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Design Constrains in three Configurations of UCAs for Distortion Free Orbital Angular Momentum Modes Generation
Antenna array is one of the methods which can generate Orbital Angular Momentum (OAM) waves. However, OAM waves generated by different antenna arrays have different characteristics of Electric-field (E-field) components’ distribution and radiation patterns. In order to solve this problem, we derive E-field formulas of OAM waves generated by different kinds of dipole antenna array in this paper. The dipole antenna arrays are arranged by three methods: 1) antenna elements are in the same direction of y axis, 2) antenna elements are in the radial direction and 3) antenna elements are in the azimuthal direction. Results show that x components, y components and z components carry different OAM modes under the three conditions. Simulation results show that the same direction antenna array produces the best OAM waves because the y component is dominated by OAM mode l and RHCP/LHCP waves are negligible in energy, while the pure OAM waves carried by the z components generated by the other two antenna arrays have little energy. In addition, only the radiation pattern of l=0 produced by the same direction antenna array does not have a null zone in the propagation direction. Radiation patterns of l=±1 do not have null zones in the propagation direction generated by the other two antenna arrays.
By enabling very high bandwidth for radio communications, the millimeter-wave (mmWave), which can easily be integrated with massive-multiple-input-multiple-output (massive- MIMO) due to small antenna size, has been attracting growing attention as a candidate for the fifth-generation (5G) and 5Gbeyond wireless communications networks. On the other hand, the communication over the orthogonal states/modes of orbital angular momentum (OAM) is a subset of the solutions offered by massive-MIMO communications. Traditional massive-MIMO based mmWave communications didn’t concern the potential spectrum-efficiency-gain (SE-gain) offered by orthogonal states of OAM. However, the highly expected maximum SE-gain for OAM and massive-MIMO communications is the product of SEgains offered by OAM and multiplexing-MIMO. In this paper, we propose the OAM-embedded-MIMO (OEM) communication framework to obtain the multiplicative SE-gain for joint OAM and massive-MIMO based mmWave wireless communications. We design the parabolic antenna for each uniform circular array antenna to converge OAM signals. Then, we develop the mode-decomposition and multiplexing-detection scheme to obtain the transmit signal on each OAM-mode of each transmit antenna. Also, we develop the OEM-water-filling power allocation policy to achieve the maximum multiplicative SE-gain for OEM communications. The extensive simulations obtained validate and evaluate our developed parabolic antenna based converging method, mode-decomposition and multiplexing-detection scheme, and OEM-water-filling policy, showing that our proposed OEM mmWave communications can significantly increase the spectrum-efficiency as compared with traditional massive-MIMO based mmWave communications.
Monopole patch antenna systems, which can generate orbital angular momentum (OAM) waves at 2.4GHz, are proposed in this paper. The proposed antenna systems have advantages of simple planar structure and small size of antenna element. Design, simulation, fabrication and measurement of the proposed antenna systems are presented. Two feeding networks, which constitute the proposed antenna systems with monopole patch antenna array, are designed to generate modes 1 and 2 of OAM waves. The antenna systems for both modes are shown to be effective in generating OAM waves of modes 1 and 2 from both simulation and three types of measurement: radiation pattern, phase distribution and phase gradient. Simulation and measurement results of radiation pattern and phase distribution have shown very close results. Phase gradient measurement results has verified that the generated waves from the antenna systems are indeed OAM waves.
This paper gives a feasible and simple solution of generating OAM-carrying radio beams. Eight Vivaldi antenna elements connect sequentially and fold into a hollow cylinder. The circular Vivaldi antenna array is fed with unit amplitude but with a successive phase difference from element to element. By changing the phase difference at the steps of 0, ±45°, ±90°, ±135°, and 180°, the OAM radio beam can be generated with mode numbers 0, ±1, ±2, ±3, and 4. Simulations show that the OAM states of ±2 and ±3 are the same as the traditional states, while the OAM states of 0, ±1, and 4 differ at the boresight. This phenomenon can be explained by the radiation pattern difference between Vivaldi antenna and tripole antenna. A solution of distinguishing OAM states is also proposed. The mode number of OAM can be distinguished with only 2 receivers.
The experimental evidence that radio techniques can be used for synthesizing and analyzing non-integer electromagnetic (EM) orbital angular momentum (OAM) of radiation is presented. The technique used amounts to sample, in space and time, the EM field vectors and digitally processing the data to calculate the vortex structure, the spatial phase distribution, and the OAM spectrum of the radiation. The experimental verification that OAM-carrying beams can be readily generated and exploited by using radio techniques paves the way to an entirely new paradigm of radar and radio communication protocols.
Novel measurement and approximation methodologies for studying orbital angular momentum (OAM) modes in radio beams, i.e., electromagnetic beam modes having helical phase fronts, are presented. We show that OAM modes can be unambiguously determined by measuring two electric field components at one point, or one electric field component at two points.
In a series of fundamental proof-of-principle experiments, comprising
numerical, controlled laboratory, and real-world experimentation, we have shown
that it is possible to use the angular momentum physical layer for radio
science and radio communication applications. Here we report a major, decisive
step toward the realization of the latter, in the form of the real-world
experimental demonstration that a radio beam carrying orbital angular momentum
(OAM) can readily be digitally phase shift modulated and that the information
thus encoded can be effectively transferred in free space to a remote receiver.
The experiment was carried out in an urban setting and showed that the
information transfer is robust against ground reflections and interfering radio
signals. The importance of our results lies in the fact that digital phase
shift keying (PSK) protocols are used in many present-day wireless
communication scenarios, allowing new angular momentum radio implementations to
use methods and protocols that are backward compatible with existing linear
momentum ones.
Recent discoveries concerning rotating (helical) phase fronts and orbital angular momentum (OAM) of laser beams are applied to radio frequencies and comprehensive simulations of a radio OAM system are performed. We find that with the use of vector field-sensing electric and magnetic triaxial antennas, it is possible to unambiguously estimate the OAM in radio beams by local measurements at a single point, assuming ideal (noiseless) conditions and that the beam axis is known. Furthermore, we show that conventional antenna pattern optimization methods can be applied to OAM-generating circular arrays to enhance their directivity.
We have shown experimentally that it is possible to propagate and use the properties of twisted non-monochromatic incoherent radio waves to simultaneously transmit to infinity more radio channels on the same frequency band by encoding them in different orbital angular momentum states. This novel radio technique allows the implementation of, at least in principle, an infinite number of channels on one and the same frequency, even without using polarization or dense coding techniques. An optimal combination of all these
physical properties and techniques represents a solution for the problem of radio band congestion. Our experimental findings show that the vorticity of each twisted electromagnetic wave is preserved after the propagation, paving the way for entirely new paradigms in radio communication protocols.
Laser light with a Laguerre-Gaussian amplitude distribution is found to have a well-defined orbital angular momentum. An astigmatic optical system may be used to transform a high-order Laguerre-Gaussian mode into a high-order Hermite-Gaussian mode reversibly. An experiment is proposed to measure the mechanical torque induced by the transfer of orbital angular momentum associated with such a transformation.
We show numerically that vector antenna arrays can generate radio beams that exhibit spin and orbital angular momentum characteristics similar to those of helical Laguerre-Gauss laser beams in paraxial optics. For low frequencies (< or = 1 GHz), digital techniques can be used to coherently measure the instantaneous, local field vectors and to manipulate them in software. This enables new types of experiments that go beyond what is possible in optics. It allows information-rich radio astronomy and paves the way for novel wireless communication concepts.
The orbital angular momentum (OAM or vortex) waves are expected to provide ten-fold and larger increases in
wireless data rates, required for short-range communications within the beyond 5G and 6G concept of allconnected
life and industry. We address the specifics of short-range communications employing OAM-carrying
waves generated by small uniform circular arrays (UCAs) at lower, i.e., 10 GHz, transmission frequencies. Comparing
the link budgets obtained using (i) asymptotic analytical formulas, (ii) numerical electromagnetic simulations,
and (iii) measurements on two pairs of manufactured prototypes comprising 8 microstrip-patch-element
UCAs, we point out the limitations of simplified models which do not account for various effects, such as coupling,
parasitic radiation, and insertion loss. The observed effects are expected to be relevant at millimeter-wave
frequencies as well.
The vortex electromagnetic waves carrying the orbital angular momentum (OAM) are an increasing subject of study, and the design of a system capable of generating such waves is also of crucial importance. In this letter, a helical circular array (HCA) has been proposed to generate OAM radio beams. The proposed HCA has a more straightforward and more feasible scheme when compared to uniform circular arrays (UCAs) that require additional phase-shifting devices to form inter-element phases. The heights of the proposed HCA elements along the z-axis are exploited to generate the different OAM modes. For the high-order OAM modes, the height of the HCA is made more compact with the help of the proposed helical circular subarray (HCSA) configurations with spiral phase positions providing a linear phase delay with the azimuth angle. In addition, at high mode values, the HCSA structure creates a smoother OAM vortex beam than HCA. The full-wave simulation results show that the proposed HCA scheme can be used to generate vortex electromagnetic waves with a spiral phase wavefront structure.
Line-of-sight wireless communications can benefit from the simultaneous transmission of multiple independent data streams through the same medium in order to increase system capacity. A common approach is to use conventional spatial multiplexing with spatially separated transmitter/receiver antennae, for which inter-channel crosstalk is reduced by employing multiple-input-multiple-output (MIMO) signal processing at the receivers. Another fairly recent approach to transmitting multiple data streams is to use orbital-angular-momentum (OAM) multiplexing, which employs the orthogonality among OAM beams to minimize inter-channel crosstalk and enable efficient (de)multiplexing. In this paper, we explore the potential of utilizing both of these multiplexing techniques to provide system design flexibility and performance enhancement. We demonstrate a 16 Gbit/s millimeter-wave link using OAM multiplexing combined with conventional spatial multiplexing over a short link distance of 1.8 meters (shorter than Rayleigh distance). Specifically, we implement a spatial multiplexing system with a 2 × 2 antenna aperture architecture, in which each transmitter aperture contains two multiplexed 4 Gbit/s data-carrying OAM beams. A MIMO-based signal processing is used at the receiver to mitigate channel interference. Our experimental results show performance improvements for all channels after MIMO processing, with bit-error rates of each channel below the forward error correction limit of 3.8 × 10
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. We also simulate the capacity for both the 4 × 4 MIMO system and the 2 × 2 MIMO with OAM multiplexing. Our work indicates that OAM multiplexing and conventional spatial multiplexing can be simultaneously utilized to provide design flexibility. The combination of these two approaches can potentially enhance system capacity given a fixed aperture area of the transmitter/receiver (when the link distance is within a few Rayleigh distances).
Exploiting orbital angular momentum (OAM) to implement spatially multiplexed links is an active research topic, both at radio and optical frequencies. We focus on using, in the microwave range, superpositions of modes having opposite OAM values. As known, this approach simplifies dramatically the spatial field distributions, especially in phase. We stress the consequent implementation advantages, and test them experimentally, on an ad-hoc link, about 100 m long, at the unlicensed frequency of 17.2 GHz, in an urban environment. Results are compared with numerical simulations. Performances are discussed vs. those of a conventional MIMO system.
The Orbital-Angular-Momentum (OAM)-carrying radio waves may provide extra rotational degree of freedom, which may potentially increase channel capacity and spectrum efficiency for future wireless communications. It has been demonstrated that circular antenna array could radiate OAM-carrying radio beam by feeding each element with certain phase offset. In this paper, by proper analyses and extensive simulations on the spatial amplitude and phase characteristics of the radiated electromagnetic field under three different array configurations, i.e., radial array, tangential array, and uniform circular array (UCA), respectively. We found that among the above settings UCA is the best way to generate the desired OAM-carrying beam with linear excitation. We then use multiple concentric antenna rings with elements of half-wave dipoles to generate and demultiplex multiple OAM states, and both spectral analyses and simulations verified the feasibility.
This paper describes the design of an 8-element circular phased patch array antenna which can generate radio beams carrying orbital angular momentum at 10 GHz. Realistic antenna design issues are discussed, including mutual coupling and the array performance when operating in different OAM states.
We demonstrate successful transmission of 4-Gbps uncompressed video over a 60-GHz orbital angular momentum (OAM) wireless channel. Matlab simulation was employed to support the experimental work and to generate the holographic masks used. Matlab coding is a unique approach which can produce any desired shape on copper or dielectric plates by mean of a commercial routing tool. We believe this is the first reported transmission of 4-Gbps uncompressed video over the 60-GHz OAM wireless channel. Good agreement was achieved between the simulated and measured results. Practical opportunities for multi-gigabit future wireless communications are available.
In order to achieve multi-gigabit transmission (projected for 2020) for the use in interplanetary communications, the usage of large number of time slots in pulse-position modulation (PPM), typically used in deep-space applications, is needed, which imposes stringent requirements on system design and implementation. As an alternative satisfying high-bandwidth demands of future interplanetary communications, while keeping the system cost and power consumption reasonably low, in this paper, we describe the use of orbital angular momentum (OAM) as an additional degree of freedom. The OAM is associated with azimuthal phase of the complex electric field. Because OAM eigenstates are orthogonal the can be used as basis functions for N-dimensional signaling. The OAM modulation and multiplexing can, therefore, be used, in combination with other degrees of freedom, to solve the high-bandwidth requirements of future deep-space and near-Earth optical communications. The main challenge for OAM deep-space communication represents the link between a spacecraft probe and the Earth station because in the presence of atmospheric turbulence the orthogonality between OAM states is no longer preserved. We will show that in combination with LDPC codes, the OAM-based modulation schemes can operate even under strong atmospheric turbulence regime. In addition, the spectral efficiency of proposed scheme is N2/log<sub>2</sub>N times better than that of PPM.