Multi-beam tilting array and two-dimensional direction finding method

Abstract

The application discloses a multi-beam tilting array surface and a two-dimensional direction finding method. The array surface comprises a plurality of elevation sub-arrays and a DBF beam forming and processing network. The elevation is analog synthesized. Each elevation sub-array has independent elevation beam scanning control. After the elevation is synthesized, the elevation sub-array is connected to the rear-end beam forming and processing network. The application can eliminate the azimuth direction finding error caused by the conical effect under the high elevation condition, and solve the problem that the edge beam elevation angle deviates downward due to the array surface tilting, so that when the target enters from the low elevation and the large azimuth angle, the target may fall into the edge beam null depth, and the system direction finding is affected.

Description

Technical Field

[0001] This invention belongs to the field of multi-beam array design technology, and particularly relates to a multi-beam tilted array and a two-dimensional direction finding method. Background Technology

[0002] Digital multi-beam amplitude ratio direction finding technology is a passive direction finding method commonly used in large-scale electronic warfare arrays. It has the advantages of simple principle, stable performance, and high accuracy. Its direction finding principle is as follows: multiple fixed adjacent intersecting beams simultaneously cover a certain airspace, and the target direction is located by comparing the received power ratio of adjacent beams.

[0003] Digital multibeamforming uses digital technology to achieve phase shifting and beamforming, offering advantages over analog multibeamforming such as larger instantaneous coverage area and more flexible beam pointing and shaping. Typically, for large arrays with element sizes ranging from hundreds to thousands of yuan, cost constraints necessitate analog synthesis for elevation and one-dimensional DBF (Digital Beamforming) for azimuth to generate multiple digital beams for amplitude comparison and direction finding. When the target signal enters from a low elevation angle, the direction finding accuracy is high. However, as the elevation angle of the target signal relative to the array increases, the beam azimuth angle deviates from the antenna axis due to the conic effect. This conic effect leads to a gradual increase in azimuth direction finding error at high elevation angles, and the larger the true azimuth angle of the target, the greater the azimuth error.

[0004] Furthermore, for large land-based or vehicle-mounted passive air-to-air direction-finding arrays, to ensure the safety of the large array and to fully utilize the elevation beam energy, the array is usually tilted upwards at a certain angle in the elevation dimension, causing the array beam to tilt upwards. For example... Figure 1 The diagram shows a coordinate system under elevation tilt. After the transformation from array to system spatial coordinates, the main lobes of each beam that were originally at the same elevation angle under the system coordinates will no longer be on the same elevation plane, but will present a parabolic distribution with the opening downwards. The descent of the edge beams is particularly obvious, which means that even in the low elevation angle airspace of the system, when the incoming wave enters from a large azimuth angle, it may fall into the sidelobes of the edge beams or into the zero depth, affecting the system's direction finding.

[0005] It should also be noted that while a two-dimensional all-digital array can achieve two-dimensional beam coverage across the entire spatial domain, theoretically compensating for the conic effect and problems introduced by array tilt, for arrays of hundreds or thousands in size, the all-digital architecture will lead to a significant increase in array hardware costs and a huge increase in signal processing workload. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art by providing a multi-beam tilted array and a two-dimensional direction finding method, which solves the azimuth direction finding error introduced by the conic effect under high elevation angle conditions, and at the same time solves the problem that the elevation angle of the edge beams drops due to the tilt of the array, and the main lobe of the beam cannot cover the target.

[0007] The objective of this invention is achieved through the following technical solution:

[0008] A multi-beam tilting array, the array comprising:

[0009] Several elevation subarrays, each including several receiving antennas and delay devices, each receiving antenna transmitting the received signal to the elevation combining network through a radio frequency receiving channel containing the delay device, after elevation combining, the combined signal is transmitted to the DBF beamforming and processing network through a radio frequency output channel, and each elevation subarray includes an independent elevation beam scanning control unit.

[0010] The DBF beamforming and processing network receives the digital signals synthesized from each elevation subarray and performs beamforming and subsequent processing.

[0011] Furthermore, the radio frequency receiving channel includes a limiter, a low-noise amplifier, a digitally controlled delay device, and a digitally controlled attenuation device connected in series. The elevation subarray performs broadband scanning and elevation shaping of the elevation beam through digitally controlled delay and digitally controlled attenuation. The limiter is connected to the output of the receiving antenna, and the digitally controlled attenuation device is connected to the elevation combining network.

[0012] Furthermore, the RF output channel includes a first mixer, an amplifier, a second mixer, and an AD acquisition device connected in series. The first mixer is connected to the output of the pitch synthesis network, and the AD acquisition device is connected to the DBF beamforming and processing network.

[0013] On the other hand, the present invention also provides a two-dimensional direction finding method, which is implemented based on any of the aforementioned multi-beam tilted arrays, and the method includes:

[0014] Using an independent beam control unit, each elevation subarray simultaneously forms multiple independently pointing simulated wide beams in elevation, and the elevation angle of the incoming wave is measured in the array geodetic coordinate system to obtain the first direction finding angle.

[0015] The control of the pitch subarray delay device performs high-gain electronic scanning of the array pitch, pointing the beam towards the first direction finding angle;

[0016] At the first direction finding angle, the azimuth multi-beam coverage azimuth working area is formed by DBF beamforming and processing network to complete the azimuth direction finding of the incoming wave in the front geodetic coordinate system and obtain the second direction finding angle.

[0017] The first and second direction finding angles are transformed from the array geodetic coordinate system to the system coordinate system to obtain the azimuth and elevation angles of the incoming wave in the system coordinate system.

[0018] Furthermore, the elevation direction finding of the incoming wave in the array geodetic coordinate system to obtain the first direction finding angle includes:

[0019] The elevation angle of the incoming wave relative to the geodetic coordinate system of the front surface is obtained by using the elevation multibeam amplitude comparison, and the elevation angle is the first direction finding angle.

[0020] Furthermore, the process of determining the azimuth of the incoming wave in the frontal geodetic coordinate system to obtain the second direction finding angle includes:

[0021] By using azimuth amplitude measurement, the azimuth angle of the incoming wave in the frontal geodetic coordinate system is obtained, and the azimuth angle is the second direction-finding angle.

[0022] Furthermore, the method also includes:

[0023] Before controlling the elevation subarray to perform high-gain electronic scanning of the array elevation, the array beam control is achieved by configuring full-array elevation simulation delay. The array element elevation delay calculation methods include:

[0024]

[0025] Where τ represents the pitch delay of the array element, Y represents the pitch coordinates of the array element relative to the reference point in the array surface coordinate system, β represents the pitch angle of the incoming wave relative to the array surface coordinate system, and C represents the speed of light in free space.

[0026] Furthermore, the transformation between the array surface geodetic coordinate system and the system coordinate system includes:

[0027] The azimuth and pitch angle information of the target in the system coordinate system is obtained from the tilt transformation formula. The tilt transformation formula includes:

[0028]

[0029] Where α represents the azimuth angle of the incoming wave relative to the array coordinate system, β represents the elevation angle of the incoming wave relative to the array coordinate system, α' represents the azimuth angle of the incoming wave relative to the system coordinate system, β' represents the elevation angle of the incoming wave relative to the system coordinate system, and A represents the tilt angle of the array relative to the system. When the array is tilted upward, the sign is negative.

[0030] The beneficial effects of this invention are as follows:

[0031] This invention is based on the commonly used one-dimensional DBF array architecture. In elevation, it achieves elevation amplitude comparison direction finding capability through independent subarray beam control and subarray division. Elevation electronic scanning compensation significantly reduces system direction finding errors at high elevation angles. Furthermore, the entire elevation simulation and azimuth digital amplitude comparison direction finding are primarily performed in the array coordinate system. The high-gain beam consistently covers the direction of arrival, eliminating the need to consider beam drop caused by array tilt in the system coordinate system. Finally, the two-dimensional angles measured in the array coordinate system are converted using a formula to obtain the direction of arrival in the system coordinate system. This scheme, based on amplitude comparison direction finding, is simple to implement and highly suitable as a supplementary direction finding method for long-range direction finding arrays at close range and high elevation angles. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the coordinate system under pitch and tilt.

[0033] Figure 2 This is a schematic diagram of a multi-beam tilted array according to an embodiment of the present invention;

[0034] Figure 3 This is a flowchart of the two-dimensional direction finding method according to an embodiment of the present invention;

[0035] Figure 4 This is a schematic diagram of the orientation error of the airspace under tilted conditions;

[0036] Figure 5 This is a simulation diagram of the improved orientation measurement error;

[0037] Figure 6 This is a simulation diagram of the improved pitch direction finding error. Detailed Implementation

[0038] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that, unless otherwise specified, the following embodiments and features described therein can be combined with each other.

[0039] Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0040] When the array element size is large, traditional digital multibeam direction finding methods have high accuracy when the incoming wave enters from a low elevation angle. However, as the elevation angle of the incoming signal relative to the array increases, the beam azimuth angle will deviate from the antenna axis due to the conic effect of the antenna array. This conic effect will cause the azimuth direction finding error to gradually increase at high elevation angles. For large land-based or vehicle-mounted passive tilting direction finding arrays, when the incoming wave enters from a large azimuth angle, the beam drop effect may cause it to fall into the sidelobes of the edge beams or into null depth, affecting the system's direction finding.

[0041] To address the aforementioned technical problems, the following embodiments of a multi-beam tilted array and a two-dimensional direction finding method are proposed according to the present invention.

[0042] Example 1

[0043] Reference Figure 2 ,like Figure 2 The diagram shown is a schematic of the multi-beam tilt array in this embodiment. This array is designed based on the existing one-dimensional azimuth digital multi-beam array architecture. The elevation is synthesized using analog methods, and the RF receiving channel includes digitally controlled delay and attenuators, which can be used for broadband elevation beam scanning and elevation shaping. Each elevation subarray has independent elevation beam scanning control, and after elevation synthesis, it is connected to the back-end beamforming and processing network.

[0044] In this embodiment, the radio frequency receiving channel includes a limiter, a low-noise amplifier, a digitally controlled delay device, and a digitally controlled attenuation device connected in series. The elevation subarray performs broadband scanning and elevation shaping of the elevation beam through digitally controlled delay and digitally controlled attenuation. The limiter is connected to the output of the receiving antenna, and the digitally controlled attenuation device is connected to the elevation combining network.

[0045] In this embodiment, the radio frequency output channel includes a first mixer, an amplifier, a second mixer, and an AD acquisition device connected in series. The first mixer is connected to the output of the pitch synthesis network, and the AD acquisition device is connected to the DBF beamforming and processing network.

[0046] Reference Figure 3 ,like Figure 4 The diagram shown is a flowchart of the two-dimensional direction finding method in this embodiment. This method is based on the aforementioned multi-beam tilted array, and its workflow is as follows:

[0047] With independent elevation beam control, each column of the array can function as an independent subarray. Therefore, the array can simultaneously generate multiple azimuth wide beams and overlapping elevation narrow beams to achieve full airspace coverage.

[0048] Elevation multibeam direction finding in the array coordinate system does not have conic effect error. Under ideal working conditions where the antenna elements, receiving channels, and A / D amplitude and phase are completely consistent, the error is basically 0. Therefore, the elevation angle β of the target relative to the array coordinate system can be obtained by comparing the amplitude of elevation multibeams.

[0049] Based on this target elevation angle information, the array beam control is configured by setting the full array elevation simulation delay. The array element elevation delay is calculated as follows (1).

[0050]

[0051] In the formula:

[0052] Y represents the elevation coordinate of the array element relative to the reference point in the array surface coordinate system, in mm;

[0053] β represents the elevation angle of the incoming wave relative to the frontal plane coordinate system, in degrees.

[0054] C represents the speed of light in free space, with units of 3 × 10⁻⁶. 11 m / s:

[0055] First, the high-gain beam of the electronically scanned elevation array is pointed to the target elevation angle. Then, a digital multi-beam azimuth is formed on the target elevation angle to cover the entire azimuth airspace. By azimuth amplitude measurement, the azimuth angle α of the incoming wave in the array coordinate system can be obtained. Finally, the azimuth and elevation angle information of the target in the system coordinate system is obtained by the tilt angle conversion formula (2).

[0056]

[0057] In the formula:

[0058] α represents the azimuth angle of the incoming wave relative to the frontal coordinate system;

[0059] β represents the elevation angle of the incoming wave relative to the frontal coordinate system;

[0060] α' represents the azimuth angle of the incoming wave relative to the system coordinate system;

[0061] β' represents the pitch angle of the incoming wave relative to the system coordinate system;

[0062] A represents the tilt angle of the array relative to the system. When the array is tilted upwards, the sign is negative.

[0063] This embodiment is based on the commonly used one-dimensional DBF array architecture. In elevation, it achieves elevation direction finding capability through independent subarray beam control and appropriate subarray division. Elevation electronic scanning compensation significantly reduces system direction finding errors at high elevation angles. Furthermore, the entire elevation simulation and azimuth digital amplitude comparison direction finding are primarily performed in array coordinates. The high-gain beam consistently covers the direction of arrival, eliminating the need to consider the edge beam elevation drop caused by array tilt in the system coordinate system. Finally, the two-dimensional angles measured in the array coordinate system are converted using a formula to obtain the direction of arrival in the system coordinate system. This scheme, based on amplitude comparison direction finding, is simple to implement and highly suitable as a supplementary direction finding method for over-the-horizon reconnaissance equipment.

[0064] Example 2

[0065] Taking a 32 azimuth × 24 elevation array as an example, with an azimuth-elevation spacing of 0.4λ, the system's direction-finding working airspace is 0–40° elevation and -45°–45° azimuth, with a radiation pattern step of 0.2° and a target arrival wave step of 5°. The entire airspace is covered by 24 beams, and the overlap between two adjacent beams in the azimuth plane is less than 3dB. Under ideal working conditions where the antenna elements, receiving channels, and A / D amplitude and phase are completely consistent, the azimuth direction-finding error after amplitude comparison is calculated through simulation when the incoming wave enters from different directions.

[0066] Reference Figure 4 ,like Figure 4 The diagram shows the azimuth and orientation error in the airspace under tilted conditions. From... Figure 4 As can be seen, the tilt of the array has no additional impact on the accuracy of the direction finding. As the elevation angle of the incident wave increases, the error of the system's amplitude direction finding will gradually increase. At high elevation angles, the closer the beam is to the edge, the greater the error, which can reach ±12° at most, seriously affecting the system's performance.

[0067] After adopting the multi-beam tilted array and two-dimensional direction finding method provided in the aforementioned embodiments, refer to Figure 5 and Figure 5 ,like Figure 5 The image shown is a simulation diagram of the improved azimuth and direction finding error. Figure 6 The diagram shown is a simulation illustration of the improved elevation direction finding error. Under the same simulation conditions, the maximum azimuth direction finding error of the system is improved to ±0.4°, and the elevation error is ±0.2°, with a significant improvement in accuracy, verifying its feasibility.

[0068] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A two-dimensional direction finding method, characterized in that, The method is applied to a multi-beam tilting array, which includes: a beam control unit, a pitch subarray delay device, a pitch subarray, and a DBF beamforming and processing network. Using an independent beam control unit, each elevation subarray simultaneously forms multiple independently pointing simulated wide beams in elevation, and the elevation angle of the incoming wave is measured in the array geodetic coordinate system to obtain the first direction finding angle. The control of the elevation subarray delay device performs high-gain electronic scanning of the array surface elevation, pointing the elevation beam towards the first direction-finding angle; before the control of the elevation subarray performs high-gain electronic scanning of the array surface elevation, the array beam control is configured with full-array elevation simulation delay, and the array element elevation delay calculation method includes: ； in, Y represents the pitch delay of the array element, and Y represents the pitch coordinates of the array element relative to the reference point in the array plane coordinate system. The pitch angle of the incoming wave relative to the frontal plane is represented by C, and the speed of light in free space is represented by C. At the first direction finding angle, the azimuth multi-beam coverage azimuth working area is formed by DBF beamforming and processing network to complete the azimuth direction finding of the incoming wave in the front geodetic coordinate system and obtain the second direction finding angle. The first and second direction finding angles are transformed from the array geodetic coordinate system to the system coordinate system to obtain the azimuth and elevation angles of the incoming wave in the system coordinate system.

2. The two-dimensional direction finding method as described in claim 1, characterized in that, The elevation and direction finding of the incoming wave in the geodetic coordinate system of the array to obtain the first direction finding angle includes: The elevation angle of the incoming wave relative to the geodetic coordinate system of the front surface is obtained by using the elevation multibeam amplitude comparison, and the elevation angle is the first direction finding angle.

3. The two-dimensional direction finding method as described in claim 1, characterized in that, The completion of the azimuth determination of the incoming wave in the geodetic coordinate system of the front surface, and the obtaining of the second direction-finding angle, includes: By using azimuth amplitude measurement, the azimuth angle of the incoming wave in the frontal geodetic coordinate system is obtained, and the azimuth angle is the second direction-finding angle.

4. The two-dimensional direction finding method as described in claim 1, characterized in that, The transformation between the geodetic coordinate system and the system coordinate system includes: The azimuth and pitch angle information of the target in the system coordinate system is obtained from the tilt transformation formula. The tilt transformation formula includes: ； in, This represents the azimuth angle of the incoming wave relative to the frontal coordinate system. This represents the elevation angle of the incoming wave relative to the frontal plane in the coordinate system. This represents the azimuth angle of the incoming wave relative to the system coordinate system. This represents the pitch angle of the incoming wave relative to the system coordinate system. This indicates the tilt angle of the array relative to the system. When the array is tilted upwards, the sign is negative.

5. A multi-beam tilting array, characterized in that, Applied to the two-dimensional direction finding method according to any one of claims 1-4, the array surface comprises: Several elevation subarrays, each including several receiving antennas and delay devices, each receiving antenna transmitting the received signal to the elevation combining network through a radio frequency receiving channel containing the delay device, after elevation combining, the combined signal is transmitted to the DBF beamforming and processing network through a radio frequency output channel, and each elevation subarray includes an independent elevation beam scanning control unit. The DBF beamforming and processing network receives the digital signals synthesized from each elevation subarray and performs beamforming and subsequent processing.

6. The multi-beam tilting array as described in claim 5, characterized in that, The radio frequency receiving channel includes a limiter, a low-noise amplifier, a digitally controlled delay device, and a digitally controlled attenuation device cascaded in sequence. The elevation subarray performs broadband scanning and elevation shaping of the elevation beam through digitally controlled delay and digitally controlled attenuation. The limiter is connected to the output of the receiving antenna, and the digitally controlled attenuation device is connected to the elevation combining network.

7. The multi-beam tilting array as described in claim 5, characterized in that, The radio frequency output channel includes a first mixer, an amplifier, a second mixer, and an AD acquisition device cascaded in sequence. The first mixer is connected to the output of the pitch synthesis network, and the AD acquisition device is connected to the DBF beamforming and processing network.

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