CN112858994B - Amplitude comparison direction finding method based on uniform circular array - Google Patents
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- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
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Abstract
The invention belongs to the technical field of electronic reconnaissance and relates to a radial direction finding method based on a uniform circular array. The invention provides a method for carrying out amplitude comparison direction finding by utilizing a uniform circular array, which combines a DBF technology, utilizes the characteristic that the circular array can provide an omnibearing azimuth angle, is divided into an omnibearing search stage and a local positioning and tracking stage by a mode of twice wave beam formation, carries out amplitude comparison direction finding and finishes the direction measurement and estimation of a signal source. The method has the advantages that the method can realize 360-degree omnidirectional direction finding of direction finding by an amplitude comparison method, effectively improves direction finding precision, more accurately estimates the incident angle information of signals, and is simple and good in effect.
Description
Technical Field
The invention belongs to the technical field of electronic reconnaissance and relates to a radial direction finding method based on a uniform circular array.
Background
With the increasingly dense electromagnetic spectrum, the higher pulse density and the application of high-power electronic equipment, the electromagnetic environment is more and more complex, the traditional electronic reconnaissance device has the problems of low sensitivity and short sight, after the sensitivity is improved, the signal density received by a receiver is greatly increased, the pulse overlapping probability is greatly improved, and the practical problems of poor environment adaptability, wrong parameter measurement, serious azimuth increase and the like are faced. Under the large background of rapid development of radar technology, when a new technology and means are sought for electronic reconnaissance, it is urgent to improve the receiving processing capability, weak signal detection capability, information processing capability and the like of radar reconnaissance.
The Digital Beamforming (DBF) technology based on the array antenna can greatly improve the anti-interference capability of the radar system, and has been rapidly popularized and applied in the field of electronic reconnaissance in recent years. The DBF technology can adaptively form airspace anti-interference and form a plurality of independently controllable beams, and has higher signal-to-noise ratio; the antenna has better self-correction performance, can obtain lower side lobes, and can reduce the batch increase rate of signal processing at the rear end. Meanwhile, in the aspect of array antenna selection, compared with a uniform linear array, a uniform circular array has good space symmetry, and meanwhile, the omnidirectional detection performance and the like, and the excellent characteristics mean that the circular array has wide application prospects, and the number of radar systems based on the circular array is increasing.
In practical application, due to the large scale of the array, digital beams of the array are generally synthesized by only using a part of sub-array elements around an array element corresponding to a main beam, and a DBF synthesis directional diagram of the array often has the problems of small beam width, poor sensitivity, poor main lobe beam gain and the like.
Disclosure of Invention
The invention aims to solve the problems, provides a range-comparing direction-finding method based on a uniform circular array, combines a DBF technology, utilizes the characteristic that the circular array can provide an omnibearing azimuth angle, is divided into an omnibearing search stage and a local positioning and tracking stage through a mode of twice wave beam formation, carries out range-comparing direction-finding and finishes the direction measurement and estimation of a signal source.
The technical scheme of the invention is as follows:
a self-adaptive amplitude-comparison direction-finding method based on a uniform circular array DBF technology realizes accurate estimation of a signal incidence direction by carrying out beam forming on a target signal in a space and direction-finding by a beam amplitude-comparison method, takes the estimation of the signal incidence direction at an angle theta as an example in the following steps, and is characterized by comprising the following steps of:
s1, the method of forming a digital beam using a uniform circular array, for example, the array shown in fig. 1, includes setting M antenna elements arranged at equal intervals along the entire circumference. And entering a searching stage, wherein the circular array forms a plurality of independent beams covering 360-degree azimuth angles, and the arc length required for forming one beam is 2K +1 antenna subunits. The pattern function of the formed ith receive beam is:
where γ is the signal incidence angle. And K is the number of the sub-array elements on one side except the main array element during the beam forming in the searching stage. a is 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:
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 beam maximum, i.e. the beam pointing angle.
S2, based on the uniform circular array digital beam formed by the DBF technique, the antenna formed by the sub-array elements and having a plurality of independent main lobe beams adjacent to each other covers 360 ° azimuth, and the incident signal is processed, so as to obtain the directional pattern function of the i-th receiving beam outputted by the digital beam forming, in this case:
wherein, X i Is the received signal of the ith unit in the form of:
a i1 amplitude weighting coefficients determined for the element patterns. W 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 amplitude weighting coefficients determined to reduce antenna side lobes. The maximum value theta of the beam pointing azimuth angle at the moment is obtained by comparing amplitude values output by different beams 1 . And enters a tracking phase.
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 elementThe beam pointing direction of the element is rotated by an angle delta theta along the clockwise direction, the delta theta is determined by the number M of the antenna units, namely the angle delta theta is 2 pi/M or the angle delta theta is 360 DEG/M, and theta is formed 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 beam of Δ θ, calculating an amplitude ratio between two adjacent beams, and measuring the relationship between the theoretical ratio amplitude and the incident deflection angle in fig. 5 to obtain the incoming wave direction. As shown in FIG. 2, if the incoming wave signal is located near the axis of the nth antenna, the maximum output amplitude of the nth antenna is obtained by the digital beam forming technique, and the logarithmic signal amplitude values output by the nth antenna and the two adjacent antennas are respectively set to be A n-1 (t)、A n (t)、A n+1 (t), the ratio of the outputs of every two channels is:
R n0 ＝A n (t)/A n-1 (t)
R n1 ＝A n (t)/A n+1 (t)
and comparing the obtained ratio with a database, wherein the database is an amplitude characteristic library constructed by utilizing the relation between a theoretical value obtained by amplitude comparison of output voltage values of adjacent beams and an actual incidence deflection angle under an ideal condition, namely, a plurality of incidence angles are selected at equal intervals within the range of [0 degrees and 360 degrees ] according to the precision requirement, and different corresponding ratios under different incidence angles are obtained to obtain the amplitude characteristic library. And obtaining an accurate measurement value of the incident azimuth angle through comparison.
The method has the advantages that the method can realize 360-degree omnidirectional direction finding of direction finding by an amplitude comparison method, effectively improves direction finding precision, more accurately estimates the incident angle information of the signal, and has simple method and good effect.
Drawings
FIG. 1 is a schematic diagram of a method for forming a circular array digital beam
FIG. 2 is a schematic view of amplitude comparison and direction finding
In the search stage of fig. 3, the beam forming pattern of the circular array antenna
In the tracking phase of fig. 4, the beam forming pattern of the circular array antenna
FIG. 5 is a graph of theoretical ratio of amplitude of circular array in search phase and tracking phase
FIG. 6 is a graph showing the variation of direction-finding accuracy with the SNR of a signal in a search phase and a tracking phase
Detailed Description
The technical solution of the present invention will be further explained with reference to the drawings and simulations.
In this example, matlab is used to perform simulation verification on the proposed method, and for simplicity, the following assumptions are made for the algorithm model:
1. the uniform circular array reconnaissance antenna array and the target are both in an XY plane;
2. mutual coupling between antenna elements, antenna gain, beam width, etc. are not changed with the change of the antenna beam scanning angle.
3. No amplitude and phase errors exist among array channels, and only Gaussian white noise exists in an electromagnetic environment.
The number of the circular array antennas is set to be 100 array elements, a plurality of independent beams are formed at intervals of 3.6 degrees at this time, the direction of an incident signal is a central angle of two adjacent array elements, namely, the deviation angle of the incident angle and the axis of the adjacent beam is equal to 1.8 degrees. In the search stage, the number of subarray elements is set to 25, the array antenna directional pattern at this time is obtained through beam forming, as shown in fig. 3, and meanwhile, the beam amplitude output value and the beam pointing angle θ of the beam are found through traversing 100 beams covering 360 degrees 1 . Entering a tracking phase for the angle theta 1 Three adjacent beams are formed, and then an array antenna directional pattern is obtained, as shown in fig. 4, by comparing the output amplitude values of the three beams, azimuth angle information of the signal is obtained. The uniform circular array antenna forms a beam covering 360 degrees of azimuth.
The simulation results are shown in the figure:
during the search phase, the half-power beamwidth of the antenna pattern shown in fig. 3 is 6 °, and the sidelobe level is-7 dB with respect to the main lobe; during the tracking phase, the antenna pattern shown in fig. 4 has a half-power beamwidth of 4 ° and sidelobe levels of-8 dB with respect to the main lobe. The beam width of an antenna directional pattern is reduced in the tracking stage, the main lobe beam gain is higher, and the direction finding precision is higher, so that the method has better direction finding effect than an amplitude method.
As can be seen from the results of fig. 5, when the signal is incident at a central angle between two adjacent beams, the beam output ratio amplitude is 1. The circular array ratio amplitude is gradually increased along with the reduction of the incident deviation angle, and due to the characteristic of an antenna directional diagram in the tracking stage, when the incident deviation angle is 0 degrees in the tracking stage, the ratio of the main beam output value to the adjacent beam output value is maximum, and the value of the main beam output value is obviously higher than the maximum ratio amplitude in the searching stage.
As can be seen from the results in fig. 6, compared with the case of performing direction finding by amplitude comparison only in the search stage, the direction finding accuracy is significantly improved after the tracking stage is performed, and the improvement effect is very significant and the direction finding error is reduced by nearly 50% under the condition of low signal-to-noise ratio. Under conditions of high signal-to-noise ratio, the direction finding error is also smaller than that in the case of amplitude direction finding only in the search phase. Therefore, the method has better direction finding effect than the amplitude method.
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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