A signal direction finding method in a complex environment based on a non-uniform linear array

Abstract

The present invention relates to a signal direction finding method in a complex environment based on a non-uniform linear array, comprising: receiving signals through a plurality of paths of antennas of the non-uniform linear array, and taking the signal data received by the shortest baseline as short baseline signal data and the signal data received by the longest baseline as long baseline signal data; obtaining the incident azimuth angle according to the short baseline signal data and the long baseline signal data; calculating the maximum baseline length based on the incident azimuth angle and the signal frequency; obtaining the target short baseline in the non-uniform linear array according to the maximum baseline length; and obtaining the direction finding result according to the target short baseline. The present invention realizes higher-precision direction finding through the selection of short and long baselines.

Description

Technical Field

[0001] The present invention relates to the technical field of signal direction finding, and particularly to a signal direction finding method based on a non-uniform linear array in a complex environment. Background Art

[0002] The prior art discloses a one-dimensional long and short baseline interferometer direction finding algorithm, which specifically includes: assuming that the antenna structure of a one-dimensional long and short baseline interferometer is as Figure 10 shown, where the horizontal axes 1, 2, and 3 represent the positions of the baseline arrangement, and the distance between antennas 1 and 2 is d 1 , and the distance between antennas 1 and 3 is d 2 . If the radiation source wavelength is assumed to be λ, then according to the above array structure and the spatial position of the radiation source, the received signal phase differences of antennas 2 and 3 with respect to the reference element 1 can be obtained as follows:

[0003]

[0004] To solve the phase ambiguity, it is necessary to select a short baseline length d1 that satisfies:

[0005]

[0006] For the long baseline d 2 , since its length is greater than λ / 2, the phase difference of the received signal of the antenna corresponding to this baseline will exceed the range of (-π, π), and the accurate solution of the target azimuth angle cannot be achieved. Therefore, a short baseline is required to solve the phase ambiguity of the long baseline. Therefore, for the long and short baseline interferometer direction finding, the short baseline is mainly used for deblurring, and the long baseline is mainly used to improve the direction finding accuracy.

[0007] Assume that the complex signals received by each antenna are

[0008]

[0009] Ignoring time t and only considering the phase, the phase differences corresponding to each baseline are:

[0010]

[0011] Since the signal phase φi ∈ [-π, π], when the short baseline is less than half a wavelength and the long baseline is greater than half a wavelength, there should be the following relationship:

[0012]

[0013] Since:

[0014]

[0015] We get:

[0016]

[0017] Then, from:

[0018]

[0019] That is:

[0020]

[0021] Finally, using:

[0022]

[0023] We get:

[0024]

[0025] That is, the azimuth calculation formula is:

[0026]

[0027] Performing error analysis on the direction-finding algorithm of the one-dimensional long-short baseline interferometer is actually performing error analysis on the measured phase difference. Taking the phase difference of the short baseline as an example, the phase difference formula is as follows:

[0028]

[0029] Let θ1 = 90° - θ, then the phase difference formula is as follows:

[0030]

[0031] Taking the total differential of the phase difference formula, the result is as follows:

[0032]

[0033] Among them, represents the influence of the signal wavelength measurement error on the phase error; represents the influence of the baseline length error on the phase error. In actual engineering, the baseline length error and the wavelength measurement error are controllable. After ignoring the above two errors, the phase error is as follows:

[0034]

[0035] That is:

[0036] That is:

[0037] 1. The direction-finding error increases as the signal wavelength increases;

[0038] 2. The direction-finding error decreases as the baseline length increases;

[0039] 3. The direction finding error increases as the incident angle increases;

[0040] 4. The direction finding error increases as the phase discrimination error increases.

[0041] According to formula (1), it can be known that for the direction finding algorithm of a one-dimensional long-short baseline interferometer, in terms of the array element arrangement, the shorter the short baseline d 1 the smaller the direction finding error. However, because d 1 ≤λ, the longer the short baseline, the narrower the measurement frequency range. Therefore, the signal measurement accuracy and the frequency range often cannot be guaranteed simultaneously. SUMMARY OF THE INVENTION

[0042] The purpose of the present invention is to provide a signal direction finding method in a complex environment based on a non-uniform linear array, which realizes higher-precision direction finding through the selection of long and short baselines.

[0043] To achieve the above purpose, the present invention provides the following solutions:

[0044] A signal direction finding method in a complex environment based on a non-uniform linear array, comprising:

[0045] Receiving signals through several paths of antennas of the non-uniform linear array, and taking the signal data received by the shortest baseline as the short baseline signal data, and the signal data received by the longest baseline as the long baseline signal data;

[0046] Obtaining the incident azimuth angle according to the short baseline signal data and the long baseline signal data;

[0047] Calculating the maximum baseline length based on the incident azimuth angle and the signal frequency;

[0048] Obtaining the target short baseline in the non-uniform linear array according to the maximum baseline length;

[0049] Obtaining the direction finding result according to the target short baseline and the longest baseline.

[0050] Optionally, the method for calculating the maximum baseline length is:

[0051]

[0052] where d max is the maximum baseline length, θ is the incident azimuth angle, f is the signal frequency, and c is the speed of light.

[0053] Optionally, obtaining the target short baseline in the non-uniform linear array according to the maximum baseline length includes: comparing the maximum baseline length with the lengths of the baselines in the non-uniform linear array, and selecting the target short baseline in the non-uniform linear array.

[0054] Optionally, comparing the maximum baseline length with the lengths of the baselines in the non-uniform linear array to select the target short baseline in the non-uniform linear array includes:

[0055] Comparing the maximum baseline length with the lengths of the baselines in the non-uniform linear array to obtain the range of the maximum baseline length:

[0056] d max ∈[d i-1 ,d i , 1 < i ≤ n

[0057] Obtaining d in the non-uniform linear array i-1 , updating the shortest baseline to d i-1 , and obtaining the target short baseline, where the d i-1 is the spacing between antenna 1 and i - 1, and d i is the spacing between antenna 1 and i, and n is the number of antenna elements in the n-element array.

[0058] Optionally, obtaining the direction finding result according to the target short baseline and the longest baseline includes:

[0059] If the shortest baseline remains unchanged, the direction finding result remains unchanged;

[0060] If the shortest baseline is updated to the target short baseline, the incident azimuth angle is recalculated based on the target short baseline and the longest baseline.

[0061] The beneficial effect of the present invention is as follows: By using the idea of recursion, the present invention first uses a shorter short baseline for direction finding with lower precision for long-short baseline direction finding, and then calculates a longer short baseline d max by reverse derivation. Then, the short baseline closest to and shorter than or equal to d max in the array elements is used for direction finding, with higher precision. That is, through two selections of long-short baselines, higher-precision direction finding is achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0062] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0063] Figure 1 is a flowchart of a signal direction finding method based on a non-uniform linear array in a complex environment according to an embodiment of the present invention;

[0064] Figure 2 is a schematic diagram of a general model of a non-uniform linear array according to an embodiment of the present invention;

[0065] Figure 3 Schematic diagram of a non-uniform linear array with five array elements according to an embodiment of the present invention;

[0066] Figure 4 Flowchart of a signal direction finding method in a complex environment for a non-uniform linear array with five array elements according to an embodiment of the present invention;

[0067] Figure 5 For the embodiment of the present invention, respectively select d 1 (AB), d 2 (AC), d 3 (AD) as the measurement errors after short baselines;

[0068] Figure 6 Simulate an incident signal of 0.4 GHz according to an embodiment of the present invention;

[0069] Figure 7 Simulate an incident signal of 2.4 GHz according to an embodiment of the present invention;

[0070] Figure 8 Simulate an incident signal of 5.8 GHz according to an embodiment of the present invention;

[0071] Figure 9 Flowchart of performing a short baseline update once using the recursive idea according to an embodiment of the present invention;

[0072] Figure 10 Antenna structure diagram of a one-dimensional long and short baseline interferometer according to an embodiment of the present invention. Detailed implementation manners

[0073] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0074] To make the above objects, features, and advantages of the present invention more obvious and understandable, the present invention will be further described in detail below in conjunction with the accompanying drawings and specific implementation manners.

[0075] As Figure 1 shown, this embodiment provides a signal direction finding method in a complex environment based on a non-uniform linear array, including:

[0076] Receiving signals through several paths of antennas of the non-uniform linear array, and taking the signal data received by the shortest baseline as the short baseline signal data and the signal data received by the longest baseline as the long baseline signal data;

[0077] Specifically, as Figure 2 shown, it is a general model of a non-uniform linear array. This model contains n + 1 antenna array elements. Taking the leftmost antenna array element as the reference array element, the baseline lengths are d 1 , d 2 ……d n-1 , d n . The n + 1 paths of antennas receive signals respectively.

[0078] Based on the short baseline signal data and the long baseline signal data, obtain the incident azimuth angle;

[0079] Specifically, take the shortest baseline as the short baseline, with a length of d 1 , and the longest baseline as the long baseline, with a length of d n . Calculate the incident azimuth angle θ according to the received signal and the azimuth angle calculation formula.

[0080] The azimuth angle calculation formula is:

[0081]

[0082] where d n represents the length of the long baseline, is the phase difference between antennas 1 and 2, is the phase difference between antennas 1 and n + 1. Based on the incident azimuth angle and the signal frequency, calculate the maximum baseline length;

[0083] Specifically, substitute the incident angle θ and the signal frequency f into Equation (a), take the speed of light as, and solve for d max .

[0084] Furthermore, the method for calculating the maximum baseline length is:

[0085]

[0086] where d max is the maximum baseline length, θ is the incident azimuth angle, f is the signal frequency, and c is the speed of light.

[0087] Specifically, according to the error analysis, a short baseline as long as possible can reduce the direction finding error. Also, according to the two-antenna signal phase difference formula:

[0088]

[0089] The cosine value of the incident angle is not always 1. That is, in actual situations, d > λ / 2 does not necessarily result in phase ambiguity because the wavelength λ = c / f, where c is the speed of light. According to the above formula derivation,

[0090]

[0091] That is,

[0092]

[0093] Or,

[0094]

[0095] Therefore,

[0096]

[0097] The key of this method lies in obtaining d max , in a non-uniform array with reasonable design, there is always

[0098] d max ∈[d i-1 , d i , 1 < i ≤ n, i is an integer

[0099] where, d i-1 is the spacing between antenna 1 and i - 1, d i is the spacing between antenna 1 and i, and n is the number of n antenna elements.

[0100] According to d max , select a suitable short baseline to reduce the direction finding error.

[0101] According to the maximum baseline length, obtain the target short baseline in the non-uniform linear array;

[0102] Furthermore, obtaining the target short baseline in the non-uniform linear array according to the maximum baseline length includes: comparing the maximum baseline length with the lengths of the baselines in the non-uniform linear array, and selecting the target short baseline in the non-uniform linear array.

[0103] Specifically, according to d max , find d i-1 in the non-uniform linear array, and update the short baseline elements to the antenna elements corresponding to d i-1 , and this short baseline is the target short baseline.

[0104] According to the target short baseline and the longest baseline, obtain the direction finding result.

[0105] Furthermore, obtaining the direction finding result according to the target short baseline and the longest baseline includes:

[0106] If the shortest baseline remains unchanged, the direction finding result remains unchanged;

[0107] If the shortest baseline is updated to the target short baseline, then based on the target short baseline and the longest baseline, recalculate the incident azimuth angle according to the azimuth angle calculation formula.

[0108] Embodiment 1: Through a non-uniform linear array containing five array elements, three short baselines with different lengths are designed for selection, aiming to achieve high-precision direction finding in a relatively wide frequency range from 0.4 GHz to 6 GHz.

[0109] The preset incident signal frequency range is 0.4 - 6 GHz. Based on the non-uniform linear array as Figure 3 shown, the algorithm flow is designed as Figure 4 shown;

[0110] As Figure 3 shown, through a specific non-uniform linear array arrangement, direction finding of 0.4 - 6 GHz signals is achieved. The antenna arrangement is as follows:

[0111] There is a relationship between the signal wavelength and frequency:

[0112]

[0113] To solve the phase ambiguity, the short baseline needs to satisfy:

[0114]

[0115] Substitute f = 6 GHz into the above formula, and solve to get λ = 0.05, that is, d 1 ≥0.025, corresponding to the shortest baseline spacing. Substitute f = 0.4 GHz, and solve to get λ = 0.75, that is, d 1 ≥0.375, corresponding to the longest short baseline spacing. In this embodiment, take the intermediate value 1.5 GHz of a frequency, and calculate to get 0.1.

[0116] S1. Five antennas ABCDE respectively receive five-way IQ signals and transmit them to the GPU for calling.

[0117] S2. Take the signal data received by antennas AB as the short baseline signal data, and the signal data of antenna AE as the long baseline signal data, and obtain the incident angle θ.

[0118] S3. Substitute the incident angle θ and the signal frequency f into formula (a), and take the speed of light c = 3×10 8 , and solve for d max .

[0119] S4. According to d max and the antenna array element arrangement method, select a longer short baseline. If dmax > 0.375, then take AD as the short baseline. If 0.1 < dmax < 0.375, select AC as the short baseline. If dmax < 0.1, the short baseline remains unchanged to minimize the calculation error.

[0120] S5. If the short baseline changes, according to the new short baseline, re - use the long - short baseline algorithm to obtain the new short - baseline phase difference, and calculate the updated θ1. If the short baseline does not change, the original θ is the direction - finding result.

[0121] Algorithm simulation:

[0122] Perform algorithm simulation in the MATLAB environment. Assume that the incident signal frequency is 0.4 GHz and remains unchanged. Change the incident angle for direction - finding simulation, and obtain the measurement error after updating the short baseline as Figure 5 shown in the following figure: Among them, error1, error2, and error3 are the cases where d 1 (AB), d 2 (AC), d 3 (AD) are selected as short baselines respectively. It can be seen from the above broken - line graph that as the short baseline becomes longer, the absolute error error of direction - finding shows a downward trend, that is, error1>error2>error3. That is, without phase ambiguity, the longer the short baseline, the higher the direction - finding accuracy.

[0123] Select frequencies of 0.4 GHz, 2.4 GHz, and 5.8 GHz respectively, add a small amount of noise, simulate the actual signal after pre - processing, simulate the incident signal of 0.4 GHz, and use this algorithm to measure 5 times. The results are as Figure 6 . Simulate the incident signal of 2.4 GHz, use this algorithm to measure 5 times, and the results are as Figure 7 . Simulate the incident signal of 5.8 GHz, use this algorithm to measure 5 times, and the results are as Figure 8 . In the above Figures 6 - 8 , error1 represents the absolute error of direction - finding before updating the short baseline, error2 represents the absolute error of direction - finding after updating the short baseline, and the absolute error between θ2 calculated according to the new short baseline and the actual incident angle. After the short baseline is adjusted, the accuracy is improved.

[0124] This invention performs a short - baseline update once through the recursive idea, selects the longest possible short baseline to achieve higher - accuracy long - short baseline direction - finding. The idea is as Figure 9 shown: Sample data of multiple incident signals with a receiving frequency of f; perform direction - finding with a relatively short short baseline to ensure no phase ambiguity and obtain a lower - accuracy direction - finding angle; reverse - deduce the theoretical longest short baseline; update the short baseline according to the actual situation and re - perform direction - finding. At this time, the direction - finding accuracy will be greater than the initial direction - finding.

[0125] The embodiments described above are only descriptions of the preferred embodiments of the present invention and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention shall fall within the protection scope determined by the claims of the present invention.

Claims

1. A signal direction finding method based on a non-uniform linear array in a complex environment, characterized in that: include: Receive signals through a plurality of antennas of a non-uniform linear array, and take the signal data received by the shortest baseline as the short baseline signal data, and the signal data received by the longest baseline as the long baseline signal data; Acquire an incident azimuth according to the short baseline signal data and the long baseline signal data; Calculating a maximum baseline length based on the incident azimuth and the signal frequency; According to the maximum baseline length, obtaining a target short baseline in the non-uniform linear array; Obtaining a direction finding result according to the target short baseline and the longest baseline; The maximum baseline length is calculated as: Among them, d max is the maximum baseline length, θ is the incident azimuth, f is the signal frequency, and c is the speed of light; According to the maximum baseline length, acquiring the target short baseline in the non-uniform linear array comprises: comparing the maximum baseline length with the length of the baseline in the non-uniform linear array, and selecting the target short baseline in the non-uniform linear array; Comparing the maximum baseline length with the length of the baseline in the non-uniform linear array, and selecting a target short baseline in the non-uniform linear array includes: Compare the maximum baseline length with the length of the baseline in the non-uniform linear array to obtain the range of the maximum baseline length: d max ∈[d i-1 ,d i ],1<i≤n Get d in the non-uniform linear array i-1 , update the shortest baseline to d i-1 , obtain the target short baseline, where the d i-1 is the distance between antenna 1 and i-1, d i is the distance between antennas 1 and i, and n is the number of antenna array elements.

2. The signal direction finding method based on non-uniform linear array in complex environment according to claim 1 is characterized in that: Acquiring a direction finding result according to the target short baseline and the longest baseline includes: If the shortest baseline remains unchanged, the direction finding result remains unchanged; If the shortest baseline is updated to the target short baseline, the incident azimuth is recalculated based on the target short baseline and the longest baseline.

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