Low-loss anti-aging orbital angular momentum RFID array antenna

Abstract

The invention discloses a low-loss anti-aging orbital angular momentum RFID (Radio Frequency Identification Device) array antenna which sequentially comprises N array units, a first dielectric substrate, a metal grounding plate, a second dielectric substrate and a feed network from top to bottom, the N array units are in central symmetry and are distributed on the upper surface of the first layer of dielectric substrate at equal angular intervals along the circumference, the feeding amplitudes of the array units are the same, and the phase difference between two adjacent array units in the clockwise direction meets # imgabs0 #, l is an orbital angular momentum mode required by a radiation beam, and the number of the array units meets the condition that-N / 2 < l < N / 2; each array unit is of a circular structure, one or more strip-shaped gaps are additionally formed in each array unit, and the center position of each strip-shaped gap is located at the center position of the array unit; the metal grounding plate is provided with strip-shaped gaps corresponding to the center positions of the array units, the feed network feeds through the gaps in the metal grounding plate, the feed amplitudes of the array units are the same, and vortex electromagnetic waves are generated.

Description

Technical Field

[0001] The present invention relates to the field of wireless communication technology, and in particular to a low-loss and anti-fading orbital angular momentum RFID array antenna. Background Art

[0002] In traditional RFID (radio frequency identification) systems, data transmission usually relies on a single frequency or limited spectrum bandwidth. This means that at the same time, the same frequency can only be used to identify and communicate with one or a small number of devices, resulting in low communication efficiency of the RFID system. Although existing RFID technology can already meet some basic application requirements, with the rapid development of the Internet of Things (IoT) and the popularity of various devices, RFID systems are facing increasing challenges, especially in environments that require efficient processing of large amounts of device data and high traffic, where the system is prone to performance degradation due to frequency congestion.

[0003] In addition, the communication distance between the reader and the tag is usually greatly limited. This is because the RFID system relies on radio waves for signal transmission, and radio waves will experience significant signal attenuation as the distance increases. Especially in scenarios that require large-scale, continuous monitoring or tracking, the coverage of traditional RFID is relatively insufficient. For example, in a smart city, RFID may need to track vehicles, public equipment, or assets over a large area. If the coverage of the RFID system is insufficient, the status of the vehicle or equipment may not be effectively identified in some areas, resulting in incomplete system information or discontinuous monitoring.

[0004] In addition, the RFID signal will not only attenuate due to distance during transmission, but may also be affected by physical obstacles, environmental interference and multipath effects, further limiting its effective coverage. These factors combined further exacerbate the shortcomings of the RFID system in long-distance communication, making it difficult to adapt to large-scale, wide-coverage application requirements.

[0005] In order to solve these problems, RFID systems need to use new technical means to improve the signal transmission capability and stability. The limited coverage and signal attenuation problems of traditional RFID systems, especially in long-distance and large-scale application scenarios, are an important reason for the current need for technological innovation and improvement.

[0006] Refrigerated and frozen products must be kept in a specified low-temperature environment in all links of production, storage, transportation and sales to ensure their quality and performance. Cold-chain transportation refers to maintaining products at a specific low temperature during transportation to prevent them from spoiling. Cold-chain logistics can be achieved through sea, land and air transportation.

[0007] In cold chain logistics and the entire communication system, antennas are an indispensable core component responsible for the transmission and reception of electromagnetic waves. However, more and more wireless communication devices need to access the Internet through electromagnetic waves, which causes congestion in spectrum channels. In order to improve the utilization of spectrum resources, technologies such as amplitude modulation (AM), frequency modulation (FM), phase modulation (PM), and multiple access have been developed and used.

[0008] At present, RFID antennas are increasingly used in cold chain logistics, but they still have the following defects:

[0009] (1) Cold chain logistics sites such as refrigerated warehouses and transport carriages often have a large number of metal structures, and the goods are packed in complex and densely stacked. Metal can cause RFID signals to reflect, resulting in multipath effects, leading to signal superposition or interference, and increasing RFID reading errors. In addition, packaging materials, liquids, ice cubes, etc. can absorb or shield signals, further exacerbating signal attenuation.

[0010] (2) When the space in a cold chain warehouse is filled with goods, especially when they are densely stacked, it is difficult for RFID signals to penetrate the entire warehouse, resulting in a reading blind spot and affecting the integrity of the data.

[0011] (3) The frequent movement of goods during transportation may cause the RFID tag to temporarily leave the reading area, resulting in the loss of tracking data.

[0012] (4) Real-time monitoring of the location and status of goods is very important in cold chain logistics, but the massive amount of data collected by the RFID system will bring a large processing burden to the backend system. If the data processing or transmission speed is insufficient, it may lead to poor real-time performance and inability to monitor and track the status of goods in a timely manner, thus affecting the efficiency of logistics management. Summary of the invention

[0013] Purpose of the invention: In order to solve the problems of too many existing RFID antenna devices in cold chain logistics, resulting in congestion of spectrum channels, as well as the problems of single mode, difficulty in achieving modal multiplexing, and large divergence angle of vortex waves in the OAM generation method, the present invention proposes a low-loss and fading-resistant orbital angular momentum RFID array antenna, which can be used in the field of cold chain logistics. It can not only effectively improve the utilization of frequency bands, but also has important significance for the development of OAM multiplexing technology in the field of microwave radio frequency, and provides a new frequency multiplexing method to alleviate the increasingly crowded spectrum resources.

[0014] Technical solution: A low-loss and anti-fading orbital angular momentum RFID array antenna, which includes, from top to bottom: N array units, a first dielectric substrate, a metal ground plate, a second dielectric substrate and a feed network;

[0015] N array units are centrally symmetrical and distributed on the upper surface of the first dielectric substrate at equal angular intervals along the circumference. The feeding amplitude of each array unit is the same, and the phase difference between two adjacent array units in the clockwise direction satisfies: Where l is the orbital angular momentum mode required for the radiation beam, and the number of array elements satisfies: -N / 2<l<N / 2;

[0016] Each array unit is a circular structure, and one or more strip-shaped gaps are added to the array unit, and the center position of each strip-shaped gap is located at the center position of the array unit;

[0017] The metal ground plate is provided with a strip-shaped gap corresponding to the center position of the array unit. The feeding network is fed through the gap on the metal ground plate. The feeding amplitude of each array unit is the same, so as to generate vortex electromagnetic waves.

[0018] Furthermore, the feed network is of equal amplitude Phase difference one-point N feed network.

[0019] Furthermore, the dimensions of the first dielectric substrate and the second dielectric substrate are determined by characteristic mode theory analysis.

[0020] Furthermore, the radius size of each array unit is determined by characteristic mode theory analysis.

[0021] Furthermore, the feeding network includes: a T-type power divider with a phase difference of 45°, a T-type power divider with a phase difference of 90°, and a T-type power divider with a phase difference of 180°; the feeding network is located on the lower surface of the second dielectric substrate, and the feeding port of the feeding network is transmitted through the transmission line, and feeds each array unit through the gap on the metal ground plate;

[0022] A T-type power divider with a phase difference of 90° is connected to each of the two output ports of the T-type power divider with a phase difference of 180°, a T-type power divider with a phase difference of 45° is connected to each of the two output ports of the T-type power divider with a phase difference of 90°, and the output port of each T-type power divider with a phase difference of 45° constitutes a feeding port of the feeding network;

[0023] The T-type power divider with a phase difference of 45°, the T-type power divider with a phase difference of 90° and the T-type power divider with a phase difference of 180° are all deformations of the original T-type power divider. The deformations include: introducing an inverted U-shaped transmission line at both ends of the original T-type power divider, and the lengths of the introduced inverted U-shaped transmission lines are different.

[0024] Furthermore, the width of the U-shaped mouth of the inverted U-shaped transmission line is not less than a quarter of a wavelength.

[0025] Furthermore, a transmission line is added at the output port of each T-type power divider with a phase difference of 45° to form a feeding port of the feeding network.

[0026] Beneficial effects: Compared with the prior art, the present invention has the following advantages:

[0027] (1) Based on the circular antenna structure, the present invention designs an orbital angular momentum RFID array antenna consisting of eight uniformly arranged units. The broadband vortex wave antenna unit and its array are miniaturized and have a small divergence angle. Through a precise phase shift feeding network, the feeding phase of each antenna unit is precisely controlled, so that there is a specific phase difference between the eight circular antenna units, thereby generating vortex waves. Compared with traditional RFID electronic tags, the present invention has good low loss and anti-attenuation properties;

[0028] (2) The present invention can generate OAM vortex electromagnetic waves, which can alleviate channel pressure and significantly improve frequency band utilization. It solves the problems of single mode of OAM generation method, difficulty in realizing mode multiplexing, and large divergence angle of vortex waves when applying orbital angular momentum (OAM) technology in the field of wireless communication. It is of great significance to promote the development of OAM multiplexing technology in the field of microwave radio frequency and becomes the key foundation for applying OAM technology to wireless communication systems.

[0029] (3) The application of the OAM vortex electromagnetic waves generated by the present invention in cold chain logistics has the following advantages: OAM vortex electromagnetic waves allow multiple data streams to be transmitted at the same frequency through different orbital angular momentum modes, thereby improving the data transmission bandwidth and rate. Therefore, in cold chain logistics, RFID antennas can read cargo information more quickly and efficiently, reducing reading delays when cargo is piled up, which is extremely beneficial for real-time monitoring and management. Traditional RFID antennas may have blind spots in cold chain environments where cargo is densely stacked, while OAM vortex electromagnetic waves can increase the transmission capacity and coverage of signals, so that RFID signals can achieve reliable coverage in a wider area, helping to more comprehensively read cargo data in storage or during transportation. OAM vortex electromagnetic waves transmit data through different angular momentum modes, which can reduce the interference problem of signals in complex environments to a certain extent compared to traditional RFID. The metal structures, cargo stacking and other signal interference sources commonly seen in cold chain logistics have relatively little impact on OAM signals, which can improve the accuracy of data reading and effectively alleviate the channel pressure in the cold chain logistics system. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a schematic diagram of an N-element circular array antenna;

[0031] Figure 2 It is a front view of the antenna unit structure in the present invention;

[0032] Figure 3 is a front view of the antenna array structure of the present invention;

[0033] Figure 4 is a side view of the antenna array structure of the present invention;

[0034] Figure 5 It is a front view of the one-to-eight feeding network of the present invention;

[0035] Figure 6 is the modal significance map of different radii of the antenna array in the present invention;

[0036] Figure 7 is a simulated S-parameter diagram of the antenna array of the present invention;

[0037] Figure 8 This is the phase distribution diagram of the vortex electromagnetic wave l=1 mode of the present invention. DETAILED DESCRIPTION

[0038] This embodiment proposes a low-loss and resistant orbital angular momentum RFID array antenna, which is applied in the field of cold chain logistics. By introducing OAM vortex electromagnetic waves and utilizing their unique spatial multiplexing, mode orthogonality and propagation characteristics, the performance of the RFID system is significantly improved, especially in complex scenarios such as multi-tag, high concurrency and long-distance identification, bringing new breakthroughs to the development of RFID technology.

[0039] The technical solution of this embodiment is now further described in conjunction with the accompanying drawings.

[0040] Array antenna is a widely used beam generation method. The method of using array antenna to generate OAM beams was proposed relatively early. Generally, the more commonly used method to generate OAM beams is the circular array method.

[0041] like Figure 1 As shown, N array units are placed at equal intervals along the circumference to form a circular array. In this embodiment, N is 8; the feeding amplitude of each array element is the same, and the phase difference between two adjacent array elements in the clockwise direction satisfies: Where l is the orbital angular momentum mode required for the radiated beam. However, the number of array elements in the array antenna determines the maximum value of the OAM mode that can be generated, and the number of array elements must satisfy: -N / 2<l<N / 2.

[0042] The front view of the array unit proposed in this embodiment is as follows Figure 2 As shown, it is obtained by adding strip-shaped gaps to a circular structure, wherein at least a rectangular gap exists at the center of the array unit to facilitate feeding by the feeding network. The array antenna proposed in this embodiment is as follows Figure 3 and Figure 4As shown, it includes eight array units arranged on the upper surface of a first dielectric substrate 1, the first dielectric substrate 1, a metal ground plate 2 arranged on the lower surface of the first dielectric substrate 1, a second dielectric substrate 3 and a feeding network arranged on the lower surface of the second dielectric substrate 3.

[0043] On the metal ground plate 2 located between the first dielectric substrate 1 and the second dielectric substrate 3, there is a rectangular gap at the center position of the eight antenna units on the upper surface of the first dielectric substrate 1 to facilitate feeding by the feeding network.

[0044] A plurality of array units are distributed on the upper surface of the first dielectric substrate 1 in a centrally symmetrical manner and at equal angular intervals along the circumference; the structure of each array unit is a circular structure.

[0045] This embodiment uses a feeding network to feed electricity through the gap on the metal ground plate 2. The feeding network is a feeding network with equal amplitude and 45° phase difference of one-eighth. Through intermediate feeding, the vortex electromagnetic wave mode number l=1 is achieved. Figure 5 As shown, the feeding network of the present embodiment mainly comprises: a T-type power divider 4 with a phase difference of 45°, a T-type power divider 5 with a phase difference of 90° and a T-type power divider 6 with a phase difference of 180°; two output ports of the T-type power divider with a phase difference of 180° are connected to a T-type power divider with a phase difference of 90°, two output ports of each T-type power divider with a phase difference of 90° are connected to a T-type power divider with a phase difference of 45°, and the output port of each T-type power divider with a phase difference of 45° constitutes a feeding port of the feeding network; the feeding network is located on the lower surface of the second dielectric substrate 3, and the feeding port of the feeding network is transmitted through a transmission line, and each array unit is fed through the gap on the metal ground plate 2; the transmission line used in the present embodiment is a transmission line with an impedance of 50Ω. Specifically, the T-type power divider 4 with a phase difference of 45°, the T-type power divider 5 with a phase difference of 90°, and the T-type power divider 6 with a phase difference of 180° proposed in this embodiment are deformations of the original T-type power divider. An inverted U-shaped transmission line is introduced at both ends of the original T-type power divider, and the lengths of the introduced inverted U-shaped transmission lines are different. At the same time, in order to be conformal with the feeding network, a transmission line is added at the output port of each T-type power divider with a phase difference of 45°.

[0046] like Figure 5 As shown in the figure, according to the basic theory of orbital angular momentum, to generate an OAM vortex wave with a mode number of 1, the phase of each output port feeding into the array unit must satisfy a difference of 45°. By analogy, it is necessary to introduce a T-type power divider with a phase difference of 45° and 90°, and introduce microstrip lines of different lengths in front of its two output ports to meet the phase difference required by the output port. This can make the structures on the two arms of the T-type power divider consistent, avoiding imbalance between the two output ports. At the same time, in order to avoid coupling, the width of the U-shaped mouth of the inverted U-shaped microstrip extension line should be no less than a quarter of a wavelength.

[0047] In this embodiment, the first dielectric substrate 1 and the second dielectric substrate 3 are both FR4 dielectric substrates, the dielectric loss angle of the FR4 dielectric substrate is 0.02°, the relative dielectric constant is 4.4, the thickness of the dielectric substrate is 0.8 mm, and the area of ​​the dielectric substrate is 300 mm×340 mm. In this embodiment, the area of ​​a single antenna is approximately 830πmm2.

[0048] The selection of the array radius in this embodiment needs to take into account the particularity of the array unit. If the array radius is too small, the arms of some array units may overlap. On the contrary, if the array radius is too large, the energy radiated by the antenna will be too dispersed, thereby causing the performance of the vortex electromagnetic wave to deteriorate.

[0049] After analyzing the array antenna using the characteristic mode theory, Figure 6 The characteristic angle curves of the first four modes of array antennas with different radii between 2-3GHz are given in . As shown in the figure, it can be observed that the significance of mode 1 and mode 3 between 2-3GHz is greater than 0.707 only when the radius is 100mm. In contrast, the significance of mode 2 is always below this threshold. The significance of mode 4 near 2.45GHz is lower than 0.707, and the four modes of other radii are all lower than 0.707. This is because too small a radius may lead to resonant interference caused by overlap between array element antennas, while too large a radius will make the radiation intensity of the array element antenna too dispersed, making the vorticity not obvious enough. Therefore, it is challenging to effectively excite this mode.

[0050] Finally, the final size of the dielectric substrate was determined to be 300 mm × 300 mm through characteristic mode analysis, while the radius of the array was selected to be 100 mm.

[0051] Electromagnetic simulation is performed on the array antenna proposed in this embodiment, and the orbital angular momentum mode l=1 is obtained, and its return loss is as follows: Figure 7 It can be seen that the maximum return loss of the array unit is -29.69 dB at 2.44 GHz, and the array antenna S11 proposed in this embodiment reaches 28.85 dB at 2.45 GHz, which has good performance. Figure 8 The electric field phase distribution diagram of the OAM eddy current electromagnetic wave with mode l=1 is depicted.

[0052] In cold chain logistics, RFID tags are often placed on metal shelves, refrigerated compartments or inside cargo packaging. These environments cause the signal to be affected by multipath effects and attenuation. After the introduction of OAM technology, the anti-interference ability of the antenna is significantly improved, which can effectively reduce the loss of signals on reflective objects and ensure the reliability and accuracy of data transmission. In addition, OAM vortex electromagnetic waves can reduce the loss of electromagnetic waves during transmission through spiral propagation paths and specially designed antenna arrays. Compared with the signal loss that is prone to occur in traditional antennas in harsh environments such as humidity and temperature changes, OAM technology can transmit electromagnetic energy more efficiently, thereby reducing unnecessary energy loss and improving communication effects.

Claims

1. A low-loss and anti-fading orbital angular momentum RFID array antenna, characterized in that: From top to bottom, it includes: N array units, a first dielectric substrate, a metal grounding plate, a second dielectric substrate and a feeding network; N array units are centrally symmetrical and distributed on the upper surface of the first dielectric substrate at equal angular intervals along the circumference. The feeding amplitude of each array unit is the same, and the phase difference between two adjacent array units in the clockwise direction satisfies: Where l is the orbital angular momentum mode required for the radiation beam, and the number of array elements satisfies: -N / 2<l<N / 2; Each array unit is a circular structure, and one or more strip-shaped gaps are added to the array unit, and the center position of each strip-shaped gap is located at the center position of the array unit; The metal ground plate is provided with a strip-shaped gap corresponding to the center position of the array unit. The feeding network is fed through the gap on the metal ground plate. The feeding amplitude of each array unit is the same, so as to generate vortex electromagnetic waves.

2. The low-loss and anti-fading orbital angular momentum RFID array antenna according to claim 1, characterized in that: The feeding network is of constant amplitude Phase difference one-point N feed network.

3. The low-loss and anti-fading orbital angular momentum RFID array antenna according to claim 1, characterized in that: The sizes of the first dielectric substrate and the second dielectric substrate are determined by characteristic mode theory analysis.

4. The low-loss and anti-fading orbital angular momentum RFID array antenna according to claim 3, characterized in that: The radius size of each array unit is determined by characteristic mode theory analysis.

5. The low-loss and anti-fading orbital angular momentum RFID array antenna according to claim 1, characterized in that: The feeding network comprises: a T-type power divider with a phase difference of 45°, a T-type power divider with a phase difference of 90°, and a T-type power divider with a phase difference of 180°; the feeding network is located on the lower surface of the second dielectric substrate, and the feeding port of the feeding network is transmitted through the transmission line to feed each array unit through the gap on the metal ground plate; A T-type power divider with a phase difference of 90° is connected to each of the two output ports of the T-type power divider with a phase difference of 180°, a T-type power divider with a phase difference of 45° is connected to each of the two output ports of the T-type power divider with a phase difference of 90°, and the output port of each T-type power divider with a phase difference of 45° constitutes a feeding port of the feeding network; The T-type power divider with a phase difference of 45°, the T-type power divider with a phase difference of 90° and the T-type power divider with a phase difference of 180° are all deformations of the original T-type power divider. The deformations include: introducing an inverted U-shaped transmission line at both ends of the original T-type power divider, and the lengths of the introduced inverted U-shaped transmission lines are different.

6. The low-loss and anti-fading orbital angular momentum RFID array antenna according to claim 5, characterized in that: The width of the U-shaped mouth of the inverted U-shaped transmission line is not less than a quarter of a wavelength.

7. The low-loss and anti-fading orbital angular momentum RFID array antenna according to claim 5, characterized in that: A transmission line is added at the output port of each T-type power divider with a phase difference of 45° to form a feeding port of the feeding network.

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