A method for correcting radiation beam distortion in complex electromagnetic environments based on time reversal

Abstract

The present invention discloses a method for correcting radiation beam distortion in a complex electromagnetic environment based on time reversal, and belongs to the field of radar technology. The method first irradiates a plane wave containing the same polarization component as the array antenna from the target direction toward an array antenna in a complex environment; then performs time reversal processing on the signal received by each array element to obtain a time reversal signal; finally, the time reversal signal is re-input into the corresponding array element and transmitted simultaneously to obtain a radiation beam with the distortion corrected in the target direction. Without knowing the specific conditions such as the complex environment and array element information in advance, the method of the present invention uses time reversal to process the signal received by each array element in the array antenna, and re-transmits the processed signal along the corresponding array element to achieve accurate beam pointing, thereby correcting the beam distortion caused by the complex environment.

Description

Technical Field

[0001] The present invention belongs to the field of radar technology, and in particular relates to a method for optimizing beam distortion in complex environments based on time reversal technology. Background Art

[0002] With the development of the times, the application of electromagnetic waves is becoming more and more widespread. However, the propagation of electromagnetic waves is often affected by the environment. When the environmental information changes drastically and the antenna cannot point in the normal direction, it is necessary to correct the distorted beam to achieve the normal beam direction.

[0003] Regarding research on beam distortion, as shown in articles such as "Robust Adaptive Beamforming under Baffle Conditions" and "Adaptive Beamforming under Finite Snapshots," traditional approaches address the impact of the main lobe of the radiation pattern by using computer analysis to optimize the limited number of snapshots and colored noise in the environment, thereby adaptively optimizing the distorted beam. Traditional programming methods for addressing beam distortion introduce different judgment factors, increasing or changing these factors to optimize the beam generation by generation. However, such algorithms often struggle to balance algorithm complexity, accuracy, and convergence speed. Furthermore, when factors affecting the antenna main lobe expand to include drastic changes in the spatial medium, different spatial environments may require determining the relative position of the environment and reprogramming the model. Furthermore, complex information such as the position of antenna elements and the mutual coupling between elements can affect the applicability of the original analysis methods. Summary of the Invention

[0004] The present invention aims to overcome the challenges of modeling unknown complex environments and array element coupling by providing a method for correcting beam distortion caused by complex electromagnetic environments based on time reversal. Without requiring prior knowledge of the complex environment or array element information, the method uses time reversal to process the signal received by each element in the array antenna and retransmits the processed signal along the corresponding element to achieve precise beam pointing, thereby correcting beam distortion caused by the complex environment.

[0005] The technical solution adopted by the present invention to solve the problem is:

[0006] A method for correcting radiation beam distortion in a complex electromagnetic environment based on time reversal includes the following steps:

[0007] S1. Irradiate a plane wave from the target direction toward the array antenna in a complex environment, where the plane wave contains the same polarization component as the array antenna;

[0008] S2. Record the signal received by each element of the array antenna and perform time reversal processing on the signal to obtain a time reversal signal;

[0009] S3. The time-reversed signal is re-input into the corresponding array element and transmitted simultaneously to obtain a radiation beam with the distortion corrected in the target direction.

[0010] Furthermore, step S1 is specifically as follows:

[0011] S11. Analyze the entire system in a spherical coordinate system, with the center of the array antenna as the origin of the spherical coordinate system. Direction illumination plane wave s(t), where θ d is the angle component of the plane wave relative to the array antenna in the spherical coordinate system, is the plane wave relative to the array antenna in the spherical coordinate system The angle component, s(t), is the expression of the amplitude of the plane wave changing with time;

[0012] S12. Consider the complex environment with linear time invariance as a linear time invariant channel, and the array antenna in the complex environment as a linear time invariant system. The signal Y(t) of the plane wave transmitted in the target direction in the linear time invariant system after passing through the complex environment can be written as:

[0013]

[0014] Where Y(t)=[y1(t), y2(t),...,y N (t)] T Represents the matrix composed of the signals received by each array element, y n (t) is the signal received by the nth array element, n = 1, 2, ..., N, (.) T To perform a transpose transformation on the matrix; Indicates convolution operation. is the impulse response of the receiving mode.

[0015] Furthermore, step S2 is specifically as follows:

[0016] Perform time reversal on the signal received by each element in the array antenna Y(-t) = [y1(-t), y2(-t), ..., y N (-t)] T , and get the time-reversed signal:

[0017]

[0018] Furthermore, step S3 is specifically as follows:

[0019] In the time domain, neglecting propagation loss and time delay, the radiated electric field is written as:

[0020]

[0021] in To excite the radiation electric field of the array antenna, is the impulse response of the transmit mode, represents the relative position of the array element in the system, c i (t) is the excitation of the i-th transient element; when c i (t) is the time-reversed signal y i (-t), the distorted beam is improved.

[0022] In order to illustrate the feasibility of the present invention, further analysis is performed in the frequency domain:

[0023] Performing Fourier transform on equation (2) yields:

[0024]

[0025] Where (ω) is the representation of the corresponding frequency domain, * (.) is the conjugate of the original expression; let:

[0026]

[0027] a(ω)=Y * (ω) (5)

[0028] Where a(ω) represents the excitation of the array antenna.

[0029] Perform Fourier transform on the radiated electric field and calculate it in matrix form:

[0030]

[0031] In the formula is the far-field pattern obtained using a(ω), and |.| represents the absolute value of the corresponding formula. From the formula, we can find It depends on P tx (θ, φ, t) and P rx The inner product of (θ, φ, t) is because a(ω) in the time reversal beam synthesis already contains the intrinsic radiation information of the array antenna.

[0032] By further analyzing this formula, it can be deduced that the directional pattern obtained by using time reversal excitation a(ω) in the target direction is Gain This is greater than the gain achieved using any excitation c(ω) (such as traditional phase shifting in phased arrays). In other words, the time-reversal electromagnetic wave's "time-space" focusing properties improve antenna beam distortion caused by complex environments, such as mainlobe splitting and low gain at the target angle.

[0033]

[0034] Where Z0 represents the free space wave impedance, P in =c T (ω)c * (ω) represents the total input power, and c(ω) represents the arbitrary excitation signal. Assuming that all incident power is completely radiated, the target direction under arbitrary excitation is Gain for:

[0035]

[0036] in(.) H To further simplify the formula, let x(ω)=c * (ω), Then the maximum gain can be obtained:

[0037]

[0038] From the matrix operation, we can see that the problem of finding the maximum value can be transformed into finding R tx The problem of the eigenvector with the largest eigenvalue is further simplified:

[0039]

[0040] in express The maximum gain at the target direction frequency ω, ||·|| represents the constant of the corresponding formula. And the optimal excitation of the array antenna is obtained:

[0041]

[0042] Where γ is an arbitrary non-zero complex factor, that is, the array receiving signal after time reversal processing is exactly Take the maximum solution.

[0043] Therefore, in complex environments, the antenna array transmits time-reversed processed signals, which can achieve the effect of adaptive directional tracing and ensure that the target angle has the maximum gain at the target frequency. It can be seen here that in the process of time reversing the received signal, the signal of each array element has been pre-processed, and the channel information of the complex environment is adaptively processed during the process of reversing and retransmitting the received signal, and does not need to be extracted and analyzed separately. And from the formula, it can be seen that the complex environment channel information, the positional relationship between array elements and other information do not appear separately. Therefore, this method can achieve maximum gain in any complex environment and improve the beam distortion. According to the law of conservation of energy, the appearance of a stronger main lobe will weaken the energy of the side lobe, thereby optimizing the multi-lobe pattern to a single main lobe pattern; the low gain at the target angle is optimized to the high gain at the target angle.

[0044] Advantages of the present invention:

[0045] 1) This method does not require knowledge of detailed parameters in complex environments;

[0046] 2) This method does not require computer simulation optimization;

[0047] 3) This method is applicable to a variety of complex environments;

[0048] 4) This method can improve beam distortion in a wide frequency band. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 is a top view of a unit of the array antenna used in the present invention;

[0050] Figure 2 1 is a front view of a unit of the array antenna used in the present invention;

[0051] Figure 3 is the S of the array antenna used in the present invention 11 parameter diagram;

[0052] Figure 4 is the unit 6 GHz far-field radiation pattern of the array antenna used in the present invention;

[0053] Figure 5 is a top view of the array antenna used in the present invention in free space;

[0054] Figure 6 is a front view of the array antenna used in the present invention in free space;

[0055] Figure 7 6 GHz far-field radiation pattern of the array antenna used in the present invention at target angles of Phi = 0° Theta = 45° and -45° in free space;

[0056] Figure 8 This is a top view of the array antenna in a complex environment according to the present invention;

[0057] Figure 9 This is a front view of the array antenna in a complex environment according to the present invention;

[0058] Figure 10 The high-order modulated Gaussian pulse wave transmitted from Phi = 0° Theta = 45° is received by port 3 of the array antenna in a complex environment;

[0059] Figure 11 It will Figure 10 The time-reversed signal received by the port 3;

[0060] Figure 12This is a 6GHz far-field comparison of time reversal and traditional methods radiating toward Phi = 0° Theta = 45° in a complex environment;

[0061] Figure 13 This is the 6GHz spatial grayscale image radiated toward Phi=0°Theta=45° by the traditional method in a complex environment;

[0062] Figure 14 This is a 6GHz spatial grayscale image radiated toward Phi=0°Theta=45° using this method in a complex environment;

[0063] Figure 15 This is a 5GHz spatial grayscale image radiated toward Phi=0°Theta=45° using this method in a complex environment;

[0064] Figure 16 The high-order modulated Gaussian pulse wave transmitted from Phi = 0° Theta = -45° is received by port 3 of the array antenna in a complex environment;

[0065] Figure 17 It will Figure 15 The time-reversed signal received by the port 3;

[0066] Figure 18 This is a comparison of the 6GHz far field radiated toward Phi = 0° Theta = -45° using the time reversal technique and the traditional method in a complex environment.

[0067] Figure 19 This is the 6GHz spatial grayscale image radiated toward Phi = 0° Theta = -45° by the traditional method in a complex environment;

[0068] Figure 20 This is a 6GHz spatial grayscale image radiated toward Phi = 0°Theta = -45° using this method in a complex environment;

[0069] Figure 21 This is a 5GHz spatial grayscale image radiated toward Phi=0°Theta=-45° using this method in a complex environment. DETAILED DESCRIPTION

[0070] The present invention will be further described below with reference to the accompanying drawings.

[0071] Figure 1 、 Figure 2 The antenna shown is a patch antenna composed of a basic rectangular patch antenna and a parasitic unit. The antenna shown in the present invention is 30 mm long, 25 mm wide, and 4 mm thick, and adopts a coaxial back-feed feeding method. Figure 3 is the S of the unit antenna 11Parameter diagram, using the unit's broadband characteristics of less than -10dB in 5GHz~6Ghz, combined with Figure 4 It can be seen from the far-field radiation pattern of the unit that the unit radiates directly upward in both the xoz plane and the yoz plane. Therefore, this embodiment adopts this unit as the basic unit of the array antenna.

[0072] Figure 5 、 Figure 6 Shown is the free space Figure 1 The array antenna composed of the units shown is a 1×8 linear array arranged along the X direction. Since the units have good far-field radiation characteristics in both the xoz and yoz planes, the units are arranged with a center distance of 25mm (approximately 0.5λ corresponding to 6GHz). And according to the phased array formula for linear array arrangement Where α is the phase difference of the input signal of each unit, and θ is the angle along the normal on the xoz plane, that is, the target angle. In this embodiment, taking ±45° as an example, we first observe the far-field pattern of the linear array in free space at 6GHz. Figure 7 As shown, the linear array can normally point at ±45° in free space.

[0073] like Figure 8 and Figure 9 As shown, relative to Figure 5 The free space of the linear array is covered with a dielectric layer with non-parallel upper and lower surfaces to simulate a complex environment. The dielectric layer is 100mm wide and 300mm long, with the lower surface parallel to the xoy plane and the upper surface parallel to the xoy plane. The form of fluctuations.

[0074] A modulated Gaussian pulse with the same polarization as the array is transmitted from the target direction at Phi = 0° and Theta = 45°. The pulse frequency is 4-8 GHz. For a clear and intuitive demonstration, the signal at port 3 is used as an example. Figure 10 The pulse signal received by the linear array port 3 is transmitted last according to the time reversal operation method, and the signal received first is transmitted first, so the following is obtained: Figure 11 The signal shown. Figure 10 The comparison can intuitively demonstrate the characteristics of this method in signal processing. Finally, the time-reversed signal is input to the corresponding array element and transmitted simultaneously.

[0075] Figure 12The 6GHz xoz plane far-field patterns obtained in a complex environment using the traditional phased array phase shifting method and this method respectively. As can be seen from the figure, in the complex environment of this embodiment, the maximum peak of the result obtained using the traditional phased array phase shifting method appears near 10°, and a side lobe that is weaker than the main lobe but equally large appears near 50°, which can be regarded as beam distortion in a complex environment. The result obtained using this method has only one maximum peak at the target angle Phi = 0° and Theta = 45°, and the size of the first side lobe is much smaller than the main lobe. The result obtained is similar to the far-field pattern in free space. Comparing the maximum peak size on the xoz plane, this method has a 3dB gain effect compared to the traditional method.

[0076] Figure 13 The 2D grayscale image of the traditional phased array phase-shifting method in a complex environment shows a linear progression of color depth, with darker colors representing greater energy in that area. Clearly, in complex environments, the traditional phased array phase-shifting method has a strong energy concentration near Theta = 10°. However, a light spot slightly below Theta = 10° appears in the target area at Theta = 45° and Phi = 0°. Multiple dark spots or bands of light appear throughout the entire Theta > 0° region. The presence of numerous spots and bands indicates severe beam distortion in the complex environment. Figure 14 In order to utilize this method in a complex environment, the 6GHz 2D grayscale image also has a linear change in color depth, and the darker the color, the greater the energy of the area. Figure 14 The overall color is light, and only at Theta = 45°Phi = 0° does a very concentrated spot of light appear. Other areas also have energy, but the depth of the obvious spots or light bands is less than Figure 13 The light band shown in the figure proves that its intensity is much smaller than the target angle. This proves that the use of this method can re-converge the originally split and chaotic beams, thus optimizing the beam distortion. Figure 13 The maximum energy is 15.5, Figure 14 The maximum energy value is 30.8, and the target angle has a gain change greater than twice (3dB), which can better demonstrate the advantage of this method in correcting beam distortion.

[0077] Figure 15 This 2D grayscale image shows a 5 GHz signal using this method in a complex environment. The color depth changes linearly, with darker colors representing higher energy. It is clear that this method can correct beam distortion at 5 GHz after a single time reversal, with a more concentrated spot appearing at Theta = 45° and Phi = 0°. This demonstrates the broadband correction capabilities of this method.

[0078] Figures 16-21 for Figures 10-15 Repeated experiments, in which Figure 16The high-order modulated Gaussian pulse wave transmitted from Phi = 0° and Theta = -45° is received by the array antenna port 3 in a complex environment; Figure 17 It will Figure 15 The signal received by the port 3 is time-reversed; Figure 18 This is a comparison of the 6GHz far-field radiation at Phi = 0° and Theta = -45° using the time reversal technique and the traditional method in a complex environment. Figure 19 This is a 6GHz spatial grayscale image radiated toward Phi = 0° and Theta = -45° using the traditional method in a complex environment; Figure 20 This is a 6GHz spatial grayscale image radiated toward Phi = 0° and Theta = -45° using this method in a complex environment; Figure 21 This is a 5GHz spatial grayscale image of the radiation at Phi = 0° and Theta = -45° using this method in a complex environment. Under the same coverage layer, the target angle is changed to Theta = -45° and Phi = 0°. The change in target angle is equivalent to changing the complex environment of the array antenna, which can be obtained from Figures 16-21 It can be seen that for different complex environments, this method can still optimize the beam distortion, indicating that this method is applicable to different complex environments.

[0079] In summary, the present invention discloses a method for correcting beam distortion based on time reversal. By time-reversing and retransmitting a previously received signal, the method adaptively processes channel information in complex environments, allowing the previously distorted beam to converge and be corrected. This method provides a method for correcting beam pointing without requiring knowledge of every point in the complex environment, and is applicable to a variety of complex environments.

Claims

1. A method for correcting radiation beam distortion in a complex electromagnetic environment based on time reversal, characterized in that: The following steps are involved: S1. Irradiate a plane wave from the target direction toward the array antenna in a complex environment, where the plane wave contains the same polarization component as the array antenna; S2. Record the signal received by each element of the array antenna and perform time reversal processing on the signal to obtain a time reversal signal; S3. Re-input the time-reversed signal into the corresponding array element and transmit it simultaneously to obtain a radiation beam with corrected distortion in the target direction; Wherein, step S1 is specifically as follows: S11. Analyze the entire system in a spherical coordinate system, with the center of the array antenna as the origin of the spherical coordinate system. Direction illumination plane wave s(t), where θ d is the angle component of the plane wave relative to the array antenna in the spherical coordinate system, is the plane wave relative to the array antenna in the spherical coordinate system The angle component, s(t), is the expression of the amplitude of the plane wave changing with time; S12. Consider the complex environment with linear time invariance as a linear time invariant channel, and the array antenna in the complex environment as a linear time invariant system. The signal Y(t) of the plane wave transmitted in the target direction in the linear time invariant system after passing through the complex environment can be written as: Where Y(t)=[y1(t),y2(t),...,y N (t)] T Represents the matrix composed of the signals received by each array element, y n (t) is the signal received by the nth array element, n = 1, 2, ..., N, (.) T To perform a transpose transformation on the matrix; Indicates convolution operation. is the impulse response of the receiving mode; Step S2 is specifically as follows: Perform time reversal on the signal received by each element in the array antenna Y(-t) = [y1(-t), y2(-t), ..., y N (-t)] T , and get the time-reversed signal: Step S3 is as follows: In the time domain, neglecting propagation loss and time delay, the radiated electric field is written as: in To excite the radiation electric field of the array antenna, is the impulse response of the transmit mode, represents the relative position of the array element in the system, c i (t) is the excitation of the i-th transient element; when c i (t) is the time-reversed signal y i (-t), the distorted beam is improved.

Images