A multi-element very low frequency transmitting antenna system and a method of tuning thereof

Abstract

The application provides a multi-unit very low frequency transmitting antenna system and a tuning method thereof, and belongs to the technical field of very low frequency transmitting antennas. The system comprises a plurality of antenna units, a plurality of tuning booths, a plurality of low-voltage feeders, a transmitter and a plurality of ground networks. The plurality of tuning booths are respectively located near the center of each group of antenna units, and each tuning booth is composed of a plurality of adjustable coils with the same structure. The tuning booth is connected to the root of the antenna unit. The plurality of low-voltage feeders are respectively connected to the transmitter and the plurality of tuning booths. The transmitter is located at the geometric center of the antenna array formed by the plurality of antenna units. The transmitter is connected to the low-voltage feeder through a shunt device and a high-voltage isolation switch. The plurality of ground networks are respectively laid around the plurality of antenna units. The ground network is composed of a plurality of locally radiating ground networks. The plurality of ground networks are connected through metal ground network conductors or remain independent and not connected. The application significantly reduces the complexity and difficulty of antenna design and construction, and reduces the dependence on the terrain of the antenna array.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of very low frequency transmitting antenna, in particular to a multi-unit very low frequency transmitting antenna system and a tuning method thereof. BACKGROUND

[0002] Very low frequency communication refers to a communication mode using radio waves with a frequency in the range of 3-30 kHz for long-distance signal transmission. The waves in this frequency band have the advantages of stable propagation, strong penetration ability and good anti-interference performance, and can be applied to the communication of ocean surface ships.

[0003] Traditional very low frequency transmitting antennas usually adopt T-shaped iron tower antennas, umbrella-shaped iron tower antennas and valley antennas. These antennas all use the structure of vertical antennas, and have the problem of large structure. Taking the Jim Creek antenna in the United States as an example, as a valley antenna, it is composed of 10 top-loaded lines and 12 support towers with a height of 200 feet. The support towers support the top-loaded lines with a length of 5640-8700 feet in Z zigzag form above the valley between two large mountains. The northwest corner antenna in Australia is a single group of thirteen-tower umbrella-shaped antenna, which has 13 support towers, the highest of which reaches 387m, and the radius of the umbrella-shaped antenna reaches 1260m, and the single group of antennas occupies an area of 5 square kilometers.

[0004] The existing very low frequency transmitting station antenna has the following defects:

[0005] The structure is complex, resulting in a long construction period; the antenna occupies a large scale of land, and has very strict requirements for the terrain, such as the valley antenna which requires a large enough valley depth, and the iron tower antenna which needs a complete and flat site.

[0006] In order to reduce the restriction of the very low frequency transmitting antenna on the antenna site and reduce the complexity of the antenna structure design and construction, effective measures need to be taken to reduce the size of the antenna. However, the reduction of the size of the antenna will bring some problems, such as increasing the voltage at the root and bottom of the antenna, reducing the power of the transmitting system, and further reducing the communication support distance of the transmitting station. SUMMARY

[0007] The present application provides a multi-unit very low frequency transmitting antenna system and a tuning method thereof to overcome the defects of the prior art. The system forms an array through spatial coupling of multiple units and adopts a flexible and reliable feeding mode to enhance the anti-attack capability of the very low frequency transmitting antenna array.

[0008] The present application provides a multi-unit very low frequency transmitting antenna system and a tuning method thereof which are completely different in structure and have superior performance.

[0009] The first aspect of the present application provides a multi-unit VLF transmitting antenna system, comprising: a plurality of antenna units, a plurality of tuning booths, a plurality of low-voltage feeders, a transmitter and a plurality of ground networks;

[0010] The plurality of antenna units are vertical antennas of the same structure and are excited with equal amplitude and in phase.

[0011] The plurality of tuning booths are respectively located near the center of each group of antenna units, and each tuning booth comprises a plurality of tuning coils of the same structure, and the tuning booth is connected to the root of the antenna unit.

[0012] The plurality of low-voltage feeders are respectively connected to the transmitter and the plurality of tuning booths, and the low-voltage feeder is composed of two concentric metal cylinders.

[0013] The transmitter is located at the geometric center of the antenna array formed by the plurality of antenna units, and the transmitter is connected to the low-voltage feeder through a shunt device and a high-voltage disconnector.

[0014] The plurality of ground networks are respectively laid around the plurality of antenna units, and each ground network comprises a plurality of local ground networks laid in a radial manner, and the plurality of ground networks are connected by metal ground network conductors or remain independent and disconnected.

[0015] According to the multi-unit VLF transmitting antenna system, the horizontal distance between the centers of the plurality of antenna units is not greater than one-tenth of the working wavelength, and the height of the plurality of antenna units is one-thirtieth of the working wavelength.

[0016] According to the multi-unit VLF transmitting antenna system, the antenna unit is a self-standing metal tower antenna with a ground-insulated bottom.

[0017] According to the multi-unit VLF transmitting antenna system, the conductors of the ground network are copper conductors with good conductivity.

[0018] According to the multi-unit VLF transmitting antenna system, the transmitter room comprises a shunt device and a plurality of high-voltage disconnectors, and each high-voltage disconnector is connected to a low-voltage feeder.

[0019] The second aspect of the present application provides a tuning method applied to any of the above multi-unit VLF transmitting antenna systems, and the method comprises the following steps:

[0020] The transmitter excites the plurality of antenna units through the low-voltage feeder and the tuning booth.

[0021] The transmitter realizes two feeding modes of full feeding tuning mode and multi-antenna multi-tuning mode by controlling the on-off of the high-voltage disconnector.

[0022] In the full-feed tuning mode, the signal transmitter excites all the antenna units in parallel through the low-voltage feeder;

[0023] In the multi-antenna multi-tuning mode, the signal transmitter excites only the group of antenna units connected thereto through the low-voltage feeder, and the rest of the antenna units are excited through spatial coupling.

[0024] According to the tuning method, comprising:

[0025] The signal transmitter excites all the antenna units in parallel through the low-voltage feeder, so that the input current of each antenna unit is equal.

[0026] According to the tuning method, comprising:

[0027] In the multi-antenna multi-tuning mode, the signal transmitter excites only the group of antenna units connected thereto through the low-voltage feeder, and the rest of the antenna units are excited through spatial coupling.

[0028] According to the tuning method, comprising: the signal transmitter reasonably distributes power to each antenna unit through the shunt device, ensuring that each antenna unit obtains appropriate excitation power, thereby improving the signal transmitting effect of the entire antenna system.

[0029] According to the tuning method, the signal transmitter switches between different working modes through the on-off control of the high-voltage isolating switch, to adapt to different signal transmitting requirements and environmental conditions.

[0030] The multi-unit VLF signal transmitting antenna system and the tuning method thereof provided by the application have the following beneficial effects compared with the prior art:

[0031] The multi-unit VLF signal transmitting antenna system divides a single large antenna into multiple small-scale single antenna elements, sets a tuning booth at the root of each antenna unit, and arranges a signal transmitter in the middle of the antenna array, to realize two feed modes of full-feed tuning mode and multi-antenna multi-tuning mode. The application significantly reduces the complexity of antenna design and construction, reduces the dependence on the terrain of the antenna site, and enhances the anti-attack capability of the VLF signal transmitting antenna array. By using antenna units with equal amplitude and in-phase excitation and tuning booths with the same structure, and by connecting the signal transmitter and the tuning booths through the low-voltage feeder, the application not only improves the flexibility and reliability of the system, but also retains the low-loss characteristic of the traditional ground net through the design of the local radiating ground net, while reducing the strict requirement for the flatness of the site. BRIEF DESCRIPTION OF DRAWINGS

[0032] In order to more clearly illustrate the technical solutions in the present application or the prior art, the accompanying drawings needed to be used in the description of the embodiments or the prior art will be briefly introduced. Obviously, the accompanying drawings in the following description are only some embodiments of the present application, and all other drawings obtained by those of ordinary skill in the art without creative work based on these drawings also belong to the protection scope of the present application.

[0033] Fig. 1 is the overall structure schematic diagram of the multi-unit very low frequency signaling antenna system provided by the present application;

[0034] Fig. 2 is the structure schematic diagram of the full feeding tuning mode of the multi-unit very low frequency signaling antenna system provided by the present application;

[0035] Fig. 3 is the structure schematic diagram of the multi-unit very low frequency signaling antenna system provided by the present application;

[0036] In the figure: 1. Antenna unit, 2. Tuning pavilion, 3. Low-voltage feeder, 4. Very low frequency signaling machine, 5. Ground net, 41. Shunt device, 42. High-voltage isolating switch. DETAILED DESCRIPTION

[0037] In order to make the purpose, technical solutions and advantages of the present application more clear, the technical solutions in the present application will be clearly and completely described below by combining the accompanying drawings in the present application. Obviously, the described embodiments are only some embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work also belong to the protection scope of the present application.

[0038] It should be noted that in the description of the embodiments of the present application, the terms "comprising", "including", or any other variant thereof are intended to cover a non-exclusive inclusion, so that a process, method, article or apparatus that includes a series of elements not only includes those elements, but also includes other elements not explicitly listed, or further includes elements inherent in such a process, method, article or apparatus. Without more limitations, the element defined by the statement "comprising a" does not exclude the presence of additional identical elements in the process, method, article or apparatus that includes the element. The terms "upper", "lower", and the like indicate the orientation or positional relationship shown in the drawings based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application. Unless otherwise specified and limited, the terms "mounting", "connecting", "connecting" should be understood broadly, for example, it can be fixedly connected, or it can be detachably connected, or integrally connected; it can be mechanically connected, or it can be electrically connected; it can be directly connected, or it can be indirectly connected through an intermediate medium, or it can be connected inside two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0039] The multi-unit very low frequency signaling antenna system provided by the present application comprises: a plurality of antenna units, a plurality of tuning booths, a plurality of low-voltage feeders, a signaling machine and a plurality of ground nets.

[0040] The plurality of antenna units are straight antennas of the same structure and are excited by equal amplitude and in phase;

[0041] The plurality of tuning booths are respectively located near the center of each group of antenna units, the tuning booths are composed of a plurality of structureally identical tunable coils, and the tuning booths are connected to the roots of the antenna units;

[0042] The plurality of low-voltage feeders are respectively connected to the signaling machine and the plurality of tuning booths, and the low-voltage feeders are composed of two concentric metal cylinders;

[0043] The signaling machine is located at the geometric center of the antenna array formed by the plurality of antenna units, and the signaling machine is connected to the low-voltage feeders through a shunt device and a high-voltage disconnector;

[0044] The plurality of ground nets are respectively laid around the plurality of antenna units, the ground nets are composed of a plurality of locally laid ground nets, and the plurality of ground nets are connected or kept independent by metal ground net wires.

[0045] In one embodiment of the present application, a multi-element VLF transmitting antenna system is constructed to achieve efficient and flexible communication functions. The system comprises a plurality of antenna elements which are excited in-phase with equal amplitude and have substantially uniform vertical antenna structures. In order to achieve effective tuning of each antenna element, a plurality of tuning booths are arranged near the central position of each antenna element. Each tuning booth is composed of a plurality of structurally identical tunable coils, and the tuning booths are closely connected to the roots of the antenna elements to ensure accurate transmission and tuning of signals.

[0046] In order to effectively transmit signals from the transmitter to each tuning booth, a plurality of low-voltage feeders are provided. These low-voltage feeders are composed of two concentric inner and outer metal cylinders with good electrical conductivity, ensuring the stability and efficiency of the signal transmission during transmission. The transmitter is placed at the geometric center of the antenna array composed of a plurality of antenna elements, and is connected to the low-voltage feeders through a shunt device and a high-voltage disconnector.

[0047] In addition, in order to improve the overall performance and adaptability of the antenna system, a plurality of ground nets are laid around each antenna element. These ground nets are composed of a plurality of radiating local ground nets, which can be connected or kept independent by metal ground net wires according to actual needs, not only reducing ground loss, but also improving the radiation efficiency of the antenna system, while enhancing the system's adaptability to different terrains and environments.

[0048] In practical applications, the system can achieve its functions in various ways. For example, the antenna elements can adopt different forms of vertical antenna structures, such as self-standing metal tower antennas with ground-insulated bottoms, or other antenna forms with similar characteristics.

[0049] In an alternative embodiment, the height of the antenna elements is relatively small compared to the operating wavelength, which is one-thirtieth of the operating wavelength (30 kHz wavelength).

[0050] Preferably, the antenna elements are a metal self-standing tower with a ground-insulated bottom, or a T-shaped, г-shaped or umbrella-shaped antenna with a top-loaded antenna.

[0051] Preferably, the horizontal distance between the centers of the antenna elements is not greater than one-tenth of the operating wavelength (30 kHz wavelength). At this distance, the spatial coupling energy between the antenna elements is not significantly affected by the surrounding terrain, and the performance of the antenna array remains essentially unchanged while maintaining the uniformity of the antenna structure, thereby reducing the sensitivity to the antenna site.

[0052] The tunable coils in the tuning booths can be adjusted according to different operating frequencies and environmental conditions to achieve optimal tuning results.

[0053] The tuning pylon is composed of multiple adjustable coils with the same structure, which are located near the center of each antenna unit.

[0054] The material and structure of the low-voltage feeder can also be selected according to specific needs, such as using different metal materials with different electrical conductivity to optimize signal transmission efficiency. The low-voltage feeder is a coaxial feeder composed of two concentric inner and outer metal cylinders with good electrical conductivity. Preferably, the length of the low-voltage feeder between the transmitter room and the tuning pylon is equal.

[0055] The location and connection method of the transmitter can also be adjusted according to the specific layout of the antenna array to ensure uniform distribution and efficient transmission of signals. The transmitter is connected to the tuning pylon at the root of each antenna unit through the low-voltage feeder, and the transmitter is preferably located at the geometric center of the antenna array composed of multiple antennas.

[0056] Preferably, the transmitter room includes a shunt device and multiple high-voltage disconnectors, each connected to a low-voltage feeder. The transmitter is connected to the low-voltage feeder through the shunt device and high-voltage disconnectors, and preferably each low-voltage feeder is provided with a set of high-voltage disconnectors.

[0057] The design and laying method of the ground net can also be optimized according to the terrain and environmental conditions, such as using local ground nets of different shapes and sizes, or using ground net wires of different materials to improve the performance and adaptability of the system. Specifically, the ground net can be composed of multiple local ground nets radiating around the antenna unit, and the local ground nets can be connected or not connected through metal ground net wires.

[0058] The multi-unit very low frequency signaling antenna system of the present application not only effectively solves the complexity and limitations of traditional large single antenna structures, but also reduces the complexity and difficulty of antenna design and construction, reduces the dependence on the terrain of the antenna array, and enhances the anti-attack capability of the antenna system.

[0059] Based on the above multi-unit very low frequency signaling antenna system, the present application also provides a tuning method applied to any of the above multi-unit very low frequency signaling antenna systems, the method comprising the following steps:

[0060] The transmitter excites the multiple antenna units through the low-voltage feeder and the tuning pylon;

[0061] The transmitter realizes two feeding modes of full feeding tuning mode and multi-antenna multi-tuning mode by controlling the on-off of the high-voltage disconnectors;

[0062] In the full feeding tuning mode, the transmitter excites all the antenna units in parallel through the low-voltage feeder.

[0063] In the multi-antenna multi-tuning mode, the transmitter excites only the group of antenna elements connected to it through the low-voltage feeder, while the other antenna elements are excited through spatial coupling.

[0064] The direct excitation tuning and indirect excitation tuning of the antenna elements are controlled by a high-voltage disconnect switch.

[0065] In the multi-tuned feeding process of a multi-element very low frequency (VLF) transmitting antenna, all high-voltage disconnect switches are closed, and each tuning pavilion is directly excited for tuning. The transmitter provides feed excitation to all antenna elements via a low-voltage feed line in parallel. Due to the close spacing between antenna elements, the radiation resistance of each element is equal to the mutual coupling resistance induced by other elements. With full feed, the resistance of an antenna element is n times its own radiation resistance (where n is the number of antenna elements), reducing the input current of a single antenna element and thus simplifying the tuning pavilion design. For each antenna element, the ground grid size remains unchanged, and the ground loss resistance remains constant. Because the antenna resistance increases while the loss resistance remains constant, the radiation efficiency of the antenna element is significantly improved.

[0066] Compared to the fully fed tuning mode, the multi-antenna multi-tuning mode has the following significant advantages:

[0067] On the one hand, reliability is improved because each antenna element can be directly excited, and the system can still work when the low-voltage feeder is damaged, resulting in higher reliability;

[0068] On the other hand, cost optimization is achieved. While maintaining the antenna system performance, only one set of low-voltage feeder 3 needs to be built, and other units can work through coupling to reduce the system construction cost.

[0069] Furthermore, in order to provide a clearer explanation of the technical solution of the present invention, the following description is provided in conjunction with... Figs. 1 to 3 The technical solution of the present invention will be further described in conjunction with a specific embodiment.

[0070] like Fig. 1 As shown, the multi-element very low frequency (VLF) transmitting antenna system of this invention consists of antenna element 1, tuning pavilion 2, low-voltage feeder 3, VLF transmitter 4, ground network 5, etc.

[0071] The multi-element antenna array consists of four identical antenna elements 1, all with equal amplitude and in-phase excitation. Each antenna element 1 is a monopole antenna, specifically a self-supporting metal tower antenna with its base insulated from the ground. The antenna height is 250m–350m, which is one-thirtieth of the operating wavelength. The horizontal distance between the centers of each antenna element 1 is 1000m, which is one-tenth of the operating wavelength.

[0072] Each group of antennas is laid with a radial ground net 5 centered on the unit, and the conductive wire is selected as copper wire with good conductivity. The radial ground nets of each unit can be connected by metal wires to form a unified large ground net, or can remain independent and not connected.

[0073] Each group of antenna units 1 is near the center position and is constructed with a group of adjustable coils of the same structure to form a tuning pavilion 2. Each group of tuning pavilions 2 corresponds to one antenna unit 1, and each group of tuning pavilions 2 corresponds to connecting one antenna unit 1.

[0074] The multi-unit transmitting antenna system constructs a transmitting room in the center position of the antenna array, and arranges a very low frequency transmitter 4 inside. Four groups of low-voltage feed lines 3 are constructed between the transmitter and each group of tuning pavilions, and the low-voltage feed line 3 is a coaxial feed line composed of two concentric copper cylinders. The length of each group of low-voltage feed lines 3 should be as equal as possible, and the length error is not more than 10m.

[0075] In addition to arranging a very low frequency transmitter 4 inside the transmitter room, a shunt device 41 and four high-voltage disconnectors 42 are also arranged. Each group of high-voltage disconnectors 42 is connected to a low-voltage feed line 3. By controlling the on-off of the high-voltage disconnector 42, direct excitation or non-direct excitation of the antenna unit 1 can be realized. The distance between the antenna units is one tenth of the working wavelength, and the spatial coupling between each antenna unit is strong. By turning on and off the high-voltage disconnector, the full-feed tuning mode and the multi-antenna multi-tuning mode are realized.

[0076] As shown in Fig. 2 is a full-feed tuning mode schematic diagram of a 4-antenna unit. The very low frequency transmitter 4 excites all 4 groups of antenna units 1 in parallel through the low-voltage feed line 3, and all high-voltage disconnectors 42 inside the transmitter room are closed. Since the distance between the antenna units is close, the radiation resistance of each unit itself is equal to the mutual coupling resistance induced by other single antenna units, and the full-feed antenna unit resistance is 4 times the self-radiation resistance. The input current of a single group of antenna units is reduced, the tuning pavilion coil current is reduced, and the design difficulty of the tuning pavilion is reduced. The size of the antenna unit ground net remains unchanged, and the ground loss resistance remains constant. The antenna resistance increases while the loss resistance remains unchanged, which significantly improves the radiation efficiency of the antenna unit.

[0077] As shown in Fig. 3The multi-antenna multi-tuning mode schematic diagram of a 4-antenna unit is shown. In the transmitting station, only one set of high-voltage disconnectors 42 is closed, and the other high-voltage disconnectors are disconnected. The VLF transmitting machine 4 excites the antenna unit 1 connected to it through the low-voltage feeder 3, that is, the corresponding tuning booth is directly excited and tuned. The remaining three sets of antenna units are excited through space coupling, and the corresponding tuning booths need to be tuned and grounded. Like the full-feed mode, the radiation resistance of the antenna unit itself is equal to the mutual coupling resistance induced by other single antenna units, and the total resistance of each antenna unit is 4 times the radiation resistance of the antenna unit itself. The input current of the single set is reduced, the design difficulty of the tuning booth is reduced, and the radiation efficiency of the antenna is improved as in the full-feed mode.

[0078] The application also provides a multi-unit VLF transmitting antenna system and a tuning method thereof, which has the following beneficial effects compared with the prior art:

[0079] 1) The application breaks through the structure of a large single antenna, decomposes the VLF antenna into n (n≥2) independent antenna units with the same structure, forms an array through space coupling, significantly reduces the design and construction complexity of the antenna, greatly reduces the dependence on super-large sites and special terrain (such as deep valleys), and enables the antenna array to be flexibly deployed in a conventional site.

[0080] 2) The application adopts a local radiation ground net design, and each unit ground net can be independently laid or interconnected through a wire. This design retains the low-loss characteristics of the traditional ground net while reducing the strict requirements for site flatness.

[0081] 3) The application has a flexible and reliable feeding mode, adopts a distributed deployment of tuning booths and a centralized feeding arrangement design, supports two tuning modes of full-feed tuning mode and multi-antenna multi-tuning mode, increases the working mode of the antenna system, and improves the reliability and survivability. Both modes reduce the current flowing through the antenna unit and the tuning booth, and reduce the design difficulty of the tuning coil.

[0082] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the application, and not to limit them. Although the application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that they can modify the technical solutions described in the foregoing embodiments, or make equivalent substitutions for some technical features. These modifications or substitutions do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the application.

[0083] For example, the independent ceramic insulator unit can be provided with a skirt to increase the creepage distance; the pre-tightening mechanism can also adopt the mode of a central through-pull rod; the number of layers and the number of each layer of the insulator unit can be adjusted according to the actual load and voltage requirements. These modifications and modifications shall fall within the protection scope defined in the claims attached to the present application.

Claims

1. A multi-element very low frequency (VLF) transmitting antenna system, characterized in that, include: Multiple antenna units (1), multiple tuning booths (2), multiple low-voltage feeders (3), one transmitter (4), and multiple grounding grids (5); The multiple antenna elements (1) are vertical antennas with the same structure and equal amplitude and phase excitation; The multiple tuning pavilions (2) are located near the center of each group of antenna units (1). Each tuning pavilion (2) is composed of multiple tunable coils with the same structure. The tuning pavilion (2) is connected to the root of the antenna unit (1). The plurality of low-voltage feeders (3) are respectively connected to the transmitter (4) and the plurality of tuning pavilions (2), and the low-voltage feeders (3) are composed of two concentric metal cylinders; The transmitter (4) is located at the geometric center of the antenna array composed of the multiple antenna elements (1). The transmitter (4) is connected to the low-voltage feed line (3) through a splitter and a high-voltage disconnector. The transmitter (4) realizes two feeding modes, full-feed tuning mode and multi-antenna multi-tuning mode, by controlling the on and off of the high-voltage disconnector. In the full-feed tuning mode, the transmitter (4) excites all the antenna elements (1) in parallel through the low-voltage feed line (3). In the multi-antenna multi-tuning mode, the transmitter (4) excites only the group of antenna elements (1) connected to it through the low-voltage feed line (3), and the other antenna elements (1) are excited through spatial coupling. The multiple ground grids (5) are laid out with the multiple antenna units (1) as the center. The ground grids (5) are composed of multiple radially laid local ground grids. The multiple ground grids (5) are connected by metal ground grid wires or remain independent and unconnected.

2. The multi-element very low frequency transmitting antenna system according to claim 1, characterized in that, The horizontal distance between the centers of the plurality of antenna elements (1) is no greater than one-tenth of the working wavelength, and the height of the plurality of antenna elements (1) is one-thirtieth of the working wavelength.

3. The multi-element very low frequency transmitting antenna system according to claim 2, characterized in that, The antenna unit (1) is a self-standing metal tower antenna with its bottom insulated from the ground.

4. The multi-element very low frequency transmitting antenna system according to claim 1, characterized in that, The grounding grid (5) uses copper conductors.

5. The multi-element very low frequency transmitting antenna system according to claim 1, characterized in that, The transmitter (4) room includes a branching device and multiple high-voltage disconnect switches, which are respectively connected to a low-voltage feeder (3).

6. A tuning method for a multi-element very low frequency transmitting antenna system as described in any one of claims 1 to 5, characterized in that, The method includes the following steps: The transmitter (4) excites the plurality of antenna elements (1) through the low-voltage feeder (3) and the tuning pavilion (2); The transmitter (4) achieves two power supply modes, namely full-feed tuning mode and multi-antenna multi-tuning mode, by controlling the on / off state of the high-voltage disconnect switch; In the fully fed tuning mode, the transmitter (4) excites all the antenna elements (1) in parallel through the low-voltage feed line (3). In the multi-antenna multi-tuning mode, the transmitter (4) excites only the group of antenna elements (1) connected to it through the low-voltage feeder (3), while the other antenna elements (1) are excited through spatial coupling.

7. The tuning method according to claim 6, characterized in that, include: The transmitter (4) excites all the antenna elements (1) in parallel through the low-voltage feed line (3) so that the input current of each antenna element (1) is equal.

8. The tuning method according to claim 6, characterized in that, include: In the multi-antenna multi-tuning mode, the transmitter (4) excites only the group of antenna elements (1) connected to it through the low-voltage feed line (3), while the other antenna elements (1) are excited through spatial coupling.

9. The tuning method according to claim 6, characterized in that, include: The transmitter (4) distributes power reasonably to each antenna unit (1) through the splitter device, ensuring that each antenna unit (1) receives appropriate excitation power, thereby improving the transmission effect of the entire antenna system.

10. The tuning method according to claim 6, characterized in that, The transmitter (4) switches between different working modes by controlling the on / off state of the high-voltage disconnect switch to adapt to different transmission needs and environmental conditions.

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