1536-1225 (c) 2018 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/LAWP.2018.2810238, IEEE Antennas and Wireless Propagation Letters > REPLACE THIS LINE WITH YOUR PAPER IDENTIFICATION NUMBER (DOUBLE-CLICK HERE TO EDIT) < 1 Abstract—A novel design of electrically small, extremely thin and horizontally polarized magnetic dipole antenna is proposed. It is composed of multiple folded arms packed in an extremely thin height of 0.0016λ, with the electrical size ka of 0.276. The radiation efficiency is 87 % from the simulation. The radiation properties are investigated and its operation as a small magnetic dipole antenna is confirmed. A 3D printing technology is used for building the prototype due to the complexity of the proposed structure. The experimental results show good agreement with the computed expectation values. Index Terms—3D printing technology, electrically small antennas, folded dipole antennas, low-profile antennas, magnetic dipole antennas. I. INTRODUCTION HEORY, design and experimental validation of electrically small antennas have been a popular topic of research along with the explosive growth of small electronics. Generally, the electrical size ka less than 0.5 is considered as an electrically small antenna, where k is a wave propagation constant in free space and a is the radius of the imaginary sphere enclosing the antenna. Various designs have been reported for the electrically small electric antenna that approach the lower radiation Q bound of Chu and Thal with high radiation efficiency [1-5]. Its counterpart electrically small magnetic antenna, however, gains a relatively less attention although it could be effectively used in specific applications such as near-field wireless power transfer system and biomedical implants where electromagnetic couplings can be severely affected by surrounding dielectric materials [6-7]. The facts that electrically small magnetic dipole suffers from two times higher Q than the electric dipole in the same size, and it is usually not easy to utilize the ground plane for measurement might be the reasons for the less numbers of design. Nevertheless, notable designs have been reported, for example, a folded slot spherical helix, multi-arm spherical helix, spherical split ring resonator antennas, just to mention a few [8- 9]. They constructively form the current in the ߶-direction while minimizing the current in the ߠ-direction. Such the Manuscript received September 21, 2017. This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT & Future Planning (NRF- 2015R1C1A1A02037549) and in part by the Basic Research Laboratory (BRL) of the National Research Foundation (NRF-2017R1A4A1015744) funded by the Korean government. effectively illuminated spherical volume achieved a Q-value closely approaching the lower bound. Moreover, a more favorable manufacturing methodology applied wire-cage shape small magnetic antenna was also reported recently [10]. Although the radiation performance would be worse than the volumetric small magnetic antennas, small and low-profile form is also desired for practical purposes. It generally has an easier form factor to handle. Several horizontally polarized magnetic dipole antennas realized in a patch form, thus low- profile, are found in the literature [11-13]. Most of them are designed for GHz frequency bands and are not necessarily electrically very small though. A split ring resonator based small magnetic antenna at 400 MHz reported in [14] is impressively small with ka less than 0.1, but experiences a poor radiation efficiency less than 3 %. In this paper, we propose a simple yet effective design concept for the self-resonant, electrically small, and highly efficient low profile magnetic dipole antenna. We realize it using 3D printing (3DP) technology. The frequency around 200 MHz is chosen for the convenience of building the prototype and carrying out the measurement. The 3DP technology is being widely used in antenna engineering as a means of reproducing the radiation properties of the existent antennas with low cost and light weight [15-16], realizing novel designs [17-18], building customized, flexible substrate and phantoms [19-20]. The proposed antenna in this paper would be challenging to fabricate without the aid of the 3DP technology. In the following sections, design, radiation characteristic analysis, fabrication and measurement results will be discussed. II. ANTENNA DESIGN Principally, all polarizations can be constructed by the combination of radiating ܧ ߠcomponent of a small electric dipole and radiating ܧ߶ component of a small loop (or magnetic dipole). When they are combined with different strength and phase difference close to 90°, elliptical polarization is formed. In [21], electrically small elliptically polarized (EP) folded spherical helix dipole antenna was studied, in which both vertical and horizontal currents are configured in the antenna The authors are with the Department of Electrical Engineering, Chungnam National University, Daejeon 34134, Republic of Korea (e-mail: ijyoon@ cnu.ac.kr). Investigation of 3D Printed, Electrically Small and Thin Magnetic Dipole Antenna Myeongjun Kong, Student Member, IEEE, Su-Hyeon Lee, Student Member, IEEE, Geonyeong Shin, Student Member, IEEE, Junghyo Nah, Member, IEEE, and Ick-Jae Yoon, Member, IEEE T