Fundamental wave and multi-order harmonic combined regulation and control method based on space-time coding metasurface and multi-source direction finding method

Abstract

The invention discloses a fundamental wave and multi-order harmonic wave combined regulation and control method and a multi-source direction finding method based on a space-time coding metasurface, and the method comprises the steps: enabling each metasurface unit to periodically switch the working state on the space-time coding metasurface, and enabling the coding state in the period to form a time coding sequence; each group of time coding sequences controls the propagation direction of fundamental waves through the basic space phase coding of each metasurface unit; the harmonic amplitude is adjusted by adjusting the duty ratio of the time coding sequence; the propagation direction of harmonic waves is adjusted by adjusting the time shift parameter of the time coding sequence; and determining the duty ratio and the time shift of each group of time coding sequences to obtain a space-time coding matrix. Based on the combined regulation and control method, accurate direction finding of multiple signal source incoming wave directions is realized through a sensing matrix.

Description

Technical Field

[0001] The present invention belongs to the field of novel artificial electromagnetic materials, and specifically relates to a fundamental wave and multi-order harmonic joint control method based on a time-space coding metasurface and a multi-source direction finding method. Background Art

[0002] Space-time coded metasurfaces are an important branch of metamaterials and metasurfaces. Their constituent units can respond dynamically in the spatial dimension and periodically switch working states in the temporal dimension, thereby achieving precise control of electromagnetic waves in the spatial and frequency domains. The space-time coding matrix is ​​used to describe the coding state of each unit on the space-time coded metasurface in the space-time dimension. Space-time coded digital metasurfaces have many interesting applications, such as programmable non-reciprocity, harmonic processing, analog signal processing, radar waveform generation, and wireless communications. For space-time coded digital metasurfaces, the design of the space-time coding matrix is ​​both critical and complex. The traditional method for obtaining the space-time coding matrix is ​​to use iterative optimization (such as particle swarm optimization algorithm), but this requires a lot of computing resources and hours of computing time. The computational complexity of traditional optimization algorithms is very high, which makes the efficiency of obtaining the space-time coding matrix very low, especially when the matrix dimension becomes larger, which to some extent hinders the practical application of space-time coded digital metasurfaces. Summary of the invention

[0003] Purpose of the invention: In order to solve the problems of high computational complexity and low efficiency of traditional methods for obtaining space-time coding matrices, the present invention proposes a fundamental wave and multi-order harmonic joint control method based on space-time coding metasurface and a multi-source direction finding method, which can realize accurate direction finding of incoming wave directions from multiple sources.

[0004] Technical solution: A method for joint control of fundamental wave and multi-order harmonics based on space-time coding metasurface, comprising the following steps:

[0005] According to the target propagation direction of the fundamental wave, a corresponding space-time coding matrix is ​​designed for the space-time coding metasurface;

[0006] Under the control of the space-time coding matrix, the space-time coding metasurface generates multi-order harmonics while deflecting the fundamental wave to the target direction, thus achieving joint control of the fundamental wave and multi-order harmonics.

[0007] The specific operations of designing a corresponding space-time coding matrix for the space-time coding metasurface according to the target propagation direction of the fundamental wave include:

[0008] On the space-time coding metasurface, each metasurface unit switches its working state periodically, and the coding state within the period forms a time coding sequence; each group of time coding sequences controls the propagation direction of the fundamental wave through the basic spatial phase coding of each metasurface unit; the harmonic amplitude is adjusted by adjusting the duty cycle of the time coding sequence; the propagation direction of the harmonic is adjusted by adjusting the time shift parameter of the time coding sequence;

[0009] Determine the duty cycle and time shift of each group of time coding sequences to obtain the space-time coding matrix;

[0010] The duty cycle of the time coding sequence is adjusted according to the following steps:

[0011] The value of a part of the code of each group of time code sequences is adjusted to the basic spatial code of each hypersurface unit plus a fixed offset, and the ratio of the length of this part of the code to the total length of the time code sequence is defined as the duty cycle.

[0012] Furthermore, the basic spatial phase encoding of each metasurface unit is obtained according to the following steps:

[0013] According to the target propagation direction of the fundamental wave, the phase response distribution of the space-time coding metasurface is determined to obtain the basic phase response of each column of metasurface units. The basic phase response of each column of metasurface units is quantized into corresponding discrete values ​​to obtain the basic spatial phase coding of each column of metasurface units.

[0014] Furthermore, the value of a portion of the code of each group of time code sequences is adjusted to the basic spatial code of each column of the hypersurface unit plus a fixed offset, which is expressed as:

[0015]

[0016] In the formula, τ n represents the length of the coding sequence with the offset added to the time coding sequence of the nth column of the hypersurface unit, t represents the time, A n represents the basic spatial phase encoding of the metasurface unit in the nth column, and d represents the offset;

[0017] Assuming the period is T0, the ratio of the length of this part of the code to the total length of the time code sequence is defined as the duty cycle, expressed as τ n / T0.

[0018] Furthermore, the propagation direction of the harmonic is adjusted by adjusting the time shift parameter of the time coding sequence, which is expressed as: Γ(tt s ), where t s is the time shift parameter.

[0019] Furthermore, the duty cycle and time shift of each group of time coding sequences are determined to obtain a space-time coding matrix, which is expressed as:

[0020]

[0021] in, Represents the time shift parameter of the nth column of the time-coded sequence.

[0022] The present invention discloses a multi-source direction finding method based on a space-time coding metasurface, comprising the following steps:

[0023] Assuming the direction angle The incoming waves from K sources illuminate the space-time coding metasurface, and the direction angle θ is analyzed. r The amplitude of the vth harmonic in the modulated electromagnetic wave received Select the Q-order harmonic amplitudes to form a vector with dimension Q, calculate the unit vector corresponding to the vector, normalize the harmonic amplitudes, and form the harmonic amplitude vector

[0024] Assume that a single source with a directional angle θ is shining on the space-time coding metasurface. r The harmonic amplitude vector y(W1,θ r ,θ); select P direction angles θ as needed 1 ,θ 2 ,…,θ P , covering the directional angle range of the K sources to be detected, and the corresponding P harmonic amplitude vectors are combined into a sensing matrix H(W1,θ r ), expressed as:

[0025] H(W1,θ r )=[y(W1,θ r ,θ 1 ),y(W1,θ r ,θ 2 ),…,y(W1,θ r ,θ P )] T

[0026] Where W1 represents the space-time coding matrix of the space-time coding hypersurface, y(W1,θ r ,θ 1 ) indicates the azimuth angle θ r The direction angle received from The harmonic amplitude vector of the source;

[0027] According to the perception matrix H(W1,θ r ) and harmonic amplitude vector The correlation coefficient is calculated and expressed as

[0028]

[0029] By analyzing the distribution of the correlation coefficient, the direction angle estimation of K sources is obtained;

[0030] The space-time coding matrix W1 of the space-time coding metasurface is designed according to the following steps:

[0031] On the space-time coding metasurface, each metasurface unit switches its working state periodically, and the coding state within the period forms a time coding sequence; each group of time coding sequences controls the propagation direction of the fundamental wave through the basic spatial phase coding of each metasurface unit; the harmonic amplitude is adjusted by adjusting the duty cycle of the time coding sequence; the propagation direction of the harmonic is adjusted by adjusting the time shift parameter of the time coding sequence;

[0032] Determine the duty cycle and time shift of each group of time coding sequences to obtain the space-time coding matrix;

[0033] The duty cycle of the time coding sequence is adjusted according to the following steps:

[0034] The value of a part of the code of each group of time code sequences is adjusted to the basic spatial code of each hypersurface unit plus a fixed offset, and the ratio of the length of this part of the code to the total length of the time code sequence is defined as the duty cycle.

[0035] Furthermore, the value of a portion of the code of each group of time code sequences is adjusted to the basic spatial code of each column of the hypersurface unit plus a fixed offset, which is expressed as:

[0036]

[0037] In the formula, τ n represents the length of the coding sequence with the offset added to the time coding sequence of the nth column of the hypersurface unit, t represents the time, A n represents the basic spatial phase encoding of the metasurface unit in the nth column, and d represents the offset;

[0038] Assuming the period is T0, the ratio of the length of this part of the code to the total length of the time code sequence is defined as the duty cycle, expressed as τ n / T0.

[0039] Furthermore, the propagation direction of the harmonic is adjusted by adjusting the time shift parameter of the time coding sequence, which is expressed as: Γ(tt s ), where t s is the time shift parameter.

[0040] Furthermore, the duty cycle and time shift of each group of time coding sequences are determined to obtain a space-time coding matrix, which is expressed as:

[0041]

[0042] in, Represents the time shift parameter of the nth column of the time-coded sequence.

[0043] Furthermore, the method of obtaining the direction angle estimation of the K sources by analyzing the distribution of the correlation coefficient includes:

[0044] By analyzing the peak distribution of the correlation coefficient, the direction angle estimation of K sources is obtained, or

[0045] Based on the distribution of the correlation coefficient, the direction angle estimation of K sources is obtained according to the orthogonal matching algorithm.

[0046] Beneficial effects: Compared with the prior art, the present invention has the following advantages:

[0047] (1) The method of the present invention does not require iterative optimization. On the basis of spatial coding, time shift and duty cycle are introduced as core variables of space-time coding design. The corresponding space-time coding matrix can be directly generated according to the needs. It is very efficient and can simultaneously control the fundamental wave and multi-order harmonics. It has a high degree of freedom and realizes the joint control of the fundamental wave propagation and the amplitude and spatial distribution of multi-order harmonics.

[0048] (2) In the present invention, on the space-time coding metasurface, each basic unit periodically switches its working state, and the coding state within the period forms a time coding sequence. Each group of time coding sequences controls the propagation direction of the fundamental wave through basic spatial phase coding; adjusts the harmonic amplitude through the duty cycle; and adjusts the propagation direction of the harmonic through the time shift parameter;

[0049] (3) Based on the joint control method, the present invention realizes accurate direction finding of the incoming wave directions of multiple signal sources through the sensing matrix;

[0050] (4) The method of the present invention greatly improves the ability of the space-time coding metasurface to control electromagnetic waves in the spatial and frequency domains, and has great application potential in the fields of communication and perception. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 A schematic diagram of a fundamental wave and multi-order harmonic joint control method and a multi-source direction finding method based on a space-time coding metasurface;

[0052] Figure 2 It is a schematic diagram of the process of designing the space-time coding matrix for joint regulation of fundamental wave and multi-order harmonics;

[0053] Figure 3 It shows the regulation effect of different duty cycles and time shifts on the amplitude and spatial distribution of multi-order harmonics;

[0054] Figure 4 The figure shows the received harmonic spectrum distribution, the distribution of correlation coefficients and the azimuth estimation results of each source when there are different numbers of sources. DETAILED DESCRIPTION

[0055] In order to make the purpose, technical solution and advantages of the present invention more clear, the technical solution of the present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0056] Embodiment 1:

[0057] Figure 1 A schematic diagram of a method for joint control of fundamental wave and multi-order harmonics and a multi-source direction finding method based on space-time coding metasurface is shown. This method is based on space coding, introduces time shift and duty cycle as variables in space-time coding design, and can simultaneously control the propagation of fundamental wave and the amplitude and spatial distribution of multi-order harmonics. By analyzing the amplitude distribution of multi-order harmonics, accurate direction finding can be achieved for multiple sources. The method of this embodiment includes:

[0058] On the space-time coding metasurface, each metasurface unit switches its working state periodically, and the coding state within the period forms a time coding sequence; each group of time coding sequences controls the propagation direction of the fundamental wave through the basic spatial phase coding of each metasurface unit; the harmonic amplitude is adjusted by adjusting the duty cycle of the time coding sequence; the propagation direction of the harmonic is adjusted by adjusting the time shift parameter of the time coding sequence;

[0059] The duty cycle and time shift of each group of time coding sequences are determined to obtain the space-time coding matrix.

[0060] The solution proposed in this embodiment is now further described. It mainly includes the following steps:

[0061] Step 1: According to the target propagation direction of the fundamental wave, the phase response distribution of the coding metasurface is determined to obtain the basic phase response of the time coding sequence corresponding to each unit. The phase response of each unit is discrete and needs to be quantized into corresponding discrete values ​​to obtain the basic spatial phase code A0 of each column of units; the basic spatial phase code is replicated in the time dimension to obtain a space-time coding matrix W0 that is unchanged in the time dimension.

[0062] Now, let’s take a coded metasurface composed of N columns of 2-bit reflective units as an example. Each unit can switch between four states, corresponding to four phase responses, namely (-π / 2, 0, π / 2, π), which are digitally represented as “0”, “1”, “2” and “3”. When we want the coded metasurface to deflect the incident wave in the normal direction to θ c In the direction, the phase response of the nth column unit can be expressed as:

[0063] Φn =-(n-1)k c d(sinθ c )

[0064] The phase response is quantized into corresponding discrete values ​​and encoded into the corresponding digital code A n , the basic spatial phase coding is replicated in the time dimension to obtain the space-time coding matrix W0 which is unchanged in the time dimension, which can be expressed as a periodic time function with a period of T0: Γ n (t) = A n , where Γ n (t) represents the reflection coefficient of the nth column unit, A n Represents the basic spatial phase encoding of the nth column of cells.

[0065] Step 2: Based on the basic spatial coding, each group of time coding sequences adjusts the value of a part of the coding to its basic spatial phase coding A0 plus a fixed offset value d. The ratio of the length of this part of the coding to the length of the overall time coding sequence is defined as the duty cycle. The higher the duty cycle, the larger the harmonic amplitude; the lower the duty cycle, the smaller the harmonic amplitude, and the more uniform the amplitude distribution of each order of harmonics. The specific operations include:

[0066] The time coding sequence of the nth column unit in a period T0 can be expressed as:

[0067]

[0068] In the formula, τ n represents the length of the coding sequence with the offset value added to the time coding sequence of the nth column of the hypersurface unit, τ n / T0 is the duty cycle of the time coding sequence.

[0069] Step 3: Introduce the variable time shift t in each set of time-coded series s , and obtain a new time coding sequence Γ(tt s ), according to the Fourier transform principle, the time shift corresponds to the phase change in the frequency domain, thereby affecting the phase response of the harmonics. Therefore, this embodiment controls the phase response of each order of harmonics by time shifting, thereby changing the spatial distribution of each order of harmonics.

[0070] Figure 3 The regulation effect of different duty cycles and time shifts on the amplitude and spatial distribution of harmonics is demonstrated. The higher the duty cycle, the larger the harmonic amplitude, and the lower the duty cycle, the smaller the harmonic amplitude and the more uniform the amplitude distribution of each order of harmonics. The time shift determines the phase response of each order of harmonics, thereby changing the spatial distribution of each order of harmonics.

[0071] Step 4: By adjusting the duty cycle and time shift of each group of time coding sequences, a new space-time coding matrix W1 is formed, which deflects the fundamental wave to the target direction and generates multi-order harmonics, thereby realizing the joint regulation of the fundamental wave and multi-order harmonics; specifically, it includes:

[0072] After determining the duty cycle and time shift of the time coding sequence, the time coding sequence of the nth column unit can be expressed in the period as:

[0073]

[0074] Among them, τ n Indicates the length of the coding sequence with the offset value added, and the duty cycle is τ n / T0.

[0075] The duty cycle and time shift of each time coding sequence can be the same or different. When the time shift of each time coding sequence is an arithmetic progression, the phase response of the harmonic presents a gradient distribution. Each time coding sequence obtains a new time coding sequence according to its own duty cycle and time shift, and together constitutes a new space-time coding matrix W1.

[0076] The design of the space-time coding matrix is ​​the core of the space-time coding metasurface. The design method proposed in this embodiment further improves the ability of the space-time coding metasurface to control electromagnetic waves in the spatial domain and frequency domain, and has great application potential in the fields of communication and perception. This method does not require iterative optimization, but introduces two variables, duty cycle and time shift. It can directly generate the corresponding space-time coding matrix according to demand, and can simultaneously control the fundamental frequency wave and multi-order harmonics. It has a high degree of freedom and is significantly more efficient than the traditional method of obtaining the space-time coding matrix.

[0077] Embodiment 2:

[0078] Based on Example 1, this example proposes a method for joint control of fundamental wave and multi-order harmonics based on space-time coding metasurface, such as Figure 2 As shown, based on spatial coding, two variables, time shift and duty cycle, are introduced to achieve joint control of fundamental wave and multi-order harmonics. The following steps are included:

[0079] According to the target propagation direction of the fundamental wave, the method shown in Example 1 is used to design a corresponding space-time coding matrix for the space-time coding metasurface;

[0080] Under the control of the space-time coding matrix, the space-time coding metasurface generates multi-order harmonics while deflecting the fundamental wave to the target direction, thereby realizing the joint regulation of the fundamental wave and multi-order harmonics.

[0081] This embodiment is based on space coding, and introduces time shift and duty cycle as variables in space-time coding design, which can simultaneously regulate the propagation of the fundamental frequency wave and the amplitude and spatial distribution of multi-order harmonics.

[0082] Embodiment 3:

[0083] On the basis of Example 1, this embodiment proposes that the present invention discloses a multi-source direction finding method based on a space-time coding metasurface, comprising the following steps:

[0084] With N=16, τ n =τ0 = T0 / 32, A n =0, d=1, all N columns of cells share the same duty cycle τ0 / T0, and Γ n+1 (t) = Γ n (t-T0 / 16), so its periodic reflection coefficient can be expanded into a Fourier series:

[0085]

[0086] Among them, t s =T0 / 16. Considering It can be found and have the same amplitude, but due to the time offset t s , their phase difference is 2πvt s / T0. Therefore, when the coding metasurface is incident at an angle of θ i When the plane wave with a wavelength of = 0° is irradiated, the beam direction of the vth harmonic in the reflected wave can be expressed as:

[0087]

[0088] Therefore, assuming that the direction angle θ i 1 ,θ i 2 ,…,θ i K The incoming waves from K sources irradiate the coding metasurface, and the direction angle θ is analyzed. r The amplitude y of the vth harmonic in the modulated electromagnetic wave received v (W1,θ r ,θ i 1 ,θ i 2 ,…,θ i K ), select the Q-order harmonic amplitude, together form a vector with dimension Q, and calculate the unit vector corresponding to the vector, normalize the harmonic amplitude, and form the harmonic amplitude vector y(W1,θ r ,θ i 1 ,θ i 2 ,…,θ iK );

[0089] Assume that a single source with a directional angle θ is shining on the space-time coding metasurface. r The harmonic amplitude vector y(W1,θ r ,θ); select P direction angles θ as needed 1 ,θ 2 ,…,θ P , covering the directional angle range of the K sources to be detected, and the corresponding P harmonic amplitude vectors are combined into a sensing matrix H(W1,θ r ), expressed as:

[0090] H(W1,θ r )=[y(W1,θ r ,θ 1 ),y(W1,θ r ,θ 2 ),…,y(W1,θ r ,θ P )] T

[0091] Where W1 represents the space-time coding matrix of the space-time coding hypersurface, y(W1,θ r ,θ 1 ) represents the azimuth angle θ r The signal received from the direction angle θ i 1 The harmonic amplitude vector of the source;

[0092] According to the perception matrix H(W1,θ r ) and the harmonic amplitude vector y(W1,θ r ,θ i 1 ,θ i 2 ,…,θ i K ), the correlation coefficient is calculated and expressed as

[0093] z(W1,θ r ,θ i 1 ,θ i 2 ,…,θ i K )=H(W1,θ r )·y(W1,θ r ,θ i 1 ,θ i 2 ,…,θ i K) By analyzing the distribution of the correlation coefficient, the direction angle estimation of the K sources is obtained, which specifically includes: analyzing the peak distribution of the correlation coefficient, or obtaining the incoming wave directions of the K sources according to the orthogonal matching algorithm.

[0094] This embodiment realizes accurate direction finding of the incoming wave directions of multiple sources based on the sensing matrix, and the computational complexity of the direction finding estimation for multiple sources is low.

[0095] Figure 4 It shows that when different numbers of sources illuminate the space-time coding metasurface, the received multi-order harmonic amplitude distribution and the corresponding correlation coefficient distribution are obtained, and the angle estimation value of each source is obtained using the orthogonal matching algorithm.

[0096] The above is only a preferred embodiment of the present invention. Since the present invention has a clear design concept and a wide range of application prospects, this design method can be applied to microwave, millimeter wave, terahertz and other frequency bands. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A method for joint control of fundamental wave and multi-order harmonics based on spatiotemporal coding metasurface, characterized in that: The following steps are involved: According to the target propagation direction of the fundamental wave, a corresponding space-time coding matrix is ​​designed for the space-time coding metasurface; Under the control of the space-time coding matrix, the space-time coding metasurface generates multi-order harmonics while deflecting the fundamental wave to the target direction, thus achieving joint control of the fundamental wave and multi-order harmonics. The specific operations of designing a corresponding space-time coding matrix for the space-time coding metasurface according to the target propagation direction of the fundamental wave include: On the space-time coding metasurface, each metasurface unit switches its working state periodically, and the coding state within the period forms a time coding sequence; each group of time coding sequences controls the propagation direction of the fundamental wave through the basic spatial phase coding of each metasurface unit; the harmonic amplitude is adjusted by adjusting the duty cycle of the time coding sequence; the propagation direction of the harmonic is adjusted by adjusting the time shift parameter of the time coding sequence; Determine the duty cycle and time shift of each group of time coding sequences to obtain a space-time coding matrix; The duty cycle of the time coding sequence is adjusted according to the following steps: The value of a part of the code of each group of time code sequences is adjusted to the basic spatial code of each hypersurface unit plus a fixed offset, and the ratio of the length of this part of the code to the total length of the time code sequence is defined as the duty cycle.

2. According to claim 1, a method for joint control of fundamental wave and multi-order harmonics based on space-time coding metasurface is characterized in that: The basic spatial phase encoding of each metasurface unit is obtained according to the following steps: According to the target propagation direction of the fundamental wave, the phase response distribution of the space-time coding metasurface is determined to obtain the basic phase response of each column of metasurface units. The basic phase response of each column of metasurface units is quantized into corresponding discrete values ​​to obtain the basic spatial phase coding of each column of metasurface units.

3. The method for designing a space-time coding matrix for simultaneously regulating a fundamental frequency wave and multi-order harmonics according to claim 1, characterized in that: The value of a portion of the code of each group of time code sequences is adjusted to the basic spatial code of each column of the hypersurface unit plus a fixed offset, which is expressed as: In the formula, τ n represents the length of the coding sequence with the offset added to the time coding sequence of the nth column of the hypersurface unit, t represents the time, A n represents the basic spatial phase encoding of the metasurface unit in the nth column, and d represents the offset; Assuming the period is T0, the ratio of the length of this part of the code to the total length of the time code sequence is defined as the duty cycle, expressed as τ n / T0.

4. The method for designing a space-time coding matrix for simultaneously regulating a fundamental frequency wave and multi-order harmonics according to claim 3, characterized in that: The propagation direction of the harmonic is adjusted by adjusting the time shift parameter of the time coding sequence, which is expressed as: Γ(tt s ), where t s is the time shift parameter.

5. The method for designing a space-time coding matrix for simultaneously regulating a fundamental frequency wave and multi-order harmonics according to claim 4, characterized in that: The duty cycle and time shift of each group of time coding sequences are determined to obtain a space-time coding matrix, which is expressed as: in, Represents the time shift parameter of the nth column of the time-coded sequence.

6. A multi-source direction finding method based on space-time coding metasurface, characterized in that: The following steps are involved: Assuming the direction angle The incoming waves from K sources illuminate the space-time coding metasurface, and the direction angle θ is analyzed. r The amplitude of the vth harmonic in the modulated electromagnetic wave received Select the Q-order harmonic amplitudes to form a vector with dimension Q, calculate the unit vector corresponding to the vector, normalize the harmonic amplitudes, and form the harmonic amplitude vector Assume that a single source with a directional angle θ is shining on the space-time coding metasurface. r The harmonic amplitude vector y(W1,θ r ,θ); select P direction angles θ as needed 1 ,θ 2 ,…,θ P , covering the directional angle range of the K sources to be detected, and the corresponding P harmonic amplitude vectors are combined into a sensing matrix H(W1,θ r ), expressed as: H(W1,θ r )=[y(W1,θ r ,θ 1 ),y(W1,θ r ,θ 2 ),…,y(W1,θ r ,θ P )] T Where W1 represents the space-time coding matrix of the space-time coding hypersurface, y(W1,θ r ,θ 1 ) represents the azimuth angle θ r The direction angle received from The harmonic amplitude vector of the source; According to the perception matrix H(W1,θ r ) and harmonic amplitude vector The correlation coefficient is calculated and expressed as By analyzing the distribution of the correlation coefficient, the direction angle estimation of K sources is obtained; The space-time coding matrix W1 of the space-time coding metasurface is designed according to the following steps: On the space-time coding metasurface, each metasurface unit switches its working state periodically, and the coding state within the period forms a time coding sequence; each group of time coding sequences controls the propagation direction of the fundamental wave through the basic spatial phase coding of each metasurface unit; the harmonic amplitude is adjusted by adjusting the duty cycle of the time coding sequence; the propagation direction of the harmonic is adjusted by adjusting the time shift parameter of the time coding sequence; Determine the duty cycle and time shift of each group of time coding sequences to obtain the space-time coding matrix; The duty cycle of the time coding sequence is adjusted according to the following steps: The value of a part of the code of each group of time code sequences is adjusted to the basic spatial code of each hypersurface unit plus a fixed offset, and the ratio of the length of this part of the code to the total length of the time code sequence is defined as the duty cycle.

7. The multi-source direction finding method based on space-time coding metasurface according to claim 6, characterized in that: The value of a portion of the code of each group of time code sequences is adjusted to the basic spatial code of each column of the hypersurface unit plus a fixed offset, which is expressed as: In the formula, τ n represents the length of the coding sequence with the offset added to the time coding sequence of the nth column of the hypersurface unit, t represents the time, A n represents the basic spatial phase encoding of the metasurface unit in the nth column, and d represents the offset; Assuming the period is T0, the ratio of the length of this part of the code to the total length of the time code sequence is defined as the duty cycle, expressed as τ n / T0.

8. The multi-source direction finding method based on space-time coding metasurface according to claim 7, characterized in that: The propagation direction of the harmonic is adjusted by adjusting the time shift parameter of the time coding sequence, which is expressed as: Γ(tt s ), where t s is the time shift parameter.

9. The multi-source direction finding method based on space-time coding metasurface according to claim 7, characterized in that: The duty cycle and time shift of each group of time coding sequences are determined to obtain a space-time coding matrix, which is expressed as: in, Represents the time shift parameter of the nth column of the time-coded sequence.

10. The multi-source direction finding method based on space-time coding metasurface according to claim 6, characterized in that: The method of obtaining the direction angle estimation of the K sources by analyzing the distribution of the correlation coefficient includes: By analyzing the peak distribution of the correlation coefficient, the direction angle estimation of K sources is obtained, or Based on the distribution of the correlation coefficient, the direction angle estimation of K sources is obtained according to the orthogonal matching algorithm.

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