Course beacon directional diagram adaptive optimization method

Abstract

The invention discloses a self-adaptive optimization method for a heading beacon directional diagram. The method comprises the following steps: initializing LOC antenna array element parameters and obstacle parameters; calculating the angle range of the LOC antenna radiation field influenced by the obstacle; respectively designing expected directional diagrams of CSB signals and SBO signals radiated by the LOC antenna; the directional diagrams of CSB signals and SBO signals radiated by the LOC antenna are adaptively optimized; and evaluating the channel performance of the optimized optimal directional diagram. According to the method, the characteristic of robustness of the adaptive processing technology is fully utilized, the feed amplitude and the feed phase of the heading beacon antenna are adaptively calculated according to the area range of the radiation field influenced by the obstacle, and the horizontal guiding performance of an existing dual-frequency heading beacon system on an airplane can be improved on the premise that the number of antenna array elements is not increased. When the course beacon system is installed and debugged, the feed amplitude and phase can be adjusted in a self-adaptive mode according to the airport environment, and the installation and debugging workload is reduced.

Description

Technical Field

[0001] The present invention relates to a method for optimizing a localizer beacon directional diagram, and more particularly to a method for adaptively optimizing a localizer beacon directional diagram. Background Art

[0002] The localizer (LOC) is a component of the Instrument Landing System (ILS), the most widely used precision approach and landing system in civil aviation. It provides horizontal guidance information for aircraft during approach and landing by radiating signals of a specific field pattern through an array antenna. However, the radiation field of the LOC antenna is susceptible to multipath interference caused by obstacles such as buildings and trees near the runway. When the aircraft is aligned with the runway, the channel structure bends, resulting in reduced horizontal guidance performance for the aircraft.

[0003] Existing LOC systems often use a dual-frequency structure (channel, clearance) to mitigate the impact of multipath interference. Four signals are generated, including channel carrier plus sideband (CSB) signal, channel suppressed carrier double-sideband signal (SBO) signal, clearance CSB signal and clearance SBO signal, and then radiated by antenna array elements with fixed feed amplitude and phase, to synthesize a fixed channel pattern in space. This fixed pattern will affect the multipath interference suppression capability of the array antenna, and cannot handle multipath interference in any direction, resulting in high site requirements in actual installation and application. It may require manual experience to adjust the feed coefficient, making installation and debugging difficult, and even requiring the removal of obstacles to ensure the horizontal guidance performance of LOC, resulting in economic losses.

[0004] The adaptive processing method can design a suitable weighting vector to make the processed received signal adaptively generate a null in the interference direction to suppress interference. It is widely used in modern radar, communication systems, satellite navigation and other fields. LOC works in the very high frequency band with a long wavelength. Multipath interference can be considered as mirror reflection after obstacles. Therefore, the angle range of the radiation field affected can be obtained according to the specific obstacle position of the airport, and then the adaptive processing method can be applied to form a new feed amplitude and phase coefficient to produce a route field type that meets the operation of a specific airport and improve economic benefits. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a method for adaptively optimizing a direction beacon pattern, which can reduce the influence of multipath obstacles, in order to overcome the shortcomings of the prior art.

[0006] The technical solution adopted by the present invention is: a method for adaptively optimizing a heading beacon pattern, comprising the following steps:

[0007] 1) Initialize the parameters of the LOC antenna elements and the obstacle parameters;

[0008] 2) Calculate the angular range of the LOC antenna radiation field affected by the obstacle according to the LOC antenna element parameters and the obstacle parameters;

[0009] 3) Design the desired radiation patterns of the CSB signal and the SBO signal radiated by the LOC antenna respectively according to the angular range of the LOC antenna radiation field affected by the obstacle;

[0010] 4) Adaptive optimize the radiation patterns of the CSB signal and the SBO signal radiated by the LOC antenna according to the designed desired radiation patterns of the CSB signal and the SBO signal radiated by the LOC antenna;

[0011] 5) Evaluate the lane performance of the optimized optimal radiation pattern.

[0012] A method for adaptively optimizing the radiation pattern of a localizer of the present invention makes full use of the robust characteristics of the adaptive processing technology. According to the area range of the radiation field affected by the obstacle, the feeding amplitude and feeding phase of the localizer antenna are calculated adaptively. Without increasing the number of antenna elements, the horizontal guidance performance of the existing dual - frequency localizer system for aircraft can be improved. When the localizer system based on the method for adaptively optimizing the radiation pattern of the localizer of the present invention is installed and debugged, the feeding amplitude and phase can be adaptively adjusted according to the airport environment, reducing the workload of installation and debugging. The localizer system based on the method for adaptively optimizing the radiation pattern of the localizer of the present invention can form new feeding amplitude and phase coefficients according to the specific obstacle positions at the airport, protecting the existing airport infrastructure as much as possible and reducing the installation economic cost. Brief Description of the Drawings

[0013] Figure 1 is a flowchart of a method for adaptively optimizing the radiation pattern of a localizer of the present invention;

[0014] Figure 2 is the normalized lane CSB and SBO radiation patterns before adaptive optimization in the presence of obstacles;

[0015] Figure 3 is the normalized lane CSB and SBO radiation patterns after optimization using the method of the present invention;

[0016] Figure 4 is the comparison of DDM in the azimuth angle before and after optimization using the method of the present invention;

[0017] Figure 5 is the comparison of DDM in the distance before and after optimization using the method of the present invention. Detailed Embodiment

[0018] The following will make a detailed description of an adaptive optimization method for the direction pattern of a localizer beacon in the present invention in combination with embodiments and drawings.

[0019] An adaptive optimization method for the direction pattern of a localizer beacon in the present invention regards the multipath propagation path in the presence of obstacles as the specular reflection through the obstacles, and then obtains the angular range affected by the obstacles on the radiation field according to the positional relationship between the obstacle reflection surface and the localizer antenna array. Based on this, a desired direction pattern is constructed, and the adaptive processing method is used to calculate the new antenna feed amplitude and feed phase according to the requirements of the desired direction pattern, and an optimized direction pattern is generated.

[0020] As Figure 1 shown, an adaptive optimization method for the direction pattern of a localizer beacon in the present invention includes the following steps:

[0021] 1) Initialize the LOC antenna element parameters and obstacle parameters; including:

[0022] Taking the center of the LOC antenna as the origin, the runway center line as the X-axis, and the runway plane as the XOY plane to establish a coordinate system; setting the distance from each element of the LOC antenna to the origin, and the projection coordinates on the XOY plane of the farthest and nearest reflection points of the obstacle reflection surface from the LOC antenna respectively.

[0023] 2) Calculate the angular range affected by the obstacles on the radiation field of the LOC antenna according to the LOC antenna element parameters and obstacle parameters; including:

[0024] Based on the principle of mirror reflection, according to the projection coordinates on the XOY plane of the farthest and nearest reflection points of the obstacle reflection surface from the LOC antenna respectively, calculate the angular range affected by the obstacles on the radiation field of the LOC antenna, where the minimum value of the affected angle is the arccosine value of the ratio of the projection of the distance from the farthest reflection point of the obstacle from the LOC antenna to the origin on the X-axis to the distance from the farthest reflection point of the obstacle from the LOC antenna to the origin; the maximum value of the affected angle is the arccosine value of the ratio of the projection of the distance from the nearest reflection point of the obstacle from the LOC antenna to the origin on the X-axis to the distance from the nearest reflection point of the obstacle from the LOC antenna to the origin.

[0025] 3) Design the desired direction patterns of the CSB signal and SBO signal radiated by the LOC antenna respectively according to the angular range affected by the obstacles on the radiation field of the LOC antenna

[0026] The requirements for the designed desired radiation pattern are as follows: The desired radiation pattern of the CSB signal has the maximum radiation field in the main lobe at the 0° direction, forms nulls in the side lobes within the angle range affected by obstacles, and sets the maximum side lobe level threshold within other angle ranges; The desired radiation pattern of the SBO signal has a null in the main lobe at the 0° direction, forms nulls in the side lobes within the angle range affected by obstacles, and sets the maximum side lobe level threshold within other angle ranges; Normalize and logarithmically transform both the desired radiation pattern of the CSB signal and the desired radiation pattern of the SBO signal with the maximum radiation field level of the desired radiation pattern of the CSB signal. At this time, the maximum radiation field level of the desired radiation pattern of the CSB signal is 0 dB. The null levels within the angle range affected by obstacles and the maximum side lobe level thresholds within other angle ranges in the desired radiation patterns of the CSB signal and the SBO signal are set based on the number of array elements of the LOC antenna, the actual situation of the radiation field, and the requirements on the basis of 0 dB. The null level value within the angle range affected by obstacles should be lower than the maximum side lobe level threshold within other angle ranges.

[0027] 4) According to the desired radiation patterns of the CSB signal and the SBO signal radiated by the designed LOC antenna, adaptively optimize the radiation patterns of the CSB signal and the SBO signal radiated by the LOC antenna

[0028] To adaptively optimize the LOC radiation pattern, first calculate the steering vector of the LOC antenna array elements, then based on the least mean square error criterion, design the weighting vector to minimize the mean square error between the actual radiation pattern and the desired radiation pattern, then generate the actual radiation pattern according to the steering vector and the weighting vector, and finally determine the optimal weighting vector and the optimal actual radiation pattern according to the convergence of the actual radiation pattern. It includes:

[0029] (4.1) Adaptively calculate the weighting vector of the LOC antenna array elements.

[0030] First, determine the steering vectors of the CSB signal and the SBO signal radiated by the LOC antenna, without considering the co - feeding and reverse - feeding characteristics of the CSB signal and the SBO signal into the steering vector. Taking the center of the LOC antenna as the zero point, The steering vectors of the CSB signal and the SBO signal radiated by an LOC antenna with

[0031] (1)

[0032] Since the LOC antenna is a log - periodic antenna, the steering vector formula (1) contains the array factor of the log - periodic antenna , where represents the angle deviating from the X - axis of the runway center line, with a value range of - 90° to 90°; and represent the steering vectors of the CSB signal and the SBO signal respectively; represents the The distance from an array element to the central origin; Indicates the carrier wavelength of the signal; Indicates the imaginary unit.

[0033] One method to calculate the optimal weighting vector is to minimize the mean square error between the obtained actual radiation pattern and the desired radiation pattern according to the minimum mean square error criterion. The mean square error formula is expressed as:

[0034] (2)

[0035] Where Indicates the number of sampling points within the affected angular range; Indicates the th angular value within the affected range; Indicates the virtual interference power artificially applied at the angle ; Indicates the angle of the desired radiation pattern; Indicates the angle of the actual radiation pattern generated during the adaptive process, expressed as where Indicates the weighting vector; Indicates the steering vector at the angle ; Indicates the transpose.

[0036] According to the minimum mean square error criterion, the optimal weighting vector is obtained by minimizing the mean square error formula:

[0037] (3)

[0038] Where, is the optimal weighting vector; is the covariance matrix, is the cross-correlation vector, and are respectively expressed as:

[0039] (4)

[0040] In the actual process of solving the optimal weighting vector, it is necessary to continuously iterate and adjust the virtual interference power according to the requirements of the desired radiation pattern. The virtual interference power applied at during the (k + 1)th iteration is expressed as:

[0041] (5)

[0042] Where, indicates the virtual interference power applied at the angle The virtual interference power. In the first iteration, set the virtual interference power to a number greater than 0; Denote the angle The actual pattern of LOC at the k-th iteration; Denote the iteration gain, which reflects the convergence speed of the iterative algorithm and determines the number of iterations;

[0043] Secondly, calculate the covariance matrix and cross-correlation vector for the (k + 1)-th iteration according to the virtual interference power. The calculation formulas are as follows:

[0044] (6)

[0045] Among them, the term added to the covariance matrix Is to ensure the stability of the algorithm, The value is a number greater than 0, Denote the identity matrix;

[0046] Then calculate the weighted vector of the LOC antenna elements at the (k + 1)-th iteration according to the iteratively updated covariance matrix and cross-correlation vector:

[0047] (7)

[0048] Among them, Denote the weighted vector at the (k + 1)-th iteration; Denote the covariance matrix at the (k + 1)-th iteration; Denote the cross-correlation vector at the (k + 1)-th iteration. In addition, the pattern of the CSB signal has a maximum radiation field in the 0° direction, while the pattern of the SBO signal has a null in the 0° direction. Therefore, when calculating the weighted vectors of the CSB signal and the SBO signal, constraint conditions And Need to be added respectively, where And Denote the steering vectors of the CSB signal and the SBO signal at 0° respectively, And Denote the weighted vectors of the CSB signal and the SBO signal under the constraint conditions respectively. After adding the constraint conditions, the weighted vectors of the CSB signal and the SBO signal at the (k + 1)-th iteration are respectively expressed as And ;

[0049] (4.2)Generate the patterns of the CSB signal and the SBO signal.

[0050] Calculate the actual patterns of the CSB signal and the SBO signal at the (k + 1)-th iteration according to the weighted vectors calculated in step (1):

[0051] (8)

[0052] Among them, and respectively represent the actual CSB signal and the SBO signal pattern in the (k + 1)-th iteration, and respectively represent the weighted vectors of the CSB signal and the SBO signal in the (k + 1)-th iteration.

[0053] (4.3) Judge the convergence of the pattern.

[0054] Judge whether the error between the pattern generated in step (2) and the desired pattern is less than the set value . If it is less than the set value , it is considered that the pattern has converged. At this time, the weighted vector obtained in step (1) is the optimal weighted vector, and the pattern calculated in step (2) is the optimal pattern; if it is greater than or equal to the set value , it is considered that the pattern has not converged, and return to step (1) to continue iteratively calculating the weighted vector until the pattern converges.

[0055] 5) Evaluate the channel performance of the optimized optimal pattern; including:

[0056] Calculate the modulation depth difference DDM for providing horizontal guidance information for the aircraft using the optimal CSB signal and SBO signal patterns obtained in step 4):

[0057] (9)

[0058] Among them, and respectively represent the optimal patterns of the CSB signal and the SBO signal obtained in step 4); then, compare the calculated DDM with the DDM limit specified by the International Civil Aviation Organization (ICAO) and output a DDM detection report.

[0059] The effect of an adaptive optimization method for the course beacon pattern of the present invention can be further illustrated by the following experimental results.

[0060] Experimental description: Taking the dual - frequency 16 - element LOC antenna as an example, the feeding parameters in the technical manual it provides are used as the parameters before optimization. The "before optimization" results described in subsequent experiments and descriptions are all obtained using the feeding parameters provided in the technical manual. Further, the parameters of the obstacles near the runway are set as follows: Taking the center of the LOC antenna as the origin, the center line of the runway as the X - axis, and the runway plane as the XOY plane to establish a coordinate system. The projection coordinates of the left and right ends of the obstacle reflection surface on the XOY plane are (1000m, 375m) and (1000m, 425m) respectively, and the height of the obstacle is the same as that of the LOC antenna and parallel to the runway surface. A method for adaptive optimization of the localizer pattern is used to optimize the CSB and SBO patterns of the LOC course.

[0061] Figure 2 The normalized CSB signal and SBO pattern of the course before adaptive optimization in the presence of obstacles;

[0062] According to the mirror reflection principle, when the multipath signals reflected by the obstacle are equivalent to the direct signals emitted by the mirror virtual antenna, the affected angular range of the LOC radiation field is calculated based on the reflection points at the farthest distances from the left and right ends of the obstacle. According to the obstacle parameters set in this experiment, it will affect the pattern of the LOC radiation in the angular range of about 20° - 35°. As can be seen from Figure 2 it, due to the influence of the obstacle, the patterns of the CSB signal and SBO signal of the course are distorted in the angular range of about 20° - 35°, and the level value increases.

[0063] Figure 3 The normalized CSB signal and SBO pattern of the course after optimization using a method for adaptive optimization of the localizer pattern of the present invention;

[0064] As can be seen from Figure 3 it, a method for adaptive optimization of the localizer pattern of the present invention forms a "wide null" in the angular range affected by the obstacle, suppressing the influence of the obstacle in this angular range. Due to the energy conservation limitation, the level of the pattern in other angular ranges not affected by the obstacle increases. Tables 1 and 2 respectively show the feeding parameters of each element after optimizing the CSB signal and SBO signal of the course using a method for adaptive optimization of the localizer pattern proposed in the present invention under the experimental conditions, and give the complex weighting vectors, amplitudes, and phases respectively.

[0065] Table 1 Feeding parameters of each element of the CSB pattern of the course after adaptive optimization

[0066]

[0067] Table 2 Feeding parameters of each element of the SBO pattern of the course after adaptive optimization

[0068]

[0069] Figure 4 For comparing the DDM on the azimuth before and after optimization using an adaptive optimization method for the course beacon pattern of the present invention;

[0070] The differential modulation DDM is used on the approach surface to indicate that the aircraft "flies left" or "flies right". ICAO has specified the value range of DDM: with the runway center as the reference, within the range of DDM from 0 to 0.188, DDM changes linearly with the angular displacement; within the range of angles from 0.188 of DDM to ±10°, DDM should be greater than 0.180; within the range from ±10° to ±35°, DDM should be greater than 0.155. From Figure 4 It can be seen that the DDM value within the angle range of approximately -4° to 4° after optimization is greater than the DDM before optimization. This is because the main lobe of the approach CSB pattern after adaptive optimization becomes narrower, and the narrower the main lobe pattern, the less affected it is by the multipath of obstacles.

[0071] Figure 5 For comparing the DDM on the distance before and after optimization using an adaptive optimization method for the course beacon pattern of the present invention;

[0072] Figure 5 The dashed line in [] represents the DDM jitter limit range specified by ICAO for operation III on the approach surface. From Figure 5 It can be seen that within the distance range affected by obstacles, the DDM curve without optimization exceeds the limit range specified by ICAO, and the DDM curve after optimization using the method proposed in the present invention meets the ICAO requirements, indicating that the adaptive optimization method alleviates the influence of obstacles.

Claims

1. A method for adaptive optimization of a heading beacon pattern, characterized in that: The steps include: 1) Initialization of LOC antenna array element parameters and obstacle parameters; 2) Calculate the angle range of the LOC antenna radiation field affected by obstacles based on the LOC antenna array element parameters and obstacle parameters; 3) According to the angular range in which the LOC antenna radiation field is affected by obstacles, the expected directivity patterns of the CSB signal and SBO signal radiated by the LOC antenna are designed respectively; 4) Adaptively optimizing the directional patterns of the CSB signal and the SBO signal radiated by the LOC antenna according to the expected directional patterns of the CSB signal and the SBO signal radiated by the designed LOC antenna; 5) Evaluate the channel performance of the optimized optimal direction diagram.

2. The method for adaptive optimization of a localizer pattern according to claim 1, characterized in that: Step 1) includes: establishing a coordinate system with the center of the LOC antenna as the origin, the centerline of the runway as the X-axis, and the runway plane as the XOY plane; setting the distance from each array element of the LOC antenna to the origin, and the projection coordinates of the farthest and nearest reflection points of the obstacle reflection surface from the LOC antenna on the XOY plane.

3. The method for adaptive optimization of a localizer pattern according to claim 1, characterized in that: Step 2) includes: based on the mirror reflection principle, according to the projection coordinates of the farthest and nearest reflection points of the obstacle reflection surface from the LOC antenna on the XOY plane, respectively, calculating the angle range of the LOC antenna radiation field affected by the obstacle, wherein the minimum value of the affected angle is the arccosine value of the ratio of the projection on the X-axis of the distance from the farthest reflection point from the obstacle to the LOC antenna to the origin and the distance from the farthest reflection point from the obstacle to the LOC antenna to the origin; the maximum value of the affected angle is the arccosine value of the ratio of the projection on the X-axis of the distance from the nearest reflection point from the obstacle to the LOC antenna to the origin and the distance from the nearest reflection point from the obstacle to the LOC antenna to the origin.

4. The method for adaptive optimization of a localizer pattern according to claim 1, characterized in that: The expected radiation pattern requirements in step 3) are as follows: the expected radiation pattern of the CSB signal has a maximum radiation field in the 0° direction of the main lobe, the side lobes in the angle range affected by obstacles form a null, and the maximum level threshold of the side lobes in other angle ranges is set; the expected radiation pattern of the SBO signal has a null in the 0° direction of the main lobe, the side lobes in the angle range affected by obstacles form a null, and the maximum level threshold of the side lobes in other angle ranges is set; The expected radiation pattern of the CSB signal and the expected radiation pattern of the SBO signal are both normalized and logarithmically transformed with the maximum radiation field level of the expected radiation pattern of the CSB signal. At this time, the maximum radiation field level of the expected radiation pattern of the CSB signal is 0dB. The null level within the angle range affected by obstacles and the maximum level threshold of the side lobes in other angle ranges of the expected radiation patterns of the CSB signal and the SBO signal are set on the basis of 0dB according to the number of array elements of the LOC antenna, the actual situation and requirements of the radiation field, and the null level value within the angle range affected by obstacles must be lower than the maximum level threshold of the side lobes in other angle ranges.

5. The method for adaptive optimization of a localizer pattern according to claim 1, characterized in that: Step 4) includes: (4.1) Adaptively calculate the weight vector of the LOC antenna array element First, the steering vector of the CSB and SBO signals radiated by the LOC antenna is determined. The co-directional feeding and reverse feeding characteristics of the CSB and SBO signals are not considered in the steering vector. The center of the LOC antenna is taken as the zero point. The steering vectors of the CSB and SBO signals radiated by the LOC antenna of the array element are expressed as: （1） in, represents the array factor of the log-periodic antenna; Indicates the angle from the runway centerline X axis, ranging from -90° to 90°; and Respectively represent the steering vectors of the CSB signal and the SBO signal; Indicates The distance from each array element to the center origin; Indicates the carrier wavelength of the signal; represents an imaginary unit; According to the minimum mean square error criterion, the mean square error formula is minimized to obtain the optimal weighted vector: （2） in, is the optimal weight vector; is the covariance matrix, is the cross-correlation vector, and Respectively expressed as: （3） in, Indicates the number of sampling points within the affected angle range; Indicates the first Angle values; Indicated in angle The artificially applied virtual interference power; Indicates angle The expected direction diagram on ; superscript represents transpose; Indicates angle The steering vector on ; In the process of solving the optimal weighted vector, the virtual interference power is adjusted iteratively according to the requirements of the desired directional pattern, and the virtual interference power is applied to the k+1th iteration process. The virtual interference power is expressed as: （4） in, Indicates that the kth iteration is applied at the angle In the first iteration, the virtual interference power is set to a number greater than 0; Indicates angle The actual LOC pattern of the previous k-th iteration; represents the iterative gain; Secondly, the covariance matrix and cross-correlation vector of k+1 iterations are calculated according to the virtual interference power. The calculation formula is as follows: （5） in, The value is greater than 0. represents the identity matrix; Then, the weight vector of the LOC antenna element at the k+1 iteration is calculated based on the iteratively updated covariance matrix and cross-correlation vector: （6） in, represents the weight vector of the k+1th iteration; represents the covariance matrix of the k+1th iteration; represents the cross-correlation vector of the k+1th iteration; in addition, constraints need to be added when calculating the weighted vectors of the CSB signal and the SBO signal respectively and ,in and Respectively represent the steering vectors of CSB signal and SBO signal at 0°, and They represent the weight vectors of the CSB signal and the SBO signal under the constraint conditions respectively; the weight vectors of the CSB signal and the SBO signal of the k+1th iteration after adding the constraint conditions are respectively expressed as and ; (4.2) Generate CSB signal and SBO signal directional diagram According to the weighted vector calculated in step (1), the directional diagrams of the actual CSB signal and SBO signal of the k+1th iteration are calculated respectively: （7） in, and They represent the actual CSB signal and SBO signal directional diagrams of the k+1th iteration respectively, and denote the weight vectors of the CSB signal and the SBO signal of the k+1th iteration respectively; (4.3) Determining the convergence of the directional pattern Determine whether the error between the directional pattern generated in step (2) and the expected directional pattern is less than the set value If it is less than the set value , then the directional pattern is considered to have converged. At this time, the weighted vector obtained in step (1) is the optimal weighted vector, and the directional pattern calculated in step (2) is the optimal directional pattern. If it is greater than or equal to the set value , then the directional pattern is considered not to have converged, and the process returns to step (1) to continue iteratively calculating the weighted vector until the directional pattern has converged.

6. The method for adaptive optimization of a localizer pattern according to claim 1, characterized in that: Step 5) includes: using the optimal CSB signal and SBO signal directional patterns obtained in step 4) to calculate the modulation difference DDM for providing horizontal guidance information to the aircraft: （8） in, and They represent the optimal directivity diagrams of the CSB signal and the SBO signal obtained in step 4) respectively; then, the calculated DDM is compared with the DDM limit specified by the International Civil Aviation Organization (ICAO) and a DDM detection report is output.

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