A Circular Array Direction Finding Method Based on Phase Difference Calibration

Abstract

The present invention provides a circular array direction finding method based on phase difference calibration, belonging to the technical field of communication countermeasures, and providing a design idea of phase difference calibration for traditional circular array direction finding technology; it includes: obtaining the phase difference fitting curve of the receiver channel through polynomial fitting technology, performing phase difference calibration, so that after the phase difference of the circular array direction finding system is equivalent to the phase difference of the antenna array, establishing a response sample set and carrying out the direction finding process; adopting the circular array correlation interference direction finding technology, calculating and based on the preliminary direction finding result, completing the quadratic fitting process of the phase difference fitting curve through the left and right data points at the direction finding maximum value, and obtaining the final direction finding result based on the response sample set, and further evaluating the direction finding accuracy and correcting the fitting algorithm when calculating the phase difference fitting curve; the present invention designs from the overall process idea of direction finding, especially provides the idea design of phase difference calibration, solves the problem of phase difference accuracy, and improves the flexibility and practicability of the circular array direction finding technology.

Description

Technical Field

[0001] The present invention belongs to the technical field of communication countermeasures and is applied to the process of circular array direction finding technology for communication targets. Specifically, it is a circular array direction finding method based on phase difference calibration. Background Art

[0002] One of the most important missions of a reconnaissance system is azimuth measurement. With the continuous development of modern electronic technology, the requirements for the volume, weight, cost performance, etc. of direction finding equipment are becoming increasingly stringent. The successful development of circular array interferometer direction finding technology has solved the contradiction between omnidirectional coverage, wide bandwidth, high-precision direction finding and volume. Such a direction finding system that is wide open in both frequency and azimuth is very suitable for use on small reconnaissance direction finding platforms.

[0003] In circular array interferometer direction finding technology, the accuracy of phase difference measurement is a key point. In the prior art, mainly only theoretical introductions are made for circular array related interferometer direction finding, and the phase difference of antenna array elements also adopts theoretical values based on antenna size and frequency band. Therefore, the following problems are brought: due to the limitations of process manufacturing technology, there is often a large difference between the theoretical phase difference of the antenna itself and the actual phase difference, which cannot meet engineering applications and it is difficult to meet the indicators. As a result, due to the phase difference accuracy problem, circular array interferometer direction finding technology is not conducive to engineering implementation, cannot be applied to more scenarios, and the obtained direction finding effect is not good. Summary of the Invention

[0004] In order to solve the problems involved in the background art, the present invention starts from the design ideas of the entire process of direction finding, the phase difference calibration idea of combining data fitting and look-up table, the verification of direction finding accuracy and the feedback idea of the fitting algorithm, and the idea of further improving the direction finding accuracy through quadratic curve fitting based on the initial direction finding result. Thus, the problem of phase difference accuracy is well solved, the flexibility of circular array direction finding technology is improved, and the practicability is enhanced.

[0005] The present invention adopts the following technical solutions to achieve the purpose:

[0006] A circular array direction finding method based on phase difference calibration, comprising:

[0007] Obtaining a phase difference fitting curve of the receiver channel through polynomial fitting technology for phase difference calibration;

[0008] After the phase difference of the circular array direction finding system is equivalent to the phase difference of the antenna array through phase difference calibration, establishing a response sample set for the direction finding process;

[0009] Adopting circular array related interferometer direction finding technology to calculate an initial direction finding result. According to the initial direction finding result, after completing the quadratic fitting process of the phase difference fitting curve through the left and right data points at the direction finding maximum value, based on the response sample set, obtaining the direction finding result;

[0010] During the direction finding process, according to the direction finding result, the direction finding accuracy is evaluated, and based on the direction finding accuracy, the fitting algorithm of the polynomial fitting technique when obtaining the phase difference fitting curve is corrected.

[0011] Specifically, the antenna array includes an 8-element directional antenna and an omnidirectional antenna.

[0012] Furthermore, the receiver is a dual-channel receiver. The first receiving channel receives signals from the 8-element directional antenna, and the second receiving channel receives signals from the omnidirectional antenna; the phase difference between the phase values of the signals received by the two receiving channels at the same moment is the phase difference of the receiver channels.

[0013] Furthermore, the phase difference calibration includes:

[0014] Verify the consistency of the phase differences of the receiver channels. After passing the verification, measure the phase differences of the receiver channels and record them to form a phase difference table of the receiver channels;

[0015] Adopt the polynomial fitting technique. According to the phase difference table, complete the calculation of the dual-channel phase differences at all frequencies and obtain the phase difference fitting curve of the receiver channels;

[0016] Based on the phase difference fitting curve, calibrate the receiver phase differences. After completion of the calibration, the phase differences of the entire circular array direction finding system are equivalent to the phase differences of the antenna array.

[0017] Specifically, the verification of the consistency of the phase differences of the receiver channels is as follows: Use a waveform generator to generate two signals with a phase difference of a, and input them into the two receiving channels of the receiver respectively. Verify whether the phase difference of the receiver is a. If not, correct the receiver; then increase or decrease the phase value of one of the signals by x, and verify whether the phase difference of the receiver is a±x at this time. If not, correct the receiver.

[0018] Specifically, the measurement of the phase differences of the receiver channels is as follows: Use the same signal source and input signals into the two receiving channels of the receiver at uniform frequency intervals, and measure the phase differences between the signals received by the receiver at different frequencies.

[0019] Furthermore, during the calibration of the receiver phase differences in the phase difference calibration process, the calibration standard is: the phase difference value of the receiver channels is zero or approximately zero.

[0020] Further, when establishing the response sample set, based on the phase difference formed by the signal source in the antenna array, the phase difference of the antenna array is measured truly to form a standard library of the phase difference of the antenna array; after obtaining the phase difference fitting curve in the process of phase difference calibration, based on the standard library of the phase difference of the antenna array and making the phase difference of the receiver channel zero or approximately zero, the process of establishing the response sample set is realized.

[0021] Preferably, when evaluating the direction finding accuracy, in the process of the fitting algorithm based on the polynomial fitting technology for correcting the direction finding accuracy, a signal source can be independently selected for accuracy testing. The acquisition of the direction finding accuracy data value specifically includes:

[0022] Set up the signal source and the circular array direction finding system, where the circular array direction finding system is installed on a rotatable turntable;

[0023] Reset the turntable, test and record the angle of the signal source relative to the circular array direction finding system at this time, denoted as the initial angle;

[0024] Set the frequency point and amplitude of the signal source, and set the direction finding frequency of the circular array direction finding system to align the 0-degree direction of the antenna array with the direction of the signal source antenna;

[0025] Rotate the turntable to align the direction of the antenna array with the direction of the signal source antenna at ±5°, ±10°, ±15°, ±20°, ±25°, ±30°, ±35°, ±40°, ±45° in turn, and perform the direction finding process for the signal source. The number of measurements for each angle is greater than 10 times;

[0026] Measure and record the data values obtained in each angle direction, and repeat the test for each angle;

[0027] The direction finding accuracy data value is calculated by the following formula:

[0028]

[0029] In the formula, Δθ is the direction finding accuracy value; α 0 is the measurement value at the 0-degree azimuth; α j is the measurement value at the jth azimuth; α’ j is the true value of the jth degree azimuth angle; j is the azimuth ordinal number.

[0030] In summary, due to the adoption of this technical solution, the beneficial effects of the present invention are as follows:

[0031] Compared with the methods used in existing circular array direction finding systems, the circular array direction finding method of the present invention is applied to an antenna array with omnidirectional antennas and 8-element directional antennas. Through the overall idea of direction finding, the phase difference of the entire direction finding system is effectively equivalent to the phase difference of the array element antennas, that is, the phase difference of the dual-channel receiver is made zero or approximately zero through phase difference calibration. At this time, the phase difference of the target signal reaching the receiver only depends on the difference between the antenna array elements.

[0032] Under this characteristic, in the direction finding process under the action of the phase difference calibration idea, the establishment of the response sample set is more accurate, making the direction finding result more accurate. At the same time, through the direction finding accuracy verification and the feedback process of the fitting algorithm, the phase difference calibration process is further optimized and improved; the present invention is ultimately beneficial to the engineering implementation of circular array phase difference calibration, solves the design scope of the circular array correlation interference direction finding method based on broadband communication signals, can adapt to more application scenarios, and generates greater efficiency. Brief Description of the Drawings

[0033] Figure 1 It is a schematic diagram of the overall process of the method of the present invention;

[0034] Figure 2 It is a schematic diagram for verifying the consistency of the receiver channel phase difference;

[0035] Figure 3 It is a schematic diagram for measuring the receiver channel phase difference according to frequency points;

[0036] Figure 4 It is a schematic diagram of the dual-channel phase difference of all frequency points after polynomial fitting;

[0037] Figure 5 It is a schematic diagram of the structure of the direction finding accuracy test process;

[0038] Figure 6 It is a schematic diagram of the initial value of phase difference measurement and the direction finding result. Detailed Embodiment

[0039] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. Usually, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0040] Accordingly, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. 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 scope of protection of the present invention.

[0041] A circular array direction finding method based on phase difference calibration. The schematic diagram of the entire process of this method can be seen Figure 1 , and specifically includes:

[0042] Obtain the phase difference fitting curve of the receiver channel through polynomial fitting technology for phase difference calibration;

[0043] After the phase difference of the circular array direction finding system is equivalent to the phase difference of the antenna array through phase difference calibration, establish a response sample set for the direction finding process;

[0044] Adopt the circular array correlation interference direction finding technology to calculate the preliminary direction finding result. According to the preliminary direction finding result, through the left and right data points at the direction finding maximum value, complete the second-order fitting process of the phase difference fitting curve, and then obtain the direction finding result based on the response sample set;

[0045] During the direction finding process, evaluate the direction finding accuracy according to the direction finding result, and modify the fitting algorithm in the polynomial fitting technology when obtaining the phase difference fitting curve based on the direction finding accuracy.

[0046] In this embodiment, the circular array direction finding system applying this method includes an antenna array and a receiver; this method is for the case where the antenna array is configured with 1 eight-element directional antenna and 1 omnidirectional antenna, and the directional antenna and the omnidirectional antenna thus form signal outputs of two channels; therefore, the receiver paired with the antenna array is a dual-channel receiver. The first receiving channel receives the signal from the eight-element directional antenna, and the second receiving channel receives the signal from the omnidirectional antenna; the difference in the phase values of the signals received by the two receiving channels at the same moment is the phase difference of the receiver channel.

[0047] The design idea of this method is thus proposed to ultimately solve the problem of phase difference accuracy through phase difference calibration, making the final direction finding result more accurate and facilitating the wider application of the circular array direction finding system; therefore, the design idea of this method includes the entire process of circular array correlation interference direction finding, phase difference calibration combining data fitting and look-up table, direction finding accuracy verification and feedback on the fitting algorithm, and second-order curve fitting based on the preliminary direction finding result.

[0048] The following details how this method performs the phase difference calibration process, including:

[0049] Verify the consistency of the phase difference of the receiver channel. After verification, measure the phase difference of the receiver channel and record it to form a phase difference table of the receiver channel;

[0050] Adopt polynomial fitting technology, and according to the phase difference table, complete the calculation of the two-channel phase difference for all frequency points to obtain the phase difference fitting curve of the receiver channel;

[0051] Calibrate the receiver phase difference based on the phase difference fitting curve. After calibration, the phase difference of the entire circular array direction finding system is equivalent to the phase difference of the antenna array.

[0052] The goal of this process is to calibrate the phase difference between the two signal receiving channels of the receiver, based on the phase difference fitting curve obtained through measurement and calculation; as Figure 2 shown, first, it is necessary to verify the consistency of the receiver channel phase difference. Use a waveform generator. In this embodiment, it is recommended to use the Tektronix AWG-70002A waveform generator to input signals of two channels to the receiver to represent the process that in the actual direction finding process, one channel of the receiver receives the omnidirectional antenna signal and the other channel receives the directional antenna signal; first, set the initial phases of the two-channel signals emitted by the waveform generator to make their initial phases different. For example, the initial phase of channel 1 is 0 degrees and the initial phase of channel 2 is 30 degrees. At this time, the phase difference displayed on the receiver should be 30 degrees or -30 degrees, and this value can be recorded as a. If not, correct the receiver; after correct calibration, try to change the phase value of any channel. For example, change the phase value of channel 2 to 31 degrees, that is, increase it by 1 degree. At this time, the phase difference displayed on the receiver should be a + 1 degree or a - 1 degree. If not, correct the receiver; when the above two steps are completed, the consistency of the receiver two-channel phase difference is verified.

[0053] Then measure the phase difference of the receiver channel. As Figure 3 shown, use the same signal source, input the omnidirectional channel signal and the directional channel signal to the receiver through a power divider, adjust the signal source to input signals to the receiver at a uniform frequency interval, measure the phase difference between the two-channel signals received by the receiver at different frequencies, and record in detail the phase difference table of the two channels of the receiver.

[0054] During the process of adjusting the uniform frequency interval, for a relatively smooth frequency range or the frequency range corresponding to higher frequencies, adopt polynomial fitting technology. According to the phase difference table, complete the calculation of the two-channel phase difference for all frequency points, so as to obtain the phase difference fitting curve of the receiver channel. See Figure 4 .

[0055] According to the phase difference fitting curve obtained by looking up the table in this phase difference table and the polynomial fitting technique, the phase difference of the dual channels of the receiver is calibrated. The calibration standard is: making the phase difference of the dual channels of the receiver zero or approximately zero; after this calibration is completed, for the target signal arriving at the receiver through the antenna array, that is, the phase difference between the directional channel signal and the omnidirectional channel signal will only depend on the phase difference between the antenna arrays. At this time, the process of phase difference calibration is completed. Based on the design idea of this method as a premise, the remaining content of the circular array direction finding process can be carried out.

[0056] This embodiment makes the following description of the response sample set in the circular array direction finding method:

[0057] The incoming wave of the target signal generates induced current on the antennas in the antenna array. Since there is a time difference in the arrival of the incoming wave at the antennas, a phase difference will be generated. The dual-channel receiver in this embodiment has a directional antenna channel and an omnidirectional antenna channel, where the omnidirectional antenna channel is used as a reference; corresponding to the incoming wave direction of the target signal and the operating frequency of the circular array direction finding system, a corresponding set of phase differences will be generated. In the receiver, there is a response sample set of the antenna array. This corresponding sample set is a standard circular array response sample set collected in the full frequency band and all directions when the circular array direction finding system equipment leaves the factory; the circular array correlation interferometric direction finding process is to perform correlation processing on the measured circular array response and the standard sample set in the response sample set, find the most similar sample, and according to the position of this sample in the response sample set, thereby obtain the incident azimuth of the target signal and achieve direction finding.

[0058] In this embodiment, one of the cores of direction finding is the phase difference calibration process that equates the phase difference of the dual channels of the entire receiver to the phase difference of the antenna array. Therefore, according to the calibration standard, the channel phase difference will be calibrated to zero or approximately zero to establish the response sample set; based on the phase difference formed by the signal source in the antenna array, the phase difference of the antenna array is measured truly to form a standard library of the antenna array phase difference; after the phase difference fitting curve is obtained in the phase difference calibration process, based on the standard library of the antenna array phase difference and making the phase difference of the receiver channels zero or approximately zero, the process of establishing the response sample set is realized.

[0059] During the direction finding process, for each frequency point, the phase differences between multiple intermediate frequency signals are calculated pairwise. According to the principle that FFT does not change the relative phase, this phase difference reflects the phase difference of the signal arriving at multiple antenna elements in the antenna array; using the principle of correlation interferometer direction finding, the phase difference data for each frequency point is correlated with the established response sample set to obtain a correlation curve, and finally the corresponding bearing is obtained to achieve target direction finding.

[0060] Moreover, during the execution of the method, the phase differences obtained multiple times can be averaged multiple times to give a more accurate phase difference as a more accurate initial value for the correlation interferometric direction finding algorithm, further improving the direction finding accuracy.

[0061] This embodiment also provides that after the phase difference calibration and the establishment of the response sample set are completed, the direction finding accuracy can be tested and evaluated during or before the actual direction finding process. Then, the fitting algorithm of the polynomial fitting technology can be further corrected according to the direction finding accuracy. One signal source and one antenna within the reconnaissance frequency range of the receiver can be selected for accuracy testing, as Figure 5 shown.

[0062] The acquisition of the direction finding accuracy data values specifically includes:

[0063] Set up the signal source and the circular array direction finding system, where the circular array direction finding system is installed on a rotatable turntable;

[0064] Reset the turntable, test and record the angle of the signal source relative to the circular array direction finding system at this time, and record it as the initial angle;

[0065] Set the frequency point and amplitude of the signal source, and set the direction finding frequency of the circular array direction finding system to align the 0-degree direction of the antenna array with the direction of the signal source antenna;

[0066] Rotate the turntable to align the direction of the antenna array with the direction of the signal source antenna at ±5°, ±10°, ±15°, ±20°, ±25°, ±30°, ±35°, ±40°, ±45° in turn, and perform the direction finding process for the signal source. The number of measurements for each angle is greater than 10 times;

[0067] Measure and record the data values obtained in each angle direction, and repeat the test for each angle;

[0068] The direction finding accuracy data values are calculated by the following formula:

[0069]

[0070] In the formula, Δθ is the direction finding accuracy value; α 0 is the measurement value at the 0-degree azimuth; α j is the measurement value at the jth azimuth; α’ j is the true value of the jth degree azimuth angle; j is the azimuth ordinal number.

[0071] The evaluation result of this direction finding accuracy can be applied to the fitting algorithm in the polynomial fitting process, so that the phase difference calibration process can be optimized and adjusted, the establishment of the response sample set can be more accurate, and finally the entire circular array direction finding process can be more precise.

[0072] Figure 6 It shows the phase difference values of each element of the antenna array printed before inputting the relevant interference direction finding algorithm during the use of this method. Based on such data, it is beneficial to carry out the algorithm analysis and optimization process.

[0073] The method of this embodiment utilizes the ingenious equivalence of the phase difference between the two channels of the receiver to the phase difference of the array elements of the antenna array in the fields of communication and countermeasure, gives the overall design idea of circular array related interferometric direction finding, proposes an effective and feasible phase difference calibration method, which is conducive to the engineering implementation of circular array phase difference calibration, solves the design of circular array related interferometric direction finding method based on broadband communication signals, can adapt to more application scenarios, and can produce greater effects; Since the traditional theory of circular array direction finding is relatively mature, the phase difference calibration design idea and key details proposed in this embodiment for different engineering implementations will further optimize and improve the direction finding results and improve the direction finding accuracy.

Claims

1. A circular array direction finding method based on phase difference calibration, characterized in that, it includes: Obtaining the phase difference fitting curve of the receiver channel through polynomial fitting technology for phase difference calibration; After the phase difference of the circular array direction finding system is equivalent to the phase difference of the antenna array through phase difference calibration, establishing a response sample set for the direction finding process; Adopting the circular array correlation interference direction finding technology to calculate the initial direction finding result. According to the initial direction finding result, through the left and right data points at the direction finding maximum value, after completing the quadratic fitting process of the phase difference fitting curve, based on the response sample set, obtaining the direction finding result; During the direction finding process, according to the direction finding result, evaluating the direction finding accuracy, and correcting the fitting algorithm of the polynomial fitting technology when obtaining the phase difference fitting curve based on the direction finding accuracy; The antenna array includes an 8-element directional antenna and an omnidirectional antenna; The receiver is a dual-channel receiver. The first receiving channel receives the signal from the 8-element directional antenna, and the second receiving channel receives the signal from the omnidirectional antenna; The phase difference between the phase values of the signals received by the two receiving channels at the same moment is the phase difference of the receiver channel; The phase difference calibration includes: Verifying the consistency of the phase difference of the receiver channel. After passing the verification, measuring the phase difference of the receiver channel and recording it to form a phase difference table of the receiver channel; Adopting polynomial fitting technology to complete the calculation of the dual-channel phase difference at all frequency points according to the phase difference table, and obtaining the phase difference fitting curve of the receiver channel; According to the phase difference fitting curve, calibrating the receiver phase difference. After completion of the calibration, the phase difference of the entire circular array direction finding system is equivalent to the phase difference of the antenna array; The verification of the consistency of the phase difference of the receiver channel is specifically: using a waveform generator to generate two signals with a phase difference of a, and inputting them into the two receiving channels of the receiver respectively to verify whether the phase difference of the receiver is a. If not, correct the receiver; then increase or decrease the phase value of one of the signals by x, and verify whether the phase difference of the receiver at this time is a±x. If not, correct the receiver; When evaluating the direction finding accuracy, during the process of correcting the fitting algorithm of the polynomial fitting technology according to the direction finding accuracy, a signal source can be independently selected for accuracy testing. The acquisition of the direction finding accuracy data value specifically includes: Setting up a signal source and a circular array direction finding system, where the circular array direction finding system is installed on a rotatable turntable; Resetting the turntable, testing and recording the angle of the signal source relative to the circular array direction finding system at this time, denoted as the initial angle; Setting the frequency point and amplitude of the signal source, and setting the direction finding frequency of the circular array direction finding system to align the 0-degree direction of the antenna array with the signal source antenna direction; Rotating the turntable to align the direction of the antenna array with the signal source antenna direction at ±5°, ±10°, ±15°, ±20°, ±25°, ±30°, ±35°, ±40°, ±45° in turn, and performing the direction finding process for the signal source. The number of measurements at each angle is greater than 10 times; Measuring and recording the data values obtained at each angle direction, and repeating the test for each angle; The direction finding accuracy data value is calculated by the following formula: Wherein, is the direction finding accuracy value; is the measurement value at the 0-degree azimuth; is the th measurement value of the azimuth; is the th true value of the degree azimuth angle; is the azimuth ordinal number.

2. A circular array direction finding method based on phase difference calibration according to claim 1, characterized in that, the phase difference of the measurement receiver channel is specifically: using the same signal source, inputting signals into two receiving channels of the receiver at uniform frequency intervals, and measuring the phase difference between the signals received by the receiver at different frequencies.

3. A circular array direction finding method based on phase difference calibration according to claim 1, characterized in that, the calibration standard is: the phase difference of the receiver channel is zero or approximately zero.

4. A circular array direction finding method based on phase difference calibration according to claim 1, characterized in that, for establishing the response sample set, based on the phase difference formed by the signal source in the antenna array, the phase difference of the antenna array is actually measured to form a standard library of the phase difference of the antenna array; after obtaining the phase difference fitting curve in the phase difference calibration process, based on the standard library of the phase difference of the antenna array and making the phase difference of the receiver channel zero or approximately zero, the process of establishing the response sample set is realized.

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