Effect of atmospheric angular momentum turbulence on the orbital of hollow vortex beams

The phase fluctuation of Laguerre-Gaussian （LG） vortex beams induced by atmospheric turbulence affects the quantum phase associated with azimuth coordinates and affects the orbital angular momentum of the vortex beams. The measurement of orbital angular momentum is affected by the change in the classical phase and the quantum phase in the Hilbert space. This paper analyzes the additional random complex phase of the vortex beam generated by the atmospheric turbulence and discusses the effect of atmospheric turbulence on the orbital angular momentum of an LG vortex beam using the photon state-vector function. The distributions of the classical phase of vortex beams affected by turbulence of different strengths are calculated and compared with the case for LG vortex beams transmitted through free space. Results show that the atmospheric turbulence affects the phase value of LG vortex beams transmitted in the external field and significantly affects the beam phase structure in the near field. However, the effect of turbulence on the phase of vortex beams is insignificant for a transmission range z 〉 2000 m while the phase values vary slowly and gradually become constant.     

Pattern synthesis of the multimode orbital angular momentum beams based on the fruit fly optimization algorithm

The multimode orbital angular momentum (OAM) radio waves can be used to multiplex 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 convergent 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 synthesized simultaneously to realize less than ?30 dB SLL of the multimode OAM patterns. 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.     

A wideband transmission metasurface for generating Bessel beam carrying orbital angular momentum

Orbital angular momentum (OAM) microwave waves have received increasing research interest because of their potential to improve communication capacity and radar resolution. However, the traditional orbital angular momentum wave has the problem of diffraction divergence. The ideal Bessel beam with orbital angular momentum has the property of nondiffraction. Hence, the Bessel beam carrying orbital angular momentum has great research potential. In this work, a wideband transmission metasurface for generating Bessel beam carrying OAM is designed, fabricated, and measured. And it is the first experimental to show that the Bessel beam carrying OAM has higher gain and lower crosstalk than the traditional OAM wave in far field transmission.     

Transformation optics‐based horn antenna for focusing orbital angular momentum beams

In this article, a transformation optics (TO)‐based orbital angular momentum antenna is presented. By applying the coordinate transformation, the electromagnetic wave can be arbitrarily manipulated. A TO‐based horn antenna working at 5 GHz is designed. The simulation results show that by adopting the proposed TO‐based filling, the main lobe angle is reduced by 4° and the maximum gain is improved by 6.4 dB. At the same time, the proposed horn antenna has high aperture efficiency.     

Implementing orbital angular momentum modes using single‐fed rectangular patch antenna

Wireless transmission based on orbital angular momentum (OAM) can improve spectrum utilization, but it requires effective OAM mode generation. Using the characteristic mode analysis, it is easy to obtain degenerate mode distributions of the symmetric rectangular patch. The coupling phase difference of 90° between two degenerate modes can be implemented by disrupting the symmetry. In that case, a single feed structure located at the common position of equal mode current amplitudes can excite two degenerate modes to synthesize OAM modes. When the fundamental degenerate modes of the rectangular patch antenna are used, only the field component along the beam direction has the characteristics of the first order OAM. To achieve higher order OAM modes, the patch structure should be further adjusted. By introducing slots in the patch edges and grounding the patch at its center, the single‐fed rectangular patch antenna can radiate the vortex wave carrying the second order OAM. Furthermore, the OAM mode performance such as mode purity can be analyzed by the modal excitation coefficients.     

Generation of Bessel beams with 3D‐printed lens

In this article, the 3D‐printed dielectric lens is proposed to generate Bessel beam in millimeter‐wave band. The dielectric lens is made of many square unit cells with the side length of a half wavelength. The unit cells with different thicknesses generate different insertion phase shift to the transmitted millimeter wave. The insertion phase distribution of the lens is calculated by comparing the phase distributions of the incident Gaussian beam and the desired output Bessel beam. Three types of lenses are simulated and fabricated using 3D printing technology with Nylon. The measured magnitude and phase distributions of zero‐order Bessel beam agree with the simulated results very well and the measured phase distributions of the first‐order Bessel beam carry orbital angular momentum.     

Pattern synthesize of a cylindrical conformal array antenna by PSO algorithm

Pattern synthesize of conformal array antennas is often a challenging problem. Various optimization algorithms such as genetic, particle swarm optimization (PSO), and invasive weed optimization have already been used for pattern synthesizing of conformal arrays. In this paper, a focused beam is synthesized for a quarter cylindrical conformal array antenna using the PSO algorithm with small computations. The desired pattern is a focused beam at θ = 90° and ? = 45° with 10° beamwidth in elevation and 15° beamwidth in azimuth with ?20 dB side‐lobe level. This method can be used in general for synthesizing arbitrary desired patterns and array geometries.     

Efect of atmospheric turbulence on the orbital angular momentum of hollow vortex beams

The phase fluctuation of Laguerre-Gaussian(LG)vortex beams induced by atmospheric turbulence afects the quantum phase associated with azimuth coordinates and afects the orbital angular momentum of the vortex beams.The measurement of orbital angular momentum is afected by the change in the classical phase and the quantum phase in the Hilbert space.This paper analyzes the additional random complex phase of the vortex beam generated by the atmospheric turbulence and discusses the efect of atmospheric turbulence on the orbital angular momentum of an LG vortex beam using the photon state-vector function.The distributions of the classical phase of vortex beams afected by turbulence of diferent strengths are calculated and compared with the case for LG vortex beams transmitted through free space.Results show that the atmospheric turbulence afects the phase value of LG vortex beams transmitted in the external feld and signifcantly afects the beam phase structure in the near feld.However,the efect of turbulence on the phase of vortex beams is insignifcant for a transmission range z>2000 m while the phase values vary slowly and gradually become constant.     

A dual‐polarized cylindrical conformal array antenna suitable for unmanned aerial vehicles

A dual‐polarized X‐band conformal array antenna is presented for unmanned aerial vehicles with polarimetric radars/sensors. Starting from the planar structure, the array antenna consisted of sixteen 2 × 2 subarrays is conformal to the cylinders with various curvature radii to fit the payload box of the airborne vehicle. The return losses are almost constant even if the curvature radius changes. Measured radiation patterns are compared with various curvatures at the same frequencies. The array can be easily placed on the aircraft payload or fuselage due to its ultra thin thickness, ultra lightweight, and conformal structure, which has potential airborne applications in polarimetric radar surveillance, remote sensing, and wireless communications. © 2010 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2011.     

X波段的圆极化微带共形阵天线的仿真与设计

为了满足X频段机载雷达天线的指标要求,使得矩形平面天线与柱面共形,通过并联侧馈方式进行馈电。在微带共形阵天线的相关理论基础上,阵元采用介电常数2.2,厚度为0.5mm的介质基板。通过HFSS12对微带共形阵天线进行仿真设计并优化。实验结果表明,在X波段内实现了方位面的全向扫描,实测阻抗带宽为9.80-10.20GHz,最大增益可达10dB,全向辐射性能稳定,满足了指标要求。     

Trunk motion control during the flight phase while hopping considering angular momentum of a humanoid

In previous studies, various stabilizing control methods for humanoids during the stance phase while hopping and running were proposed. Although these methods contribute to stability while hopping and running, it is possibility that the control during the flight phase could also affect the stability. In this study, we investigated whether the control during the flight phase can affect the stability of a humanoid while running. To achieve stable hopping, we developed a control system that accounts for the angular momentum of the whole body during the flight phase. In this system, the angular momentum generated by the motion of the lower body in each time interval is calculated during the flight phase, and the trunk joints are controlled to generate the angular momentum necessary to compensate for the deviation of the waist posture, which is used as the reference point for the motion coordinate system of the robot. Once the proposed control system was developed and simulated, we found that the hopping duration in the unconstrained state was extended.     

基于轨道角动量的双频阵列天线的设计与分析

随着通信技术的蓬勃发展,通信频带变得越来越拥挤。为了提升频谱效率和信道容量,基于轨道角动量的思想,以同轴馈电的贴片微带天线为阵元,设计了一种可以携带轨道角动量涡旋电磁波的双频微带阵列天线。HFSS的仿真结果表明,该天线的-10 dB带宽为11.37～22.77 GHz和25.06～31.71 GHz,可以产生多种模态值的OAM波束,而且各个模态的OAM波束具有良好的对称性和旋转性,并且在中心频率21 GHz和27 GHz能同时产生OAM涡旋电磁波。该系统在未来的移动通信(6G)具有广阔的应用前景。     

A 2 × 2 array antenna with circular polarization and conical beam radiation

A circular disk patch antenna loaded with a hemi‐circular slot is initially proposed for achieving circular polarization (CP). To exhibit broad CP bandwidth that can cover the WLAN 2.4 GHz operating band, the patch antenna is fed by an L‐shaped probe. To further attain conical beam radiation with peak gain of ～8 dBic at ±30 degrees theta angle (θ), a 2 × 2 array type is proposed in this study, in which four circular disk patch array elements are arranged in a sequentially rotated fashion via a corporate feed network. Here, desirable 3‐dB axial ratio (AR) bandwidth and 10‐dB impedance bandwidth of ～5% and 21% were measured. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE 24:223–228, 2014.     

An efficient method of generating vortex electromagnetic wave based on double‐layer transmissive metasurface

A broadband double‐layer transmissive metasurface (TMS) for effective generate vortex electromagnetic wave is presented in this paper. The proposed TMS consists of two types of elements. The first element is composed of a multi‐resonant dipole and four metal vias. The metal vias increase the coupling strength between the upper and lower layers to improve transmission efficiency. On the basis of the first element, the second element adds stubs to ensure sufficient phase shift. The far‐field cross polarisation is eliminated by special element arrangement. Then, a centre‐fed linear polarisation TMS is designed to generate orbital angular momentum beams with mode l = ? 1. The proposed TMS is designed, manufactured and measured to verify the proposed design. The measured results indicate that a maximum gain of 20.8 dBi and narrow divergence angle of ±5° are achieved at 18 GHz. Furthermore, mode purity is higher than 86.1% within the 17 to 19 GHz band. The proposed double‐layer TMS saved costs, reduced weight and without assembly error is a good candidate for OAM generator.     

Design of conical DRH antennas for K and Ka frequency bands

Two conical double‐ridged horn (DRH) antennas for K and Ka frequency bands are presented. Detailed simulation and experimental investigations are conducted to understand their behaviors and optimize for broadband operation. The designed antennas were fabricated with 0.01 mm accuracy and satisfactory agreement of computer simulations and experimental results was obtained. The designed conical DRH antennas have voltage standing wave ratio (VSWR) less than 2.1 and 2.2 for the frequency ranges of 18–26.5 GHz (K band) and 26.5–40 GHz (Ka band), respectively. Meanwhile, the proposed antennas exhibit low cross‐polarization, low sidelobe level, and simultaneously achieve slant polarization as well as symmetrical radiation patterns in the entire operating bandwidth. An exponential impedance tapering is used at the flare section of the horns. Moreover, a new cavity back with a conical structure is used to improve the VSWR. Numerous simulations via Ansoft HFSS and CST Microwave Studio CAD tools have been made to optimize the VSWR performance of the designed antennas. Simulation results show that the VSWR of the proposed antennas is sensitive to the probe spacing from the ridge edge and the cavity back structure. The designed conical DRH antennas are most suitable as a feed for the reflectors of radar systems and satellite applications. Results for VSWR, far‐field E‐plane and H‐plane radiation patterns, and gain of the designed antennas are presented and discussed. © 2011 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2011.     

Quasistatic analysis of cylindrical coplanar waveguide with multilayer dielectrics

CAD-oriented analytic formulas are given for calculating the quasistatic parameters of the cylindrical CPW with three dielectrics. The effects of the dielectric materials on the quasistatic characteristics are investigated by using conformal mapping techniques. The calculated results are compared with those obtained for a corresponding planar CPW and a cylindrical CPW with a single dielectric. The curvature effects on the quasistatic characteristics are discussed. Moreover, the present expressions can also be extended to the cylindrical CPW with multilayer dielectrics. © 1998 John Wiley & Sons, Inc. Int J RF and Microwave CAE 8: 303–314, 1998.     

箭载共形相控阵卫星数据链通信仿真研究

利用中继星作为通信中继,在运载火箭发射的全程中火箭与中继星都视线可见,不存在遮挡,可以实现对运载火箭的不间断测控。文章对运载火箭共形相控阵卫星数据链传输过程中的自由空间衰减、大气衰减、火焰衰减、极化衰减、天线指向误差损耗、雨衰等进行了分析,并对火箭飞行过程中,S波段箭载共形相控阵卫星数据链的安全裕度进行了仿真。     

柔性梁线接触碰撞的动力学建模和实验研究

研究作旋转运动的柔性梁的线接触正碰撞问题.基于Goldsmith的线接触撞击力模型,分别用基于小变形的混合坐标法和基于大变形的绝对坐标法建立了柔性梁的动力学方程,考虑了几何非线性效应.在此基础上,进一步考虑非线性阻尼项的影响,将Hunt,Crossley的阻尼模型推广到线接触问题.介绍了柔性梁线接触碰撞的实验方法.计算结果显示,在考虑阻尼的情况下,计算结果与实验结果吻合很好.比较了混合坐标法和绝对坐标法的撞击力计算结果,与实验结果对比表明,绝对坐标法更适用于大变形的撞击问题.     

Synthesis of concurrent multibeam and conical beam antenna arrays

An approach is presented to synthesize linear and planar antenna arrays to have concurrent multibeam radiation patterns as well as desired sidelobe levels. This approach is based on zeros perturbation of the pattern of linear arrays. Multibeam planar arrays are synthesized by both multiplying and transforming multibeam linear arrays. Besides, planar arrays having conical or ring type beam are synthesized by applying a special transformation to dual‐beam linear arrays. Some examples are brought to verify the effectiveness of the proposed approach for both linear and planar arrays.     

Attitude manoeuvre of spacecraft with long cantilever beam appendage by momentum wheel

Attitude manoeuvre of spacecraft with a long cantilever beam appendage by momentum wheel is studied. The dynamics equation of the main body is derived by conservation of angular momentum. The dynamics equation of the appendage is derived by force equilibrium principle. Two feedback control strategies of the momentum wheel are applied for the attitude manoeuvre of the main body. The lateral vibration of the appendage is suppressed by active control in proportion to its lateral displacement and velocity. The variation of residual nutation angle of the spacecraft or the residual transversal angular velocity of the main body in the manoeuvre process is researched with changes of steady state time of the manoeuvre, appendage parameters, control parameters on the appendage and appendage location. In addition, spacecraft response is researched when there are no active controls on the appendage.