Method for generating arbitrary-order OAM waves by co-phase feeding of low-order OAM array elements in a ring array

Abstract

A method for generating arbitrary-order OAM waves by co-phase feeding of a low-order OAM array element ring array relates to the field of microwave and antenna technology. N low-order OAM antenna radiating elements are used as array elements, and the array elements are evenly distributed on a ring to form a uniform ring array, and each array element of the uniform ring array is fed in phase; the different positions of the array elements form a uniform spatial phase difference, which is synthesized with the spiral phase of the array element itself to generate ±(1-N)-order vortex waves. The array is easy to arrange and the feeding network is simple; OAM waves of different orders are generated by selecting the number of array elements. The complex feeding network is omitted, the antenna volume is reduced, and the difficulty of antenna design is reduced. Higher-order vortex waves can be generated, breaking through the limitation that the traditional OAM antenna ring array can only generate vortex waves lower than N / 2 order. The array elements can be selected and replaced according to the actual application. The vortex wave presents a phase singularity in the direction of the array axis, and first appears as a fixed first-order OAM in the area close to the array axis, and then presents a (1-N)-order vortex wave in the area.

Description

Technical Field

[0001] The invention relates to the technical field of microwaves and antennas, and in particular to a method for generating arbitrary-order OAM (Orbital Angular Momentum) waves by co-phase feeding of a low-order OAM (Orbital Angular Momentum) array element ring array with simple feeding. Background Art

[0002] In recent years, with the rapid development of wireless communication technology, the problem of frequency band utilization has gradually become prominent. As the number of users is increasing and the frequency range used for wireless communication is fixed, the problem of bandwidth allocation has become increasingly serious. Vortex wave communication, as a method that is expected to solve the problem of insufficient bandwidth due to low frequency band utilization, has attracted extensive research. Vortex wave is an electromagnetic wave containing orbital angular momentum, with a spiral phase distribution and annular field intensity distribution. Vortex waves of different modes are orthogonal to each other during propagation, and this orthogonal characteristic allows vortex waves of different modes to be multiplexed together, thereby realizing spatial multiplexing based on orbital angular momentum. Since it has an infinite number of achievable modes in theory, vortex waves are considered to be a solution for achieving high-speed, large-capacity, and high-bandwidth utilization communications.

[0003] The generation and reception of vortex waves is one of the key technologies of vortex wave communication. In summary, there are usually the following methods to generate vortex waves:

[0004] (1) Spiral phase plate method: The spiral phase plate method refers to a method of generating vortex waves by passing an ordinary plane wave through a spiral phase plate. The spiral phase plate can distort the wavefront of the plane wave, that is, it generates vortex waves. The spiral phase plate is a microwave dielectric substrate whose thickness changes proportionally with the azimuth angle. When a plane wave is incident on the surface of the spiral phase plate, since the thickness of the phase plate changes with the azimuth angle, the plane waves incident at each azimuth angle will have a path difference. This path difference causes a phase delay, and the plane wave will have a corresponding spiral wavefront structure after transmitting through the spiral phase plate.

[0005] (2) Helical reflector antenna: The working principle of the spiral reflector antenna is similar to that of the spiral phase plate, but it uses the unevenness of the reflector surface to make the reflected wave have different path lengths at different azimuths, thereby producing a phase difference.

[0006] (3) Uniform circular antenna array: The use of a circular antenna array is one of the classic methods for generating vortex waves. The main principle of this method is to arrange the array elements into a circular array with equal spacing, apply signals with different phase differences to the array elements, and superimpose them to obtain a vortex wave with continuous phase changes along the azimuth. Uniform circular array is one of the most commonly used methods for generating vortex waves. This method is simple and intuitive to design and easy to implement. The disadvantage is that in order to achieve continuous phase changes, a complex feeding network is often required, which makes the overall structure complicated and limits the miniaturization of the antenna array. Summary of the invention

[0007] The purpose of the present invention is to address the above-mentioned problems in the prior art and provide a method for generating arbitrary-order OAM waves by co-phase feeding of a low-order OAM array element ring array with simple feeding, which is a method for generating arbitrary-order vortex waves with simple structure and easy implementation. The method utilizes the superposition principle of vortex wave generation by array elements and antenna arrays.

[0008] The specific steps of the present invention are: using N low-order OAM antenna radiating elements as array elements, evenly distributing the array elements on a circular ring to form a uniform circular ring array, and feeding each array element of the uniform circular ring array in phase; the different positions of the array elements form a uniform spatial phase difference, which is synthesized with the spiral phase of the array element itself to generate ±(1-N) order vortex waves.

[0009] The array elements are evenly distributed on the ring, making the array easy to deploy; each array element is fed in phase, making the feeding network simple; and by selecting the number of array elements, OAM waves of different orders can be generated.

[0010] In particular, the low-order OAM antenna radiating element as an array element can be a regular polygon, a circle, a ring or other structures; the low-order OAM antenna radiating element can be implemented as a patch structure on a dielectric substrate with a ground plane, or a patch or wire structure without a ground plane; the low-order mode of the OAM radiating element is selected, and the simplest is to select a single antenna element that can realize the 1st-order OAM mode. A certain number of low-order OAM antenna radiating elements are evenly distributed on a ring with rotational symmetry; a feeding structure is implemented for the OAM radiating array elements on the same radius ring to be fed in phase.

[0011] The N low-order OAM antenna radiating elements are evenly distributed on the same circle at a central angle of 360 / N degrees. Considering the influence of the feeding position and the perimeter of the array element lλ, a spatial phase difference of (360×l) / N degrees is introduced between adjacent array elements.

[0012] The in-phase feeding of each array element of the uniform circular array is performed by starting the feeding point with the center of the circular ring as the starting point, connecting with each array element through a feeder line, and feeding each array element in-phase; the feeder line can be various transmission lines such as microstrip line, coplanar waveguide, parallel double line, etc.

[0013] The vortex wave radiated by the circular array is a phase singularity in the direction of the circular array rotation axis, that is, the array axis. The inner small area close to the circular array axis is a vortex wave with a fixed order of first order, while the outer area is a (1-N) order vortex wave whose order is completely determined by the number of array elements.

[0014] The present invention uses the in-phase feeding method for the uniform circular ring array elements, eliminating the complex feeding network in the traditional antenna array OAM generation method, greatly reducing the size of the antenna, and reducing the difficulty of antenna design. In addition, this method can generate higher-order vortex waves, breaking through the limitation that the traditional OAM antenna ring array can only generate vortex waves below the N / 2 order. Moreover, the array elements of the OAM in-phase feeding uniform circular ring array can be replaced according to actual applications, and an OAM antenna array that meets the corresponding requirements can be designed. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is an overall structural framework diagram of an embodiment of the present invention.

[0016] Figure 2 It is a front schematic diagram of an antenna according to an embodiment of the present invention.

[0017] Figure 3 FIG. 4 is a schematic diagram of the back side of an antenna according to an embodiment of the present invention.

[0018] Figure 4 FIG. 4 is a schematic diagram of an intermediate ground plane according to an embodiment of the present invention.

[0019] Figure 5 Schematic diagram of the layout of the back feeder conductor strips according to an embodiment of the present invention.

[0020] Figure 6 Schematic diagram of the front radiation array element structure according to an embodiment of the present invention.

[0021] Figure 7 : is a reflection coefficient curve of the feeding end according to an embodiment of the present invention.

[0022] Figure 8 This is the phase distribution diagram of the vortex wave generated by the antenna at 4.6GHz. DETAILED DESCRIPTION

[0023] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0024] The embodiment of the present invention uses N low-order OAM antenna radiating elements as array elements, and evenly distributes the array elements on a circular ring to form a uniform circular ring antenna array, and feeds each array element of the uniform circular ring antenna array in phase; the different positions of the array elements form a uniform spatial phase difference, which is synthesized with the spiral phase of the array element itself to generate ±(1-N) order vortex waves.

[0025] The array elements are evenly distributed on the ring, making the array easy to deploy; each array element is fed in phase, making the feeding network simple; and by selecting the number of array elements, OAM waves of different orders can be generated.

[0026] The low-order OAM antenna radiating element as an array element can be a regular polygon, a circle, a ring or other structures; the low-order OAM antenna radiating element can be implemented as a patch structure on a dielectric substrate with a ground plane, or a patch or wire structure without a ground plane; the low-order mode of the OAM radiating element is selected, and the simplest is to select a single antenna element that can realize the 1st-order OAM mode. A certain number of low-order OAM antenna radiating elements are evenly distributed on a ring with rotational symmetry; a feeding structure is implemented for the OAM radiating array elements on the same radius ring to be fed in phase.

[0027] In the circular antenna array with uniformly distributed array elements, N array elements are evenly spaced on the circle at a central angle of 360 / N degrees. Considering the influence of the feeding position and the circumference of the array element lλ, a spatial phase difference of (360×l) / N degrees is introduced between adjacent array elements.

[0028] The feeding network of each array element evenly distributed on the circular antenna array takes the center of the circular ring as the starting feeding point and is connected to each array element through a transmission line to achieve in-phase feeding; the actual structure of the transmission line is determined by the specific array element antenna. For example, if the array element is a microstrip antenna structure, the transmission line can be a microstrip line.

[0029] The in-phase fed uniform circular ring antenna array based on low-order OAM array elements has a vortex wave pattern after the array element vortex wave and the ring array vortex wave are superimposed. In a small central area close to the array axis, a ±1-order vortex wave is generated, while its peripheral area generates a ±(1-N)-order vortex wave determined only by the number of array elements.

[0030] A specific embodiment is given below. In this embodiment, the number of array elements N=8 is used to generate -7th order vortex waves.

[0031] See also Figures 1 to 3 , is a patch antenna structure array, including an upper dielectric plate 1, a lower dielectric plate 2, a metal ground plane 3, a microstrip feed line conductor strip 4, a circular patch 5, a reactance arc segment 6 and a via 7; the upper dielectric plate 1 and the lower dielectric plate 2 are in close contact, the metal ground plane 3 is sandwiched between the upper dielectric plate 1 and the lower dielectric plate 2, the lower bottom surface of the lower dielectric plate 2 is used as the microstrip feed line conductor strip 4, the upper surface of the upper dielectric plate 1 is provided with a metal patch composed of a circular patch 5 and a reactance arc segment 6, and the via 7 connects the microstrip feed line conductor strip 4 and the metal patch. The conductor center 8 on the lower surface of the lower dielectric substrate 2 is the connection position of the feeding port. The upper dielectric plate 1 and the lower dielectric plate 2 both use a relative dielectric constant ε r =2.2FR4 high frequency dielectric substrate with a thickness of 0.8mm.

[0032] See also Figure 4 The whole is a square ground plane, and there are 8 feeding ports at the center of the conductor. The area of ​​the upper dielectric plate 1 and the lower dielectric plate 2 is consistent with the ground plane, and is a square, and the side length W0 can be in the range of 30mm≤W0≤55mm.

[0033] See also Figure 5 , is the bottom-layer microstrip feed line conductor strip 4, which is evenly spaced from the center of the square to the outside in rectangular spokes of equal length and width. There are 8 strips in total, which are used to feed the 8 array element patches in phase. The length l0 and width w1 of the feed line conductor strip can be selected as follows: 35mm≤l0≤60mm, 1mm≤w1≤5mm.

[0034] See also Figure 6 , the 8 antenna array element patches are circular patches 5 loaded by reactance arc segments 6, and their centers are evenly distributed on a circle with a radius of l0. The radius of circular patch 5 is r0, the radius of the loaded reactance arc segment 6 is r1, and the central angle of the circle is The parameters can be selected: 10mm≤r0≤25mm, 15mm≤r1≤30mm, The circular patch 5 is connected to the microstrip conductor strip 4 through a via 7 on a tangent line of one side. The reactance arc segment 6 is outside the circular ring and is parallel to the radius of the circular patch 5 pointing to the via. Angle,

[0035] Figure 7 The S11 parameter result at the feeding port of the antenna array of the embodiment shows that the operating frequency band range of the antenna array is: 4.59-4.61 GHz. Near 4.6 GHz, the S11 of the antenna array is less than -15 dB.

[0036] Figure 8 The phase distribution of the antenna array at 4.6 GHz is shown in the example. The observation area is a 600 mm square with a side length of 100 mm from the antenna surface. Figure 8 It can be clearly seen that the central area close to the antenna array axis is a 1st-order vortex wave, while the outer area is a -7th-order vortex wave.

[0037] When the array elements in the antenna array of the embodiment are rotated in the opposite direction, -1st order and 7th order vortex waves can be presented in the corresponding observation area.

[0038] The array element structure in the antenna array of the embodiment is not limited to this, and regular polygonal, circular or annular patches that can generate vortex waves can all realize the vortex wave characteristics of the embodiment.

[0039] The present invention provides a method for generating arbitrary-order OAM waves based on the co-phase feeding of low-order OAM (Orbital Angular Momentum) array elements and uniform circular arrays. The method generates high-order vortex waves by superposition synthesis of vortex waves generated by array elements and vortex waves generated by spatial phase differences between co-phase feeding array elements. It uses low-order or even simple first-order OAM single antenna radiating elements as uniform circular array elements, and feeds each array element in phase. When the number of array elements is N, it can generate ±(1-N)-order vortex waves. Since each array element is fed in phase, a complex feeding structure can be omitted; since the order of the generated vortex wave is only determined by the number of array elements, it is easy to realize high-order OAM modes; since the array elements use low-order OAM antenna elements, it is convenient to select array elements and replace different array elements. The vortex waves generated by this OAM antenna array, except for the phase singularity in the array axis direction, first appear as fixed first-order OAM in the area close to the array axis, and then appear as (1-N)-order vortex waves in the area.

[0040] The above embodiment is an implementation mode of the present invention, but the implementation mode of the present invention is not limited by the said embodiment. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement modes and shall be included in the protection scope of the present invention. The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiment. The above embodiment and description are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, and these changes and improvements shall fall within the scope of the protection required.

Claims

1. A method for generating arbitrary-order OAM waves by co-phase feeding of low-order OAM array elements in a ring array, characterized in that The specific steps are: use N The low-order OAM antenna radiating elements are used as array elements, and the array elements are evenly distributed on the ring to form a uniform ring array. Each array element of the uniform ring array is fed in phase; the different positions of the array elements form a uniform spatial phase difference, which is synthesized with the spiral phase of the array element itself to produce ±(1- N )-order vortex wave; The low-order OAM antenna radiating element adopts a regular polygonal, circular or ring structure; the low-order OAM antenna radiating element adopts a patch structure on a dielectric substrate with a ground plane, or a patch or wire structure without a ground plane.

2. The method for generating arbitrary-order OAM waves by in-phase feeding of a low-order OAM array element ring array as claimed in claim 1, characterized in that By selecting the number of array elements, OAM waves of different orders can be generated.

3. The method for generating arbitrary-order OAM waves by in-phase feeding of a low-order OAM array element ring array as claimed in claim 1, characterized in that Said N The low-order OAM antenna radiating element is 360 / N The degrees are evenly distributed on the same circle.

4. The method for generating arbitrary-order OAM waves by in-phase feeding of a low-order OAM array element ring array as claimed in claim 1, characterized in that The in-phase feeding is performed on each array element of the uniform circular array, and the center of the circular array is used as the starting feeding point, and each array element is connected to each array element through a feeder line, and each array element is fed in-phase.

5. The method for generating arbitrary-order OAM waves by in-phase feeding of a low-order OAM array element ring array as claimed in claim 4, characterized in that The feed line is selected from a microstrip line, a coplanar waveguide or a parallel two-wire transmission line.

6. The method for generating arbitrary-order OAM waves by in-phase feeding of a low-order OAM array element ring array as claimed in claim 1, characterized in that The vortex wave radiated by the circular array is a phase singularity in the direction of the circular array rotation axis, that is, the array axis. The inner small area close to the circular array axis is a vortex wave with a fixed order of first order, while the outer area is a vortex wave with an order completely determined by the number of array elements (1- N ) order vortex wave.

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