2018 International Symposium on Antennas and Propagation (ISAP 2018) [ThP-43] October 23~26, 2018 / Paradise Hotel Busan, Busan, Korea

Multi-beam Transmitarray Design Using Principle of Superposition

Chang-Hyun Lee1, Sang Wook Chi1, Jae-Gon Lee2, and Jeong-Hae Lee1 1Department of Electronic and Electrical Engineering, Hongik University, Seoul 04066, Korea 2Metamaterial Electronic Device Research Center, Hongik University, Seoul 04066, Korea

Abstract –This paper introduces a multiple 0 340 20 method using the principle of superposition. Using the principle 1.00 of superposition, it is possible not only to form multiple beams 320 40 very simply, but also to suppress side lobes or to separate two 0.75 300 60 adjacent beams. In this paper, the realization of those 0.50 mentioned above using the principle of superposition is explained using an array factor theory, and a dual beam 0.25 280 o 80  =0 transmitarray antenna with a superstrate consisting of unit cells  0.00 arranged in 11 11 is designed using the principle of o x  =180 superposition. The gains of antenna was simulated to be 14.22 260  100 dBic and 15.64 dBic at =0o and 180o when =20o. 0.25

0.50 Index Terms — Transmitting antenna, metasurface, multi- 240 120 beam antenna, multiple beamforming, circular . 0.75 220 140 1.00 200 160 180 1. Introduction Fig. 1.Nomalized array factor for dual beamforming Multi-beam antennas have numerous applications such as o o o at =0 and 180 when =10 electronic countermeasures, satellite communications, microwave power transfer (MPT), and multiple-target radar Therefore, in order to steer the beam at θ0 and ϕ0, the phase systems [1]. Recently, multi-beam antenna using a differences have to be set as transmitarray has attracted a growing interest in the area of high-gain antennas due to their numerous advantages [2]. (2). In this paper, a multi-beam transmitarray antenna based on metasurface is designed using principle of superposition. When M and N are odd and the m-th element on the x-axis This method can form multi-beams with a simpler process and the n-th element on the y-axis are denoted as m and n, than the conventional methods using an optimization respectively, the phase of the m by n element for single beam algorithm [3] or the Fourier series [4]. Using the forming is expressed as superposition principle, a phase set for multiple (3). beamforming can be easily obtained through the sum of o phase sets for single beam steering. In addition, it is possible The phase of the center element was set to 0 and used as a to suppress side lobes and separate adjacent beams by giving reference. In order to calculate the phase set for dual beam, a specific phase difference between phase sets for single- the principle of superposition is used. Using the principle, beam steering. Finally, a beamforming method using the the phase set for dual beam forming can be easily obtained principle of superposition is described through the array by adding the phase sets for single beam steering calculated o factor theory, and a transmitarray antenna dual beam at =0 from (3). The applied source set for dual beam at {ϕ1,θ1} and o o and 180 when =20 is designed. {ϕ2,θ2}is expressed as j12st j nd jdual em, n  ej em, n Adual e m, n (4) mn, 1st 2nd   2. Multi-beam Forming Method Using Principle of mn, and mn, are the phase of m by n element for single Superposition beam steering at {ϕ1,θ1} and {ϕ2,θ2}, respectively. ϕ∆ is a phase that is added collectively to the phase set for forming When the array distances are d in x-axis and d in y-axis, x y the second beam, and this value can be used to form null or the array factor of the array is expressed as improve the gain in a specific angle. Fig. 1 shows the array (1) factor for dual beamforming at =0o and 180o when =10o. o When ϕ∆ is 0 , the two beams are too close to each other, so where M and N are the number of arrays in the x and y that the beam patterns are combined and cannot serve as a direction, respectively, and β and β are the phase difference o x y double beam. However, if ϕ∆ is set to 180 for the destructive between adjacent units in x and y direction, respectively. interference at the center of the two beams, a null is

751 2018 International Symposium on Antennas and Propagation (ISAP 2018) October 23~26, 2018 / Paradise Hotel Busan, Busan, Korea

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(a) Fig. 3. Full-wave simulated of the designed transmitarray antenna with dual-beam at =0o and 180o when 12.8mm =20o the array factor theory that the suppression and the 62mm(=1.2l0) adjacent beam separation are also possible in addition to the simple formation of multiple beams by employing the principle of superposition for multiple beamforming. Finally, (b) it is shown that the proposed multiple beamforming method Fig. 2. The structure of the designed transmitarray antenna can be applied very simply by designing a dual-beam (a) Top view (b) Side view transmitarray antenna. The proposed multiple beamforming generated between the two beams and two beams are method is expected to open the way for simply designing separated as shown in Fig.1. Side-lobe suppression is also functional devices with multi-beam. More details will be possible using this principle. It is also applicable to the mentioned at the presentation. formation of more than three beams. In order to confirm the multiple beamforming method, a Acknowledgment dual-beam transmitarray antenna is designed. The superstrate of the transmitarray antenna consists of five metallic layers This research was supported in part by Basic Science separated by four substrates to cover full transmission phase Research Program through the National Research Foundation variation of 2 and the metallic layers [5] are designed to of Korea (NRF) funded by the Ministry of Education (No. circular patches with the same dimension to operate as 2015R1A6A1A03031833) and in part by the MSIT(Ministry circular polarized transmitarray antenna. The superstrate is of Science and ICT), Korea, under the ITRC(Information Technology Research Center) support program(IITP-2018- 11 x 11 array of unit cells of size 0.387λ0 x 0.387λ0 at the operation frequency of 5.8GHz. The unit edge etched patch 2016-0-00291) supervised by the IITP(Institute for Information & communications Technology Promotion)” CP antenna of 0.5l0 x 0.5l0 at 5.8GHz is chosen as a feed antenna, and it feeds at 1.2l0 away from the superstrate as shown in Fig. 2. The gains at two beams are simulated to be References 14.22 dBic and 15.64 dBic, respectively. The aperture [1] R. C. Hansen, Antennas, Wiley Series in Microwave efficiency is confirmed to be 29.5% which is relatively high. and Optical Engineering. New York: Wiley, 1998. The aperture efficiency was calculated using the following [2] A. Yu, F. Yang, A. Z. Elsherbeni, and J. Huang, “Transmitarray equation [6]. antennas: An overview,” In USNC/URSI Radio Science Meeting, Jul. 2011. [3] H. X. Xu, T. Cai, Y. Q. Zhuang, Q. Peng, G. Wang, and J. G. Liang, (5) “Dual-Mode transmissive metasurface and its applications in multibeam transmitarray,” IEEE Transactions on Antennas where N represents the number of beams and Gi, i, and A Propagation, vol. 65, no. 4, pp.1797-1806, 2017. are the gain and steering angle of each beam, and aperture [4] W. L. Stutzman, and G. A. Thiele, Antenna theory and design. John (superstrate) area. The full-wave simulated radiation pattern Wiley & Sons, 2012. [5] M. Li, and N. Behdad, “Wideband true-time-delay microwave lenses of designed circular polarized transmitarray antenna is based on metallo-dielectric and all-dielectric lowpass frequency shown in Fig 3. selective surfaces,” IEEE Transactions on Antennas Propagation, vol. 61, no. 8, pp.4109-4119, 2013. [6] P. Nayeri, F. Yang, A. Z. Elsherbeni, "Design and experiment of a 3. Conclusion single-feed quad-beam ", IEEE Transactions on Antennas Propagation, vol. 60, no. 2, pp. 1166-1171, Feb. 2012. This paper presents a multiple beamforming method using the principle of superposition. It is confirmed through

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