Target microwave correlation imaging method based on frequency agility MIMO radar
阅读说明：本技术 基于频率捷变mimo雷达的目标微波关联成像方法 (Target microwave correlation imaging method based on frequency agility MIMO radar ) 是由 全英汇 张瑞 李亚超 朱圣棋 邢孟道 于 2021-08-24 设计创作，主要内容包括：本发明属于雷达信号处理技术领域,具体公开了一种基于频率捷变MIMO雷达的目标微波关联成像方法,本发明通过发射信号的载频在脉冲间进行随机捷变,同时结合正交匹配追踪算法,在获得稳定的成像结果同时,提高了成像算法对噪声扰动的容忍度,增强了算法的稳健性。(The invention belongs to the technical field of radar signal processing, and particularly discloses a target microwave correlation imaging method based on a frequency agility MIMO radar.)
1. The target microwave correlation imaging method based on the frequency agility MIMO radar is characterized by comprising the following steps:
(1) setting M transmitting antennas at transmitting end of MIMO radar, setting a receiving antenna at receiving end, arranging each antenna in linear order, and setting distance between adjacent transmitting antennas to beAnd the first antenna is taken as a reference antenna, wherein M is more than or equal to 2, and lambda represents the wavelength;
(2) m transmitting antennas of the MIMO radar transmit frequency-agile signals at a frequency hopping interval delta f, and then the transmitting signals of the M transmitting antennas in the l pulse areL is equal to {1, 2, …, L }, wherein L represents the total number of pulses;indicating fast time, tl＝lTrIndicating slow time, TrRepresenting a pulse repetition period;
(3) the imaging plane is uniformly divided into Q imaging grids with the same size, and the scattering point of the target is positioned in the center of the imaging grids, so that the scattering coefficient of the target is represented as beta ═ beta1，β2，…，βQ]TWherein { }TDenotes the vector transposition operation, βqRepresents the scattering coefficient of the scattering point of the object at the center of the qth imaging grid, Q ∈ {1, 2, …, Q };
(4) in the first pulse, the receiving antenna receives a scattering coefficient betaqTarget echo signal ofTarget echo signals received in the first pulsePerforming pulse compression to obtain target echo signal S after pulse pressureq(tl)；
(5) According to the target echo signal S after pulse pressureq(tl) Define r on the imaging planeqReference signal s ofref(tl，rq) The target echo signal after pulse pressure is rewritten to be represented by a reference signal: sq(tl)＝βqsref(tl，rq)；
(6) Receiving echo signals S (t) of all Q imaging grid targets received by a receiving antenna in the ith pulsel) Expressed by reference signals and written in a matrix form as a target equation;
(7) solving the target equation by using an orthogonal matching pursuit algorithm to obtain an estimated value of a target scattering coefficientNamely the target microwave correlation imaging result.
2. The target microwave correlation imaging method based on the frequency agility MIMO radar as claimed in claim 1, wherein in step 2, the expression of the transmission signals of the M transmission antennas in the ith pulse is:
where rect (-) denotes a rectangular envelope, TPIndicating the pulse width, mu the modulation frequency,denotes the M-th transmit antenna at the carrier frequency of the l-th pulse, M ∈ {1, 2, …, M }, fcWhich indicates the starting carrier frequency and,indicating that the mth transmit antenna modulates the codeword at the frequency of the ith pulse,is determined using a rand function, and Δ f denotes the hop interval.
3. The method of claim 1, wherein the scattering coefficient received by the receiving antenna is βqTarget echo signal ofThe expression of (a) is:
wherein the content of the first and second substances,representing the transmitted signal of the m-th transmitting antennaThrough a scattering coefficient of betaqTime delay, R, of the reflected target to the receiving antennatrans，mRepresenting the position vector, R, of the m-th transmitting antenna in the imaging planerec，1Representing the position vector, r, of a receiving antenna in the imaging planeqThe position vector of the q imaging grid is represented, | | | | | represents the norm, and c represents the speed of light;
the target echo signal received in the ith pulsePerforming pulse compression treatment, specifically:
wherein, denotes the transposed operation symbol, t denotes the full time;
simplifying the formula to obtain a target echo signal S after pulse pressureq(tl)：
Where sinc (·) denotes the sinc function, B denotes the signal bandwidth,representing the transmitted signal of the 1 st transmitting antenna by a scattering coefficient betaqThe time delay after reflection of the target at the receiving antenna,representing the transmitted signal of the 2 nd transmitting antenna by a scattering coefficient betaqThe time delay after reflection of the target at the receiving antenna,the transmitted signal of the Mth transmitting antenna is represented by the scattering coefficient betaqThe time delay of the target arriving at the receiving antenna after reflection.
4. The frequency agile MIMO radar based target microwave correlation imaging method of claim 3, wherein r is on the imaging planeqThe reference signal expression here is:
where sinc (·) denotes the sinc function, B denotes the signal bandwidth,denotes the M-th transmit antenna at the carrier frequency of the l-th pulse, M ∈ {1, 2, …, M }, fcWhich indicates the starting carrier frequency and,indicating that the mth transmit antenna modulates the codeword at the frequency of the ith pulse,is determined using a rand function, af denotes the hop interval,the transmitted signal of the m-th transmitting antenna is represented by the scattering coefficient betaqThe time delay of the target arriving at the receiving antenna after reflection.
5. The frequency agile MIMO radar based target microwave correlation imaging method of claim 1, wherein S (t)l) Expressed as:
writing the above equation in matrix form:
S＝Sref·β
the above formula is the target equation;
wherein, S ═ S (t)1)，S(t2)，…S(tl)，…，S(tL)]TA total echo signal vector, S, representing L pulses received by the radar receiving antennarefRepresents a reference signal matrix of the specific form:
reference signal matrix SrefThe (l, q) th element s in (1, q)ref(tl，rq) Indicates the first pulse in rqThe reference signal at Q ∈ {1, 2, …, Q }, Q representing the number of imaging grids.
6. The target microwave correlation imaging method based on the frequency agility MIMO radar as claimed in claim 5, wherein the solving the target equation by using the orthogonal matching pursuit algorithm comprises:
(7.1) initialization residual e0Initializing a set of column sequence numbers S Indicating empty set, initializationWherein Sref_0Is expressed as Λ0Selected reference signal matrix SrefThe number of iterations n is 1Setting the maximum iteration number as K, wherein K is Q;
(7.2) calculate the column number found in the nth iteration
Wherein s isj_n-1Representation matrix Sref_n-1J th column of (e)n-1Denotes the residual, λ, of the n-1 th iterationnIndicates the column number found in the nth iteration, arg indicates when<en-1，sj>The value of j is taken when | is the maximum value, | | represents the operation of taking the absolute value,<>representing an inner product operation;
(7.3) updating the set of column indices Λ for the nth iterationn＝Λn-1∪{λnWherein, Λn-1The column sequence number set representing the (n-1) th iteration is in a union operation;
(7.4) set of column indices by nth iteration ΛnSelecting a reference signal matrix S corresponding to the column numberrefIs set of columns Sref_n；
(7.5) calculating an estimated value of the scattering coefficient vector of the target at the nth iteration
(7.6) calculating the residual error value corresponding to the nth iteration
(7.7) allowing n to be n + 1; and (4) judging whether the current iteration number satisfies n and K, if so, returning to the step (7.2), otherwise, indicating that the solving process of the orthogonal matching pursuit algorithm is finished, and outputting the result of the step (7.5).
7. The frequency agile MIMO radar based target microwave correlation imaging method according to any one of claims 1-6, wherein the method is applied to both static platform scenarios and moving platform scenarios.
Technical Field
The invention relates to the technical field of radar signal processing, in particular to a radar imaging technology, and specifically relates to a target microwave associated imaging method based on a frequency agile MIMO radar, which can be applied to the MIMO radar and realizes target microwave associated imaging.
Background
The frequency agility means that the carrier frequency of adjacent pulse signals transmitted by the radar changes rapidly within a certain frequency range, and each carrier frequency can change according to a certain rule or randomly.
The MIMO radar is a radar system of a new system which transmits orthogonal waveforms through a plurality of transmitting ends, and a plurality of receiving ends receive and jointly process each path of scattering signals. The MIMO radar obtains wide space coverage capacity through a transceiving separation technology, multi-channel echo data are obtained through transmitting orthogonal waveforms and receiving end matched filtering, multiple functions can be achieved based on the characteristics, the actual application range is widened, the system superiority of the MIMO radar is the key, and the system superiority is superior to that of the traditional phased array radar.
Microwave correlation imaging is an emerging imaging method, which originates from optical correlation imaging and can complement the traditional imaging method because it does not depend on the relative motion relationship between radar and target. The microwave correlation imaging method adopts microwaves as a signal source, and a space-time two-dimensional random radiation field is constructed in a specific imaging area to simulate a randomly fluctuated light field in classical thermal light source intensity correlation imaging. The microwave signal source forms a random radiation field with spatial and temporal two-dimensional incoherent characteristics by emitting randomly modulated signals that are incoherently superimposed in space. And carrying target information in the echo through the interaction of the radiation field and the target area, and carrying out operation processing on the echo signals and the random radiation field through a specific imaging algorithm to obtain an imaging result of the target in the detection plane. Aiming at a target microwave correlation imaging method based on a frequency agility MIMO radar, the existing research mainly comprises the following steps:
zhou Xiao Li, microwave correlation imaging theory and method based on sparsity [ D ]. national defense science and technology university, 2017; a microwave correlation imaging method based on a least square method is provided to perform staring imaging on a target by utilizing a random frequency hopping waveform model, but the method is sensitive to model errors and noise, and imaging failure can be caused by small signal disturbance.
Research on several new systems and new methods to improve radar imaging quality [ D ]. university of sienna electronics technology, 2015; based on a phased array radar system, a super-resolution associated imaging algorithm based on compressed sensing is provided to carry out super-resolution imaging on a target, but the method has overlarge calculated amount and is not beneficial to real-time processing of the algorithm.
Talent, zhangxin, ruanfeng, liuhui forward view imaging for missile-borne radar based on space-time two-dimensional random radiation field [ J ]. fire-controlled radar technology, 2016, 45 (03): 1 to 6; a forward-looking imaging method based on gradient projection sparse reconstruction is provided, but the imaging quality is reduced when a radar platform moves or a target moves.
Some of the methods in the above studies are sensitive to model errors and noise; some methods are too large in calculation amount and are not beneficial to real-time processing of the algorithm; in some methods, the imaging quality is reduced when the radar platform moves or the target moves. In summary, there is no ideal frequency agility MIMO radar target microwave correlation imaging method in the prior art.
Disclosure of Invention
Aiming at the problems in the prior art, the invention aims to provide a target microwave correlation imaging method based on a frequency agility MIMO radar.
In order to achieve the purpose, the invention is realized by adopting the following technical scheme.
A target microwave correlation imaging method based on a frequency agility MIMO radar comprises the following steps:
(1) setting M transmitting antennas at transmitting end of MIMO radar, setting a receiving antenna at receiving end, arranging each antenna in linear order, and setting distance between adjacent transmitting antennas to beAnd the first antenna is taken as a reference antenna, wherein M is more than or equal to 2, and lambda represents the wavelength;
(2) m transmitting antennas of the MIMO radar transmit frequency-agile signals at a frequency hopping interval delta f, and then the transmitting signals of the M transmitting antennas in the l pulse are L represents the total number of pulses;indicating fast time, tl＝lTrIndicating slow time, TrRepresenting a pulse repetition period;
(3) the imaging plane is uniformly divided into Q imaging grids with the same size, and the scattering point of the target is positioned in the center of the imaging grids, so that the scattering coefficient of the target is represented as beta ═ beta1，β2，…，βQ]TWherein { }TDenotes the vector transposition operation, βqRepresents the scattering coefficient of the scattering point of the object at the center of the qth imaging grid, Q ∈ {1, 2, …, Q };
(4) in the first pulse, the receiving antenna receives a scattering coefficient betaqTarget echo signal ofTarget echo signals received in the first pulsePerforming pulse compression to obtain target echo signal S after pulse pressureq(tl)；
(5) According to the target echo signal S after pulse pressureq(tl) Define r on the imaging planeqReference signal s ofref(tl，rq) The target echo signal after pulse pressure is rewritten to be represented by a reference signal: sq(tl)＝βqsref(tl，rq)；
(6) Receiving echo signals S (t) of all Q imaging grid targets received by a receiving antenna in the ith pulsel) Expressed by reference signals and written in a matrix form as a target equation;
(7) solving the target using an orthogonal matching pursuit algorithmEquation to obtain the estimated value of the scattering coefficient of the targetNamely the target microwave correlation imaging result.
Compared with the prior art, the invention has the beneficial effects that:
(1) the invention improves the tolerance to noise disturbance. Although the prior art can realize high-resolution imaging, the imaging result has a plurality of side lobes, the width of a main lobe is widened to a certain extent, the main lobe is very sensitive to noise, and imaging failure can be caused by small noise disturbance. The invention carries out random agility among pulses through the carrier frequency of the transmitting signal, and combines the orthogonal matching tracking algorithm, thereby improving the tolerance of the imaging algorithm to noise disturbance and enhancing the robustness of the algorithm while obtaining a stable imaging result.
(2) The application range is wide. The existing imaging technology is mainly based on a synthetic aperture radar system or an inverse synthetic aperture radar system for imaging, but the radar imaging mechanism of the system is seriously dependent on the relative motion relationship between a radar platform and a target, and cannot be applied to static scenes, and the imaging technology has low adaptability to different imaging scenes and limited application range. The frequency agile MIMO radar adopted by the invention can be used for both a static platform scene and a moving platform scene, and is suitable for different imaging scenes.
Drawings
The invention is described in further detail below with reference to the figures and specific embodiments.
FIG. 1 is a flow chart of an implementation of the present invention;
FIG. 2 is a diagram of simulation results for an original target scene using the present invention;
fig. 3 is a diagram of simulation results of microwave correlation imaging results using the present invention.
Detailed Description
Embodiments of the present invention will be described in detail below with reference to examples, but it will be understood by those skilled in the art that the following examples are only illustrative of the present invention and should not be construed as limiting the scope of the present invention.
Referring to fig. 1, the target microwave associated imaging method based on the frequency agility MIMO radar provided by the invention includes the following steps:
(1) setting M transmitting antennas at transmitting end of MIMO radar, setting a receiving antenna at receiving end, arranging each antenna in linear order, and setting distance between adjacent transmitting antennas to beAnd the first antenna is taken as a reference antenna, wherein M is more than or equal to 2, and lambda represents the wavelength;
in the embodiment, for an MIMO radar detection scene with one target, it is assumed that the MIMO radar transmitting end has M transmitting antennas and the receiving end has 1 receiving antenna, so that a far-field narrow-band condition is satisfied.
(2) M transmitting antennas of the MIMO radar transmit frequency-agile signals at a frequency hopping interval delta f, and then the transmitting signals of the M transmitting antennas in the l pulse are L represents the total number of pulses;indicating fast time, tl＝lTrIndicating slow time, TrRepresenting a pulse repetition period;
where rect () denotes the rectangular envelope, TPIt is shown that the width of the pulse,indicating fast time, tl＝lTrDenotes the slow time, ∈ {1, 2, …, L }, L denotes the total number of pulses, TrIndicating the pulse repetition period, mu the modulation frequency,denotes the M-th transmit antenna at the carrier frequency of the l-th pulse, M ∈ {1, 2, …, M }, fcWhich indicates the starting carrier frequency and,indicating that the mth transmit antenna modulates the codeword at the frequency of the ith pulse,the choice of value can be determined using a rand function, Δ f representing the hop interval.
(3) The imaging plane is uniformly divided into Q imaging grids with the same size, and the scattering point of the target is positioned in the center of the imaging grids, so that the scattering coefficient of the target is represented as beta ═ beta1，β2，…，βQ]TWherein { }TDenotes the vector transposition operation, βqRepresents the scattering coefficient of the scattering point of the object at the center of the qth imaging grid, Q ∈ {1, 2, …, Q };
(4) in the first pulse, the receiving antenna receives a scattering coefficient betaqTarget echo signal ofTarget echo signals received in the first pulsePerforming pulse compression to obtain target echo signal S after pulse pressureq(tl)；
(4.1) in the first pulse, the scattering coefficient received by the receiving antenna is betaqThe target echo signal of (a) is:
wherein the content of the first and second substances,representing the transmitted signal of the m-th transmitting antennaThrough a scattering coefficient of betaqTime delay, R, of the reflected target to the receiving antennatrans，mRepresenting the position vector, R, of the m-th transmitting antenna in the imaging planerec，1Representing the position vector, r, of a receiving antenna in the imaging planeqThe position vector at the qth imaging grid is represented, | | · | |, represents the norm, and c represents the speed of light.
(4.2) the scattering coefficient received by the receiving antenna in the first pulse is betaqEcho signal ofPerforming a pulse compression operation:
where denotes the transposed operation symbol and t denotes the full time.
The above formula is simplified to obtain echo signalsThe expression of the pulse compression result of (1) is:
where L ∈ {1, 2, …, L }, sinc (.) denotes the sinc function, B denotes the signal bandwidth,representing the transmitted signal of the 1 st transmitting antenna by a scattering coefficient betaqThe time delay after reflection of the target at the receiving antenna,representing the transmitted signal of the 2 nd transmitting antenna by a scattering coefficient betaqThe time delay after reflection of the target at the receiving antenna,the transmitted signal of the Mth transmitting antenna is represented by the scattering coefficient betaqThe time delay of the target arriving at the receiving antenna after reflection.
(5) According to the target echo signal S after pulse pressureq(tl) Define r on the imaging planeqReference signal s ofref(tl，rq) The target echo signal after pulse pressure is rewritten to be represented by a reference signal: sq(tl)＝βqsref(tl，rq)；
Defining r in the imaging planeqThe reference signal is:
target echo signal S after pulse pressure in step (4)q(tl) Can be further written as:
Sq(tl)＝βqsref(tl，rq)。
(6) receiving echo signals S (t) of all Q imaging grid targets received by a receiving antenna in the ith pulsel) Expressed by reference signals and written in a matrix form as a target equation;
according to the step (5), echo signals S (t) of all Q targets in the imaging grid received by the receiving antenna in the ith pulse are calculatedl)：
Writing the above equation in matrix form:
S＝Sref·β
the above equation is the target equation.
Wherein, S ═ S (t)1)，S(t2)，…S(tl)，…，S(tL)]TAnd the total echo signal vector of the L pulses received by the radar receiving antenna is represented. SrefRepresents a reference signal matrix of the specific form:
reference signal matrix SrefThe (l, q) th element s in (1, q)ref(tl，rq) Indicates the first pulse in rqThe reference signal at Q ∈ {1, 2, …, Q }, Q representing the number of imaging grids, L ∈ {1, 2, …, L }, L representing the total number of pulses, t ∈ {1, 2, …, L }, andlindicating a slow time.
(7) Solving the target equation by using an orthogonal matching pursuit algorithm to obtain an estimated value of a target scattering coefficientNamely the target microwave correlation imaging result.
The solving process of the orthogonal matching pursuit algorithm comprises the following steps:
(7.1) initialization residual e0Initializing a set of column sequence numbers S Indicating empty set, initializationWherein Sref_0Is expressed as Λ0Selected reference signal matrix SrefSetting the maximum iteration number as K, and setting the maximum iteration number as Q;
(7.2) calculate the column number found in the nth iteration
Wherein s isj_n-1Representation matrix Sref_n-1J th column of (e)n-1Denotes the residual, λ, of the n-1 th iterationnIndicates the column number found in the nth iteration, arg indicates when<en-1，sj>The value of j is taken when | is the maximum value, | | represents the operation of taking the absolute value,< >representing the inner product operation.
(7.3) updating the set of column indices Λ for the nth iterationn＝Λn-1∪{λnWherein, Λn-1The column order set representing the (n-1) th iteration, and the U represents the union operation.
(7.4) set of column indices by nth iteration ΛnSelecting a reference signal matrix S corresponding to the column numberrefIs set of columns Sref_n；
(7.5) calculating an estimated value of the scattering coefficient vector of the target at the nth iteration
(7.6) calculating the residual error value corresponding to the nth iteration
(7.7) allowing n to be n + 1; and (4) judging whether the current iteration number satisfies n and K, if so, returning to the step (7.2), otherwise, indicating that the solving process of the orthogonal matching pursuit algorithm is finished, and outputting the result of the step (7.5).
Solution obtained in step (7.5)Namely the target microwave correlation imaging result.
Simulation experiment
The effect of the present invention is further explained by simulation experiments.
The simulation parameters are shown in table 1:
TABLE 1 simulation parameters of the present invention
Parameter symbol
Description of parameters
Unit of
Numerical value
M
Number of array elements
-
16
fc
Center frequency
GHz
14
Δf
Frequency hopping interval
MHz
9.15
B
Bandwidth of
MHz
24
Tp
Pulse width
μs
30
Tr
Number of pulses
-
32
PRF
Pulse repetition frequency
KHz
25
Δr
Coarse resolution cell size
m
3.125
nrn
Number of distance sampling points
-
4320
target_n
Number of target points
-
8
Q
Number of cells
-
51×51
size
Mesh size
m2
1
Second, simulation content
Under the simulation parameters, the target microwave correlation imaging method based on the frequency agility MIMO radar is adopted to simulate the airplane model, and the airplane model is shown in figure 2. In practice, the specific parameters are used to enable the aircraft target to be correctly imaged, and the result is shown in fig. 3.
As can be seen from fig. 3, each of the 8 scattering points in the aircraft model can be accurately and clearly imaged, as indicated by the labels in fig. 3.
The simulation experiment verifies the correctness, effectiveness and reliability of the method.
Although the present invention has been described in detail in this specification with reference to specific embodiments and illustrative embodiments, it will be apparent to those skilled in the art that modifications and improvements can be made thereto based on the present invention. Accordingly, such modifications and improvements are intended to be within the scope of the invention as claimed.
- 上一篇：一种医用注射器针头装配设备
- 下一篇：阵列快速成像方法及其应用