useful for beam scanning and frequency agile applications that require improved spectral efficiency, [8]. Numerous reconfiguration techniques have been used to achieve the aforementioned characteristics. Electrical reconfig- uration techniques have been extensively used after the intro- duction of the radio frequency micro-electro-mechanical sys- tem (RF-MEMS) providing very high isolation and achieving a switching speed of 1-200 µsec, [9]–[11]. Switches with pin diodes have been also introduced showing an improved speed of 1-100 nsec, [12]. Varactors have also been used, [13], [14], to reconfigure antennas through changes in their capacitance. Moreover, photo-conductors have been incorporated into an- tenna designs as optical switches, which are activated by a This work was supported by the Air Force Office of Scientific Research under grant FA9550-18-1-0191 and the National Science Foundation under Grant EFRI 1332348. The authors are with the Department of Electrical and Computer Engi- neering, Florida International University, Miami, FL 33174, USA (email: mhamz005@fiu.edu, kzekios@fiu.edu, georgako@fiu.edu) laser beam, [15]–[19]. Methods based on material alterations have been introduced, such as techniques based on graphene plasmonics, [20], liquid crystals, [21], ferro-electric thin films, [22]. A different approach compared to all the above is mechan- ical reconfiguration. Typical mechanical methods are based on fluidic technology, [23], and micro-motors, [24], or more recently, antennas with mechanical actuators, [25], and origami based designs, [2], [4], [6], [26], [27], that can physically morph providing multifunctional and reconfigurable perfor- mance. The latter is the approach followed in this work for the design of the proposed array. Arrays can be linear, planar or conformal and are designed for full scan or limited scan, [33], where full scan normally means ±60 ◦ or more from broadside. Most of the times the antenna arrays are designed in one plane consisting of multiple, usually stationary antenna elements. There is also an important class of applications for arrays which require them to conform to shaped surfaces (e.g., the surface of an aircraft, missile, etc.), [8]. Additionally, non-planar arrays can cover a larger area if appropriately placed on a cylindrical or spherical surface, [34]. Significant work has been done in both areas of planar, [35]–[37], and non-planar arrays, [38]–[42]. However, there is limited work for arrays that can operate as planar and non-planar by changing their configuration in real time. Only in [39], [40], a phased array was reported that can self adjust by conforming its shape. In both cases, the arrays were developed on flexible substrates. To the authors knowledge, no arrays have been designed on rigid thick substrates that are capable of transforming their shape in real time. In this paper for the first time, a physically reconfigurable antenna array is developed on a single rigid substrate. The proposed array is able to transform from its planar to its non- planar state using origami design. Even though origami started as the art of folding paper, the evolution of technology along with innovations from scientists enabled the application of origami to the fields of science, math and engineering. Several origami designs have been already developed in antennas, [2], [4], [6], [26]–[32], and mechanics, [43], [44]. Origami structures are categorized into rigidly, [45], and non-rigidly, [46], foldable structures. In fact, depending on the application, it is favorable to use either rigidly, [47], or non-rigidly, [48], foldable structures. In the field of antennas, rigid structures are preferable, especially when antenna systems experience extreme environments. One of the major problems of foldable antennas, though, is that they crack after a finite number of folding/unfolding cycles. Even flexible materials are not suit-