A fundamental wave and multi-order harmonic joint control method and multi-source direction finding method based on space-time coding metasurface

Abstract

The present invention discloses a method for jointly controlling fundamental waves and multi-order harmonics based on a space-time coding metasurface, as well as a multi-source direction-finding method. The method comprises: on the space-time coding metasurface, each metasurface unit periodically switches its operating state, and the coding states within the period form a time-coding sequence; each set of time-coding sequences controls the propagation direction of the fundamental wave through the fundamental spatial phase coding of each metasurface unit; the amplitude of the harmonics is adjusted by adjusting the duty cycle of the time-coding sequence; the propagation direction of the harmonics is adjusted by adjusting the time-shift parameters of the time-coding sequence; and the duty cycle and time shift of each set of time-coding sequences are determined to obtain a space-time coding matrix. Based on this joint control method, accurate direction-finding of the incoming wave directions of multiple signal sources is achieved 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 and a multi-source direction finding method based on a time-space coding metasurface. Background Art

[0002] Space-time coding metasurfaces are an important branch of metamaterials and metasurfaces. Their constituent units can dynamically respond in the spatial dimension and periodically switch their operating states in the temporal dimension, thereby achieving precise control of electromagnetic waves in the spatial and frequency domains. A space-time coding matrix is ​​used to describe the coding state of each unit on the space-time coding metasurface in the space-time dimension. Space-time coding digital metasurfaces have many interesting applications, such as programmable nonreciprocity, harmonic processing, analog signal processing, radar waveform generation, and wireless communications. For space-time coding digital metasurfaces, the design of the space-time coding matrix is ​​both critical and complex. Traditional methods for obtaining the space-time coding matrix use iterative optimization (such as particle swarm optimization), but this requires extensive computing resources and hours of computation time. The high computational complexity of traditional optimization algorithms makes obtaining the space-time coding matrix inefficient, especially as the matrix dimension increases, which to some extent hinders the practical application of space-time coding digital metasurfaces. Summary of the Invention

[0003] Purpose of the invention: 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 method for jointly controlling fundamental waves and multi-order harmonics based on space-time coding metasurfaces and a multi-source direction-finding method, which can realize accurate direction-finding of the incoming wave directions of multiple sources.

[0004] Technical solution: A method for joint control of fundamental wave and multi-order harmonics based on spatiotemporal coding metasurface, including 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 deflects the fundamental wave to the target direction while generating multi-order harmonics, thus achieving joint control of the fundamental wave and multi-order harmonics.

[0007] The above-mentioned design of a corresponding space-time coding matrix for the space-time coding metasurface according to the target propagation direction of the fundamental wave includes the following specific operations:

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

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

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

[0011] The value of a part of the code in each group of time code sequences is adjusted to the basic spatial code of each metasurface 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, thereby obtaining 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 values ​​of a portion of the codes of each group of time code sequences are adjusted to the basic spatial code of each column of the hypersurface unit plus a fixed offset, which is expressed as:

[0015]

[0016] Where, τ n It represents the length of the coding sequence with the offset added to the time coding sequence of the nth column of the metasurface unit, t represents 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 harmonics 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 set of time coding sequences are determined to obtain a spatiotemporal 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 irradiated 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 forming the corresponding P harmonic amplitude vectors 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 metasurface, y(W1,θ r ,θ 1 ) represents 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 periodically switches its working state, and the coding state within the period forms a time coding sequence. Each set of time coding sequences controls the propagation direction of the fundamental wave through the basic spatial phase coding of each metasurface unit. The amplitude of the harmonics is adjusted by adjusting the duty cycle of the time coding sequence. The propagation direction of the harmonics is adjusted by adjusting the time shift parameter of the time coding sequence.

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

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

[0034] The value of a part of the code in each group of time code sequences is adjusted to the basic spatial code of each metasurface 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 values ​​of a portion of the codes of each group of time code sequences are adjusted to the basic spatial code of each column of the hypersurface unit plus a fixed offset, which is expressed as:

[0036]

[0037] Where, τ n It represents the length of the coding sequence with the offset added to the time coding sequence of the nth column of the super surface unit, t represents 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 harmonics 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 set of time coding sequences are determined to obtain a spatiotemporal 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 estimates of the K sources by analyzing the distribution of the correlation coefficients 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 coefficients and using an orthogonal matching algorithm, the direction angle estimates of the K sources are obtained.

[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, each basic unit on the space-time coding metasurface periodically switches its working state, and the coding state within the period forms a time coding sequence. Each set 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 Schematic diagram of a fundamental wave and multi-order harmonics joint control method and multi-source direction finding method based on space-time coding metasurface;

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

[0053] Figure 3 It shows the 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, correlation coefficient distribution and azimuth estimation results of each source under different numbers of sources. DETAILED DESCRIPTION

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

[0056] Example 1:

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

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

[0059] The duty cycle and time shift of each set 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 invariant in the time dimension.

[0062] Take a coding metasurface composed of N rows 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 the coding metasurface is expected 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 time dimension-invariant space-time coding matrix W0, 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 unit.

[0065] Step 2: Based on the basic spatial code, each time code sequence adjusts the value of a portion of the code to its basic spatial phase code A0 plus a fixed offset value d. The ratio of the length of this portion of the code to the length of the entire time code 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 harmonic. The specific operations include:

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

[0067]

[0068] Where, 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 super surface unit, τ n / T0 is the duty cycle of the time code sequence.

[0069] Step 3: Introduce the variable time shift t into each set of time-coded series s , and obtain the new time code 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 results show that different duty cycles and time shifts can regulate the amplitude and spatial distribution of harmonics. The higher the duty cycle, the larger the harmonic amplitude, while 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 set of time coding sequences, a new space-time coding matrix W1 is formed. While deflecting the fundamental wave to the target direction, multi-order harmonics are generated, achieving joint control of the fundamental wave and multi-order harmonics. Specifically, the following steps are performed:

[0072] After determining the duty cycle and time shift of the time coding sequence, the time coding sequence of the n-th column unit can be expressed as follows within the period:

[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 code sequence can be the same or different. When the time shift of each time code sequence is an arithmetic progression, the phase response of the harmonics exhibits a gradient distribution. Each time code sequence is generated based on its own duty cycle and time shift, and together they form 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 and frequency domains, and has great application potential in the fields of communication and perception. This method does not require iterative optimization and 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] Example 2:

[0078] Based on Example 1, this example proposes a method for jointly controlling fundamental waves and multi-order harmonics based on a space-time coding metasurface. Figure 2 As shown in the figure, 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 control 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] Example 3:

[0083] Based on Example 1, this embodiment proposes a multi-source direction finding method based on a space-time coded metasurface disclosed by the present invention, 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 with an angle of θ i When the plane wave with angle = 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 illuminate the coding metasurface and analyze the direction angle θ r The amplitude of the vth harmonic in the modulated electromagnetic wave received is y v (W1,θ r ,θ i 1 ,θ i 2 ,…,θ i K ), select the Q-order harmonic amplitude, together to 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 irradiated 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 forming the corresponding P harmonic amplitude vectors 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 metasurface, y(W1,θ r ,θ 1 ) represents the azimuth angle θ r The signal received at the direction angle θ i 1 The harmonic amplitude vector of the source;

[0092] According to the perception matrix H(W1,θ r ) and harmonic amplitude vector y(W1,θ r ,θ i 1 ,θ i 2 ,…,θ i K ), calculate the correlation coefficient, 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, specifically including: 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 implements 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 description is merely a preferred embodiment of the present invention. Due to the clear design concept and broad application prospects of the present invention, this design method can be applied to microwave, millimeter wave, terahertz, and other frequency bands. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and such improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for joint control of fundamental wave and multi-order harmonics based on spatiotemporal coding metasurface, characterized by: 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 deflects the fundamental wave to the target direction while generating multi-order harmonics, thus achieving joint control of the fundamental wave and multi-order harmonics. The above-mentioned design of a corresponding space-time coding matrix for the space-time coding metasurface according to the target propagation direction of the fundamental wave includes the following specific operations: On the space-time coding metasurface, each metasurface unit periodically switches its working state, and the coding state within the period forms a time coding sequence. Each set of time coding sequences controls the propagation direction of the fundamental wave through the basic spatial phase coding of each metasurface unit. The amplitude of the harmonics is adjusted by adjusting the duty cycle of the time coding sequence. The propagation direction of the harmonics is adjusted by adjusting the time shift parameter of the time coding sequence. Determine the duty cycle and time shift of each set of time coding sequences to obtain the space-time coding matrix; The duty cycle of the time code sequence is adjusted according to the following steps: The value of a part of the code in each group of time code sequences is adjusted to the basic spatial code of each metasurface 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. The method for joint control of fundamental wave and multi-order harmonics based on spatiotemporal coding metasurface according to claim 1, 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, thereby obtaining 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 joint control of fundamental wave and multi-order harmonics based on spatiotemporal coding metasurface 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: ； Where, Indicates the n The length of the coding sequence with the offset added to the time coding sequence of the column metasurface unit, t represents time, Indicates the n The basic spatial phase encoding of the column metasurface unit, d represents the offset; Assuming the period is 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, which is expressed as .

4. The method for joint control of fundamental wave and multi-order harmonics based on spatiotemporal coding metasurface according to claim 3, characterized in that: The propagation direction of the harmonics is adjusted by adjusting the time shift parameters of the time coding sequence, which is expressed as: , where is the time shift parameter.

5. The method for joint control of fundamental wave and multi-order harmonics based on spatiotemporal coding metasurface according to claim 4, characterized in that: The duty cycle and time shift of each set of time coding sequences are determined to obtain a space-time coding matrix, which is expressed as: ； in, Indicates the n Time-shift parameters for time-coded series.

6. A multi-source direction finding method based on a space-time coding metasurface, characterized by: The following steps are involved: Assuming the direction angle of K The incoming wave from the source is irradiated on the space-time coding metasurface, and the modulated electromagnetic wave received at the azimuth angle is analyzed. v harmonic amplitude , select Q The order harmonic amplitudes together form a dimension of Q The vector of the harmonic amplitude is formed by calculating the unit vector corresponding to the vector and normalizing the harmonic amplitude. ; Assumed direction angle θ A single source of irradiates the space-time coding metasurface at an azimuth angle of The harmonic amplitude vector received at ; Select P direction angles as needed , covering the direction to be measured K The directional angle range of the source is composed of the corresponding P harmonic amplitude vectors into a perception matrix , expressed as: ； Where, represents the space-time coding matrix of the space-time coding hypersurface, Indicates the azimuth The direction angle received from The harmonic amplitude vector of the source; According to the perception matrix and harmonic amplitude vectors , calculate the correlation coefficient, expressed as ； By analyzing the distribution of the correlation coefficient, we can obtain K Estimation of the direction angle of a source; The space-time coding matrix of the space-time coding metasurface It is designed according to the following steps: On the space-time coding metasurface, each metasurface unit periodically switches its working state, and the coding state within the period forms a time coding sequence. Each set of time coding sequences controls the propagation direction of the fundamental wave through the basic spatial phase coding of each metasurface unit. The amplitude of the harmonics is adjusted by adjusting the duty cycle of the time coding sequence. The propagation direction of the harmonics is adjusted by adjusting the time shift parameter of the time coding sequence. Determine the duty cycle and time shift of each set of time coding sequences to obtain the space-time coding matrix; The duty cycle of the time code sequence is adjusted according to the following steps: The value of a part of the code in each group of time code sequences is adjusted to the basic spatial code of each metasurface 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: ； Where, Indicates the n The length of the coding sequence with the offset added to the time coding sequence of the column metasurface unit, t represents time, Indicates the n The basic spatial phase encoding of the column metasurface unit, d represents the offset; Assuming the period is 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, which is expressed as .

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 harmonics is adjusted by adjusting the time shift parameters of the time coding sequence, which is expressed as: , where 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 set of time coding sequences are determined to obtain a space-time coding matrix, which is expressed as: ； in, Indicates the n Time-shift parameters for time-coded series.

10. The multi-source direction finding method based on space-time coding metasurface according to claim 6, characterized in that: By analyzing the distribution of the correlation coefficient, we can obtain K The direction angle estimation of each source includes: By analyzing the peak distribution of the correlation coefficient, we can obtain K direction angle estimate of a source, or Based on the distribution of the correlation coefficient, according to the orthogonal matching algorithm, we get K Estimation of the direction angle of a source.

Images