A broadband vortex electromagnetic wave steering method

Abstract

The application discloses a broadband vortex electromagnetic wave steering method and belongs to the technical field of phased array radars. First, according to a broadband vortex electromagnetic wave electric field model of an antenna array under broadband signal excitation, a pointing angle deviation |θ T ‑θ0(l,f)| between a main lobe pointing direction θ0(l,f) of the vortex electromagnetic wave under different modes l and frequencies f and a target elevation angle θ T is obtained. The pointing angle deviation is used as a corresponding steering angle of the vortex electromagnetic wave beam under different modes l and frequencies f, and a secondary phase shift that needs to be added to the n-th array element under the corresponding mode l and frequency f is calculated. The secondary phase shift is superposed with an initial phase of the n-th array element to obtain a total phase shift that needs to be applied to the n-th array element under the mode l and the frequency f, and the phase of the antenna array is regulated according to the total phase shift. Wherein, n = 1, 2, …, N, and N is the total number of array elements of the antenna array. Compared with the prior art, the application can effectively suppress the divergence phenomenon of the vortex electromagnetic wave beam under the broadband condition.

Description

Technical Field

[0001] This invention relates to the field of phased array radar technology, and in particular to a broadband vortex electromagnetic wave direction adjustment method. Background Technology

[0002] Radar imaging technology is not limited by natural conditions and has important applications in fields such as space target surveillance, remote sensing mapping, and ocean observation. Most existing high-resolution radars are based on the range-Doppler principle, achieving high range resolution by transmitting broadband signals and high azimuth resolution by utilizing the large virtual synthetic aperture formed by the relative motion between the radar and the target. However, they rely on the lateral relative motion between the radar and the target and lack forward-looking imaging capabilities, only able to detect and track targets using side-looking or oblique-looking methods. To address this, solutions such as monopulse imaging technology and array radar imaging technology have been proposed, which can improve the angular resolution of radar to some extent. However, the resolution is limited by the aperture size and cannot obtain detailed azimuth information of the target.

[0003] Orbital angular momentum (OAM) is a physical quantity related to the phase wavefront distribution of electromagnetic waves. When orbital angular momentum modulation is applied to conventional electromagnetic waves, vortex electromagnetic waves are formed, whose phase wavefronts exhibit a helical structure. This allows for the modulation of desired information, enhancing the information transmission and acquisition capabilities of electromagnetic waves. When using electromagnetic vortex waves with multi-mode orbital angular momentum for target detection, differentially distributed electromagnetic excitations will be formed at different scattering points of the target within the beam, resulting in more spatial information contained in the target's scattered echo. Utilizing vortex electromagnetic waves can overcome the resolution limitation caused by the real aperture beamwidth when using conventional planar electromagnetic wave illumination, providing a feasible solution for high-resolution forward-looking radar imaging. However, unlike high-frequency optical vortices, electromagnetic vortex beams exhibit significant divergence, displaying a hollow radiation characteristic. The size of the annular main lobe illumination area of ​​the vortex electromagnetic wave increases with propagation distance, posing limitations on transmission distance and application obstacles for target detection. Electromagnetic vortex imaging requires high-bandwidth microwave signals to achieve high range resolution and multiple different modes to achieve azimuth resolution. However, its main lobe pointing varies with the beam frequency and the number of modes, and the lower the frequency or the higher the number of modes, the more severe the main lobe divergence. Previously, methods for adjusting the main lobe pointing caused by different modes, such as using multiple concentric ring arrays, three-element antennas, and phased array technology, have been proposed. However, these methods require relatively complex hardware systems and only address the divergence problem caused by the number of modes, ignoring the differences in beam directivity between different frequencies, thus failing to achieve high-performance target detection and sensing. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a broadband vortex electromagnetic wave direction adjustment method that does not require additional hardware devices. It can simultaneously generate broadband vortex electromagnetic waves and effectively suppress the beam divergence phenomenon of vortex electromagnetic waves under broadband conditions by simply designing and controlling the phase of each array element signal.

[0005] The present invention specifically adopts the following technical solutions to solve the above-mentioned technical problems:

[0006] A broadband vortex electromagnetic wave phase modulation method first obtains the main lobe pointing θ0(l,f) and target elevation angle θ of the vortex electromagnetic wave under different modes l and frequencies f based on the broadband vortex electromagnetic wave electric field model of the antenna array under broadband signal excitation. T The pointing angle deviation between |θ T -θ0(l,f)|;Using the pointing angle deviation as the guiding angle corresponding to the vortex electromagnetic beam under different modes l and frequencies f, the secondary phase shift that needs to be added to the nth array element under the corresponding mode l and frequency f is calculated. Compare it with the initial phase of the nth element. The total phase shift required to be applied to the nth element under mode l and frequency f is obtained by superposition. The phase of the antenna array is then adjusted accordingly, where n = 1, 2, ..., N, and N is the total number of elements in the antenna array.

[0007] Preferably, the antenna array is a uniform circular array, and the nth element in mode l and frequency f needs to be subjected to an additional quadratic phase shift. Calculate according to the following formula:

[0008]

[0009] In the formula, c is the speed of light, and φ T φ is the target azimuth angle. n Let be the azimuth angle of the nth array element.

[0010] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0011] This invention uses a software method to design additional secondary phase shifts for array elements based on the main lobe pointing differences of different modes and frequencies. This can effectively suppress the divergence of vortex electromagnetic beams under broadband conditions, effectively improve the radiation energy at the target, and requires no additional hardware, resulting in lower system implementation costs. Attached Figure Description

[0012] Figure 1 This is a flowchart illustrating the broadband vortex electromagnetic wave orientation process in a specific embodiment.

[0013] Figure 2The radiation patterns of vortex electromagnetic waves in different modes when the beam is tuned forward and backward at a frequency of 18 GHz.

[0014] Figure 3 The diagram shows the vortex electromagnetic wave pattern at different sweep frequencies when the beam-forward and backward modes are set to 7. Detailed Implementation

[0015] To address the shortcomings of existing technologies, the solution of this invention is to add a secondary phase shift to the array elements under broadband conditions to address the main lobe pointing differences of different modes and frequencies, thereby suppressing the divergence phenomenon of vortex electromagnetic beams under broadband conditions.

[0016] The broadband vortex electromagnetic wave direction-adjusting method proposed in this invention is as follows:

[0017] First, based on the broadband vortex electromagnetic wave electric field model of the antenna array under broadband signal excitation, the main lobe pointing θ0(l,f) and target elevation angle θ of the vortex electromagnetic wave under different modes l and frequencies f are obtained. T The pointing angle deviation between |θ T -θ0(l,f)|;Using the pointing angle deviation as the guiding angle corresponding to the vortex electromagnetic beam under different modes l and frequencies f, the secondary phase shift that needs to be added to the nth array element under the corresponding mode l and frequency f is calculated. Compare it with the initial phase of the nth element. The total phase shift required to be applied to the nth element under mode l and frequency f is obtained by superposition. The phase of the antenna array is then adjusted accordingly, where n = 1, 2, ..., N, and N is the total number of elements in the antenna array.

[0018] To facilitate public understanding, the technical solution of the present invention will be described in detail below through a specific embodiment and in conjunction with the accompanying drawings:

[0019] In this embodiment, the antenna array uses the most commonly used uniform circular array to generate vortex electromagnetic waves, and its direction-adjusting process is as follows: Figure 1 As shown, it includes the following steps:

[0020] The first step is to construct a broadband vortex electromagnetic wave electric field model based on the traditional method of generating vortex electromagnetic beams using a uniform circular array:

[0021] N antenna elements are uniformly arranged on a circle of radius *a* to form a uniform circular transmitting array. The larger the number of antennas *N*, the more types of orbital angular momentum modes carried by the vortex electromagnetic waves that the transmitting array can generate; the smaller the array radius *a*, the fewer sidelobes of the generated vortex electromagnetic waves. A broadband swept-frequency signal with bandwidth *B* is applied to each antenna element for excitation, wherein the excitation signal has the same frequency and amplitude. The modulation phase difference between two adjacent elements is... That is, the nth array element has an initial phase. l represents the number of orbital angular momentum modes. Based on this, an electric field model is constructed for broadband vortex electromagnetic waves carrying different orbital angular momentum modes. For any point P(r,θ,φ) in the far field, the normalized field strength of the vortex electromagnetic wave generated at point P when the swept signal frequency is f and the set mode is l can be expressed as:

[0022]

[0023] J l (.) represents the first-order Bessel function of the lth order.

[0024] The parameters can be determined according to the specific detection requirements. In this embodiment, the number of antennas N is 60, the radius of the circular array a is 8.16cm, the bandwidth of the swept frequency signal is 8GHz (18GHz–26GHz), and the generated vortex electromagnetic waves have modes l=0,±1,±2,…,±7 respectively.

[0025] The second step is to determine the main lobe direction of the generated vortex electromagnetic wave under different modes and frequencies:

[0026] The direction of the maximum gain angle θ0 of the vortex electromagnetic wave is defined as the main lobe direction, and its quantitative relationship with the array radius, signal frequency, and number of modes can be precisely expressed by the Bessel function. For a given array radius a, the main lobe direction of the vortex electromagnetic wave beam is precisely calculated based on the position of the maximum value of the Bessel function corresponding to different frequencies f and modes l.

[0027]

[0028] The third step is to assume that the azimuth and elevation angles of the area where the target is located are φ. T and θ T The main lobe of the vortex electromagnetic wave is annular. To align the position of the annulus with the target, this invention selects the path with the smallest beam axis movement angle, that is, moving the beam axis along the target azimuth direction or its opposite direction. Based on the relationship between the expected pointing direction and the main lobe region, the deviation |θ| between the expected pointing direction and the actual pointing angle of the vortex electromagnetic wave beam can be calculated for different frequencies and modes. T -θ0(l,f)|.

[0029] Fourthly, the broadband vortex electromagnetic waves generated in the first step based on the traditional model have the same pointing beam axis. The direction of this beam axis can be adjusted based on the steering vector of the circular array. When the beam axis steering angle is (θ) d ,φ d When ), the guiding vector of the circular array is:

[0030]

[0031] Where φ1…φN This represents the azimuth angle of the 1st to Nth array elements;

[0032] If the pointing angle deviation calculated in the third step is set as the guiding angle corresponding to vortex electromagnetic beams of different frequencies and modes, and the original beam axis is adjusted, the main lobe can illuminate the target. Therefore, the secondary phase shift required for each array element under different adjustment angles is calculated:

[0033]

[0034] In the formula, c is the speed of light, and φ n Let be the azimuth angle of the nth array element.

[0035] The fifth step involves combining the secondary phase shift calculated in the fourth step with the existing broadband vortex electromagnetic wave generation model. If the generated broadband vortex electromagnetic waves are all directed towards the target, then when the sweep signal frequency is f and the set mode is l, the total phase shift required to be applied to the nth array element is:

[0036]

[0037] Based on this, the model of the vortex electromagnetic wave after the direction adjustment can be reconstructed. For any point P(r,θ,φ) in the far field, the normalized field strength of the vortex electromagnetic wave generated at point P when the frequency of the sweep signal is f and the set mode is l can be expressed as:

[0038]

[0039] This generates broadband vortex electromagnetic waves.

[0040] To verify the technical effect of this invention, the radiation patterns in the elevation dimension of broadband vortex electromagnetic waves were simulated and compared using both the traditional vortex electromagnetic wave generation method and the method of this invention. For ease of verification, it is assumed that the target to be detected is located on the original vortex electromagnetic wave beam axis, i.e., the target coordinates satisfy (θ). T ,φ T ) = (0,0). Figure 2 (a) and (b) in the figure are the radiation patterns of vortex electromagnetic waves of different modes when the beam is tuned and the frequency is swept back and forth at 18 GHz. Figure 3 (a) and (b) in the figure show the radiation patterns of vortex electromagnetic waves at different sweep frequencies when the beam-adjustment mode is 7. Simulation results show that, compared with traditional vortex electromagnetic wave generation methods, the beam generated by the broadband vortex electromagnetic wave direction-adjustment method proposed in this invention can point to the target with its main lobe at different frequencies and in different modes, while exhibiting smaller side lobe transformations. This allows the wide-bandwidth and multi-mode vortex electromagnetic waves to effectively detect targets, thereby improving the performance of applications such as target identification and new radar systems.

Claims

1. A broadband vortex electromagnetic wave direction modulation method, characterized in that, First, based on the broadband vortex electromagnetic wave electric field model of the antenna array under broadband signal excitation, the electric field of the vortex electromagnetic wave in different modes is obtained. l and frequency f The main lobe points to pitch angle with target i T Pointing angle deviation between | i T - i 0( l , f Using the aforementioned pointing angle deviation as different modes l and frequency f The steering angle corresponding to the lower vortex electromagnetic beam is calculated in the corresponding mode. l and frequency f Next n Each element needs to be subjected to a secondary phase shift. , and the first n Initial phase of each array element Overlay to obtain the pattern l and frequency f Next n The total phase shift required for each element And based on this, the phase of the antenna array is adjusted, wherein, n =1, 2, ..., N , N The total number of elements in the antenna array.

2. The broadband vortex electromagnetic wave direction adjustment method as described in claim 1, characterized in that, The antenna array is a uniform circular array, in mode... l and frequency f Next n Each element needs to be subjected to a secondary phase shift. Calculate according to the following formula: In the formula, c At the speed of light, The target azimuth angle, For the first n The azimuth angle of each array element.

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