A method for adaptive optimization of localizer pattern

Abstract

A method for adaptively optimizing the direction pattern of a heading beacon includes: initializing LOC antenna array element parameters and obstacle parameters; calculating the angular range of the LOC antenna radiation field affected by obstacles; respectively designing the desired direction patterns of the CSB signal and the SBO signal radiated by the LOC antenna; adaptively optimizing the direction patterns of the CSB signal and the SBO signal radiated by the LOC antenna; and evaluating the course performance of the optimized optimal direction pattern. The present invention fully utilizes the robustness of the adaptive processing technology and adaptively calculates the feeding amplitude and feeding phase of the heading beacon antenna according to the area range of the radiation field affected by obstacles. This can improve the horizontal guidance performance of the existing dual-frequency heading beacon system for aircraft without increasing the number of antenna elements. During installation and debugging, the heading beacon system of the present invention can adaptively adjust the feeding amplitude and phase according to the airport environment, thereby reducing the installation and debugging workload.

Description

Technical Field

[0001] The present invention relates to a method for optimizing a localizer pattern, and in particular to a method for adaptively optimizing a localizer pattern. 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 radiates a specific signal pattern from an array antenna, providing lateral guidance information to aircraft during approach and landing. However, the LOC antenna's radiation field is susceptible to multipath interference caused by obstacles such as buildings and trees near the runway. This can cause the runway structure to bend when an aircraft is aligned with the runway, reducing its lateral guidance performance.

[0003] Existing LOC systems often use a dual-frequency structure (channel and clearance) to mitigate the impact of multipath interference. This system generates four signals: a channel carrier plus sidebands (CSB) signal, a channel suppressed carrier double-sideband (SBO) signal, a clearance CSB signal, and a clearance SBO signal. These signals are radiated by antenna array elements with fixed feed amplitudes and phases, creating a spatially superimposed fixed channel pattern. This fixed pattern compromises the array antenna's multipath interference suppression capabilities and is unable to handle multipath interference from any direction. This leads to high site requirements for actual installation and application, potentially requiring manual adjustment of the feed coefficient, making installation and commissioning difficult, and even requiring the removal of obstacles to ensure LOC horizontal guidance performance, resulting in economic losses.

[0004] Adaptive processing methods, by designing appropriate weighting vectors, can adaptively null the processed received signal in the direction of interference to suppress interference. These methods are widely used in modern radar, communication systems, and satellite navigation. LOC operates in the very high frequency band, which has a long wavelength. Multipath interference can be considered as specular reflections from obstacles. Therefore, the angular range of the affected radiation field can be determined based on the specific obstacle location at an airport. Adaptive processing methods can then be applied to generate new feed amplitude and phase coefficients, producing a flight path pattern tailored to specific airport operations and improving economic efficiency. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a method for adaptively optimizing a localizer pattern that can reduce the influence of multipath obstacles in order to overcome the shortcomings of the existing technology.

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

[0007] 1) Initialization of LOC antenna array element parameters and obstacle parameters;

[0008] 2) Calculate the angular range of the LOC antenna radiation field affected by obstacles based on the LOC antenna array element parameters and obstacle parameters;

[0009] 3) Based on the angular range of the LOC antenna radiation field affected by obstacles, design the expected directivity patterns of the CSB signal and SBO signal radiated by the LOC antenna respectively;

[0010] 4) Adaptively optimizing the directional patterns of the CSB and SBO signals radiated by the designed LOC antenna based on the desired directional patterns of the CSB and SBO signals radiated by the LOC antenna;

[0011] 5) Evaluate the channel performance of the optimized optimal direction pattern.

[0012] The present invention provides a method for adaptively optimizing the direction beacon pattern, which fully utilizes the robustness of adaptive processing technology and adaptively calculates the feeding amplitude and feeding phase of the direction beacon antenna according to the range of the area where the radiation field is affected by obstacles. This method can improve the horizontal guidance performance of the existing dual-frequency direction beacon system for aircraft without increasing the number of antenna array elements. During installation and commissioning, the direction beacon system based on the method for adaptively optimizing the direction beacon pattern of the present invention can adaptively adjust the feeding amplitude and phase according to the airport environment, thereby reducing the installation and commissioning workload. The direction beacon system based on the method for adaptively optimizing the direction beacon pattern of the present invention can form new feeding amplitude and phase coefficients according to the specific obstacle locations at the airport, thereby protecting the existing infrastructure of the airport as much as possible and reducing the economic cost of installation. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0014] Figure 2 are the normalized channel CSB and SBO patterns before adaptive optimization when obstacles are present;

[0015] Figure 3 It is the normalized channel CSB and SBO direction diagram after optimization using the method of the present invention;

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

[0017] Figure 5 It is a comparison of DDM in distance before and after optimization using the method of the present invention. DETAILED DESCRIPTION

[0018] A method for adaptively optimizing a localizer pattern according to the present invention will be described in detail below with reference to the embodiments and accompanying drawings.

[0019] The present invention provides a method for adaptively optimizing the localizer pattern. The method regards the multipath propagation path in the presence of an obstacle as a mirror reflection of the obstacle, and then calculates the angular range of the radiation field affected by the obstacle based on the positional relationship between the obstacle's reflecting surface and the localizer antenna array. The desired pattern is constructed accordingly, and an adaptive processing method is used to calculate the new antenna feed amplitude and feed phase according to the desired pattern requirements to generate an optimized pattern.

[0020] like Figure 1 As shown, a method for adaptively optimizing a localizer pattern of the present invention comprises the following steps:

[0021] 1) Initialization of LOC antenna array element parameters and obstacle parameters; including:

[0022] Establish a coordinate system with the LOC antenna center as the origin, the runway centerline as the X-axis, and the runway plane as the XOY plane. Set the distance from each LOC antenna element to the origin, as well as the projection coordinates of the obstacle reflection surface's farthest and closest reflection points from the LOC antenna on the XOY plane.

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

[0024] Based on the principle of mirror reflection, the angular range of the LOC antenna's radiation field affected by the obstacle is calculated based on the projection coordinates of the reflection points farthest and closest to the obstacle's reflecting surface on the XOY plane. The minimum affected angle is the arccosine of the ratio of the projection on the X-axis of the distance from the reflection point farthest from the LOC antenna to the origin to the distance from the reflection point farthest from the obstacle to the origin. The maximum affected angle is the arccosine of the ratio of the projection on the X-axis of the distance from the reflection point closest to the LOC antenna to the origin to the distance from the reflection point closest to the obstacle to the LOC antenna to the origin.

[0025] 3) Based on the angular range of the LOC antenna radiation field affected by obstacles, design the expected directivity patterns of the CSB signal and SBO signal radiated by the LOC antenna respectively.

[0026] The design of the expected radiation pattern requires: the expected radiation pattern of the CSB signal has a maximum radiation field in the 0° direction of the main lobe, the side lobes within the angle range affected by obstacles form nulls, and the maximum level thresholds of the side lobes in other angle ranges are set; the expected radiation pattern of the SBO signal has a null in the 0° direction of the main lobe, the side lobes within the angle range affected by obstacles form nulls, and the maximum level thresholds of the side lobes in other angle ranges are set; the expected radiation pattern of the CSB signal and the expected radiation pattern of the SBO signal are both normalized and logarithmically transformed based on 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 thresholds 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 thresholds of the side lobes in other angle ranges.

[0027] 4) Adaptively optimize the directional patterns of the CSB and SBO signals radiated by the designed LOC antenna based on the desired directional patterns of the CSB and SBO signals radiated by the LOC antenna

[0028] Adaptive optimization of the LOC pattern first requires calculating the steering vector of the LOC antenna element. Then, based on the minimum mean square error criterion, the weighting vector is designed to minimize the mean square error between the actual pattern and the expected pattern. The actual pattern is then generated based on the steering vector and the weighting vector. Finally, the optimal weighting vector and the optimal actual pattern are determined based on the convergence of the actual pattern. This includes:

[0029] (4.1) Adaptively calculate the weight vector of the LOC antenna array element.

[0030] First, the steering vector of the CSB and SBO signals radiated by the LOC antenna is determined. The co-feeding and reverse feeding characteristics of the CSB and SBO signals are not taken into account 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:

[0031] (1)

[0032] Since the LOC antenna is a log-periodic antenna, the steering vector equation (1) contains the array factor of the log-periodic antenna. ,in Indicates the angle from the runway centerline X axis, ranging from -90° to 90°; and Represent the steering vectors of CSB signal and SBO signal respectively; Indicates the The distance from each array element to the center origin; Indicates the carrier wavelength of the signal; Represents an imaginary unit.

[0033] One method of calculating the optimal weighted vector is to minimize the mean square error between the actual pattern and the expected pattern based on the minimum mean square error criterion. The mean square error formula is:

[0034] (2)

[0035] in Indicates the number of sampling points within the affected angle range; Indicates the number of Angle value; Indicates the angle The artificially imposed virtual interference power; Indicates angle The desired direction pattern on ; Indicates angle The actual directional pattern generated by the above adaptive process is expressed as ,in represents the weight vector; Indicates angle The steering vector on ; Indicates transpose.

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

[0037] (3)

[0038] in, is the optimal weight vector; is the covariance matrix, is the cross-correlation vector, and Respectively expressed as:

[0039] (4)

[0040] In the actual process of solving the optimal weighted vector, it is necessary to continuously iteratively adjust the virtual interference power according to the requirements of the desired pattern, and apply it to the k+1th iteration process. The virtual interference power is expressed as:

[0041] (5)

[0042] in, Indicates that the kth iteration is applied at the angle The virtual interference power is set to a number greater than 0 in the first iteration; Indicates angle The actual LOC pattern of the last k iteration; It represents the iterative gain, which reflects the convergence speed of the iterative algorithm and determines the number of iterations;

[0043] Secondly, the covariance matrix and cross-correlation vector of k+1 iterations are calculated based on the virtual interference power. The calculation formula is as follows:

[0044] (6)

[0045] Among them, the term added to the covariance matrix This is to ensure the stability of the algorithm. The value is greater than 0. represents the identity matrix;

[0046] 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:

[0047] (7)

[0048] in, represents the weight vector of the k+1th iteration; represents the covariance matrix of the k+1th iteration; In addition, the CSB signal’s directional pattern has a maximum radiation field in the 0° direction, while the SBO signal’s directional pattern has a null in the 0° direction. Therefore, constraints need to be added separately when calculating the weighted vectors of the CSB and SBO signals. and ,in and Represent the steering vectors of CSB signal and SBO signal at 0° respectively, and Respectively represent the weight vectors of CSB signal and SBO signal under the constraint condition. The weight vectors of CSB signal and SBO signal at the k+1th iteration after adding the constraint condition are respectively represented as and ;

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

[0050] According to the weighted vector calculated in step (1), the directional patterns of the actual CSB signal and SBO signal of the k+1th iteration are calculated respectively:

[0051] (8)

[0052] in, and represent the actual CSB signal and SBO signal directional patterns of the k+1th iteration, respectively. and represent the CSB signal and SBO signal weight vectors of the k+1th iteration respectively.

[0053] (4.3) Determine the convergence of the directional pattern.

[0054] 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 , it is considered that the directional pattern has not converged, and return to step (1) to continue iteratively calculating the weighted vector until the directional pattern converges.

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

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

[0057] (9)

[0058] in, and They represent the optimal directivity patterns 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.

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

[0060] Experimental Description: This experiment uses a dual-band, 16-element LOC antenna as an example. The feed parameters provided in the technical manual are used as the pre-optimization parameters. The "pre-optimization" results described in subsequent experiments and descriptions all use the feed parameters provided in the technical manual. The parameters for obstacles near the runway are further set: a coordinate system is established with the LOC antenna center as the origin, the runway centerline as the X-axis, and the runway plane as the XOY plane. The projection coordinates of the left and right ends of the obstacle's reflective surface on the XOY plane are (1000m, 375m) and (1000m, 425m), respectively. The obstacle height is the same as the LOC antenna and parallel to the runway surface. The adaptive optimization method for the localizer pattern provided by the present invention is used to optimize the CSB and SBO patterns of the LOC channel.

[0061] Figure 2 are the normalized channel CSB signals and SBO patterns before adaptive optimization when obstacles exist;

[0062] According to the mirror reflection principle, when the multipath signal reflected by the obstacle is equivalent to the direct signal transmitted by the mirror virtual antenna, the angle range affected by the LOC radiation field is calculated based on the reflection point farthest from the left and right ends of the obstacle. According to the obstacle parameters set in this experiment, the direction pattern of the LOC radiation within the angle range of about 20°~35° will be affected. Figure 2 It can be seen from the figure that due to the influence of obstacles, the direction patterns of the channel CSB signal and SBO signal are distorted in the angle range of about 20°~35°, and the level value increases.

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

[0064] from Figure 3 As can be seen from the figure, the adaptive optimization method for the localizer pattern of the present invention creates a "wide null" in the angular range affected by obstacles, suppressing the impact of obstacles within this angular range. However, due to energy conservation constraints, the directional pattern level in other angular ranges unaffected by obstacles increases. Tables 1 and 2 respectively show the optimized feed parameters for the channel CSB and SBO signals using the adaptive optimization method for the localizer pattern of the present invention under the experimental conditions, providing the complex weight vector, amplitude, and phase, respectively.

[0065] Table 1 Feed parameters of each element in the channel CSB pattern after adaptive optimization

[0066]

[0067] Table 2 Feed parameters of each element in the channel SBO pattern after adaptive optimization

[0068]

[0069] Figure 4 To compare the DDM on the azimuth angle before and after optimization using a localizer directional pattern adaptive optimization method of the present invention;

[0070] The difference in modulation (DDM) is used on the course surface to indicate whether the aircraft is flying left or right. ICAO stipulates the value of DDM: based on the runway center, within the range of DDM 0 to 0.188, DDM changes linearly with angular displacement; within the range of DDM 0.188 to ±10°, DDM should be greater than 0.180; from ±10° to ±35°, DDM should be greater than 0.155. Figure 4 It can be seen that the DDM value in 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 channel CSB pattern becomes narrower after adaptive optimization. The narrower the main lobe pattern, the less it is affected by obstacle multipath.

[0071] Figure 5 To compare the DDM of the distance before and after optimization using a localizer directional pattern adaptive optimization method of the present invention;

[0072] Figure 5 The dotted line in the figure indicates the DDM jitter limit range of the III operation specified by ICAO on the channel surface. Figure 5 It can be seen that within the distance range affected by obstacles, the DDM curve before optimization exceeds the limit range specified by ICAO. The DDM curve optimized using the method proposed in this invention meets the ICAO requirements, indicating that the adaptive optimization method has a role in alleviating the impact of obstacles.

Claims

1. A method for adaptive optimization of a localizer pattern, characterized in that: The steps include: 1) Initialization of LOC antenna array element parameters and obstacle parameters; 2) Calculate the angular range of the LOC antenna radiation field affected by obstacles based on the LOC antenna array element parameters and obstacle parameters; 3) Based on the angular range of the LOC antenna radiation field affected by obstacles, design the expected directivity patterns of the CSB signal and SBO signal radiated by the LOC antenna respectively; The desired pattern requirements are as follows: the desired pattern of the CSB signal has a maximum radiation field in the 0° direction of the main lobe, the side lobes within the angle range affected by obstacles form a null, and the maximum level threshold of the side lobes within other angle ranges is set; the desired pattern of the SBO signal has a null in the 0° direction of the main lobe, the side lobes within the angle range affected by obstacles form a null, and the maximum level threshold of the side lobes within other angle ranges is set; The expected directivity patterns of the CSB signal and the SBO signal are both normalized and logarithmically transformed using the maximum radiation field level of the expected directivity pattern of the CSB signal. In this case, the maximum radiation field level of the expected directivity pattern of the CSB signal is 0 dB. The null level within the angle range affected by obstacles and the maximum level thresholds of the side lobes within other angle ranges of the expected directivity patterns of the CSB and SBO signals are set on the basis of 0 dB according to the number of array elements of the LOC antenna, the actual conditions of the radiation field, and the requirements. The null level within the angle range affected by obstacles must be lower than the maximum level thresholds of the side lobes within other angle ranges. 4) Adaptively optimizing the directional patterns of the CSB and SBO signals radiated by the designed LOC antenna based on the desired directional patterns of the CSB and SBO signals radiated by the LOC antenna; 5) Evaluate the channel performance of the optimized optimal direction pattern.

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

3. The method for adaptive optimization of a localizer pattern according to claim 1, wherein: Step 2) includes: based on the principle of mirror reflection, according to the projection coordinates of the reflection points farthest and closest to the obstacle's reflecting surface from the LOC antenna on the XOY plane, calculating the angular 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 reflection point farthest from the obstacle to the LOC antenna to the origin to the distance from the reflection point farthest 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 reflection point closest to the obstacle to the LOC antenna to the origin to the distance from the reflection point closest to the obstacle to the LOC antenna to the origin.

4. The method for adaptive optimization of a localizer pattern according to claim 1, wherein: Step 4) includes: (4.1) Adaptive calculation of 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-feeding and reverse feeding characteristics of the CSB and SBO signals are not taken into account 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 Represent the steering vectors of CSB signal and SBO signal respectively; Indicates the 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 optimal weight vector is obtained by minimizing the mean square error formula: （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 value; Indicates the angle The artificially imposed virtual interference power; Indicates angle The expected direction pattern on represents transpose; Indicates angle The steering vector on ; In the process of solving the optimal weighted vector, the virtual interference power is continuously adjusted iteratively according to the requirements of the desired 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 The virtual interference power is set to a number greater than 0 in the first iteration; Indicates angle The actual LOC pattern of the last k iteration; represents the iterative gain; Secondly, the covariance matrix and cross-correlation vector of k+1 iterations are calculated based on 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 separately when calculating the weighted vectors of the CSB signal and the SBO signal and ,in and Represent the steering vectors of CSB signal and SBO signal at 0° respectively, and They represent the weight vectors of CSB signal and SBO signal under the constraint conditions respectively; the weight vectors of CSB signal and SBO signal of k+1 iteration after adding the constraint conditions are respectively expressed as and ; (4.2) Generate CSB signal and SBO signal directional patterns According to the weighted vector calculated in step (1), the directional patterns of the actual CSB signal and SBO signal of the k+1th iteration are calculated respectively: （7） in, and represent the actual CSB signal and SBO signal directional patterns of the k+1th iteration, respectively. and denote the weight vectors of the CSB signal and SBO signal of the k+1th iteration respectively; (4.3) Determine 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 , it is considered that the directional pattern has not converged, and return to step (1) to continue iteratively calculating the weighted vector until the directional pattern converges.

5. The method for adaptive optimization of a localizer pattern according to claim 1, wherein: Step 5) includes: using the optimal CSB signal and SBO signal 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 patterns 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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