RESEARCH ARTICLE Pattern synthesis of the multimode orbital angular momentum beams based on the fruit fly optimization algorithm Qingwen Li 1,2 | Xiuping Li 1,2 | Zihang Qi 1,2 | Hua Zhu 1,2 | Yuhan Huang 1,2 | Zaid Akram 1,2 | Xing Jiang 3 1 School of Electronic Engineering, Beijing University of Posts and Telecommunications, Beijing, China 2 Beijing Key Laboratory of Work Safety Intelligent Monitoring, Beijing, China 3 Guangxi College Key Laboratory of Microwave and Optical Wave Applications Technology, Guilin University of Electronic Technology, Guilin, China Correspondence Xiuping Li, School of Electronic Engineering, Beijing University of Posts and Telecommunications, Beijing 100876, China. Email: xpli@bupt.edu.cn Funding information BUPT Excellent Ph.D. Students Foundation, Grant/Award Number: CX2019123; Opening Project of Guangxi College Key Laboratory of Microwave and Optical wave Applications Technology; Preresearch Funding of the Equipment Development Department of the Central Military Commission of China, Grant/Award Number: 6140518040116DZ08001 Abstract The multimode orbital angular momentum (OAM) radio waves can be used to mul- tiplex multiple transmission channels to increase the capacity of communication system without adding additional bandwidth. However, the divergence of the OAM beams and beam inconsistency escalate by increasing OAM mode number. Moreover, the worse sidelobe level (SLL) always appears along with a better con- vergent beam. In this article, the fruit fly optimization algorithm (FOA) is proposed to suppress the SLL in multimode OAM scenario. Based on the concentric circular array antenna (CCAA), the feeding amplitudes and the radii of the array are synthe- sized simultaneously to realize less than -30 dB SLL of the multimode OAM pat- terns. When the main lobes with different OAM modes steered to a uniform azimuth of θ =0  , the SLLs of these OAM modes are also suppressed to less than -21 dB. The advantages of FOA used in the OAM pattern synthesis are verified by comparing it with the genetic algorithm (GA). The FOA-based synthesis has a simpler implementation flow diagram which reduces the time of synthesis to 39.5% of GA. KEYWORDS beam uniformity optimization, fruit fly optimization algorithm, orbital angular momentum, pattern synthesis, vortex electromagnetic wave 1 | INTRODUCTION The angular momentum of electromagnetic (EM) wave includes spin angular momentum (SAM) and orbital angular momentum (OAM). Since the OAM was first found in 1992, 1 the OAM-carrying EM wave began to be studied in the opti- cal region. 2-4 Unlike the SAM beam having plane wave front, the wave front of the OAM beam rotates around the transmis- sion axis and has orthogonal helical phase stucrures. 5 Each arm of the phase fronts can be seen as a sub-channel. Because of the character that multiplex signals at the same frequency without increasing bandwidth, 6 the application of OAM has expanded rapidly in the region of radio frequency. 7,8 More recently, the OAM was proposed to be used in radar imag- ing 9,10 in which a higher azimuth resolution is achieved by using the OAM beams. However, the application of imaging relies on the OAM beams having multiple modes. It is neces- sary to point out that the null region exists in the center of the electric field which becomes even larger by increasing the OAM mode number. 11 The energy divergence and beam inconsistency of OAM beams decrease the gain of the main lobe and bring difficulties in receiving signals from different azimuths. The circular array antenna is the most commonly used method to generate multimode OAM beams in the radar imaging. It can generate any mode by setting a proper Received: 7 December 2018 Revised: 11 April 2019 Accepted: 4 June 2019 DOI: 10.1002/mmce.21876 Int J RF Microw Comput Aided Eng. 2019;e21876. wileyonlinelibrary.com/journal/mmce © 2019 Wiley Periodicals, Inc. 1 of 10 https://doi.org/10.1002/mmce.21876