A two-dimensional direction finding system and method based on a double-long baseline time modulation array

Abstract

The application provides a two-dimensional direction finding system and method based on a double-long baseline time modulation array, comprising an antenna array module for receiving a target incident signal; a radio frequency switch module for time modulation of the received signal; a control module for controlling the switching of the radio frequency switch; a radio frequency channel module for processing the modulated received signal; and a signal processing module for spectral harmonic analysis of the received signal. The application uses a double-long baseline structure to form a four-unit time modulation array arm, thereby obtaining a larger aperture, higher gain and better signal-to-noise ratio, and thus improving the direction finding accuracy. The two time modulation array arms located on the X-axis and the Z-axis are used to independently estimate the pitch angle and the azimuth angle of the incident signal, and then the spectral harmonic analysis is used for automatic pairing, thereby realizing high-precision and low-cost two-dimensional direction finding, which can be widely applied in the fields of wireless communication, automobile navigation and positioning services.

Description

Technical Field

[0001] This invention relates to the field of antenna engineering technology, specifically a two-dimensional direction finding system and method based on a dual long baseline time modulation array, which achieves high-precision and low-cost two-dimensional direction finding functionality. Background Technology

[0002] Direction-of-arrival (DOA) estimation is a hot research topic in array signal processing, widely used in wireless communication, automotive navigation, and positioning services. Existing super-resolution direction finding methods include multi-signal classification algorithms, propagation operator algorithms, and rotation-invariant subspace algorithms. These methods require synchronous sampling of the entire array and utilize a large number of RF channels and analog-to-digital converters, increasing hardware cost and complexity. Two-dimensional ODA methods are extensions of one-dimensional ODA methods, but their application cost and complexity are even higher.

[0003] Patent document CN109799475A (application number: 201811600164.2) discloses a radio direction finding method based on harmonic energy detection using a time-modulated array. This method employs a time-modulated array, controlling N antennas in an antenna array by inputting N different control clock signals within one period. Based on the analysis of the plotted antenna array radiation pattern, the direction of an unknown target signal is determined. Its shortcomings include that the accuracy of this direction finding method cannot match that of traditional high-resolution direction finding methods, and its applicability is limited to one-dimensional direction-of-arrival estimation, failing to extend it to two-dimensional direction-of-arrival estimation.

[0004] This invention provides a two-dimensional direction finding system and method based on a dual-long-baseline time modulation array. The method uses a dual-long-baseline structure to form a four-unit time modulation array arm, thereby achieving a larger aperture, higher gain, and a better signal-to-noise ratio, thus improving direction finding accuracy. Furthermore, it extends the one-dimensional direction finding problem to a two-dimensional one, using two time modulation array arms located on the X and Z axes to independently estimate the elevation and azimuth angles of the incident signal, and then automatically pairing them through spectral harmonic analysis, achieving high-precision, low-cost two-dimensional direction finding. Summary of the Invention

[0005] Technical problem: In view of the deficiencies in the prior art, the present invention provides a two-dimensional direction finding system and method based on a dual long baseline time modulation array, which can achieve high-precision and low-cost two-dimensional direction finding function.

[0006] Technical solution: The present invention provides a two-dimensional direction finding system based on a dual long baseline time modulation array, comprising:

[0007] Antenna array module: It consists of an L-shaped array composed of four omnidirectional antennas located on the X-axis and four omnidirectional antennas located on the Z-axis, used to receive incident signals from the target;

[0008] RF switch module: includes five single-pole double-throw RF switches for time modulation of the received signal;

[0009] Control module: includes a modulation signal control board, used to control the switching of five single-pole double-throw RF switches;

[0010] RF channel module: includes low-noise amplifier, mixer, local oscillator, low-pass filter and digital-to-analog converter, used to process the modulated received signal;

[0011] Signal processing module: By performing spectral harmonic analysis on the received signal, it can distinguish the accurate solution of the double long baseline and perform two-dimensional angle pairing to obtain high-precision two-dimensional direction finding results;

[0012] The antenna array module is connected to the radio frequency switch module; the radio frequency switch module is connected to the control module; the control module is connected to the radio frequency channel module; the radio frequency channel module is connected to the signal processing module.

[0013] The antenna array module's output is connected to the RF switch module, which is controlled by the control module. The RF switch module's output is connected to the RF channel module, which in turn is connected to the signal processing module.

[0014] in,

[0015] The antenna array module consists of an L-shaped array composed of four omnidirectional antennas located on the X-axis and four omnidirectional antennas located on the Z-axis. The distance between the first and second omnidirectional antennas on the X-axis is the long baseline distance D2; the distance between the second and third omnidirectional antennas is the reference line distance D1; and the distance between the third and fourth omnidirectional antennas is the long baseline distance D2. Similarly, the distance between the first and second omnidirectional antennas on the Z-axis is the long baseline distance D2; the distance between the second and third omnidirectional antennas is the reference line distance D1; and the distance between the third and fourth omnidirectional antennas is the long baseline distance D2.

[0016] The antenna array module uses a four-element time modulation array arm composed of a dual long baseline structure. The spatial position of the dual long baseline structure is constructed to obtain a larger aperture, higher gain and better signal-to-noise ratio, thereby improving the direction finding accuracy.

[0017] The antenna array module satisfies the following relationship: the reference line distance D1 is half a wavelength distance λ / 2, and the long baseline distance D2 is three times the wavelength distance 3λ.

[0018] The direction finding method of the two-dimensional direction finding system based on a dual long baseline time modulation array of the present invention includes the following steps:

[0019] Step 1: The L-shaped array antenna receives planar electromagnetic waves from the far field. The four-element time-modulated array arm located on the X-axis is controlled by five single-pole double-throw RF switches, with T... p Time modulation is performed for the period; in T p In the first half of the cycle, switch S1 connects the left side, switch S2 connects the right side, switch S3 connects the left side, switch S4 connects the right side, and switch S5 connects the left side; in T p In the second half of the cycle, switch S1 connects the right side, switch S2 connects the left side, switch S3 connects the right side, switch S4 connects the left side, and switch S5 connects the right side.

[0020] Step 2: The first and second omnidirectional antennas located on the X-axis form the long baseline direction finding module 1; the second and third omnidirectional antennas form the reference line direction finding module; and the third and fourth omnidirectional antennas form the long baseline direction finding module 2.

[0021] Step 3: The control process of the four-unit time modulation array arm located on the Z-axis is the same as the control process of the array arm located on the X-axis in steps 1 and 2;

[0022] Step 4: The modulated signal is passed through a low-noise amplifier, mixer, low-pass filter and digital-to-analog converter to obtain the baseband signal. Its spectral harmonic characteristics are analyzed in the digital domain, and the incident direction is calculated based on the characteristic relationship between the fundamental component and the first harmonic component.

[0023] Step 5: The reference line direction finding module located on the X-axis can obtain the azimuth estimate ф0; the long baseline 1 direction finding module located on the X-axis obtains multiple azimuth estimate solutions, of which only one is correct. Among all possible solutions, the solution closest to ф0 is taken as the true solution of ф1; similarly, the solution closest to ф0 from the long baseline 2 direction finding module located on the X-axis is taken as the true solution of ф2; the weighted average of ф1 and ф2 is used to obtain the final azimuth estimate ф.

[0024] Step 6: The reference line direction finding module located on the Z-axis can obtain the pitch angle estimate θ0; the long baseline 1 direction finding module located on the Z-axis obtains multiple pitch angle estimates, of which only one is correct. Among all possible solutions, the solution closest to θ0 is taken as the true solution of θ1; similarly, the solution closest to θ0 from the long baseline 2 direction finding module located on the Z-axis is taken as the true solution of θ2; the weighted average of θ1 and θ2 is used to obtain the final pitch angle estimate θ.

[0025] Step 7: The harmonic components of the power spectrum of the signal received by the two time-modulated array arms after signal processing are expressed as T. p To distinguish the power spectrum generated by incident signals of different frequencies, the signals are symmetrically distributed around the fundamental component in a step-by-step manner. By combining the elevation and azimuth angles of the incident signals of the same frequency, two-dimensional direction finding of multiple signals is completed.

[0026] Beneficial effects: Compared with the prior art, the present invention has the following advantages.

[0027] 1. This invention uses a four-unit time modulation array arm composed of a dual long baseline structure to construct the spatial position of the dual long baseline structure to obtain a larger aperture, higher gain and better signal-to-noise ratio, thereby improving the direction finding accuracy.

[0028] 2. The one-dimensional direction finding problem is extended to the two-dimensional direction finding problem. Two time-modulated array arms located on the X-axis and Z-axis are used to independently estimate the elevation and azimuth angles of the incident signal, respectively. Then, automatic pairing is performed through spectrum harmonic analysis, realizing high-precision and low-cost two-dimensional direction finding.

[0029] 3. This invention has a simple structure and low hardware cost. It features high precision and low complexity in two-dimensional direction finding and can be widely used in fields such as wireless communication, car navigation and positioning services. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the L-shaped array structure composed of two-dimensional time modulation array arms according to the present invention.

[0031] Figure 2 This is a schematic diagram of the four-unit time modulation array arm structure using a dual long baseline structure according to the present invention.

[0032] Figure 3 Normalized power spectra for the embodiment: (a) signal received by the X-axis time modulation array arm, (b) signal received by the Z-axis time modulation array arm.

[0033] Figure 4 The scatter plot shows the angle estimation of two unrelated sources in the example.

[0034] Figure 5 The root mean square error of the joint estimation of the elevation and azimuth angles of two unrelated sources with incident directions (a) (45°, 55°) and (b) (70°, 35°) in the example is given. Detailed Implementation

[0035] The following is a brief explanation of the direction finding principle:

[0036] like Figure 2 As shown, when the carrier frequency is F c When a sinusoidal signal is incident from the far field at an angle θ onto the time modulation array arm, the received signal after passing through a single-pole double-throw switch is written as:

[0037]

[0038] Where G(t) is a periodic function, it can be expressed as:

[0039]

[0040] Where the wave number β = λ / 2π, and λ is the incident wave wavelength. The periodic modulation function G(t) is expanded by a Fourier series as follows:

[0041]

[0042] Where the Fourier coefficient b of the kth harmonic is... k It can be represented as

[0043]

[0044] For a reference line direction finding module with a spacing of D1, the reference direction finding angle θ can be obtained from the fundamental component b0 and the first harmonic component b1. ref It is expressed as follows:

[0045]

[0046] For long baseline direction finding module 1 with a spacing of D2, long baseline direction finding exhibits periodic ambiguity due to the periodicity of trigonometric functions:

[0047]

[0048] Substituting the wave number β=λ / 2π into (6), the long baseline orientation angle θ1 has multiple solutions (of which only one is correct):

[0049]

[0050] Among all possible solutions, choose the one closest to θ. ref The solution is taken as the true solution for θ1; similarly, for long baseline direction finding module 2 with a spacing of D2, the long baseline direction finding angle θ2 has multiple solutions, and the one closest to θ is taken. ref The solution is taken as the true solution of θ2; the weighted average of θ1 and θ2 is used to obtain the final angle estimate θ.

[0051] Apply the above principles to Figure 1 The four-element time modulation array arm located on the X-axis and the four-element time modulation array arm located on the Z-axis are used to obtain high-precision azimuth and elevation angles. By combining the elevation and azimuth angles of incident signals of the same frequency, high-precision and low-cost two-dimensional direction finding of multiple signals can be completed.

[0052] The embodiments of the present invention are described in detail below: These embodiments are implemented based on the technical solution of the present invention, and provide detailed implementation methods and specific operation processes.

[0053] Example

[0054] This invention provides a two-dimensional direction finding system and method based on a dual long baseline time modulation array, the system specifically comprising:

[0055] Antenna array module: It consists of an L-shaped array composed of four omnidirectional antennas located on the X-axis and four omnidirectional antennas located on the Z-axis, used to receive incident signals from the target;

[0056] RF switch module: includes five single-pole double-throw RF switches for time modulation of the received signal;

[0057] Control module: includes a modulation signal control board, used to control the switching of five single-pole double-throw radio frequency switches;

[0058] RF channel module: includes low-noise amplifier, mixer, local oscillator, low-pass filter and digital-to-analog converter, used to process the modulated received signal;

[0059] Signal processing module: By performing spectral harmonic analysis on the received signal, it can distinguish the accurate solution of the double long baseline and perform two-dimensional angle pairing to obtain high-precision two-dimensional direction finding results;

[0060] The antenna array module is connected to the radio frequency switch module; the radio frequency switch module is connected to the control module; the control module is connected to the radio frequency channel module; the radio frequency channel module is connected to the signal processing module.

[0061] The antenna array module's output is connected to the RF switch module, which is controlled by the control module. The RF switch module's output is connected to the RF channel module, which in turn is connected to the signal processing module.

[0062] The antenna array module consists of an L-shaped array of four omnidirectional antennas located on the X-axis and four omnidirectional antennas located on the Z-axis. The distance between the first and second omnidirectional antennas on the X-axis is the long baseline distance D2; the distance between the second and third omnidirectional antennas is the reference line distance D1; and the distance between the third and fourth omnidirectional antennas is the long baseline distance D2. Similarly, on the Z-axis, the distance between the first and second omnidirectional antennas is the long baseline distance D2; the distance between the second and third omnidirectional antennas is the reference line distance D1; and the distance between the third and fourth omnidirectional antennas is the long baseline distance D2. The reference line distance D1 is half a wavelength distance λ / 2, and the long baseline distance D2 is three times the wavelength distance 3λ.

[0063] The present invention, in conjunction with the accompanying drawings, specifically includes the following working steps:

[0064] Step 1: As Figure 1As shown, assume that two sinusoidal signals with carrier frequencies of 2.6 GHz and 2.613 GHz are incident on the L-shaped array antenna from far-field directions of (45°, 55°) and (70°, 35°), respectively.

[0065] Step 2: As Figure 2 As shown, the X-axis four-element time-modulated array arm of the L-shaped array antenna is controlled by five single-pole double-throw RF switches, with T... p Time modulation is performed for the period; in T p In the first half of the cycle, switch S1 connects the left side, switch S2 connects the right side, switch S3 connects the left side, switch S4 connects the right side, and switch S5 connects the left side. In T... p In the second half of the cycle, switch S1 is on the right, switch S2 is on the left, switch S3 is on the right, switch S4 is on the left, and switch S5 is on the right; the modulation period T of the RF switches is... p It is 20us;

[0066] Step 3: The first and second omnidirectional antennas located on the X-axis form the long baseline direction finding module 1; the second and third omnidirectional antennas form the reference line direction finding module; and the third and fourth omnidirectional antennas form the long baseline direction finding module 2.

[0067] Step 4: The control process of the four-unit time modulation array arm located on the Z-axis is the same as the control process of the array arm located on the X-axis in steps 2 and 3;

[0068] Step 5: The modulated signal is passed through a low-noise amplifier, mixer, low-pass filter and digital-to-analog converter to obtain the baseband signal. Its spectral harmonic characteristics can be analyzed in the digital domain, and the incident direction can be calculated based on the characteristic relationship between the fundamental component and the first harmonic component.

[0069] Step 6: The reference line direction finding module located on the X-axis can obtain the azimuth estimate ф0; the long baseline 1 direction finding module located on the X-axis can obtain multiple azimuth estimate solutions (only one of which is correct). Among all possible solutions, the solution closest to ф0 is taken as the true solution of ф1; similarly, the solution closest to ф0 from the long baseline 2 direction finding module located on the X-axis is taken as the true solution of ф2; the weighted average of ф1 and ф2 is used to obtain the final azimuth estimate ф.

[0070] Step 7: The reference line direction finding module located on the Z-axis can obtain the pitch angle estimate θ0; the long baseline 1 direction finding module located on the Z-axis can obtain multiple pitch angle estimates (only one of which is correct). Among all possible solutions, the solution closest to θ0 is taken as the true solution of θ1; similarly, the solution closest to θ0 from the long baseline 2 direction finding module located on the Z-axis is taken as the true solution of θ2; the weighted average of θ1 and θ2 is used to obtain the final pitch angle estimate θ.

[0071] Step 8: As Figure 3 As shown, the harmonic components of the power spectrum of the signal received by the two time-modulated array arms after signal processing are expressed as T. p By symmetrically distributing the signal around the fundamental component, the power spectrum generated by incident signals of different frequencies can be distinguished; by combining the elevation and azimuth angles of incident signals of the same frequency, two-dimensional direction finding of multiple signals can be completed.

[0072] The signal-to-noise ratio of the entire direction-finding system was set to -10dB, and the system was simulated through 1000 independently implemented Monte Carlo simulations. Figure 4 As shown, the two-dimensional angle estimation scattering points are concentrated at (45°, 55°) and (70°, 35°), which means that the present invention can effectively estimate and pair the elevation and azimuth angles of the incident signal.

[0073] The signal-to-noise ratio of the entire direction-finding system was varied from -10dB to 20dB in 2dB increments, while other parameters remained constant. For example... Figure 5 As shown, at an incident angle of (45°, 55°), when the signal-to-noise ratio increases from -10dB to 20dB, the root mean square error (RMS) of the two-dimensional direction finding of this invention decreases from 0.19° to 0.0063°; at an incident angle of (70°, 35°), its RMS decreases from 0.31° to 0.0097°. Even at lower signal-to-noise ratios, the RMS of the two-dimensional direction finding of this invention remains less than 0.5°, indicating that this invention has extremely high two-dimensional direction finding accuracy. This embodiment features high precision, low cost, and low algorithm complexity, and can be widely applied in fields such as wireless communication, automotive navigation, and positioning services.

[0074] The specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various modifications or variations within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A two-dimensional direction finding system based on a dual long baseline time modulation array, characterized in that, The system includes: Antenna array module: It consists of an L-shaped array composed of four omnidirectional antennas located on the X-axis and four omnidirectional antennas located on the Z-axis, used to receive incident signals from the target; RF switch module: includes five single-pole double-throw RF switches for time modulation of the received signal; Control module: includes a modulation signal control board, used to control the switching of five single-pole double-throw radio frequency switches; RF channel module: includes low-noise amplifier, mixer, local oscillator, low-pass filter and digital-to-analog converter, used to process the modulated received signal; Signal processing module: By performing spectral harmonic analysis on the received signal, it can distinguish the accurate solution of the double long baseline and perform two-dimensional angle pairing to obtain high-precision two-dimensional direction finding results; The antenna array module is connected to the radio frequency switch module; the radio frequency switch module is connected to the control module; the control module is connected to the radio frequency channel module; the radio frequency channel module is connected to the signal processing module. The output of the antenna array module is connected to the radio frequency switch module, which is controlled by the control module. The output of the radio frequency switch module is connected to the radio frequency channel module, and the output of the radio frequency channel module is connected to the signal processing module. The antenna array module consists of an L-shaped array composed of four omnidirectional antennas located on the X-axis and four omnidirectional antennas located on the Z-axis. The distance between the first and second omnidirectional antennas on the X-axis is the long baseline distance D2; the distance between the second and third omnidirectional antennas is the reference line distance D1; and the distance between the third and fourth omnidirectional antennas is the long baseline distance D2. Similarly, the distance between the first and second omnidirectional antennas on the Z-axis is the long baseline distance D2; the distance between the second and third omnidirectional antennas is the reference line distance D1; and the distance between the third and fourth omnidirectional antennas is the long baseline distance D2. The antenna array module satisfies the following relationship: the reference line distance D1 is half a wavelength distance λ / 2, and the long baseline distance D2 is three times the wavelength distance 3λ.

2. The two-dimensional direction finding system based on a dual long baseline time modulation array according to claim 1, characterized in that, The antenna array module uses a four-element time modulation array arm composed of a dual long baseline structure. The spatial position of the dual long baseline structure is constructed to obtain a larger aperture, higher gain and better signal-to-noise ratio, thereby improving the direction finding accuracy.

3. A direction finding method for a two-dimensional direction finding system based on a dual long baseline time modulation array as described in claim 1, characterized in that, The method includes the following steps: Step 1: The L-shaped array antenna receives planar electromagnetic waves from the far field. The four-element time-modulated array arm located on the X-axis is controlled by five single-pole double-throw RF switches, with T... p Time modulation is performed for the period; in T p In the first half of the cycle, switch S1 connects the left side, switch S2 connects the right side, switch S3 connects the left side, switch S4 connects the right side, and switch S5 connects the left side; in T p In the second half of the cycle, switch S1 connects the right side, switch S2 connects the left side, switch S3 connects the right side, switch S4 connects the left side, and switch S5 connects the right side. Step 2: The first and second omnidirectional antennas located on the X-axis form the long baseline direction finding module 1; the second and third omnidirectional antennas form the reference line direction finding module; and the third and fourth omnidirectional antennas form the long baseline direction finding module 2. Step 3: The control process of the four-unit time modulation array arm located on the Z-axis is the same as the control process of the array arm located on the X-axis in steps 1 and 2; Step 4: The modulated signal is passed through a low-noise amplifier, mixer, low-pass filter and digital-to-analog converter to obtain the baseband signal. Its spectral harmonic characteristics are analyzed in the digital domain, and the incident direction is calculated based on the characteristic relationship between the fundamental component and the first harmonic component. Step 5: The reference line direction finding module located on the X-axis can obtain the azimuth estimate ф0; the long baseline 1 direction finding module located on the X-axis obtains multiple azimuth estimate solutions, of which only one is correct. Among all possible solutions, the solution closest to ф0 is taken as the true solution of ф1; similarly, the solution closest to ф0 from the long baseline 2 direction finding module located on the X-axis is taken as the true solution of ф2; the weighted average of ф1 and ф2 is used to obtain the final azimuth estimate ф. Step 6: The reference line direction finding module located on the Z-axis can obtain the pitch angle estimate θ0; the long baseline 1 direction finding module located on the Z-axis obtains multiple pitch angle estimates, of which only one is correct. Among all possible solutions, the solution closest to θ0 is taken as the true solution of θ1; similarly, the solution closest to θ0 from the long baseline 2 direction finding module located on the Z-axis is taken as the true solution of θ2; the weighted average of θ1 and θ2 is used to obtain the final pitch angle estimate θ. Step 7: The harmonic components of the power spectrum of the signal received by the two time-modulated array arms after signal processing are expressed as T. p To distinguish the power spectrum generated by incident signals of different frequencies, the signals are symmetrically distributed around the fundamental component in a step-by-step manner. By combining the elevation and azimuth angles of the incident signals of the same frequency, two-dimensional direction finding of multiple signals is completed.

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