CN112858994B - Amplitude comparison direction finding method based on uniform circular array - Google Patents

Abstract

The invention belongs to the technical field of electronic reconnaissance, and relates to a method for amplitude ratio direction finding based on a uniform circular array. The present invention provides a method for amplitude comparison and direction finding by using a uniform circular array. Combined with the DBF technology, the circular array can provide omnidirectional azimuth angle characteristics, and is divided into omnidirectional search stages by two beam forming methods. In the local positioning and tracking stage, the amplitude comparison method is carried out to complete the direction measurement and estimation of the signal source. The beneficial effects of the present invention are that the present invention can carry out 360° omnidirectional direction finding with amplitude comparison method, effectively improve the direction finding accuracy, more accurately estimate the incident angle information of the signal, the method is simple, and the effect is good.

Description

A Method of Amplitude and Direction Finding Based on Uniform Circular Array

technical field

The invention belongs to the technical field of electronic reconnaissance, and relates to a method for amplitude ratio direction finding based on a uniform circular array.

Background technique

With the increasing density of the electromagnetic spectrum, the increasing pulse density and the application of high-power electronic equipment, the electromagnetic environment is becoming more and more complex. The traditional electronic reconnaissance device faces the problem of low sensitivity and cannot see far. The signal density received by the receiver is greatly increased, the probability of pulse overlap is greatly increased, and it is also faced with practical problems such as poor environmental adaptability, incorrect parameter measurement, and serious azimuth increase. In the context of the rapid development of radar technology, it is urgent to seek new technologies and means for electronic reconnaissance, and it is urgent to improve the receiving and processing capabilities of radar reconnaissance, weak signal detection capabilities, and information processing capabilities.

The Digital Beamforming (DBF) technology based on the array antenna can greatly improve the anti-jamming capability of the radar system, and it has also been rapidly promoted and applied in the field of electronic reconnaissance in recent years. DBF technology can adaptively form airspace anti-jamming, form multiple independently controllable beams, and have high signal-to-noise ratio; the antenna has good self-correction performance, can obtain low side lobes, and can reduce the signal at the back end The batch rate for processing. At the same time, in terms of array antenna selection, compared with uniform linear arrays, uniform circular arrays have good spatial symmetry and omnidirectional detection. These excellent characteristics mean that circular arrays will have broad application prospects. Array radar systems are also increasing day by day.

In practical applications, due to the large-scale nature of the array, the digital beam generally only uses a part of the sub-array elements around the corresponding array element of the main beam for synthesis. The DBF synthesis pattern often has small beam width, poor sensitivity, main In this case, considering the passive positioning, there will always be a large error in the array direction finding.

SUMMARY OF THE INVENTION

The purpose of the present invention is to address the above problems, to provide a method for amplitude comparison and direction finding based on a uniform circular array, combined with the DBF technology, and the characteristic that the circular array can provide an omnidirectional azimuth angle. The method is divided into an all-round search stage and a local positioning and tracking stage.

The technical scheme of the present invention is:

An adaptive amplitude-comparison direction finding method based on the uniform circular array DBF technology, which can accurately estimate the signal incident direction by performing beam synthesis and beam-amplitude amplitude-comparison method direction finding on the target signal in space. The following steps are based on the angle θ. Take the signal incident direction estimation at as an example, which is characterized in that it includes the following steps:

S1. Using the digital beam forming method of a uniform circular array, taking the array shown in FIG. 1 as an example, along the entire circumference, M antenna units arranged at equal intervals are set. Entering the search phase, at this time, the circular array forms multiple independent beams covering an azimuth angle of 360°, and there are 2K+1 antenna subunits on the arc length required to form a beam. The pattern function of the formed lth receive beam is:

为第i单元与第0单元之间的空间相位差，其形式为：

是为了使波束最大值指向在△γ_l方向所需要的第i单元与第0单元之间的阵内相位差，其形式为：

△γ_l是波束最大值方向，即波束指向角度。where γ is the incident angle of the signal. K is the number of sub-array elements on one side other than the main array element used in beamforming during the search phase. a _i is the sum of the amplitude weighting coefficients introduced considering the element pattern and the amplitude weighting coefficients determined to reduce the antenna side lobes.

is the spatial phase difference between the i-th unit and the 0-th unit, and its form is:

is the intra-array phase difference between the _i -th unit and the 0-th unit required to make the maximum beam point in the direction of △γl, and its form is:

Δγ _l is the direction of the maximum beam value, that is, the beam pointing angle.

S2. Based on the uniform circular array digital beam formed by the above DBF technology, the 360° azimuth is covered by a plurality of independent antennas formed by sub-array elements and adjacent to the main lobe beam, and the incident signal is processed to obtain the digital beam forming in this case. The output pattern function of the lth receive beam is:

a_i1为单元方向图决定的幅度加权系数。W_i为形成第l个接收波束以及降低天线副瓣电平的复加权系数，其形式为：

a_i2为降低天线副瓣而确定的幅度加权系数。通过比较不同波束输出的幅度值，得到此时波束指向方位角最大值θ₁。并进入跟踪阶段。Among them, Xi is the received signal of the _i -th unit, and its form is:

a _i1 is the amplitude weighting coefficient determined by the unit pattern. Wi is the complex weighting coefficient for forming the _lth receiving beam and reducing the antenna side lobe level, and its form is:

a _i2 is the amplitude weighting coefficient determined to reduce the antenna side lobes. By comparing the amplitude values of different beam outputs, the maximum beam pointing azimuth angle θ ₁ is obtained at this time. and enter the tracking phase.

S3. Enter the tracking stage, perform digital beam forming through all the array antennas of the uniform circular array, and set the incident signal to be θ ₁ to obtain a beam pointing to θ _1. By removing the (-K) unit and adding the (K+1) No. unit , the beam pointing rotates an angle Δθ in the clockwise direction, Δθ is determined by the number of antenna elements M, that is, Δθ=2π/M or Δθ°=360°/M, forming the wave speed of θ ₁ + Δθ, and then Rotate the angle Δθ in the counterclockwise direction to obtain the beam pointing to θ ₁ -Δθ, and output the corresponding amplitude value to find the amplitude ratio between the two adjacent beams, through the relationship between the theoretical ratio amplitude and the incident declination angle in Figure 5 Measure the direction of arrival of the wave. As shown in Figure 2, if the incoming wave signal is located near the axis of the nth antenna, the digital beamforming technology is used to obtain the maximum output amplitude at the nth antenna at this time, and the logarithmic signal amplitude values of this antenna and the adjacent two antennas are assumed. The outputs are A _n-1 (t), A _n (t), and A _n+1 (t) respectively, then the ratio of the outputs of the two channels is:

R _n0 =A _n (t)/A _n-1 (t)

R _n1 =A _n (t)/A _n+1 (t)

By comparing the obtained ratio with the database, the database is an amplitude feature library constructed by using the relationship between the theoretical value obtained by the ratio of adjacent beam output voltage values and the actual incident declination angle under ideal conditions, that is, in [0°, 360° ], select several incident angles equidistantly according to the accuracy requirements, and obtain different ratios corresponding to different incident angles, and obtain the amplitude feature library. By comparison, an accurate measurement of the incident azimuth is obtained.

The beneficial effects of the present invention are that the present invention can perform 360° omnidirectional direction finding with amplitude comparison method, effectively improve the direction finding accuracy, more accurately estimate the incident angle information of the signal, the method is simple, and the effect is good.

Description of drawings

Figure 1 Schematic diagram of circular array digital beamforming method

Figure 2 Schematic diagram of amplitude ratio and direction finding

Figure 3. The beamforming pattern of the circular array antenna in the search phase

Figure 4. In the tracking stage, the beamforming pattern of the circular array antenna

Figure 5. Curves of the theoretical ratio amplitude of the circular array in the search stage and the tracking stage

Figure 6. Curves of direction finding accuracy versus signal-to-noise ratio in the search phase and the tracking phase

Detailed ways

The technical solutions of the present invention will be further described below with reference to the accompanying drawings and simulations.

This example will use matlab to simulate and verify the proposed method. For the sake of simplicity, the following assumptions are made on the algorithm model:

1. The uniform circular reconnaissance antenna array and the target are in the XY plane;

2. Mutual coupling between antenna units, antenna gain, beam width, etc. will not change with the change of the antenna beam scanning angle.

3. There is no amplitude and phase error between the array channels, and only Gaussian white noise exists in the electromagnetic environment.

The number of circular array array antennas is set to 100 array elements. At this time, multiple independent beams are formed with an interval of 3.6°, and the direction of the incident signal is the median angle of the two adjacent array elements, that is, the deviation angle between the incident angle and the adjacent beam axis is θ. =1.8°. In the search stage, the number of sub-array elements is set to 25, and the pattern of the array antenna at this time is obtained through beam forming, as shown in Figure 3. At the same time, after traversing 100 beams covering 360°, the output value of the beam amplitude and the The beam is directed at an angle θ ₁ . Entering the tracking stage, three adjacent beams are formed for the angle θ _1. At this time, the pattern of the array antenna is obtained as shown in Figure 4. By comparing the output amplitude values of the three beams, the azimuth angle information of the signal is obtained. The uniform circular array antenna forms beams covering an azimuth angle of 360°.

The simulation results are shown in the figure:

In the search phase, the half-power beam width of the antenna pattern shown in Figure 3 is 6°, and the side lobe level is -7dB relative to the main lobe; in the tracking phase, the half-power beam of the antenna pattern shown in Figure 4 is The width is 4° and the side lobe level is -8dB relative to the main lobe. In the tracking stage, the beam width of the antenna pattern is reduced, the main lobe beam gain is higher, and the direction finding accuracy is higher. It can be seen that the method is better than the amplitude method for direction finding.

It can be seen from the results in Figure 5 that when the signal is incident at the middle angle of the two adjacent beams, the beam output ratio amplitude is 1. As the incident deviation angle decreases, the circular array ratio amplitude increases gradually. Due to the characteristics of the antenna pattern in the tracking stage, when the incident deviation angle is 0° in the tracking stage, the output value of the main beam is different from that of the adjacent beam. The ratio of the output values is the largest and its value is significantly higher than the maximum ratio amplitude in the search stage.

From the results in Figure 6, it can be seen that compared with the amplitude ratio method only in the search stage, the direction finding accuracy has been significantly improved after entering the tracking stage. Under the condition of low signal-to-noise ratio, the improvement effect is very obvious. The error has dropped by nearly 50%. Under the condition of high signal-to-noise ratio, the direction finding error is also smaller than that of the amplitude method only in the search stage. It can be seen that using this method to carry out the direction finding effect of the amplitude ratio method is quite good.

Claims (1)

1. A amplitude-comparing direction-finding method based on a uniform circular array, wherein the uniform circular array is provided with M antenna units which are arranged at equal intervals d along the circumference of the array, and the angle theta is the signal incidence direction, and the amplitude-comparing direction-finding method is characterized by comprising the following steps of:

s1, in the signal search stage, the circular array forms a plurality of independent beams covering 360 ° azimuth, assuming that there are 2K +1 antenna sub-units on the arc length required for forming a beam, and the digital beam forming method using the uniform circular array obtains the directional pattern function of the i-th receiving beam as:

wherein gamma is the incident angle of signal, K is the number of sub-array elements on one side except the main array element in the process of searching the phase beam forming, a _i The sum of the amplitude weighting coefficients introduced to account for the element pattern and the amplitude weighting coefficients determined to reduce the antenna side lobes,

is the spatial phase difference between the ith cell and the 0 th cell, and is of the form:

lambda is the wavelength of the signal and,

is to direct the beam maximum at Δ γ _l The in-array phase difference between the ith cell and the 0 th cell, which is required by the direction, is of the form:

△γ _l is the direction of the maximum value of the beam, i.e. the beam pointing angle;

s2, based on the uniform circular array digital beam formed in step S1, covering 360 ° azimuth with multiple independent antennas with adjacent main lobe beams formed by sub-array elements, and processing the incident signal to obtain the directional diagram function of the i-th receiving beam output by digital beam forming, as follows:

wherein, X _i Is the received signal of the ith unit in the form of:

a _i1 amplitude weighting factor, W, determined for the element pattern _i Complex weighting coefficients for forming the l-th receive beam and for reducing the antenna side lobe level are of the form:

a _i2 the amplitude weighting coefficient determined for reducing the antenna side lobe is obtained by comparing the amplitude values output by different beams to obtain the maximum value theta of the beam pointing azimuth angle at the moment ₁ ；

S3, entering a tracking stage, and performing digital beam forming through all array antennas of the uniform circular array to make the incident signal be theta ₁ To obtain a direction theta ₁ By removing the (-K) element and adding the (K +1) th element, the beam is directed clockwise by an angle Δ θ, which is determined by the number of antenna elements M, i.e. by 2 pi/M or 360 °/M, forming θ ₁ The wave speed of the plus delta theta is rotated by the angle delta theta in the counterclockwise direction to obtain the pointed theta ₁ And outputting a corresponding amplitude value for the wave beam of the delta theta, solving the amplitude ratio between two adjacent wave beams, and measuring the relation between the amplitude ratio and the incident deflection angle in the database to obtain the incoming wave direction.

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