Dual-mode Orbital Angular Momentum Research Articles

Frequency-polarization multiplexing reflective metasurface for orbital angular momentum generation

Frequency-polarization multiplexing metasurfaces (FPMMSs) capable of generating vortex beams carrying orbital angular momentum (OAM) have facilitated the actualization of high information capacity in optical and microwave communication. However, poor frequency controllability and the deficiency of theoretical methodology for frequency modulation of meta-atom remain challenges for existing FPMMSs with orthogonal linear polarization. In this work, a strategy to customize the operating band of the “I”-shaped meta-atom (ISMA) based on phase analysis of the equivalent circuit is proposed. A frequency modulation factor is introduced to adjust the operating band of the ISMA over a wide range based on the relationships between element geometry parameters, capacitance and inductance values in the equivalent circuit model, and the reflected phase of ISMA-type meta-atom. Then, a dual-band dual-polarized meta-atom is proposed by placing subunits operating at different bands cross-orthogonally, allowing the subunits to modulate the phase independently. A dual-band dual-polarized dual-mode OAM beam generator is designed and constructed as a proof-of-concept to verify the methodology. The measured results are in excellent agreement with the simulations. The proposed methodology for customizing frequencies establishes the groundwork for the implementation of OAM-based FPMMSs for secure and high-capacity communication in 6G massive-MIMO systems.

Frequency-adjustable OAM antenna with co-divergent beams for IoT applications

A frequency-tunable Orbital Angular Momentum (OAM)-generating antenna array system is introduced for the first time to provide high-data-rate and secure communication for Internet of Things (IoT) infrastructures and devices. Propagation of simultaneous OAM modes brings about the high-data-rate and frequency tunability leads to interference suppression for secure communication. Regarding the design evolution of the proposed structure, the novel Multiple-Input-Multiple-Output (MIMO) antenna consisting of two input ports creates a 2 × 2 UCA, resulting in two 2 × 2 sub-UCA. Feeding each 2 × 2 sub-array with [0°, 90°, 180°, 270°] phase gradients in clockwise and counterclockwise states gives rise to dual-mode OAM-carrying waves with simultaneous excitation capability. It should be mentioned that each MIMO element owns frequency tunability, resulting in a frequency-adjustable dual-mode OAM antenna array. A prototypes of the suggested MIMO antenna as well as the OAM array are fabricated and measured. Changing the applied DC-voltage to the varactor diodes embedded in capacitive stubs of the antenna elements shifts the operating frequency in the MIMO antenna and consequently in the OAM array. Concerning the unique radiation characteristics of the OAM antenna, vortex beams having helical phase fronts are observed, confirming the generation of expected OAM waves. Therefore, it is asserted that the introduced structure, for the first time, proposes new features of frequency-tunability, and co-divergent simultaneous OAM propagation using the MIMO-UCA technique to provide high-data-rate and secure communication in IoT applications.

Generation of multi-OAM beams using a compact dual-mode source and a 3D-printed Luneburg lens.

In this paper, a Luneburg lens-based multi-beam orbital angular momentum (OAM) antenna is proposed to achieve the 2D beam scanning capability of dual-mode OAM beams. The proposed design is composed of nine compact dual-mode antennas as sources, and a 3D-printed Luneburg lens. The sources, i.e., octagonal patch antennas, can radiate both right-handed circularly polarized (RHCP) and left-handed circularly polarized (LHCP) OAM beams with mode number l = ±1 by switching the input ports. Then, the sources are put at multiple focal points of the Luneburg lens to generate the OAM beams in different directions, and the directivities of the OAM beams are also enhanced by the Luneburg lens. The proposed design can realize nine dual-mode OAM beams with ±30° beam scanning range in two orthogonal planes. It should be noted that the proposed design can be expanded to achieve a larger number of beams with a periodic extension of the source antennas, also a wider beam scanning range with a Luneburg lens of a larger radius.

이중 모드 OAM 통신을 위한 간단한 급전 구조를 가진 균일 원형 배열 안테나

In this paper, we propose a uniform circular array antenna with a simple feeding structure operating in the 5.2 GHz band for orbital angular momentum (OAM) mode multiplexing. The proposed antenna can generate simultaneously two types of OAM modes (l=±2) using eight radiating patches and a feed circuit consisting of one hybrid coupler and two concentric series-parallel feedlines. Because the two feedlines are designed concentrically with different radii, they do not intersect each other in the same plane, thus having the advantage of being spatially efficient. The successful creation of the two OAM modes was confirmed through the measured radiation pattern and helical phase distribution. The dual-mode OAM transmission test shows that the proposed antenna can be successfully employed for OAM mode multiplexing by obtaining >12.4 dB of isolation between the two OAM mode channels.

Multitarget Position-Sensitivity Security Transmission with OAM-DM Based on FDA

The multitarget position-sensitivity security transmission scheme with orbital angular momentum (OAM) directional modulation (DM) waveform using the uniform circular frequency diverse array (FDA) is proposed. The transmitter employs FDA to generate dual-mode range-dependent OAM beam pattern, and the direction information of OAM beam is modulated into the signal. According to the modulation method, orthogonal carrier frequency can be designed to realize multitarget position-dependent OAM pattern. In the undesired position, the intensity pattern and the phase front of the radio beam vary randomly with the digital transmission sequence. Because modulation waveform is position-dependent, the technique offers security, as the signal can be purposely distorted in other positions. The composite dual-mode OAM signal makes it more difficult for eavesdroppers to demodulate correct messages. The receiver with a single antenna employs the phase compensation and helical phase factor to restore the correct digital signal in the desired position. Numerical results show that multitarget position-sensitivity OAM-DM technology based on FDA offers the security transmission scheme.

A Low-Divergence Circularly Polarized Dual-Mode OAM Antenna Based on Higher Order Laguerre–Gaussian Modes

An open resonator antenna for orbital angular momentum (OAM) generation and dual-mode application is proposed. The excitation of OAM mode is deduced by the open resonator theory and the circular array theory. In the cavity, eight aperture coupled patch antenna elements are used to excite two higher-order Laguerre-Gaussian HE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">21</sub> modes with a 90° phase difference. Verifying by simulation and experiment, the proposed low-profile antenna can radiate left-hand or right-hand circularly polarized waves of OAM modes l=±1, which have a relatively low divergence angle of ±9° and high gain of around 13 dBi.

High-efficiency transmissive metasurface for dual-polarized dual-mode OAM generation

In this paper, a high-efficiency dual-polarized transmissive metasurface is presented for the generation of dual-mode convergent orbital angular momentum (OAM) beams. The proposed transmissive metasurface is composed of dual-polarized metasurface units, which are constructed from four stacked patches coupled through a Jerusalem-cross aperture on the interlayer ground, to complete the phase modulation for the orthogonal polarizations. The proposed transmissive metasurface units can achieve full 2π phase modulation along with low transmission loss. Converged OAM beams with modes numbers ℓx = +1 and ℓy = −2 are thus stimulated through the proposed transmissive metasurface for both orthogonal polarizations, which have been demonstratednumerically andexperimentally.

Constructing dual-frequency OAM circular patch antenna using characteristic mode theory

The current wavemodes and their distribution features of the circular patch are analyzed by using the characteristic mode theory. Then, the corresponding characteristic modes are selected and the feed structure is designed to generate the vortex waves carrying orbital angular momentum (OAM), based on the idea that the OAM mode can be realized by combining two orthogonal degenerate modes. The experimental results show that the proposed antenna can effectively implement dual-frequency dual-mode OAM waves. The first-order OAM mode of the electric field component in beam axis z direction is realized at low frequencies, while the second-order OAM mode of the z-component field is obtained at high frequencies. The phase fluctuation of the OAM modes can be explained by the excitation coefficient of the characteristic mode with quantitative properties.

An Inner- and Outer-Fed Dual-Arm Archimedean Spiral Antenna for Generating Multiple Orbital Angular Momentum Modes

Orbital angular momentum (OAM) beams have attracted great attention owing to their excellent performances in imaging and communication. In this paper, a dual-arm Archimedean spiral antenna (DASA) is proposed to generate multiple OAM states with positive and negative values by feeding at the inner and outer ends, respectively. The topological charge of radiated vortex waves is reconfigurable by tuning the operating frequency. Dual-mode OAM states are generated at different working frequencies (l = ±1 at 3 GHz, l = ±2 at 4 GHz, and l = ±3 at 4.8 GHz). Both the simulation and measurement results demonstrate that OAM beams can be generated effectively by the DASA. In addition, a conical cavity is used to increase the gain of the proposed DASA for more than 5 dBi in comparison to the traditional cylindrical cavity. Furthermore, the qualities of the generated OAM modes by the proposed DASA have been evaluated at different operating frequencies of 3 GHz, 4 GHz, and 4.8 GHz, respectively. The OAM modes purities of l = −1, −2, −3, 1, 2, and 3 are predominate with the proportion of about 81%, 70%, 74%, 78%, 77%, and 75%, respectively. Our results demonstrate that the proposed DASA has great potentials in OAM multiplexing communication systems.

A High-Gain Transmitarray for Generating Dual-Mode OAM Beams

This paper proposes a novel transmitarray antenna which can achieve high gain and produce dual-mode orbital angular momentum (OAM) beams in Ku -band. Two back-to-back wideband dual-polarized microstrip antennas are employed as the unit cells, which are connected using metalized via holes. Full 360° phase ranges can be obtained by varying the length of feeding lines in two orthogonal polarizations. Due to high isolation between the two orthogonal polarizations, dual-mode OAM beams can be formed simultaneously by tuning phase distributions in x- and y-polarizations, respectively. The approach for generating OAM beams is explained. To verify this concept, one prototype carrying 0 and +1 mode OAM beams is designed, fabricated, and measured. Experimental results demonstrate that both 0 and +1 mode OAM beams can be generated successfully, and the measured results agree well with the simulated results. Because of high directivity and focusing effects of transmitarray, the proposed +1 mode OAM beam has stable performance at a long propagation distance. The maximum gain reaches 26 and 20 dBi in 0 and +1 mode OAM beams, respectively. Meanwhile, a narrow divergence angle of ±5° is obtained in +1 mode OAM beam. Compared with other OAM antennas reported, main advantages of the proposed antenna include high gain, narrow divergence angle, low cost, planar structure, and the capability of producing dual-mode OAM beams.

Experimental Array for Generating Dual Circularly-Polarized Dual-Mode OAM Radio Beams

Recently, vortex beam carrying orbital angular momentum (OAM) for radio communications has attracted much attention for its potential of transmitting multiple signals simultaneously at the same frequency, which can be used to increase the channel capacity. However, most of the methods for getting multi-mode OAM radio beams are of complicated structure and very high cost. This paper provides an effective solution of generating dual circularly-polarized (CP) dual-mode OAM beams. The antenna consists of four dual-CP elements which are sequentially rotated 90 degrees in the clockwise direction. Different from all previous published research relating to OAM generation by phased arrays, the four elements are fed with the same phase for both left-hand circular polarization (LHCP) and right-hand circular polarization (RHCP). The dual-mode operation for OAM is achieved through the opposite phase differences generated for LHCP and RHCP, when the dual-CP elements are sequentially rotated in the clockwise direction. The measured results coincide well with the simulated ones, which verified the effectiveness of the proposed design.

A Low-Profile Dual-Polarized Microstrip Antenna Array for Dual-Mode OAM Applications

A dual-polarized dual-mode orbital angular momentum (OAM) microstrip antenna array is presented. The OAM radio beams are generated by employing a four-element antenna array with specific excitation. Each antenna element is an aperture-coupled microstrip patch antenna with a low profile of $0.1\lambda _{{\rm{0}}}$ . The quasi-cross-shaped aperture is excited by a U-shaped and an M-shaped microstrip feedline, which leads to two orthogonal polarizations. By adopting two types of phase-shifting schemes, the antenna array can be used to produce dual-mode OAM waves ( ${\rm{l}} = \pm 1$ ). The measured results show that the proposed antenna array has achieved good impedance matching over the band of 5.4–5.6 GHz, and a port-to-port isolation better than 25 dB. Moreover, the rotational phase fronts indicate waves properly bearing OAM with different states.