Polarization reconfigurable circularly polarized end-fire traveling wave antenna and wireless communication system

Abstract

This application provides a polarization-reconfigurable circularly polarized end-fire traveling-wave antenna and a wireless communication system, belonging to the field of wireless communication technology. The antenna includes a first radiating element and a second radiating element, both of which are traveling-wave antenna structures. The polarization directions of the first and second radiating elements are perpendicular to each other. The output port of the first radiating element and the input port of the second radiating element are cascaded. The second radiating element has interchangeable first and second mounting orientations. The second radiating element rotates about its longitudinal axis relative to the first mounting orientation by a first preset angle to be in the second mounting orientation. When the second radiating element is in the first mounting orientation, the antenna radiates a left-hand circularly polarized wave; when the second radiating element is in the second mounting orientation, the antenna radiates a right-hand circularly polarized wave. This application achieves an antenna that is miniaturized, low-cost, circularly polarized, and whose polarization direction can be flexibly reconfigured.

Description

Technical Field

[0001] This application relates to the field of wireless communication technology, and in particular to a polarization-reconfigurable circularly polarized end-fire traveling wave antenna and a wireless communication system. Background Technology

[0002] Achieving stable and efficient wireless communication coverage in enclosed, narrow spaces such as railway tunnels and subways is a major technical challenge. Traditional coverage solutions for such scenarios have the following shortcomings: leaky cable solutions, while providing uniform signal coverage, are extremely expensive, require laying cables along the entire length of the tunnel, are complex to install, and have weak support for multiple-input multiple-output (MIMO) technology. Distributed antenna systems require the deployment of numerous low-gain antennas and associated signal sources, resulting in complex network structures and high construction and maintenance costs.

[0003] Traditional circularly polarized antennas, such as axial-mode helical antennas, while providing circularly polarized signals to combat multipath fading, are typically large and difficult to install in space-constrained tunnels with strict safety regulations. Furthermore, their circular polarization performance bandwidth is narrow, and their polarization direction is fixed, making them inflexible for adapting to different communication needs. Alternatively, research has been conducted on achieving circular polarization using leaky-wave antennas. However, these schemes usually require special design and fabrication on each radiating stub to excite two field components with equal amplitude and orthogonal phase, thus synthesizing a circularly polarized wave. This meticulous, non-standard processing of each stub significantly increases the antenna's design complexity, fabrication difficulty, and manufacturing cost, making them unsuitable for large-scale production and engineering application. Summary of the Invention

[0004] This application provides a polarization-reconfigurable circularly polarized end-fire traveling wave antenna and a wireless communication system, which realizes an antenna that is miniaturized, low-cost, circularly polarized and whose polarization direction can be flexibly reconfigured, and can adapt to the high-quality wireless coverage requirements of complex and narrow spaces.

[0005] In a first aspect, this application provides a polarization-reconfigurable circularly polarized end-fire traveling-wave antenna, comprising: The first radiating element and the second radiating element are both traveling wave antenna structures. The polarization directions of the first radiating element and the second radiating element are perpendicular to each other. The output port of the first radiating element and the input port of the second radiating element are cascaded. The second radiating element has an interchangeable first mounting orientation and a second mounting orientation. The second radiating element rotates about the longitudinal axis by a first preset angle relative to the first mounting orientation to be in the second mounting orientation. When the second radiating element is in the first mounting orientation, the antenna radiates a left-hand circularly polarized wave. When the second radiating element is in the second mounting orientation, the antenna radiates a right-hand circularly polarized wave.

[0006] In some embodiments, the structural dimensions of the first radiating unit and the second radiating unit are configured such that, corresponding to the radiating position of the second radiating unit, there is a phase difference of a second preset angle between the radiated electromagnetic wave from the first radiating unit and the radiated electromagnetic wave of the second radiating unit itself.

[0007] In some embodiments, the traveling-wave antenna structure is a slow-wave structure, and the lengths of the first radiating element and the second radiating element both satisfy the following relationship: (β-k0)·L=π / 2; The traveling-wave antenna structure is a fast-wave structure, and the lengths of the first radiating element and the second radiating element both satisfy the following relationship: (k0-β)·L=π / 2; Wherein, β is the phase constant of the electromagnetic wave inside the traveling wave antenna structure, k0 is the phase constant of the electromagnetic wave in free space, and L is the length of the first radiating element or the length of the second radiating element.

[0008] In some embodiments, the energy ratio radiated by the first radiating element and the energy ratio radiated by the second radiating element satisfy the following relationship: X1 = (1-X1)·X2; Wherein, X1 is the proportion of energy radiated by the first radiating unit, and X2 is the proportion of energy radiated by the second radiating unit.

[0009] In some embodiments, the first radiating unit and the second radiating unit are connected by a rotary connection structure, the rotary connection structure being used to rotate the second radiating unit about a longitudinal axis to switch between the first mounting orientation and the second mounting orientation.

[0010] In some embodiments, the rotary connection structure includes a rotatable coaxial connector, the inner and outer conductors of which are used to maintain the radio frequency connection between the output port of the first radiating unit and the input port of the second radiating unit.

[0011] In some embodiments, the traveling wave antenna structure is a double-sided offset parallel plate waveguide structure, which includes a top metal plate and a bottom metal plate that extend longitudinally and are arranged parallel to each other and spaced apart. The top metal plate and the bottom metal plate have a preset offset in the lateral width direction. Multiple radial sawtooth teeth are arranged longitudinally on one side of the top metal plate and one side of the bottom metal plate, with the radial sawtooth teeth extending from the longitudinal edge toward the outside of the double-sided offset parallel plate waveguide structure.

[0012] In some embodiments, both the first radiating unit and the second radiating unit include an input port and an output port, both of which are coaxial ports. The inner conductor of the coaxial port is connected to the corresponding top metal plate, and the outer conductor of the coaxial port is connected to the corresponding bottom metal plate.

[0013] In some embodiments, the radial saw teeth are rectangular teeth, the height of the rectangular teeth is 0.1 to 0.12 times the working wavelength, and the center-to-center distance between adjacent rectangular teeth is 0.05 to 0.3 times the working wavelength.

[0014] Secondly, this application also provides a wireless communication system, including a polarization-reconfigurable circularly polarized end-fire traveling-wave antenna as described in the first aspect.

[0015] Compared to traditional circularly polarized antennas that require complex spiral structures or special stub designs, this application uses two cascaded linearly polarized traveling-wave modules with essentially identical structures. The module itself has a simple structure, greatly reducing processing difficulty and manufacturing costs, making it suitable for large-scale deployment. Circularly polarized antennas, as coverage units, offer higher channel quality and have broad market prospects. Furthermore, reliable switching between left-hand and right-hand circular polarization can be achieved by simply rotating the second radiating element mechanically. Utilizing a small, meandering tunnel leaky wave antenna provides flexibility to adapt to different communication protocols, resist specific polarization interference, or optimize link quality—capabilities lacking in traditional fixed-polarization antennas. In addition, the antenna maintains good circular polarization characteristics over a wide coverage angle, which is beneficial for improving wireless communication quality in narrow spaces such as tunnels and subways. Simultaneously, the antenna's end-fire characteristics ensure that its maximum radiation direction is along the tunnel's longitudinal direction, similar to leaky cables, but with lower deployment costs and more flexible polarization characteristics. Its modular design also allows for increased gain by adding cascaded units to meet different coverage distance requirements. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced one by one below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0017] Figure 1 This is a three-dimensional structural schematic diagram of a polarization-reconfigurable circularly polarized end-fire traveling wave antenna provided in an embodiment of this application; Figure 2 This is a front view schematic diagram of a polarization-reconfigurable circularly polarized end-fire traveling wave antenna provided in an embodiment of this application; Figure 3This is a front view schematic diagram of a polarization-reconfigurable circularly polarized end-fire traveling wave antenna provided in an embodiment of this application; Figure 4 This is a schematic diagram of the structure of a traditional axial-mode spiral antenna; Figure 5 This is a schematic diagram of the structure of a traditional leaky-wave circularly polarized antenna; Figure 6 This is a schematic diagram of a slow-wave radiation unit with a left-hand circular polarization structure and the electric field directions of the two radiation units, provided in an embodiment of this application. Figure 7 This is a schematic diagram of a right-hand circularly polarized structure of a slow-wave radiation unit and the electric field directions of the two radiation units provided in an embodiment of this application; Figure 8 This is a schematic diagram of a right-hand circularly polarized structure of a fast-wave radiation unit and the electric field directions of the two radiation units provided in an embodiment of this application; Figure 9 This is a schematic diagram of a left-handed circularly polarized structure of a fast-wave radiation unit and the electric field directions of the two radiation units provided in an embodiment of this application. Figure 10 This is a front view structural schematic diagram of a first radiating unit or a second radiating unit provided in an embodiment of this application; Figure 11 This application provides a three-dimensional radiation pattern of an antenna operating at a frequency of 2.6 GHz. Figure 12 This is an embodiment of the present application providing the axial ratio curves of an antenna in the E-plane and H-plane at a working frequency of 2.6 GHz. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0019] Figure 1 This is a three-dimensional structural schematic diagram of a polarization-reconfigurable circularly polarized end-fire traveling wave antenna provided in an embodiment of this application. Figure 2 This is a front view schematic diagram of a polarization-reconfigurable circularly polarized end-fire traveling wave antenna provided in an embodiment of this application. Figure 3 This is a front view schematic diagram of a polarization-reconfigurable circularly polarized end-fire traveling-wave antenna provided in an embodiment of this application. Combined with... Figures 1 to 3The polarization-reconfigurable circularly polarized end-fire traveling-wave antenna includes: a first radiating element 1 and a second radiating element 2. Both the first radiating element 1 and the second radiating element 2 are traveling-wave antenna structures. The polarization directions of the first radiating element 1 and the second radiating element 2 are perpendicular to each other. The output port of the first radiating element 1 and the input port of the second radiating element 2 are cascaded. The second radiating element 2 has an interchangeable first mounting orientation and a second mounting orientation. The second radiating element 2 rotates about its longitudinal axis by a first preset angle relative to the first mounting orientation to be in the second mounting orientation. When the second radiating element 2 is in the first mounting orientation, the antenna radiates a left-hand circularly polarized wave. When the second radiating element 2 is in the second mounting orientation, the antenna radiates a right-hand circularly polarized wave.

[0020] Specifically, polarization reconfigurability refers to the polarization mode of the electromagnetic waves radiated by the antenna. In this embodiment, it refers to the rotation direction of circular polarization, i.e., left-hand or right-hand rotation, which can be switched and reconfigured as needed. A circularly polarized end-fire traveling-wave antenna is an antenna capable of radiating circularly polarized electromagnetic waves, with the maximum radiation direction along the antenna structure axis, corresponding to end-fire. Simultaneously, the electromagnetic wave signal is transmitted and radiated along the antenna structure in the form of a traveling wave. The first radiating element 1 and the second radiating element 2 constitute the two basic functional modules of this antenna, each with independent signal input, transmission, radiation, and output functions. The characteristic of the traveling-wave antenna structure is that the fed electromagnetic wave energy is continuously and regularly radiated out during propagation along the antenna structure, and the remaining energy is ultimately absorbed by the matched load at the end, thus structurally avoiding strong reflected waves and having the advantage of a wide operating bandwidth.

[0021] "Perpendicular polarization directions" means that the direction of the electromagnetic wave electric field vector mainly radiated by the first radiating element 1 and the direction of the electromagnetic wave electric field vector mainly radiated by the second radiating element 2 form a 90-degree angle in space. For example, one element radiates a vertically polarized wave, and the other element radiates a horizontally polarized wave. "Cascaded connection" means that the signal output terminal of the first radiating element 1 and the input terminal of the second radiating element 2 are directly electrically connected, allowing the radio frequency signal to pass sequentially through the first radiating element 1 and the second radiating element 2. "Installation orientation" refers to the placement and orientation of the second radiating element 2 in space. "Longitudinal axis" refers to the direction extending along the length of the second radiating element 2, which is also the main direction of electromagnetic wave propagation and the direction of the end-fired beam when the second radiating element 2 is used as a traveling wave antenna. Figure 2 In direction A.

[0022] Figure 4 This is a schematic diagram of a traditional axial-mode helical antenna. (Example) Figure 4As shown, although axial-mode spiral antennas can operate with a wide bandwidth, such as ±30% or even higher of the center frequency, their bandwidth for good circular polarization performance, i.e., low axial ratio, is much narrower. Once the frequency deviates from the design center frequency, the axial ratio deteriorates rapidly, leading to a decrease in polarization purity. Axial-mode spiral antennas require an external grounded reflector, which is relatively large. Furthermore, to ensure good performance, the spiral circumference of an axial-mode spiral antenna is typically one wavelength, increasing the lateral dimension. Figure 5 This is a schematic diagram of a traditional leaky-wave circularly polarized antenna. (Example:) Figure 5 As shown, each radiating stub of a traditional leaky circularly polarized antenna requires a specially designed structure to achieve better circular polarization performance. Each stub is quite complex, which increases the antenna's manufacturing cost and complexity, making it unsuitable for large-scale deployment.

[0023] This application addresses the shortcomings of existing circularly polarized end-fire antennas, such as axial-mode helical antennas (large size, narrow circular polarization bandwidth) and complex leaky-wave antennas (high manufacturing cost and complex structure). It proposes a simplified scheme based on splicing two linearly polarized traveling-wave modules. Specifically, the embodiments of this application cascade two traveling-wave antenna structures with mutually perpendicular polarization directions, namely, a first radiating element 1 and a second radiating element 2. The signal is input from the first radiating element 1, and part of the energy is radiated by it, forming the first spatially orthogonal linearly polarized component, such as a vertical polarization component. The remaining energy is transmitted to the second radiating element 2, where it is radiated, forming the second spatially orthogonal linearly polarized component, such as a horizontal polarization component.

[0024] The key to achieving circular polarization lies in the fact that when two spatially orthogonal linearly polarized waves radiate and superimpose, they must satisfy the conditions of approximately equal amplitude and a 90-degree phase difference. This application ensures that, within the radiation region where the second radiation unit 2 is located, there is an approximately 90-degree phase difference between the wave from the first radiation unit 1 and the wave radiated by the second radiation unit 2 itself, by precisely designing the physical length, internal waveguide structure, and other structural dimensions of the first radiation unit 1 and the second radiation unit 2 itself.

[0025] This is achieved by mechanically changing the installation orientation of the second radiating unit 2 around its own longitudinal axis. Specifically, when the second radiating unit 2 is in the first installation orientation, for example, with its radiating serrations facing a specific side, the spatial orientation of its radiation field, together with the radiation field of the first radiating unit 1, synthesizes a left-handed circularly polarized wave. When switching is required, the second radiating unit 2 is rotated around its longitudinal axis by a first preset angle, preferably 180 degrees, to the second installation orientation. At this time, the spatial orientation of its radiation field is reversed, causing a change in the synthesis relationship with the radiation field of the first radiating unit 1, thereby generating a right-handed circularly polarized wave. This principle holds true for both slow-wave and fast-wave structures, only the initial correspondence differs. This switching does not involve complex circuit reconfiguration; it is accomplished solely through the relative rotation of the units, achieving reconfigurable polarization.

[0026] Figure 6 This is a schematic diagram of a left-handed circularly polarized structure under a slow-wave radiating unit and the electric field directions of the two radiating units, provided in an embodiment of this application. Figure 6 As shown, both the first radiating element 1 and the second radiating element 2 are slow-wave structures. The phase of the second radiating element 2 leads the first radiating element 1 by 90 degrees. Therefore, the phase of the electric field of the second radiating element 2 is... Where j is the imaginary unit, Figure 6 In this context, Ex represents the electric field generated by the second radiating unit 2, and Ey represents the electric field generated by the first radiating unit 1. The first radiating unit 1 and the second radiating unit 2 can form a left-handed circularly polarized wave in space. Figure 7 This is a schematic diagram of a right-hand circularly polarized structure under a slow-wave radiation unit and the electric field directions of the two radiation units, provided in an embodiment of this application. Figure 7 The second radiating unit 2 compared to Figure 6 The second radiating unit 2 rotates 180 degrees around the longitudinal axis, therefore its rotation direction is also the same as that of the second radiating unit 2. Figure 6 Conversely, the first radiating unit 1 and the second radiating unit 2 can form right-hand circularly polarized waves in space.

[0027] Figure 8 This is a schematic diagram of a right-hand circularly polarized structure under a fast-wave radiation unit and the electric field directions of the two radiation units, provided in an embodiment of this application. Figure 8 As shown, both the first radiating element 1 and the second radiating element 2 are fast-wave structures. The phase of the second radiating element 2 lags behind the first radiating element 1 by 90 degrees. Therefore, the electric field phase of the second radiating element 2 is... The first radiating unit 1 and the second radiating unit 2 can form right-hand circularly polarized waves in space. Figure 9 This is a schematic diagram of a left-handed circularly polarized structure of a fast-wave radiation unit and the electric field directions of the two radiation units provided in an embodiment of this application. Figure 9 The second radiating unit 2 compared to Figure 8The second radiating unit 2 rotates 180 degrees around the longitudinal axis, therefore its rotation direction is also the same as that of the second radiating unit 2. Figure 8 Conversely, the first radiating unit 1 and the second radiating unit 2 can form left-handed circularly polarized waves in space.

[0028] Therefore, compared to traditional circularly polarized antennas that require complex spiral structures or special stub designs, the embodiments of this application employ two cascaded linearly polarized traveling wave modules with essentially identical structures. The modules themselves have a simple structure, greatly reducing processing difficulty and manufacturing costs, making them suitable for large-scale deployment. Circularly polarized antennas, as coverage units, offer higher channel quality and have broad market prospects. Furthermore, a simple mechanical rotation of the second radiating element 2 allows for reliable switching between left-hand and right-hand circular polarization. The use of a small, meandering tunnel leaky wave antenna provides flexibility to adapt to different communication protocols, resist specific polarization interference, or optimize link quality—capabilities not found in traditional fixed-polarization antennas. Additionally, the antenna maintains good circular polarization characteristics over a wide coverage angle, which is beneficial for improving wireless communication quality in narrow spaces such as tunnels and subways. Moreover, the antenna's end-fire characteristics ensure that its maximum radiation direction is along the tunnel's longitudinal direction, similar to a leaky cable, but with lower deployment costs and more flexible polarization characteristics. Its modular design also allows for increased gain by adding cascaded units to meet different coverage distance requirements.

[0029] In some embodiments, the structural dimensions of the first radiation unit 1 and the second radiation unit 2 are configured such that, corresponding to the radiation position of the second radiation unit 2, there is a phase difference of a second preset angle between the radiated electromagnetic wave from the first radiation unit 1 and the radiated electromagnetic wave from the second radiation unit 2 itself.

[0030] Specifically, the structural dimensions include, but are not limited to, the length, width, and height of the radiating element, as well as the geometric dimensions of the radiating structure thereon. The phase difference of the second preset angle is preferably 90 degrees, which is a condition for synthesizing a standard circularly polarized wave from two spatially orthogonal linearly polarized waves of equal amplitude. To achieve high-quality circularly polarized radiation, it is necessary to control the radiated electromagnetic wave from the first radiating element 1 and the radiated electromagnetic wave from the second radiating element 2 itself to have a stable phase difference of approximately 90 degrees at the radiation region or far-field observation point where the second radiating element 2 is located. This phase difference is jointly determined by the propagation delay of the electromagnetic wave within the two radiating elements, the signal transmission delay between the two radiating elements, and the spatial path difference. By carefully designing and optimizing the structural dimensions of the first radiating element 1 and the second radiating element 2, especially their electrical lengths, this phase condition can be precisely satisfied.

[0031] Therefore, by taking the phase difference condition as the design objective and determining the structural dimensions accordingly, the embodiments of this application fundamentally ensure that the antenna can generate high-purity circularly polarized waves, i.e., low axial ratio. This enables the antenna to maintain good circular polarization performance even over a wide beam angle range, thereby improving the reliability of the communication link.

[0032] In some embodiments, the traveling-wave antenna structure is a slow-wave structure, and the lengths of the first radiating element 1 and the second radiating element 2 both satisfy the following relationship: (β-k0)·L=π / 2; The traveling wave antenna structure is a fast wave structure, and the lengths of the first radiating element 1 and the second radiating element 2 both satisfy the following relationship: (k0-β)·L=π / 2; Where β is the phase constant of the electromagnetic wave inside the traveling wave antenna structure, k0 is the phase constant of the electromagnetic wave in free space, and L is the length of the first radiating element 1 or the length of the second radiating element 2.

[0033] Specifically, a slow-wave structure refers to a structure where the propagation phase velocity of electromagnetic waves within the traveling-wave antenna structure is less than the speed of light in free space, i.e., β is greater than k0. A fast-wave structure refers to a structure where the propagation phase velocity of electromagnetic waves within the traveling-wave antenna structure is greater than the speed of light in free space, i.e., β is less than k0. The derivation of the above two formulas is based on a detailed analysis of the phase relationship between the radiation fields of the two radiating elements, considering the phase accumulation β·L of the wave propagating within the element and the phase delay k0·d of the wave propagating in the free space segment between elements, where d is related to the layout of the radiating elements and can be correlated with L under specific designs. Satisfying this formula ensures that the two radiation fields achieve the required 90-degree phase difference at a specified location.

[0034] Therefore, the embodiments of this application provide clear and quantifiable design criteria. Antenna designers can directly calculate the physical length L of the required radiating element based on the specific waveguide structure that determines the β value and the operating frequency that determines the k0 value, thereby completing the antenna design efficiently and accurately, avoiding blind parameter trial and error, and ensuring the theoretical optimality of circular polarization performance.

[0035] In some embodiments, the energy ratio radiated by the first radiating element 1 and the energy ratio radiated by the second radiating element 2 satisfies the following relationship: X1 = (1-X1)·X2; Where X1 is the energy ratio radiated by the first radiating unit 1, and X2 is the energy ratio radiated by the second radiating unit 2.

[0036] Specifically, X1 is defined as the proportion of the total energy fed into the input port of the first radiating unit 1 that is radiated out by the first radiating unit 1 itself; X2 is defined as the proportion of the energy fed into the input port of the second radiating unit 2 that is radiated out by the second radiating unit 2 itself. To achieve perfect circular polarization, not only a 90-degree phase difference is required, but also that the amplitudes of the two orthogonal components are approximately equal. In the cascaded structure of this application, this means that the total energy radiated into space by the first radiating unit 1 and the second radiating unit 2 should be approximately equal. Let the total energy input to the first radiating unit 1 be 1, and the proportion of energy radiated by the first radiating unit 1 be X1. Then, the remaining energy (1-X1) flows into the second radiating unit 2, and the proportion of energy radiated by the second radiating unit 2 is X2. The remaining (1-X2) proportion of energy flows out of the output port of the second radiating unit 2 and is absorbed by the end-matched load. The energy radiated by the second radiating unit 2 is (1-X1)·X2. Let the radiated energy of the two units be equal, i.e., X1=(1-X1)·X2. The discrete values ​​of the radiation proportions calculated by this formula are shown in Table 1.

[0037] Table 1. Emissivity and transmission coefficient of two radiating elements While satisfying the axial ratio performance, considering the energy loss and feasibility of the end load, a design instance that minimizes the transmission coefficient S12 of the two radiating elements can be selected to avoid energy loss. Figure 10 This is a front view structural schematic diagram of a first radiating element or a second radiating element provided in an embodiment of this application. Combined with... Figure 1 , Figure 2 , Figure 3 and Figure 10 L represents the total length of the first radiating unit 1 or the second radiating unit 2. For example, it is 125.5 mm, which corresponds to about 1 / 4 of the wavelength of 2.6 GHz, approximately 115 mm. Le represents the length of the radiating sawtooth 5, We represents the width of the radiating sawtooth 5, Wp represents the width of the rectangular portion of the top metal plate 3 or the bottom metal plate 4, h represents the distance between the top metal plate 3 and the bottom metal plate 4, and p represents the period of the radiating sawtooth 5. The transmission coefficient S12 of the first radiating unit 1 and the second radiating unit 2 can be adjusted by adjusting the aforementioned structural parameters of the first radiating unit 1 and the second radiating unit 2, so that their radiation coefficients can reach a certain ratio as shown in Table 1.

[0038] Therefore, the energy distribution relationship in the embodiments of this application is the key guarantee for achieving low axial ratio circular polarization. By satisfying this relationship, the polarization loss caused by elliptical polarization can be minimized, the antenna gain and efficiency can be improved, and a clear guiding goal can be provided for optimizing antenna structural parameters.

[0039] In some embodiments, the first radiating unit 1 and the second radiating unit 2 are connected by a rotary connection structure, which is used to rotate the second radiating unit 2 about a longitudinal axis to switch between a first mounting position and a second mounting position.

[0040] Specifically, the rotary connection structure refers to a mechanical and electrical connection assembly used to connect the first radiating unit 1 and the second radiating unit 2, allowing the second radiating unit 2 to rotate relative to the first radiating unit 1 about a specified axis. The rotary connection structure is the physical carrier for switching the installation orientation of the second radiating unit 2. Its core function is to maintain stable radio frequency signal transmission between the output port of the first radiating unit 1 and the input port of the second radiating unit 2 during the rotation of the second radiating unit 2. A preferred embodiment employs a rotatable coaxial connector, where the inner and outer conductors can rotate relative to each other while maintaining electrical connection through sliding contact. The output port of the first radiating unit 1 is fixedly connected to one side of the rotatable coaxial connector, and the input port of the second radiating unit 2 is fixedly connected to the rotatable side of the rotatable coaxial connector. When the rotatable side is driven to rotate, the entire second radiating unit 2 is rotated. Additionally, an angle locking mechanism can be provided to precisely fix the second radiating unit 2 in either the first or second installation orientation.

[0041] In some embodiments, the rotary connection structure includes a rotatable coaxial connector, the inner and outer conductors of which are used to maintain the radio frequency connection between the output port of the first radiating unit 1 and the input port of the second radiating unit 2.

[0042] Specifically, the rotatable coaxial connector is the core component in the rotary connection structure that realizes electrical functions. Its basic function is to maintain a stable radio frequency signal transmission path between the output port of the first radiation unit 1 and the input port of the second radiation unit 2 while allowing the second radiation unit 2 to physically rotate around its longitudinal axis, so as to ensure that the signal energy is continuously and with low loss during polarization switching.

[0043] Therefore, through the rotatable coaxial connector designed above, the embodiments of this application achieve the goal of seamlessly maintaining the RF connection during purely mechanical rotation, resolving the contradiction between movement and continuity in polarization-reconfigurable antennas, namely, the unity of mechanical mobility, electrical continuity, and RF performance stability. This structure is compact, reliable, has low insertion loss, and minimal impact on VSWR, making polarization switching operations simple, fast, and without degrading the performance of the antenna system.

[0044] In some embodiments, the traveling wave antenna structure is a double-sided offset parallel plate waveguide structure. The double-sided offset parallel plate waveguide structure includes a top metal plate 3 and a bottom metal plate 4 that extend longitudinally and are arranged parallel to each other. The top metal plate 3 and the bottom metal plate 4 have a preset offset in the lateral width direction. Multiple radial sawtooth teeth 5 are arranged longitudinally on one side of the longitudinal edge of the top metal plate 3 and one side of the longitudinal edge of the bottom metal plate 4. The radial sawtooth teeth 5 are arranged from the longitudinal edge toward the outside of the double-sided offset parallel plate waveguide structure.

[0045] Specifically, the bilateral offset parallel plate waveguide structure consists of two parallel metal plates. The top metal plate 3 and the bottom metal plate 4 are not aligned in the transverse direction perpendicular to the wave propagation direction, exhibiting a predetermined offset. Radiation sawtooth 5, periodic or non-periodic tooth-like protrusions formed on the edges of the parallel plate metal plates, are used to disturb the electromagnetic field within the waveguide, coupling energy into free space. Electromagnetic waves propagate longitudinally in the parallel plate waveguide composed of the top metal plate 3 and the bottom metal plate 4. Due to the transverse offset between the top metal plate 3 and the bottom metal plate 4, the electric field is mainly concentrated in the central overlapping region. The radiation sawtooth 5, located on one longitudinal edge of the plate, periodically disturbs the transmitted electromagnetic waves, causing some energy to radiate outwards through the sawtooth structure to the side of the waveguide with the larger offset. Each sawtooth is a small radiation source, and the radiation from all sawtooths coherently superimposes in the far field, forming the main beam in the end-firing direction. The waveguide structures of the first radiating unit 1 and the second radiating unit 2 can be completely identical, and the orthogonality of the polarization directions can be achieved only through their overall spatial orientation.

[0046] Therefore, the bilateral offset parallel plate waveguide structure of this application embodiment is simple to process and can be easily realized through printed circuit board technology or metal stamping technology. Its radiation sawtooth structure is regular, which facilitates design and parameter optimization. The structure itself has traveling wave characteristics and can easily achieve broadband matching. At the same time, this flat structure is conducive to the miniaturization and thinning of the overall antenna.

[0047] In some embodiments, the first radiating unit 1 and the second radiating unit 2 each include an input port and an output port. The input port and the output port are both coaxial ports. The inner conductor of the coaxial port is connected to the corresponding top metal plate 3, and the outer conductor of the coaxial port is connected to the corresponding bottom metal plate 4.

[0048] Specifically, the coaxial port is a coaxial transmission line interface consisting of an inner conductor, an outer conductor, and an insulating medium between them, used for feeding in or receiving radio frequency signals. For each radiating unit of the double-sided offset parallel plate waveguide structure, both its input and output are connected via coaxial ports. The specific connection method is as follows: the inner conductor of the coaxial port is welded or press-fitted to the top metal plate 3 of the waveguide; the outer conductor of the coaxial port is connected to the bottom metal plate 4 of the waveguide. This connection method can effectively excite the dominant mode in the parallel plate waveguide from the transverse electromagnetic mode in the coaxial line, achieving efficient signal transmission and conversion.

[0049] Therefore, the embodiments of this application use standard coaxial ports, which facilitates connection with common RF cables and equipment and provides good compatibility. The connection method of connecting the inner conductor to the top layer and the outer conductor to the bottom layer conforms to the electric field distribution characteristics of parallel plate waveguides, which is conducive to obtaining good impedance matching, reducing port reflection, and improving energy transmission efficiency.

[0050] In some embodiments, the radial saw teeth 5 are rectangular teeth, the height of which is 0.1 to 0.12 times the working wavelength, and the center-to-center distance between adjacent rectangular teeth is 0.05 to 0.3 times the working wavelength.

[0051] Specifically, the rectangular teeth are radiating sawtooth 5 with a rectangular cross-section, and the operating wavelength refers to the free-space wavelength corresponding to the antenna's center operating frequency. The size of the radiating sawtooth 5 directly affects the intensity of its coupled radiated energy and the phase of the radiated field. The height Le of the rectangular teeth is 0.1 to 0.12 times the operating wavelength. This height range provides a sufficiently strong coupling coefficient to ensure effective energy radiation while avoiding strong reflections or the excitation of higher-order modes due to excessive size. The center-to-center spacing p between adjacent rectangular teeth is 0.05 to 0.3 times the operating wavelength. This periodic range ensures that the radiation is continuous and non-resonant leakage radiation, which is beneficial for obtaining broadband characteristics. Too large a spacing will lead to discontinuous radiation and the appearance of grating lobes in the radiation pattern; too small a spacing will make manufacturing difficult and may reduce radiation efficiency.

[0052] Therefore, the embodiments of this application provide the key dimension design range of the radiation sawtooth 5. Through simulation and experimental verification, the sawtooth design within this range can obtain good end-fire beam, wide bandwidth characteristics and stable circular polarization axial ratio performance while ensuring sufficient radiation efficiency, providing specific parameter guidance for engineering implementation.

[0053] As a specific embodiment, after parameter adjustment, a set of optimal parameters for the first radiating unit 1 and the second radiating unit 2 are given respectively. At the same time, both radiating units satisfy the proportional condition X1=(1-X1)·X2. The specific parameters are shown in Table 2 and Table 3.

[0054] Table 2 Dimensional parameters of the first radiating element 1 (unit: mm) L Le We Wp h p 125.5 10 4 17.5 2 12.5 Table 3 Dimensional parameters of the second radiating element 2 (unit: mm) L Le We Wp h p 125.5 12 4 17.5 2 12.5 As a specific embodiment, after parameter adjustment, a set of optimal parameters for the first radiating unit 1 and the second radiating unit 2 are given respectively. At the same time, both radiating units satisfy the proportional condition X1=(1-X1)·X2. The specific parameters are shown in Table 2 and Table 3.

[0055] Figure 11 This is a three-dimensional radiation pattern of an antenna operating at a frequency of 2.6 GHz, provided in an embodiment of this application. Figure 12 This is an embodiment of the present application providing the axial ratio curves of an antenna in the E-plane and H-plane at a working frequency of 2.6 GHz. Figure 11 The three-dimensional spatial perspective visually verifies that the antenna of this application embodiment has good end-fire directional radiation characteristics at 2.6GHz, with concentrated energy and regular beam shape, making it suitable for scenarios requiring directional coverage, such as tunnels. Figure 12 The quantitative curve data strongly demonstrates that the antenna of the present application can maintain high-purity circularly polarized radiation not only in the axial direction but also in a fairly wide solid angle range at a working frequency of 2.6 GHz. The beamwidth is 54 degrees with an E-plane axial ratio of less than 3 dB and approximately 55 degrees with an H-plane axial ratio of less than 3 dB.

[0056] This application also provides a wireless communication system, including a polarization-reconfigurable circularly polarized end-fire traveling wave antenna as described in the above embodiments, and therefore possesses the beneficial effects described in the above embodiments, which will not be repeated here.

[0057] Specifically, a wireless communication system refers to a complete communication system that includes a transmitter, receiver, antenna, transmission medium, and corresponding signal processing functions. In tunnel coverage applications, multiple reconfigurable circularly polarized end-fire traveling-wave antennas can be arranged at intervals along the tunnel's longitudinal direction. Each antenna is fixed to the tunnel sidewall by its cylindrical housing and leaky cable clamps, with its end-fire direction pointing in the tunnel's extension direction. The system can remotely or locally control the azimuth of the second radiating element in each antenna according to communication requirements, selecting either left-hand or right-hand circular polarization operating modes. This reconfigurable function enables the system to dynamically optimize wireless link performance, improving overall communication capacity and stability in complex scenarios such as tunnels.

[0058] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

Claims

1. A polarization-reconfigurable circularly polarized end-fire traveling-wave antenna, characterized in that, include: The first radiating element and the second radiating element are both traveling wave antenna structures. The polarization directions of the first radiating element and the second radiating element are perpendicular to each other. The output port of the first radiating element and the input port of the second radiating element are cascaded. The second radiating element has an interchangeable first mounting orientation and a second mounting orientation. The second radiating element rotates about the longitudinal axis by a first preset angle relative to the first mounting orientation to be in the second mounting orientation. When the second radiating element is in the first mounting orientation, the antenna radiates a left-hand circularly polarized wave. When the second radiating element is in the second mounting orientation, the antenna radiates a right-hand circularly polarized wave.

2. The polarization-reconfigurable circularly polarized end-fire traveling-wave antenna according to claim 1, characterized in that, The structural dimensions of the first radiating unit and the second radiating unit are configured such that, corresponding to the radiating position of the second radiating unit, there is a phase difference of a second preset angle between the radiated electromagnetic wave from the first radiating unit and the radiated electromagnetic wave of the second radiating unit itself.

3. The polarization-reconfigurable circularly polarized end-fire traveling-wave antenna according to claim 2, characterized in that, The traveling-wave antenna structure is a slow-wave structure, and the lengths of the first radiating element and the second radiating element both satisfy the following relationship: (β-k0)·L=π / 2; The traveling-wave antenna structure is a fast-wave structure, and the lengths of the first radiating element and the second radiating element both satisfy the following relationship: (k0-β)·L=π / 2; Wherein, β is the phase constant of the electromagnetic wave inside the traveling wave antenna structure, k0 is the phase constant of the electromagnetic wave in free space, and L is the length of the first radiating element or the length of the second radiating element.

4. The polarization-reconfigurable circularly polarized end-fire traveling-wave antenna according to claim 1, characterized in that, The energy ratio radiated by the first radiating unit and the energy ratio radiated by the second radiating unit satisfy the following relationship: X1 = (1-X1)·X2; Wherein, X1 is the proportion of energy radiated by the first radiating unit, and X2 is the proportion of energy radiated by the second radiating unit.

5. The polarization-reconfigurable circularly polarized end-fire traveling-wave antenna according to claim 1, characterized in that, The first radiating unit and the second radiating unit are connected by a rotary connection structure, which is used to rotate the second radiating unit about a longitudinal axis to switch between the first installation position and the second installation position.

6. The polarization-reconfigurable circularly polarized end-fire traveling-wave antenna according to claim 5, characterized in that, The rotating connection structure includes a rotatable coaxial connector, the inner and outer conductors of which are used to maintain the radio frequency connection between the output port of the first radiating unit and the input port of the second radiating unit.

7. The polarization-reconfigurable circularly polarized end-fire traveling-wave antenna according to any one of claims 1-6, characterized in that, The traveling wave antenna structure is a double-sided offset parallel plate waveguide structure. The double-sided offset parallel plate waveguide structure includes a top metal plate and a bottom metal plate that extend longitudinally and are arranged parallel to each other and spaced apart. The top metal plate and the bottom metal plate have a preset offset in the lateral width direction. Multiple radial sawtooth teeth are arranged longitudinally on one side of the top metal plate and one side of the bottom metal plate, with the radial sawtooth teeth extending from the longitudinal edge toward the outside of the double-sided offset parallel plate waveguide structure.

8. The polarization-reconfigurable circularly polarized end-fire traveling-wave antenna according to claim 7, characterized in that, Both the first radiating unit and the second radiating unit include an input port and an output port. The input port and the output port are both coaxial ports. The inner conductor of the coaxial port is connected to the corresponding top metal plate, and the outer conductor of the coaxial port is connected to the corresponding bottom metal plate.

9. The polarization-reconfigurable circularly polarized end-fire traveling-wave antenna according to claim 7, characterized in that, The radial saw teeth are rectangular teeth, the height of which is 0.1 to 0.12 times the working wavelength, and the center-to-center distance between adjacent rectangular teeth is 0.05 to 0.3 times the working wavelength.

10. A wireless communication system, characterized in that, Including the polarization-reconfigurable circularly polarized end-fire traveling-wave antenna as described in any one of claims 1-9.

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