CN103474776A - Method for generating radio frequency orbital angular momentum beams based on annular traveling wave antenna - Google Patents

Abstract

The invention relates to a method for generating radio frequency orbital angular momentum beams based on a ring traveling wave antenna. The annular traveling wave antenna of the present invention is in the form of a circular ring in spatial distribution, and the circle is symmetrical around the Z axis. The amplitude of the excitation source at each point on the circular ring is consistent, and the phase satisfies exp( il

), the antenna excitation source propagates as a traveling wave on the ring, and the radiation of this ring traveling wave antenna in space can produce a radio frequency OAM beam of the same order as l in its phase distribution, and adjust the phase of each point on the ring distribution, different l- order radio frequency OAM beams can be generated. The method proposed by the invention can be used in the OAM wireless communication system, is integrated with the existing communication technology, and greatly improves the capacity of the communication system.

Description

A Method of Generating Radio Frequency Orbital Angular Momentum Beam Based on Ring Traveling Wave Antenna

technical field

The invention belongs to the technical field of OAM wireless communication, and relates to a method for generating a radio frequency OAM beam based on a ring traveling wave antenna.

Background technique

As the world enters the mobile Internet era, the spectrum gap for mobile communication services is becoming increasingly serious. Due to the limited high-quality spectrum resources in the low frequency band, it is difficult to meet the new demands of mobile communications only by allocating new spectrum. In this case, it is particularly important to develop new technologies to improve the efficiency of the use of bits/Hz. At present, people have done a lot of research on expanding information capacity resources based on the dimensions of frequency spectrum, phase, and amplitude of electromagnetic waves, such as improving the spectrum utilization rate of a new intelligent wireless communication technology - cognitive radio; improving the spectrum efficiency of a single carrier signal High-order coherent modulation, multi-carrier technology that nearly doubles the spectral efficiency compared with serial systems, and MIMO communication technology that can both increase spectral efficiency and double channel capacity, etc. Obviously, capacity resources based on the dimensions of frequency spectrum, phase, and amplitude have been fully developed and utilized. Although the gradual expansion in these dimensions can continue, there is not enough room to achieve a large expansion of several orders of magnitude. Therefore, it is a major scientific and technical challenge to find new physical parameter dimensions to realize electromagnetic wave communication technology and meet the demand of order-of-magnitude increase in communication capacity within limited spectrum resources. Orbital Angular Momentum (OAM) wireless communication came into being at this opportunity.

Electromagnetic waves not only have energy, but also have orbital angular momentum. Orbital angular momentum is the basic physical property of electromagnetic waves, reflecting the phase change parameters of electromagnetic waves around the azimuth direction of the propagation direction axis. For electromagnetic waves of any frequency, all OAM beams constitute a set of mutually orthogonal and infinitely many eigenmodes. OAM communication is to use the order (value l) of the OAM mode, a group of electromagnetic wave eigenmodes, as a new parameter dimension resource that can be modulated or multiplexed, that is, to use different l values to represent different encoding states or different information channels. Thereby opening up a new way to further improve the spectral efficiency. Since the value of l has an infinite value range, theoretically OAM communication has the potential to increase the amount of information carried by electromagnetic waves infinitely.

At present, the application of the parameter dimension of radio frequency OAM in the field of wireless communication is still in its infancy. Most of the research focuses on theoretical analysis. The development and development of different order radio frequency OAM beam generation methods and corresponding devices is to verify the OAM wave free space channel characteristics. Realize the basis of radio frequency OAM wireless communication system. So far, most OAM beam generation methods come from the circular array antenna idea designed by Thide et al. in 2007, but the order of the OAM beam generated by this method is limited by the number of circular array antennas. Assuming that the number of circular array antennas is N, the generated OAM beam order l must be smaller than N/2, so finding a simple and feasible radio frequency OAM beam generation method is of great significance for future radio frequency OAM high-speed communication.

Contents of the invention

The object of the present invention is to provide a method for generating a radio frequency OAM beam based on a ring traveling wave antenna and OAM beam multiplexing based on the method.

The technical solution adopted by the present invention to solve its technical problems is:

A method for generating a radio frequency OAM beam based on a ring traveling wave antenna:

的分布，其中

是圆周角，l为整数，可为正或者为负，该类天线可定义为环形行波天线。即天线激励源在圆环上呈行波传播，l的符号不同表示天线激励源在圆环上呈顺时针或者逆时针方向的行波传播。经过电磁数值计算，这类环形行波天线在空间中的辐射可产生具有螺旋相位的l阶射频OAM波束，l亦可为正或者为负。其中的射频包含微波波段和毫米波波段。Any kind of antenna, whether it is an electric source antenna or a magnetic source antenna, as long as its spatial distribution is circular, the circle is symmetrical around the Z axis, the amplitude of the excitation source at each point on the ring is the same, and the phase is along the circumference of the ring. Continuously changing, satisfying

distribution, where

is the circular angle, l is an integer, which can be positive or negative, and this type of antenna can be defined as a ring traveling wave antenna. That is, the antenna excitation source propagates as a traveling wave on the ring, and the different signs of l indicate that the antenna excitation source propagates as a traveling wave in a clockwise or counterclockwise direction on the ring. Through electromagnetic numerical calculations, the radiation of this type of annular traveling wave antenna in space can produce a spiral phase The l-order radio frequency OAM beam, l can also be positive or negative. The radio frequency includes the microwave band and the millimeter wave band.

The beneficial effect that the present invention has compared with background technology is:

The invention proposes a new method for generating radio frequency OAM beams aimed at the serious problem of spectrum resource gaps in communication services. The invention can be used in OAM wireless communication systems, and is integrated with existing communication technologies to greatly increase the capacity of the communication system. Compared with the OAM beam generation method commonly used by circular array antennas in the background technology, the radio frequency OAM beam generation method proposed by the present invention is not limited to the number of array antennas, and can realize the generation of radio frequency OAM beams of any order. In addition, through the integration of multiple annular traveling wave antennas, the design of the OAM beam multiplexer necessary for OAM high-speed communication can be realized, and the multiplexing of different orders of radio frequency OAM beams can be achieved. Phase distribution on the annular traveling wave antenna required in the present invention It is easy to implement, and the requirements can be met through a variety of technologies, avoiding the need for precise phase control of each array element in the OAM method of using a circular ring array antenna in the background art. The invention plays a very important role in constructing the radio frequency OAM wireless communication system and promoting the practical application of the radio frequency OAM wireless communication system.

Description of drawings

Fig. 1 is a structural schematic diagram of an electrical source traveling wave loop antenna;

Figure 2 is the conversion relationship between spherical coordinates and rectangular coordinates in numerical calculation;

分布，l=2时，z=1000λ电场的相位分布图；Figure 3 is the antenna current satisfying

Distribution, when l=2, the phase distribution diagram of z=1000λ electric field;

分布，l=3时，z=1000λ电场的相位分布图；Figure 4 is the antenna current satisfying

Distribution, when l=3, the phase distribution diagram of z=1000λ electric field;

分布，l=4时，z=1000λ电场的相位分布图；Figure 5 is the antenna current satisfying

Distribution, when l=4, the phase distribution diagram of z=1000λ electric field;

分布，l=5时，z=1000λ电场的相位分布图；Figure 6 is the antenna current satisfying

Distribution, when l=5, the phase distribution diagram of z=1000λ electric field;

Fig. 7 is a structural diagram of an example of a ring traveling wave antenna for generating radio frequency OAM beams.

Detailed ways

Below in conjunction with accompanying drawing, the present invention is described in further detail:

1. Generation of radio frequency OAM beams based on ring traveling wave antennas.

的分布，计算该环形行波天线在空间中的辐射场。Assuming that the loop traveling wave antenna is an electrical source antenna, as shown in Figure 1, the current distribution on the antenna satisfies

, calculate the radiation field of the loop traveling wave antenna in space.

The basic idea is: divide the circular antenna into N sections, and ensure that the length of each small section of antenna ΔL<<wavelength λ, because the current amplitude on the small section of antenna is the same, and the phase can also be regarded as the same, then the small antenna can be used as a galvanic couple pole, its far-field radiation in space can be calculated by the far-field radiation formula of the electric dipole antenna, as follows:

$\mathrm{<span\; class="notranslate">\; E.</span>}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}\sqrt{\frac{\mathrm{<span\; class="notranslate">\; \&mu;</span>}}{\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}}}\frac{{\mathrm{<span\; class="notranslate">\; jkI\&Delta;le</span>}}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; jkr</span>}}}{\mathrm{<span\; class="notranslate">\; 4</span>}\mathrm{<span\; class="notranslate">\; \&pi;r</span>}}\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}$

与直角坐标x₀,y₀,z₀的转换见图2，电偶极子天线沿z轴放置在原点。In the above formula, the spherical coordinate unit vector r ₀ ,θ ₀ ,

The transformation with rectangular coordinates x ₀ , y ₀ , z ₀ is shown in Fig. 2, and the electric dipole antenna is placed at the origin along the z-axis.

To calculate the radiation field of a ring traveling wave antenna, the radiation fields of N segments of small antennas on the entire ring must be superimposed. Considering that the placement positions of each small segment antenna are different, that is, the coordinates of the above-mentioned radiation field companies are different, and it is difficult to obtain an analytical solution after coordinate transformation. In the present invention, a numerical solution method is adopted to calculate the electric field distribution diagram of the annular traveling wave antenna in space, It is judged by the phase change of the electric field whether to generate radio frequency OAM beams of different l orders.

分布，l=2，3，4，5时天线辐射沿z轴传播1000λ时电场的相位分布图。可见，电场相位围绕传播方向轴的圆周角的变化呈现涡旋特性，且电场相位沿圆周一圈变化满足2πl，即l=2时，电场相位沿圆周一圈变化4π；l=3时，电场相位沿圆周一圈变化6π；l=4时，电场相位沿圆周一圈变化8π；l=5时，电场相位沿圆周一圈变化10π，以此类推。这一特点证明这类环形行波天线可以产生任意l阶数的射频OAM波束，只要天线上的电流分布满足

l为整数即可。Figures 3 to 6 show that the current of the ring traveling wave antenna satisfies

Distribution, when l=2, 3, 4, 5, the phase distribution diagram of the electric field when the antenna radiation propagates 1000λ along the z-axis. It can be seen that the change of the electric field phase around the angle of the propagation direction axis exhibits a vortex characteristic, and the change of the electric field phase along the circle satisfies 2πl, that is, when l=2, the electric field phase changes 4π along the circle; when l=3, the electric field The phase changes by 6π around the circle; when l=4, the phase of the electric field changes by 8π around the circle; when l=5, the phase of the electric field changes by 10π around the circle, and so on. This feature proves that this type of annular traveling wave antenna can generate any RF OAM beam of order l, as long as the current distribution on the antenna satisfies

l is an integer.

When this type of annular traveling wave antenna is a magnetic source antenna, according to the principle of electromagnetic duality, the same conclusion can be obtained, as long as the excitation source of the antenna satisfies the annular traveling wave distribution, that is, Distribution, in the space can generate l-order radio frequency OAM beams.

2. An embodiment of an annular traveling wave antenna

分布，此时金属腔上的圆环开缝相当于一个磁型源天线，向外辐射电磁波，在空间中产生阶数为l的OAM波束。同样也可以设计电型源天线，只要天线上的电流相位分布满足

分布，则可以产生阶数为l的射频OAM波束。The annular traveling-wave antenna defined by the present invention that can generate radio frequency OAM beams is easy to realize through the design of the structure, compared to the commonly used ring array antenna in the background technology to realize the OAM beam generation method that requires precise control of the phase of each array , the method of the present invention is more convenient. Fig. 7 is an embodiment of a ring traveling wave antenna capable of generating radio frequency OAM beams. The main structure of the antenna is a metal ring cavity with a ring gap on the top surface. The metal ring cavity can be regarded as being bent from a rectangular waveguide. Side, working in TE ₁₀ mode, the slit is in the middle of the narrow side. Two metal waveguides are externally connected to the 1/4 circumference of the side of the metal ring cavity as the excitation port 1 and the excitation port 2. When the excitation ports 1 and 2 input microwave sources with the same frequency and a phase difference of ±90°, the metal ring cavity The electromagnetic field in the circle is distributed as traveling waves propagating clockwise or counterclockwise around the circumference. Reasonably design the size of the metal ring cavity so that the longitudinal propagation constant k _z of the original rectangular waveguide satisfies k _z R=l, l is an integer, R is the radius of the slot in the ring cavity, and the magnetic current at the slot along the circumference satisfies

At this time, the ring slot on the metal cavity is equivalent to a magnetic source antenna, which radiates electromagnetic waves outward and generates an OAM beam of order l in space. It is also possible to design electric source antennas, as long as the current phase distribution on the antenna satisfies

distribution, a radio frequency OAM beam with order l can be generated.

3. Implementation of OAM beam multiplexing

分布的天线产生阶数为l的OAM波束，如果有一个器件，通过结构和材料的合理设计，实现多个相位具有

分布的环形行波天线的组合，那么该器件即可作为OAM波束复用器，可在空间产生多个不同l阶数的OAM波束，从而实现OAM波束的复用，为OAM高速通信打下基础。如图7所示的环形行波天线实例，可以通过大小不同的的金属环型腔实现环形行波天线的叠加，在空间中实现OAM波束的复用功能。A method for generating radio frequency OAM beams based on a ring traveling wave antenna, a phase with

Distributed antennas generate OAM beams with an order of l. If there is a device, through reasonable design of structure and materials, multiple phases can be realized.

The combination of distributed annular traveling wave antennas, then the device can be used as an OAM beam multiplexer, which can generate multiple OAM beams of different l-orders in space, thereby realizing the multiplexing of OAM beams and laying the foundation for OAM high-speed communication. In the example of the annular traveling wave antenna shown in Fig. 7, the superposition of the annular traveling wave antenna can be realized through metal ring cavities of different sizes, and the multiplexing function of the OAM beam can be realized in space.

Claims (3)

1. A method for generating radio-frequency orbital angular momentum beams based on a ring-shaped traveling-wave antenna, characterized in that: the ring-shaped traveling-wave antenna is circular in spatial distribution, and the circle is symmetrical around the Z axis, and each point on the ring is excited The source amplitude is consistent, and the phase along the circumference satisfies

Distribution,

is a circular angle, l is an integer, the antenna excitation source propagates in traveling waves on the ring, l can be positive or negative, and the different signs indicate that the antenna excitation source travels in a clockwise or counterclockwise direction on the ring. Wave propagation, the radiation of this annular traveling wave antenna in space can produce radio frequency OAM beams with the same order l in its phase distribution, and adjust the phase distribution of each point on the ring to generate radio frequency OAM beams with different l orders . 2. A method for generating a radio-frequency orbital angular momentum beam based on a circular traveling-wave antenna according to claim 1, wherein the antenna excitation source is an electric source or a magnetic source. 3. A method for generating a radio frequency orbital angular momentum beam based on a ring traveling wave antenna according to claim 1, characterized in that: said radio frequency OAM beam includes microwave and millimeter wave frequency bands.

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