CN106329108B - Multi-mode OAM electromagnetic vortex wave array antenna with double-ring structure - Google Patents
Multi-mode OAM electromagnetic vortex wave array antenna with double-ring structure Download PDFInfo
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- H—ELECTRICITY
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- H—ELECTRICITY
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Abstract
The invention discloses a multi-mode OAM electromagnetic vortex wave array antenna with a double-loop structure, which comprises a dielectric substrate, a plurality of groups of array elements, and coaxial feeder lines and input ports corresponding to the array elements, wherein the array elements adopt microstrip patch antennas; each group of array elements are uniformly distributed and arranged on one surface of the medium substrate along the circumference at set intervals, the other surface of the medium substrate is a ground plane, and the input ports are connected with the corresponding array elements through coaxial feeder lines. The invention can realize that electromagnetic vortex waves of a plurality of OAM modes are simultaneously generated at the same frequency point, the OAM electromagnetic vortex waves are used for multiplexing, and a plurality of coaxial data streams can be simultaneously transmitted in a single channel, thereby obviously increasing the system capacity and improving the wireless communication spectrum efficiency. Due to the use of the double-ring structure, the invention can effectively improve the quality of electromagnetic vortex wave signals, improve the directivity and gain of the electromagnetic vortex wave signals and obtain better antenna performance.
Description
Technical Field
The invention relates to the technical field of antennas, in particular to a multi-mode OAM electromagnetic vortex wave array antenna with a double-ring structure.
Background
According to classical electrodynamic theory, electromagnetic radiation can carry both energy and angular momentum, which consists of spin angular momentum (Spin angular momentum, SAM) describing the polarization state and orbital angular momentum (Orbital angular momentum, OAM) describing the helical phase structure. Spin angular momentum is related to the spin of photons and presents a circular polarization behavior, and Poynting predicts the existence of SAM at the beginning of the 20 th century, but SAM is not widely used until after Beth in 1936 has been experimentally verified, while Orbital Angular Momentum (OAM) is related to the spatial distribution of photons. In 1838, airy found that there was an abnormal halo formation at the focal plane of the lens; in 1967, boivin et al analysis found that there was a vortex in the fluence of the light ring that rotated about the focal plane axis, indicating the presence of orbital angular momentum in the light field; in 1974 Nye et al introduced the defect concept in crystals into the wave problem, demonstrating that phase defects in the wavefront are responsible for optical vortex generation; in 1979, vaughan et al analyzed the interference characteristics of beams with a helical wavefront; in 1981, baranova et al analyzed light vortices in the speckle light field, found that the light vortex generation probability was certain, and that high-topology charged light vortices could not be formed in the speckle field; in 1989, coultet et al analyzed laser cavities with high Fresnel numbers, found that the intra-cavity optical field had characteristics similar to superfluid vortices, and they used the Maxwell-Bloch model to illustrate the existence of vortex solutions from a theoretical perspective, facilitating research on the orbital angular momentum of the beam. Until 1992, significant progress was made in the study of OAM beams: allen et al demonstrate that LG spiral laser beams with a phase factor have orbital angular momentum per photon under paraxial approximation conditions, which conclusion is then generalized to the case of non-paraxial approximation. Since then, research into OAM applications has attracted tremendous interest.
One of the applications of OAM is to achieve manipulation of atoms and molecules, which mainly exploits its kinetic properties. In 1995, he et al found in experiments that orbital angular momentum of the OAM beam could be transferred to the material particles; in 1997, simpson et al further proposed that the orbital angular momentum of the beam was the same as the spin angular momentum, and that the particle could be rotated by applying a moment to it, and put forward the concept of an "optical wrench", which found that the optical tweezers system using OAM beams could bind particles much more than the optical tweezers using conventional Gaussian beams, and could achieve micro-operations such as fractionation and self-organization, gas capture and movement of micro-particles with higher efficiency, while mitigating damage to particles, which is important for the study of biomolecules, cells, bacteria, viruses, etc.
OAM is a natural attribute characterizing waveforms with helical phase structures, both in the optical and in the radio domain. OAM has been widely used in optics, and by introducing OAM, the transmission capability of an optical communication system is greatly expanded. In 2007, the application of photon orbital angular momentum to low frequency was first proposed by the Thide et al, and by simulation, it was verified that an electromagnetic vortex wave similar to a lager gaussian beam can be generated using a phased array antenna, a precedent for applying orbital angular momentum to wireless communication was opened, a concept for expanding wireless communication capacity by using electromagnetic vortex waves was proposed, and an idea of using an OAM carrier in wireless communication was inspired. In 2008, garcia-Escartin et al studied the problem of quantum multiplexing based on photonic OAM and analyzed a scheme of synthesizing quantum channels using a combiner and a multiplexer. In 2010 Mohammadi et al systematically studied the OAM beamforming method based on antenna arrays. In 2012, edfors et al suggested the use of OAM techniques in wireless communication systems. In the same year, tamburini et al, using a helical parabolic antenna and a yagi antenna, for the first time validated the feasibility of information transmission in wireless communications of electromagnetic waves carrying orbital angular momentum over a frequency band of 2.414 GHz. The experiment adopts a spiral parabolic antenna and a yagi antenna to respectively generate electromagnetic vortex waves and normal electromagnetic waves with OAM modes, and different beams are coded and transmitted on the same frequency point with different OAM mode values. Based on the device, the phase interferometer is used at the receiving end to measure the phase difference of the electric field in the wave beam, so that the anti-interference capability of the electromagnetic vortex wave is verified. Abhay et al analyzed the design method of a helical parabolic antenna by simulation; wang et al realized 2.56Tbits/s of data transmission in free space by using OAM multiplexing technology, and the spectrum utilization rate of the system reached 95.7bits/s. In 2013, bozinovic et al also realized data transmission on the order of T bits in an optical fiber using OAM multiplexing. A series of methods for OAM beamforming have been reported thereafter, for example, deng et al proposed using Vivaldi antenna arrays to generate OAM waves, bai et al used rectangular patch elements in circular array antennas, and also successfully generated OAM waves; tennant et al propose Time-switched array (TSA) that allows multiple harmonics of the array to generate OAM characteristics that can simultaneously generate OAM values for multiple modes. To sum up, to develop the theory and technology of OAM multiplexing, the problems of OAM carrier generation, transmission, and detection need to be systematically studied, so the generation method of OAM radio beam is a hotspot of current research.
Currently, in combination with research progress in the related art of orbital angular momentum, there are two main approaches to generate OAM radio waves in the radio frequency band, namely, an array antenna and a helical parabolic antenna. The array antenna generates a desired OAM mode wave by controlling the phase difference of the array element radiation fields; the spiral parabolic antenna generates OAM electromagnetic vortex waves in any mode by adjusting the distance between two ends of the parabolic opening. In 2011, b.thide et al generated electromagnetic vortex waves with modal value l=1 using a helical parabolic antenna that twists the parabolic antenna into a helical parabolic structure to form a continuous phase gradient that physically simulates the phase rotation of the attitude angleThe receiving end forms a phase interferometer by using two antennas, and the modal value of OAM is identified by using a phase interferometry. However, this type of OAM helical parabolic antenna also has significant drawbacks, such as high cost and difficulty in manufacturing, and the helical parabolic antenna structure used in the experiment is a single fixed structure, which is not suitable for continuous phase control, i.e., a certain geometry can only generate OAM waves of one mode, and this single structure cannot simultaneously generate multiple OAM modes, if different OAM waves need to be generatedThe beam has to be adjusted to the size of the opening, which is obviously not feasible in practical wireless communication systems.
Besides the electromagnetic wave carrying OAM generated by the antenna shaping mode, the array antenna is another method for generating the wave carrying OAM, different OAM modes can be generated by changing the feeding phase relation among array elements, namely, an array antenna structure is formed, and the structure can meet the requirement of generating multi-mode OAM. The electromagnetic wave power supply device comprises a plurality of antenna units and the like, wherein the antenna units and the like are regularly arranged into an array, the interference and superposition principle of electromagnetic waves is utilized, the feeding phase difference between the array elements is controlled through a feed network structure or according to a high-speed radio frequency switching technology, so that the energy radiated by the electromagnetic field can be redistributed in space, the uneven distribution of the space energy is realized, namely, the field of certain areas is enhanced, the field of certain areas is weakened, and the electromagnetic waves of different OAM modes can be generated by utilizing the principle through a mode of changing the feeding phase difference between the array elements. At present, research on generating OAM electromagnetic vortex waves by using an antenna array method is still in a simple structure with fewer array elements, most of the antenna arrays have the greatest limitation that the generated signal center gain is lower, the directivity is poorer, the mode number is higher, the phenomenon is more obvious, and the antenna array is obviously unfavorable to be applied to a communication system, so that better methods are needed to improve the antenna array.
With the explosive development of wireless communications, the demand for wireless spectrum resources is rapidly rising. However, current conventional command and control spectrum strategies result in significant spectrum underutilization, and thus, current licensed spectrum usage is not high. Frequency spectrum with low utilization and energy efficiency becomes a bottleneck problem which needs to be solved urgently for sustainable development of radio technology. As a promising approach to solve the problem of low spectral efficiency and break the current dead tie of insufficient spectral utilization, the orbital angular momentum has recently led to extensive research. Meanwhile, due to the inherent characteristics of electromagnetic vortex waves, the higher the modal value is, the worse the directivity is, and the center gain of signals in the transmission process is lower, the characteristics are unfavorable for the reception of the signals, and the OAM array antenna is a main obstacle for being widely applied to wireless communication systems.
Disclosure of Invention
The invention aims to solve the problems in the background art part by a double-loop structure multi-mode OAM electromagnetic vortex wave array antenna.
To achieve the purpose, the invention adopts the following technical scheme:
the multi-mode OAM electromagnetic vortex wave array antenna with the double-loop structure comprises a dielectric substrate, a plurality of groups of array elements, and coaxial feeder lines and input ports corresponding to the array elements, wherein the array elements adopt microstrip patch antennas; each group of array elements are uniformly distributed and arranged on one surface of the medium substrate along the circumference at set intervals, the other surface of the medium substrate is a ground plane, and the input ports are connected with the corresponding array elements through coaxial feeder lines.
Particularly, the multi-mode OAM electromagnetic vortex wave array antenna with the double-ring structure comprises 16 array elements in total, wherein eight array elements in each group are uniformly distributed and arranged on the medium substrate along the circumference at set intervals.
Particularly, the two groups of array elements are uniformly distributed and arranged on the dielectric substrate along the circumference with the radius of 0.6λ and 0.8λ respectively to form a dual-ring antenna array, wherein λ is the radiation wavelength of the dual-ring antenna array.
In particular, the array elements are fed with the same signal, and the phase difference between two adjacent array elements is 45 degrees; the radius of the dielectric substrate is 80.66mm.
Particularly, the number l of OAM modes generated by the multi-mode OAM electromagnetic vortex wave array antenna with the double-ring structure is as follows: -4 < l < 4, i.e. l= 0,l = ±1, l= ±2, l= ±3.
Particularly, the double-loop structure multi-mode OAM electromagnetic vortex wave array antenna works in the 5.3GHz frequency band.
The multi-mode OAM electromagnetic vortex wave array antenna with the double-ring structure can generate the orbital angular momentum electromagnetic vortex waves with good performance, and can maximally improve the frequency spectrum utilization rate and the system capacity under the condition of not increasing the bandwidth. The invention can realize the simultaneous generation of electromagnetic vortex waves of multiple OAM modes at the same frequency point, and is suitable for the most popular conventional Wi-Fi and Bluetooth wireless communication. The OAM electromagnetic vortex wave generated based on the multi-mode orbital angular momentum array antenna is used for multiplexing, and a plurality of coaxial data streams can be simultaneously transmitted on a single channel, so that the purposes of remarkably increasing the system capacity and improving the wireless communication spectrum efficiency are achieved. Meanwhile, due to the use of the double-ring structure, the invention can effectively improve the quality of electromagnetic vortex wave signals, improve the directivity and gain of the electromagnetic vortex wave signals and obtain better antenna performance. The microstrip patch antenna has the advantages of low cost, easily available materials, light weight, small volume, low profile, easy shaping, easy integration and the like.
Drawings
Fig. 1 is a schematic diagram of the overall structure of a dual-loop multi-mode OAM electromagnetic vortex wave array antenna according to an embodiment of the present invention;
fig. 2 is a schematic diagram of a microstrip patch antenna according to an embodiment of the present invention;
fig. 3 is a schematic diagram of a top view structure of a dual-ring-structure multi-mode OAM electromagnetic vortex wave array antenna according to an embodiment of the present invention;
fig. 4 is a schematic diagram of a front view structure of a dual-ring-structure multi-mode OAM electromagnetic vortex wave array antenna according to an embodiment of the present invention;
fig. 5 is a schematic diagram of a high-speed rf switch structure.
Detailed Description
In order that the invention may be readily understood, a more complete description of the invention will be rendered by reference to the appended drawings. Preferred embodiments of the present invention are shown in the drawings. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete. It will be understood that when an element is referred to as being "connected" to another element, it can be directly connected to the other element or intervening elements may also be present. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and/or" as used herein includes any and all combinations of one or more of the associated listed items.
As shown in fig. 1 to 4, a multi-mode OAM electromagnetic vortex wave array antenna 100 with a dual-loop structure in the present embodiment specifically includes a dielectric substrate 101, a plurality of groups of array elements 102, and coaxial feeder lines 103 and input ports 104 corresponding to each array element 102, where the array elements 102 adopt microstrip patch antennas; each group of array elements 102 are uniformly distributed and arranged on one surface of the dielectric substrate 101 along the circumference at respective set intervals, a metal thin layer is attached to the other surface of the dielectric substrate 101 as a grounding surface 105, and the input ports 104 are connected with the corresponding array elements 102 through coaxial feeder lines 103.
In this embodiment, the dual-ring-structure multi-mode OAM electromagnetic vortex wave array antenna 100 includes 16 array elements 102, and each group of eight array elements 102 are uniformly distributed and arranged on the dielectric substrate 101 along the circumference with a radius of 0.6λ and 0.8λ, respectively, to form a dual-ring antenna array, where λ is the radiation wavelength of the antenna array. The array elements 102 are fed with the same signals, and the phase difference between two adjacent array elements 102 is 45 degrees; the radius of the dielectric substrate 101 is one wavelength of the antenna array. The dielectric substrate 101 had a thickness of h=2 mm, and using FR4 material, dielectric constant and loss tangent were respectively epsilon=4.4 and delta=0.02.
In this embodiment, the multimode OAM electromagnetic vortex wave array antenna 100 with a dual-loop structure operates in the 5.3GHz frequency band, and the microstrip patch antenna as the array element 102 has a size of 12.722 × 17.224mm 2 And adopts the coaxial feed mode, and in general, the coaxial adapter is installed on the back of the printed circuit board, and the inner conductor of the coaxial adapter is connected on the patch so as to produce the best matching, thereby greatly simplifying the complexity of antenna design. When the multi-mode OAM electromagnetic vortex wave array antenna 100 with the double-loop structure works, the same signals are fed to the array elements 102, but successive phase delays are arranged among the array elements 102, so that after the vortex wave beam rotates around the axis for one circle, the phase is increased by 2 pi l, and the phase difference of feeding among the array elements 102 can be changed to generate no phase differenceThe same OAM modes, where l is the number of modes generated. It should be noted that, the number of the array elements 102 in the dual-ring multi-mode OAM electromagnetic vortex wave array antenna 100 determines the maximum value of the OAM modes that can be generated, that is, satisfies-N/2 < l < N/2, where N is the number of the array elements 102 in the dual-ring multi-mode OAM electromagnetic vortex wave array antenna 100, and in this embodiment, the dual-ring multi-mode OAM electromagnetic vortex wave array antenna 100 is formed by 16 array elements 102 into a dual-ring structure, so that the generated mode number ranges are (-4, 4), that is, l= 0,l = ±1, l= ±2, l= ±3.
The multi-mode OAM electromagnetic vortex wave array antenna 100 with the double-ring structure is manufactured on an FR4 dielectric substrate 101 with a relative dielectric constant of 4.4 and a thickness of 2 mm. Array radius r 1 ＝0.6λ，r 2 =0.8λ, keeping the array sidelobes at a relatively low level and providing more space for the feed network. For an n-element OAM circular phased array, all radiating elements are fed with the same phase shift increment signal. The phase shift between the array elements 102 can be calculated by 2pi/n, where the integer l is the number of OAM modes, so that rotating about the array axis, the phase will increment by 2pi geometric radians. Then "distorted" OAM-mode radio waves may be generated.
As can be seen from the radio beam electric field amplitude distribution cases with OAM mode values of l= 0,l = ±1, l= ±2, l= ±3, the OAM beam generated by the dual-loop array antenna has a spatial helical phase structure characteristic, and the spatial helical phase wavefront structures of the OAM modes of l= 0,l = ±1, l= ±2, l= ±3 are clearly visible. When the number of OAM modes i=0, all array units feed the same zero phase shift signal, and the array does not have a spiral phase wavefront, which can be regarded as a uniform circular array. When the number of OAM modes i= +1, this means that the phase difference between two adjacent array elements is +45°, a spiral phase wavefront can be generated counterclockwise; similarly, when l= -1, the phase difference between two adjacent array elements is-45 degrees, and a clockwise spiral phase wavefront can be generated. When the OAM mode is increased from ±1 to ±3, the void region at the beam center is enlarged, and the directivity thereof is changed according to the number of OAM modes. Notably, when the number of modes increases to l= ±3, the electromagnetic vortex waveThe irregular deformation of the beam phase distribution occurs, the number of the array elements determines the maximum value of the generated OAM modes, namely the finite number of the array elements exists, the number of the array elements is fixed, the integer value of the OAM modes which can be generated by the array is limited in a certain range, and the array antenna of N array elements can theoretically generate the maximum value L of the OAM modes max Can be obtained by the formula-N/2 < l < N/2. Thus, the closer the generated modal value is to L max The more pronounced the distortion of the electromagnetic vortex beam phase distribution. The reflection coefficient of the array antenna can show that the resonance frequency of each array element has good consistency, the mutual coupling effect among the array elements is relatively small, and the reflection coefficient shows that the 10dB bandwidth of the array antenna covers 5.2GHz-5.44GHz, and the resonance frequency is 5.3GHz. Meanwhile, as can be seen from the voltage standing wave ratio simulation result of the array antenna, the voltage standing wave ratio of the antenna array is smaller than 2 within the working frequency band of 5.2GHz-5.44GHz, and the performance meets the requirements. When the mode number is l=0, the main lobe direction is perpendicular to the antenna array plane, and electromagnetic energy is mainly radiated to the axis direction of the antenna array. When the number of the OAM modes is 1, a cavity appears in the axial direction of the radiation pattern, and the beam carries orbital angular momentum to become a hollow beam. As the number of modes increases, the area of the hollow part of the beam also increases, the side lobe increases and develops into a main lobe, the directivity of the array decreases, and the gain also changes. The larger the area of the cavity, the farther from the array surface, indicating that the beam will spread continuously as the propagation distance increases. The quality of the wave beam can be improved to a certain extent by means of adjusting the radius of the array, the number of array elements and the like. Actually, the double-ring structure is introduced to improve the focusing performance of the wave beam and reduce the hollow part; and increasing the number of array elements can improve the beam quality.
Since the phase structure of the wave beam is not changed basically along with the increase of the transmission distance, the OAM wave generated by the dual-loop structure multi-mode OAM electromagnetic vortex wave array antenna of the present invention should have a rotationally symmetric property, and the function values of the directional patterns on both sides of θ=0° on the radiation pattern are equal and the curves are symmetric. However, simulation results of the E-plane and the H-plane of different OAM mode values are not strictly symmetrical, which is caused by non-ideal array elements, because rectangular patches serving as array elements are not ideal dipoles, but have a geometric structure with a certain size, and as can be seen from the radiation patterns, are non-ideal pear shapes and have no rotational symmetry. Such calculation results reflect problems that may occur in practical applications to some extent. In the propagation direction, each order radiates energy in the propagation direction, but the radiation of the higher order modes is more divergent than the first few orders and is concave from the middle. When the mode values of the array OAM are l= 0,l = ±1, l= ±2, and l= ±3, it can be seen from the change condition of the radiation pattern diagrams of the E-plane and the H-plane of the patch antenna array that the number of array elements is n=16, when l=0, the main lobe radiates in the axial direction (i.e. Z-axis) of the patch antenna array, the electromagnetic energy mainly in the direction perpendicular to the array, and as the number of modes increases, the area of the main lobe becomes smaller, and the area of the side lobe increases, so in practical situations, in order to radiate more electromagnetic energy in the main lobe direction, it is necessary to consider both the main lobe and the side lobe level, and it is important to properly select the OAM mode value and the array radius. When l is not equal to 0, a cavity can appear in the axis direction of the radiation pattern, and the larger the pattern number l is, the larger the cavity is, and the beam can be narrowed by using a double ring, so that the size of the cavity is reduced to a certain extent, the directivity of the beam is changed, further explaining that the OAM spiral beam is a hollow beam, electromagnetic energy radiated by the patch antenna array is concentrated on a circular ring around the axis, no field exists near the axis, or the field becomes weak, which is the reason that the antenna pattern appears the cavity in the axis direction. By introducing the double-ring structure, the hollow property of the OAM electromagnetic vortex wave is obviously improved, and the directivity is enhanced.
According to the variation of the gains of the multi-mode OAM electromagnetic vortex wave array antenna with the double-loop structure under different values of the OAM mode values of l= 0,l = ±1, l= ±2 and l= ±3, the variation of the gains of the multi-mode OAM electromagnetic vortex wave array antenna with the double-loop structure is known to be along with angles near a center frequency pointThe maximum gain of each mode of the antenna is 7-14dB according to the progressive change of the OAM mode value and the change of the OAM mode value, so that the realization requirement of the invention on the gain target is met. Young babyLooking at the gain curve, the gain has such a bandwidth that the antenna array impedance bandwidth is very wide in the absence of a feed network, and the antenna matching of the feed network is good at 5.2GHz-5.44 GHz. In other frequency bands, the mismatch of the antenna array and the gain drop are obvious, which is caused by the variation caused by the feeding mode, and at the frequency of about 5.3GHz, the resonant frequency is exactly corresponding, and a considerable part of energy is radiated backward to cause the gain variation. It should be noted that, the various technical indexes of the microstrip antenna, such as gain, bandwidth, pattern, etc., are interrelated and affect each other, and all the technical indexes cannot be satisfied in the design, and the situation that the indexes are not mutually satisfied is definitely existed. The performance of the microstrip array antenna is improved, and a balance point is found out according to engineering requirements from the indexes. From simulation analysis of the antenna, the array antenna model can basically meet the requirements of a common antenna array, and the practical feasibility of the microstrip patch antenna array model is also verified.
The technical scheme of the invention can generate the orbital angular momentum electromagnetic vortex wave with good performance, and can maximally improve the frequency spectrum utilization rate and the system capacity under the condition of not increasing the bandwidth. The invention can realize the simultaneous generation of electromagnetic vortex waves of multiple OAM modes at the same frequency point, and is suitable for the most popular conventional Wi-Fi and Bluetooth wireless communication. The OAM electromagnetic vortex wave generated based on the multi-mode orbital angular momentum array antenna is used for multiplexing, and a plurality of coaxial data streams can be simultaneously transmitted on a single channel, so that the purposes of remarkably increasing the system capacity and improving the wireless communication spectrum efficiency are achieved. Meanwhile, due to the use of the double-ring structure, the invention can effectively improve the quality of electromagnetic vortex wave signals, improve the directivity and gain of the electromagnetic vortex wave signals and obtain better antenna performance. The microstrip patch antenna has the advantages of low cost, easily available materials, light weight, small volume, low profile, easy shaping, easy integration and the like. The invention has the following specific advantages: (1) Electromagnetic vortex waves carrying various modal orbital angular momentum can be generated, wherein the generated modal values are l= 0,l = ±1, l= ±2 and l= ±3 respectively, information carrying different OAM modes can be transmitted in a non-interference manner at the same time and at the same frequency point, and the frequency spectrum utilization rate and the system capacity are remarkably improved. (2) Compared with the traditional antenna, the antenna disclosed by the invention has good performance, and can effectively improve the quality of electromagnetic vortex wave signals and improve the directivity and gain of the electromagnetic vortex wave signals. (3) Electromagnetic vortex waves working at 5.3GHz can be generated, the method is suitable for Wi-Fi, zigBee and Bluetooth frequency bands which are most popular in the past, the method is subjected to laboratory simulation, the characteristic parameters such as gain, three-dimensional radiation patterns and directional patterns of the array antenna are obtained, and the simulation result shows that the method has good performance. The feasibility of the invention in an actual communication system is verified. (4) The OAM space multiplexing mode is formed by multiplexing multiple electromagnetic wave signals carrying OAM modes and having polarization characteristics on the same frequency point and transmitting information at the same time, and the maximization of the system capacity can be realized under the condition of not increasing the bandwidth, so that the outstanding contradiction between the current increasing bandwidth requirement and the limited frequency spectrum resource is effectively relieved.
According to the invention, an OAM technology, a rectangular microstrip patch antenna technology, a high-speed radio frequency switch technology and an array antenna design technology are uniformly applied to the invention, so that electromagnetic vortex waves of multiple OAM modes are simultaneously generated at the same frequency point, and the method is suitable for the most popular conventional Wi-Fi and Bluetooth wireless communication at present. The OAM electromagnetic vortex wave generated based on the multi-mode orbital angular momentum array antenna is used for multiplexing, and can transmit a plurality of coaxial data streams in a single channel, thereby achieving the purposes of remarkably increasing the system capacity and improving the wireless communication spectrum efficiency. The following details of the OAM technology, rectangular microstrip patch antenna technology, high-speed radio frequency switch technology and array antenna design technology used in the present invention are as follows:
1. OAM technology
In 1992, allen has been experimentally demonstrated for the first time that electromagnetic waves carry spin angular momentum and orbital angular momentum. SAM is polarization dependent and OAM is spatial phase dependent. The helical phase beam of OAM has an azimuth factorIdeally, OAM has an unlimited value of i, can be positive or negative, positive represents left-hand, negative represents right-hand, i.e., provides an unlimited number of OAM orders, and is orthogonal to each other. When orbital angular momentum is added to the electromagnetic wave, the phase wavefront of the electromagnetic wave presents a non-planar twisted structure, and can modulate required information on the non-planar twisted structure, so that the information transmission and information acquisition capacity of the electromagnetic wave are improved. Phase rotation factor->The spatial phase distribution structure of the vortex wave beams is determined, and the spatial structures of the vortex wave beams in different OAM modes are different. Compared with the traditional modulation which adopts the amplitude, phase and frequency of signals to carry information, the orbital angular momentum uses electromagnetic vortex waves carrying OAM of different modes to carry information, and the polarization modulation mode adopts a polarization state to carry information. Angular momentum of the spatial signal electromagnetic field may be expressed as
J＝∫ε 0 r×Re{E×B * The angular momentum of dV (4-1) can be decomposed into Orbital Angular Momentum (OAM) and Spin Angular Momentum (SAM)
J＝L+S (4-2)
Wherein the method comprises the steps of
S＝ε 0 ∫Re{E * ×A}dV (4-4)
Is an orbital angular momentum operator, +.>In imaginary units, a is a vector bit function. S characterizes the polarization of electromagnetic waves, L is related to the spatial phase distribution of electromagnetic waves. Applying orbital angular momentum to electromagnetic wave, adding a phase rotation factor to normal electromagnetic wave>At this time, the wave front of the electromagnetic wave is not a plane structure, but rotates around the wave beam propagation direction to present a spiral phase structure, and the electromagnetic vortex wave can be expressed as
Wherein A (r) is the amplitude of the electromagnetic wave, r represents the radiation distance to the beam central axis,for azimuth, l is the eigenvalue of orbital angular momentum.
The anti-interference performance of the electromagnetic vortex waves carrying the orbital angular momentum realizes anti-interference by utilizing the orthogonal characteristics of the electromagnetic vortex waves with different eigenvalues, and can transmit multiple paths of electromagnetic vortex waves in parallel within the same bandwidth, and the electromagnetic vortex waves with different OAM eigenvalues can not generate signal interference in theory. Thereby, the electromagnetic wave signal f 1 (t) and f 2 (t) conditions to be satisfied when mutually orthogonal
Whereas OAM states with different eigenstates are orthogonal to each other because
If the eigenvalues carried by the OAM beam are different, the result is zero when integrating the product thereof, thereby satisfying the above condition, and in theory, the OAM beam will not generate interference during transmission. For example: eigenvalues are respectively l 1 And l 2 Is a magnetic field, and is a magnetic field.
According to the characteristic that electromagnetic vortex waves of different OAM eigenvalues are mutually orthogonal, a group of OAM electromagnetic waves with different modes can be used as orthogonal bases for signal modulation, multipath signals are modulated on the electromagnetic waves with different OAM modes, and information is transmitted by utilizing an OAM multiplexing technology under ideal conditions, so that infinite transmission capacity of a communication system can be obtained. Meanwhile, by utilizing the characteristic, electromagnetic beams with different OAM modes can be separated and detected by using a group of filters with different properties at a receiving end.
2. Rectangular microstrip patch antenna technical square
The first step in designing an antenna is to select the center frequency, and the rectangular microstrip patch antenna designed herein is designed with f 0 As the center frequency.
The antenna length L can be calculated from the center frequency as follows:
L e ＝λ g /2 (4-10)
wherein lambda is g Representing the wavelength in the waveguide.
Wherein lambda is 0 Represent the free space wavelength, ε e Indicating the effective dielectric constant.
Wherein ε is r Indicating the relative permittivity of the medium.
When the thickness and relative permittivity of the dielectric substrate are determined, the effective permittivity of the antenna depends on the width of the patch. A suitably large patch width is advantageous for bandwidth, efficiency and matching of the antenna under the allowable conditions of the antenna mounting dimensions, but too large a width excites the higher order modes, thereby causing field distortion, affecting the radiating antenna of the antenna. In general, W is determined by:
the electric field of the rectangular patch antenna is cosine distributed between two radiating edges, and the theoretical distance between the two radiating edges is lambda g 2, but in practice the edge effect should be subtracted from the influence of the edge field, which brings about an increase in size. Therefore, the patch length L of the rectangular microstrip antenna is:
c represents the speed of light in vacuum, f 0 The operating frequency of the antenna is represented, deltal is the length extension caused by the edge effect, and the relation between the patch width, the thickness of the substrate and the effective relative dielectric constant is as follows:
the approximate length L and width W of the microstrip antenna can be calculated by the formulas (4-13) - (4-14).
3. High-speed radio frequency switch technology
In the invention, the double-ring structure multi-mode OAM electromagnetic vortex wave array antenna is provided with 16 identical array elements, equidistant circular antenna arrays, eight array elements are arranged in each ring, and the radii of the two rings are respectively that the continuous array elements passing through the circular array have fixed phase differencesTo generate OAM mode, wherein l is the OAM mode value to be generated, and N is the array element number. To achieve free switching of the same array between different topology charges, i can replace the phase shift component in the array feed network with a simple radio frequency switch to form a Time Switch Array (TSA). In order for the TSA to generate OAM electromagnetic waves, the array unit needs to give unitsFundamental operating frequency f of amplitude and uniform phase 0 The method comprises the steps of carrying out a first treatment on the surface of the 8 array elements of each ring in the array are sequentially electrified by switching or exciting the array elements in the circular phased array through a radio frequency switch, and the feeding time of the array elements at the same radius position of the two rings is the same, so that each array element is only connected with T S Time of/8, wherein T s Is the overall sequence switching period, and T s Determined by the period of the radio frequency switch. Therefore, the radiation frequency range of the 1 st to 8 th array elements of each ring is f 0 +f s ,f 0 +2f s ,f 0 +3f s …f 0 +8f (where f s ＝1/T s )。
As shown in fig. 5, the 16 circular phased array antenna elements are controlled using high speed radio frequency switches to generate multiple OAM radiation patterns. Pin 1 provides voltage, pin 2 is the control input, pin 3 is the active enable of low level, pin 8 is the connection PC port, pin 10 is the programming/erasing voltage port, 8 antenna elements that control the circular phased array are 8N/Cs of the radio frequency switch, respectively, namely: pins 4,5,6,7, 11, 12, 13 and 14, when enable EN is low level, 8 antennas work in sequence, and when the operation starts, pin 4 controls the first array to work Ts/8; then, the first array element stops working, and the pin 5 controls the second array element to work Ts/8; then, the second array element stops working, and the pin 6 controls the third array element to work Ts/8; and so on, and loops in turn.
Ts are different, and the OAM modes generated are different. The setting of Ts can be realized by setting time sequence switch delay parameters on line through a PC, so as to control the time sequence start and stop of the load. The singlechip is used as a main control chip, and programs are downloaded through a communication interface to realize the sequential control of opening and closing of eight paths of loads.
4. Array antenna design technique
At present, four devices for generating orbital angular momentum are mainly used at present, namely a transmission spiral surface, a transmission grating, a reflection spiral surface and an array antenna. For a beam with an OAM mode value of l, the phase offset can be determined byAnd obtaining the product. For such a phase shift to occur, each element of the array needs to be given some specific phase shift. To obtain the properties of the electric field from an array, we can use an Array Factor (AF), which depends on the displacement (and shape of the array), phase, current amplitude and number of array elements. The obtained total field of the same antenna is
Etotal=einleleelement AF (4-17) with the property of symmetry, a plurality of circular grid equal area sectors are selected. The position of each individual element is given. The radius vector of each array element center is
Angle of separation between array elements
Where m represents the ring element placed and n is the position of the selected ring. M is the total number of rings, N is the total number of array elements on each ring
The electric field expression is given by
In the increasing stage of integer multiple of 2 pi, each antenna element is fed with the same input signal, and continuous phase delay is provided between the elements by 2 pi/N, wherein l is the number of OAM modes generated by the array antenna, N is the number of the elements of the array antenna, and it should be noted that the number of the elements of the array antenna determines the maximum value of the generated OAM modes, namely, the maximum value satisfies-N/2 < l < N/2.
Note that the above is only a preferred embodiment of the present invention and the technical principle applied. It will be understood by those skilled in the art that the present invention is not limited to the particular embodiments described herein, but is capable of various obvious changes, rearrangements and substitutions as will now become apparent to those skilled in the art without departing from the scope of the invention. Therefore, while the invention has been described in connection with the above embodiments, the invention is not limited to the embodiments, but may be embodied in many other equivalent forms without departing from the spirit or scope of the invention, which is set forth in the following claims.
Claims (4)
1. The multi-mode OAM electromagnetic vortex wave array antenna with the double-loop structure is characterized by comprising a dielectric substrate, a plurality of groups of array elements, and coaxial feeder lines and input ports corresponding to the array elements, wherein the array elements adopt microstrip patch antennas; each group of array elements are uniformly distributed and arranged on one surface of the medium substrate along the circumference at set intervals, the other surface of the medium substrate is a ground plane, and the input ports are connected with the corresponding array elements through coaxial feeder lines;
the double-ring structure multi-mode OAM electromagnetic vortex wave array antenna comprises 16 array elements in total, wherein each group of eight array elements are uniformly distributed and arranged on the medium substrate along the circumference at set intervals;
the two groups of array elements are uniformly distributed and arranged on the dielectric substrate along the circumference with the radius of 0.6lambda and 0.8lambda to form a double-loop antenna array, wherein lambda is the radiation wavelength of the double-loop antenna array;
when the double-loop-structure multi-mode OAM electromagnetic vortex wave array antenna works, the same signals are fed to the array elements, but successive phase delays exist among the array elements, so that after vortex beams rotate around an axis for one circle, the phases are increased by 2 pi l, different OAM modes are generated by changing feeding phase differences among the array elements, wherein l is the generated mode number;
switching or exciting the array elements in the circular phased array through a radio frequency switch, wherein 8 array elements of each ring in the array are sequentially electrified, and the feeding time of the array elements at the same radius position of the two rings is the same;
by introducing the double-ring structure, the hollow property of the OAM electromagnetic vortex wave is obviously improved, and the directivity is enhanced.
2. The dual-loop multi-mode OAM electromagnetic vortex array antenna of claim 1, wherein said elements are fed with the same signal, the phase difference between two adjacent elements being 45 °; the radius of the dielectric substrate is 80.66mm.
3. The dual-ring structured multi-mode OAM electromagnetic vortex array antenna of claim 2, wherein an OAM mode number l generated by the dual-ring structured multi-mode OAM electromagnetic vortex array antenna is: -4 < l < 4, i.e. l= 0,l = ±1, l= ±2, l= ±3.
4. A dual ring structure multi-mode OAM electromagnetic vortex array antenna as claimed in any one of claims 1 to 3 wherein the dual ring structure multi-mode OAM electromagnetic vortex array antenna operates in the 5.3GHz band.
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| TWI692151B (en) * | 2017-11-23 | 2020-04-21 | 明泰科技股份有限公司 | Antenna array |
| CN108767474B (en) * | 2018-06-04 | 2020-12-18 | 中南大学 | Novel OAM wave beam generation device |
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| CN113991327B (en) * | 2021-09-30 | 2024-05-14 | 中国人民解放军海军工程大学 | Antenna array for improving vortex wave mode purity |
| CN114914669B (en) * | 2022-05-30 | 2023-08-04 | 中国人民解放军战略支援部队航天工程大学 | Broadband plane vortex wave antenna with multiple modes |
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