Azimuth multi-antenna high-resolution wide-band imaging radar photon-assisted de-slant receiving system

Abstract

The disclosed embodiment discloses a photon-assisted de-skew receiving system for an azimuth multi-antenna high-resolution wide-band imaging radar, the system comprising: an antenna array element, a photon-assisted de-skew receiving module and a digital signal processor; the antenna array element receives an echo signal; the photon-assisted de-skew receiving module comprises: an optical reference signal source generates an optically-carried linear frequency modulation signal; a delay unit divides the optically-carried linear frequency modulation signal into multiple reference signals and delays each reference signal; a mixing and filtering unit mixes the echo signal with the optical reference signal and filters to select the de-skew signal. The disclosed method of photon-assisted de-skew receiving can process broadband signals with a low-speed ADC, which is beneficial to further improve the radar resolution; the system structure is simplified by using optical wavelength division multiplexing and polarization multiplexing technology, which can more easily build a multi-antenna, multi-channel system; the azimuth multi-antenna technology is integrated with the photon-assisted de-skew receiving technology, and the de-skew receiving technology is extended to the application of high-resolution wide-band imaging radar.

Description

Technical Field

[0001] The present disclosure relates to the field of radar communication technology, and in particular to an azimuth multi-antenna high-resolution wide-band imaging radar photon-assisted de-slant receiving system. Background Art

[0002] Synthetic aperture radar (SAR) has all-day and all-weather remote sensing imaging capabilities, so it is widely used in the fields of earth mapping, resource exploration, disaster monitoring, etc. In order to obtain more detailed information, the requirements for image resolution are increasing. Synthetic aperture radar can obtain high azimuth resolution by equivalently synthesizing a large azimuth antenna aperture through movement in azimuth and coherent processing; to improve the resolution in the range direction, the radar needs to receive and process broadband radar signals, which puts very high requirements on the analog-to-digital converter (ADC). De-slant reception is a method for receiving linear frequency modulation signals commonly used by radars. By mixing the echo signal with the reference signal, the frequency of the de-slant signal is proportional to the delay between the echo and the reference signal. When the delay range of the echo signal is small, the signal bandwidth obtained by de-slant reception is smaller than the bandwidth of the transmitted signal, so the signal reception of broadband radar can be achieved with a low-speed ADC. However, in order to obtain the range resolution determined by the bandwidth of the transmitted signal, de-slant reception requires that the envelope of the echo signal and the reference signal completely overlap in the time domain, and only when the delay range of the echo signal is small, can de-slant reception effectively reduce the bandwidth of the signal and the sampling rate requirement for the ADC. Therefore, the processing bandwidth of the de-slant reception method is very limited. Existing high-resolution wide-band imaging radar systems are all based on matched filtering to achieve range pulse compression, which requires the complete acquisition of the frequency domain information of the echo signal. Therefore, the requirements for the ADC are very high, and it is difficult to further improve its range resolution. In 2020, the Institute of Space Information Innovation of the Chinese Academy of Sciences proposed a microwave photon de-slant reception technology based on multi-channel time division multiplexing, which not only utilizes the inherent broadband advantages of photonics technology to realize the reception of broadband signals and thus achieve high-resolution imaging in the range, but also expands the bandwidth range of de-slant reception, so that the de-slant reception technology is no longer limited to small-width surveying and mapping applications. However, due to the limitation of the minimum antenna area, that is, there is a contradiction between the range bandwidth and the azimuth resolution when selecting the radar pulse repetition frequency (PRF), this technology cannot meet the application of high-resolution wide-band imaging radar. Therefore, there is no feasible solution to realize high-resolution wide-band radar based on de-skewing receiving technology in the existing technical solutions, so that the high-resolution wide-band radar receiver still needs to rely on high-speed ADC to realize the reception of broadband signals, which limits the further improvement of its resolution to a certain extent. Summary of the invention

[0003] The disclosed embodiment provides an azimuth multi-antenna high-resolution wide-band imaging radar photon-assisted de-skewing receiving system.

[0004] In a first aspect, an embodiment of the present disclosure provides an azimuth multi-antenna high-resolution wide-band imaging radar photon-assisted de-skewing receiving system, which includes: multiple antenna array elements, a photon-assisted de-skewing receiving module, and a digital signal processor;

[0005] The multiple antenna array elements are arranged along the moving direction of the synthetic aperture radar platform and are respectively used to receive echo signals reflected by the target;

[0006] The antenna array elements correspond to the photon-assisted de-skewing receiving modules, and each photon-assisted de-skewing receiving module is used to process echo signals received by one or two antenna array elements;

[0007] The photon-assisted de-skewing receiving module comprises: an optical reference signal source, a multi-channel delay unit, a mixing filter unit and an analog-to-digital converter; wherein,

[0008] The optical reference signal source is used to generate an optically carried linear frequency modulation signal;

[0009] The multi-channel delay unit is used to divide the optical linear frequency modulation signal generated by the optical reference signal source into multiple identical reference signals, and delay the multiple identical reference signals for different times respectively;

[0010] The mixing and filtering unit is used to mix the echo signal received by the antenna array element with the optical reference signal after multi-path delay and filter to select the de-skewed signal at the target frequency;

[0011] The analog-to-digital converter is used to convert the de-skewed signal into a digital signal;

[0012] The digital signal processor is used to perform relevant radar algorithm processing on the digital signal after analog-to-digital conversion.

[0013] Furthermore, the optical reference signal source comprises: a plurality of lasers, an optical wavelength division multiplexer, an electrical signal source and an electro-optical modulator; wherein,

[0014] The multiple laser signals generated by the multiple lasers enter the optical wavelength division multiplexer, and the optical wavelength division multiplexer combines the multiple laser signals to form an optical carrier;

[0015] The electrical signal source generates an intermediate frequency reference signal, and the electro-optical modulator modulates the intermediate frequency reference signal onto the optical carrier to obtain optical linear frequency modulation signals at different optical wavelengths.

[0016] Furthermore, the multi-channel delay unit comprises: two optical wavelength division multiplexers and a plurality of optical fiber delay lines; wherein,

[0017] The two optical wavelength division multiplexers are respectively arranged at the input end and the output end of the optical fiber delay line. The wavelength division multiplexer at the input end is used to branch the optical reference signals at different optical wavelengths to different optical fiber delay lines; the wavelength division multiplexer at the output end is used to combine the delayed optical reference signals into one path;

[0018] The multiple optical fiber delay lines respectively delay the optical reference signals at different optical wavelengths in different ways.

[0019] Furthermore, the mixing and filtering unit comprises:

[0020] A polarization controller, a dual-polarization electro-optical modulator, a polarization beam splitter, two optical wavelength division multiplexers, a plurality of photodetectors, and a plurality of electrical filters; wherein,

[0021] The polarization controller is used to control the polarization direction of the optical reference signal so that it is input into the dual-polarization electro-optical modulator in a preset polarization state;

[0022] The dual-polarization electro-optical modulator is used to modulate the echo signals received by any two antenna array elements onto the optical reference signals with orthogonal polarizations to obtain the echo modulated optical signals with orthogonal polarizations;

[0023] The polarization beam splitter performs polarization demultiplexing on the echo modulated optical signal with orthogonal polarizations, that is, splits the signal into two independent echo modulated optical signals according to the polarization directions;

[0024] The optical wavelength division multiplexer performs wavelength division multiplexing on the echo modulated optical signal after polarization demultiplexing, that is, splits the echo modulated optical signal at different optical wavelengths into different optical paths;

[0025] The photoelectric detector performs photoelectric conversion on the echo modulated optical signal after wavelength division multiplexing, thereby obtaining an electrical signal after de-skew processing;

[0026] The electric filter filters each de-skewed electric signal to obtain a de-skewed signal at a target frequency.

[0027] Furthermore, the photon-assisted de-skewing receiving module further comprises:

[0028] The optical beam splitter is used to split the output signal of the multi-channel delay unit into multiple paths and then input the signals into the mixing and filtering unit.

[0029] In a second aspect, an embodiment of the present disclosure provides an azimuth multi-antenna high-resolution wideband radar imaging processing method based on de-slanted reception, comprising the following steps:

[0030] Acquire a de-slanted signal corresponding to each antenna array element within a plurality of continuous transmission pulse repetition periods of the radar; the de-slanted signal is obtained by using the azimuth multi-antenna high-resolution wide-band imaging radar photon-assisted de-slanted receiving system described in the first aspect;

[0031] For each antenna array element in each transmission pulse repetition period, based on the duration window [τ n ,τ n +mT ref ] segmenting the de-skewed signal in the time domain;

[0032] Preprocessing each segment of the de-skewed signal;

[0033] The de-skewed signals of the preprocessed segments are sorted and spliced ​​according to the delay amounts of the corresponding optical reference signals, so as to obtain a one-dimensional range pulse pressure result of the target in a wide-bandwidth scenario within each transmission pulse repetition period of each antenna array element;

[0034] For each antenna array element, the one-dimensional distance pulse compression results within the repetition period of multiple consecutive transmission pulses are arranged according to the azimuth slow time to obtain a data matrix of the distance and azimuth slow time corresponding to each antenna array element;

[0035] Perform azimuth fast Fourier transform on the data matrix of distance and azimuth slow time corresponding to each antenna array element to obtain the distance and Doppler data matrix;

[0036] A two-dimensional imaging result of the target is obtained based on the distance and the Doppler data matrix.

[0037] Furthermore, each segment of the de-skewing signal is preprocessed, including:

[0038] Performing a fast Fourier transform on each segment of the de-skewed signal;

[0039] Filtering the de-skewing signal after the fast Fourier transform using a digital filter to filter out spurious signals outside the target frequency;

[0040] Performing envelope tilting and RVP phase compensation on the de-skewed signal after filtering;

[0041] The relative distance between the target and the radar is obtained based on the frequency of the de-skewed signal after envelope skew and RVP phase compensation and the corresponding time delay of the optical reference signal.

[0042] Further, obtaining a two-dimensional imaging result of the target based on the distance and the Doppler data matrix includes:

[0043] Determine the fixed phase difference and the linear phase difference between the distance and Doppler data matrix of the antenna array element and the distance and Doppler data matrix of the reference array element;

[0044] constructing a transfer matrix using the fixed phase difference and the linear phase difference;

[0045] Reconstructing the distance and Doppler data of all the antenna array elements based on the transfer matrix to obtain unambiguous distance and Doppler data;

[0046] The unambiguous range and Doppler data are processed using a radar imaging algorithm to obtain a two-dimensional imaging result of the target.

[0047] The technical solution provided by the embodiments of the present disclosure may have the following beneficial effects:

[0048] Based on the above technical solution, it can be seen that the photon-assisted de-slanting receiving system and imaging method of the azimuth multi-antenna high-resolution wide-band imaging radar disclosed in the present invention have at least the following beneficial effects:

[0049] (1) By utilizing de-slant reception, the one-dimensional high-resolution wide-swath mapping capability is obtained in the range direction, while the PRF contradiction between the large range width and high azimuth resolution encountered in two-dimensional imaging is solved, thus realizing the application of de-slant reception technology in the field of high-resolution wide-swath radar imaging.

[0050] (2) Compared with the previous high-resolution wide-band radar, which needs to fully collect the frequency domain information of the echo signal and apply matched filtering technology to perform range pulse compression, the present invention uses the de-skewing receiving technology to effectively reduce the requirements for the ADC sampling rate, which is expected to further improve the radar resolution and reduce the difficulty and cost of implementing the receiver system.

[0051] (3) The receiver architecture proposed in the present disclosure is implemented using microwave photonic technology, which can give full play to the advantages of broadband and rich multiplexing resources of photonic technology, thereby further improving the working bandwidth of the receiver and providing the possibility of further improving the radar resolution. It can also effectively reduce the number of devices required for system implementation and greatly simplify the system structure.

[0052] It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Other features, objectives and advantages of the present disclosure will become more apparent through the following detailed description of non-limiting embodiments in conjunction with the accompanying drawings. In the accompanying drawings:

[0054] Figure 1 A schematic diagram of the architecture of an azimuth multi-antenna high-resolution wide-band imaging radar de-slant receiving system disclosed in the present invention is shown;

[0055] Figure 2 A schematic diagram showing the spatial distribution of multiple antenna array elements of the radar disclosed in the present invention is shown;

[0056] Figure 3 A schematic diagram of a photon-assisted de-skewing receiving module disclosed in the present invention is shown;

[0057] Figure 4 An algorithm flow chart of an imaging processing method of a multi-antenna high-resolution wide-band imaging radar based on de-slant reception disclosed in the present invention is shown. DETAILED DESCRIPTION

[0058] Hereinafter, exemplary embodiments of the present disclosure will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily implement them. In addition, for the sake of clarity, parts not related to the description of the exemplary embodiments are omitted in the accompanying drawings.

[0059] In the present disclosure, it should be understood that terms such as "include" or "have" are intended to indicate the presence of features, numbers, steps, behaviors, components, parts, or a combination thereof disclosed in the specification, and do not exclude the possibility that one or more other features, numbers, steps, behaviors, components, parts, or a combination thereof exist or are added.

[0060] It should also be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present disclosure may be combined with each other. The present disclosure will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0061] The present disclosure discloses a photon-assisted de-slanting receiving system and imaging method for an azimuth multi-antenna high-resolution wide-band imaging radar. For linear frequency modulation signals commonly used in radars, the multi-channel time-division multiplexing de-slanting receiving technology can utilize a low-speed ADC to receive a large-bandwidth signal to achieve high range resolution, while ensuring its wide-bandwidth mapping capability; and through the azimuth multi-antenna technology, the reconstruction of the fuzzy Doppler spectrum can be achieved, and combined with the high-resolution wide-band imaging method, the pulse repetition frequency (PRF) contradiction can be effectively alleviated, while ensuring a large mapping width and high resolution in azimuth. Therefore, through the above technology, the present disclosure can realize a high-resolution wide-band imaging radar receiver based on de-slanting reception, breaking through the limitations of the ADC rate on the signal bandwidth and resolution in previous high-resolution wide-band radars, and can reduce the difficulty and cost of implementing the system.

[0062] To achieve the above-mentioned purpose, as a first aspect of the present disclosure, a photon-assisted de-slant receiving system for azimuth multi-antenna high-resolution wide-band imaging radar is provided. Figure 1 As shown, the system includes: a plurality of antenna array elements, a photon-assisted de-skewing receiving module and a digital signal processor;

[0063] The plurality of antenna array elements are arranged along the moving direction of the synthetic aperture radar platform and are respectively used to receive echo signals; the distribution of the antenna array elements is as follows: Figure 2 As shown;

[0064] The antenna array elements correspond to the photon-assisted de-skewing receiving modules, and each photon-assisted de-skewing receiving module is used to process echo signals received by one or two antenna array elements;

[0065] The digital signal processor is used to perform relevant radar algorithm processing on the digital signal after analog-to-digital conversion.

[0066] As a second aspect of the present disclosure, a photon-assisted de-skewing receiving module is provided. Figure 3 As shown, the photon-assisted de-skewing receiving module includes: an optical reference signal source, a multi-channel delay unit, a mixing and filtering unit, and an analog-to-digital converter;

[0067] The optical reference signal source is used to generate an optically carried linear frequency modulation signal;

[0068] The multi-channel delay unit is used to divide the optical linear frequency modulation signal generated by the optical reference signal source into multiple identical reference signals, and delay the multiple identical reference signals for different times respectively;

[0069] The mixing and filtering unit is used to mix the echo signal received by the antenna array element with the optical reference signal after multi-path delay and filter to select the de-skewed signal at the target frequency;

[0070] The analog-to-digital converter is used to convert the de-skewed signal into a digital signal.

[0071] In some embodiments, the photon-assisted de-skewing receiving module further comprises:

[0072] The optical beam splitter is used to divide the output signal of the multi-channel delay unit into multiple paths and input them into the mixing and filtering unit. Since one mixing and filtering unit can only process the echo signals received by one or two antenna array elements, the optical beam splitter can be used to divide the output signal of the multi-channel delay unit into multiple paths, and provide delayed optical reference signals for multiple mixing and filtering units, thereby expanding the number of antenna array elements that can be processed.

[0073] In some embodiments, in the optical reference signal source, a frequency of f ref , the modulation frequency is k, and the period is T ref The linear frequency modulated continuous wave electrical reference signal is modulated onto optical carriers of different wavelengths, and the obtained optical reference signal is input into a multi-channel delay unit;

[0074] In the multi-channel delay unit, the optical reference signal is split into N optical signals according to different wavelengths, and the N optical signals are respectively subjected to τ1, τ2, …, τN Delay, where τ n =(n-1)τ d ,τ d Meet T e ≤(N-1)τ d <T ref , and τ d ≤T ref -T e , where T e is the pulse width of the transmitted signal in the radar transmission parameters, τ n is the delay of the nth path, τ d is the delay difference between adjacent channels. The delayed signals are combined into one optical signal and divided into multiple paths by an optical beam splitter and input into the mixing and filtering unit respectively. The number of paths of the optical beam splitter is equal to half of the number of antenna array elements.

[0075] In the frequency mixing and filtering unit, the polarization controller adjusts the polarization state of the input optical signal to obtain linear polarized light with an angle of 45° with the slow axis, and then inputs it into the dual-polarization electro-optical modulator. In the dual-polarization electro-optical modulator, two antenna array elements modulate the two orthogonal polarization states of the input light respectively to obtain polarization-multiplexed echo-modulated optical signals, and then the optical signal is polarization-demultiplexed by the polarization beam splitter to obtain two optical signals, which are respectively input into two optical wavelength division multiplexers for wavelength division multiplexing, and the obtained wavelength division multiplexing signals are respectively input into photoelectric detectors of each channel for photoelectric conversion to obtain electrical signals after photon-assisted de-skew processing, and the electrical signals after de-skew processing are selected by an electrical filter to obtain effective de-skewed frequency band signals, and the filtered signals are input into an analog-to-digital converter;

[0076] In the analog-to-digital converter, the filtered analog electrical signal is converted into a digital signal.

[0077] In some embodiments, the optical reference signal source includes: a plurality of lasers, an optical wavelength division multiplexer, an electrical signal source and an electro-optical modulator; wherein,

[0078] The multiple laser signals generated by the multiple lasers enter the optical wavelength division multiplexer, and the optical wavelength division multiplexer combines the multiple laser signals to form an optical carrier;

[0079] The electrical signal source generates an intermediate frequency reference signal, and the electro-optical modulator modulates the intermediate frequency reference signal onto the optical carrier to obtain optical linear frequency modulation signals at different optical wavelengths.

[0080] In some embodiments, the multi-channel delay unit includes: two optical wavelength division multiplexers and multiple optical fiber delay lines; wherein,

[0081] The two optical wavelength division multiplexers are respectively arranged at the input end and the output end of the optical fiber delay line. The wavelength division multiplexer at the input end is used to branch the optical reference signals at different optical wavelengths to different optical fiber delay lines; the wavelength division multiplexer at the output end is used to combine the delayed optical reference signals into one path;

[0082] The multiple optical fiber delay lines respectively delay the optical reference signals at different optical wavelengths in different ways.

[0083] In some embodiments, the mixing and filtering unit comprises:

[0084] A polarization controller, a dual-polarization electro-optical modulator, a polarization beam splitter, two optical wavelength division multiplexers, a plurality of photodetectors, and a plurality of electrical filters; wherein,

[0085] The polarization controller is used to control the polarization direction of the optical reference signal so that it is input into the dual-polarization electro-optical modulator in a preset polarization state;

[0086] The dual-polarization electro-optical modulator is used to modulate the echo signals received by the two antenna array elements onto the optical reference signals with orthogonal polarizations to obtain the echo modulated optical signals with orthogonal polarizations;

[0087] The polarization beam splitter performs polarization demultiplexing on the echo modulated optical signal with orthogonal polarizations, that is, splits the signal into two independent echo modulated optical signals according to the polarization directions;

[0088] The optical wavelength division multiplexer performs wavelength division multiplexing on the echo modulated optical signal after polarization demultiplexing, that is, splits the echo modulated optical signal at different optical wavelengths into different optical paths;

[0089] The photoelectric detector performs photoelectric conversion on the echo modulated optical signal after wavelength division multiplexing, thereby obtaining an electrical signal after de-skew processing;

[0090] The electrical filter filters each de-skewing electrical signal to obtain a de-skewing signal within a target frequency band.

[0091] As a third aspect of the present disclosure, Figure 4 As shown, an imaging processing method of a multi-antenna high-resolution wide-band imaging radar based on de-slant reception is provided, comprising the following steps:

[0092] The echo signals received by each antenna are de-skewed and digitized by ADC before being input into the digital signal processor. In the digital signal processor, the signals from each antenna array element are first processed separately in the range direction. For the signal of one antenna array element, the time duration window [τ n ,τ n +mTref ] The de-skewed signal is segmented in the time domain, and the segmented de-skewed signal is subjected to fast Fourier transform. The spurious signals outside the target frequency of the effective de-skewed signal are further filtered by a digital filter, and then the de-skewed signal is envelope tilted and compensated for the residual video phase (RVP). The relative distance between the target and the radar can be obtained according to the frequency of the de-skewed signal and the delay of the corresponding reference signal. The de-skewed signals after each segment of the processing are sorted and spliced ​​according to the delay of the corresponding reference signal to obtain a one-dimensional distance pulse pressure result of the target in a wide-width scene. The distance pulse pressure result is a short-time pulse signal obtained by matching a signal with a long pulse width. The above processing is performed on the echo signal within each transmission pulse repetition period of the radar transmitter, that is, all echo signals in the radar transmission pulse repetition period, that is, the period from when the radar transmits a pulse signal to before the next pulse signal is transmitted, are subjected to the above processing, so as to obtain a one-dimensional distance pulse pressure result corresponding to the radar transmission pulse repetition period. Arrange the one-dimensional range pulse pressure results of each transmitted pulse according to the azimuth slow time, that is, arrange them based on the time between the transmission pulse repetition cycles to obtain a data matrix of distance and azimuth slow time. Repeat the above processing steps to obtain a data matrix of distance and azimuth slow time after processing the echo signals of each antenna array element. Perform azimuth fast Fourier transform on the data matrix of distance and azimuth slow time obtained by each antenna to obtain a range-Doppler data matrix. It should be noted that one of the antenna array elements can be arbitrarily selected as a reference array element based on actual needs.

[0093] In order to achieve wide-band surveying and avoid range ambiguity, the PRF of the radar will be set to a small value. Therefore, if you want to use a large Doppler bandwidth to achieve high azimuth resolution, Doppler ambiguity will occur, and it is necessary to use multiple antennas in azimuth to resolve the ambiguity. Since the antenna array elements are evenly arranged in azimuth, assuming that the interval between adjacent array elements is d, the interval between the pth array element and the first array element (i.e., the reference array element) is (p-1)d, and there is a fixed phase difference and a linear phase difference related to the Doppler frequency between the distance-Doppler data of the pth array element and the reference array element. The fixed phase difference and the linear phase difference are used to construct the transfer matrix H between the unambiguous distance-Doppler data U of the reference array element and the fuzzy distance-Doppler data A between each antenna. The Doppler spectrum is reconstructed by solving the linear equation group A=HU to obtain unambiguous distance-Doppler data, that is, the unambiguous distance-Doppler data corresponding to each antenna array element is obtained. The unambiguous distance-Doppler data is processed using traditional radar imaging algorithms such as ωk, and a high-resolution wide-band two-dimensional imaging result can be obtained.

[0094] Based on the above technical solution, it can be known that the photon-assisted de-slanting receiving system and imaging method of the azimuth multi-antenna high-resolution wide-band imaging radar disclosed in the present invention have at least one of the following beneficial effects:

[0095] (1) By utilizing de-slant reception, the one-dimensional high-resolution wide-swath mapping capability is obtained in the range direction, while the PRF contradiction between the large range width and high azimuth resolution encountered in two-dimensional imaging is solved, thus realizing the application of de-slant reception technology in the field of high-resolution wide-swath radar imaging.

[0096] (2) Compared with the previous practice of using matched filtering technology to perform range pulse compression in high-resolution wide-band radars, the present invention uses de-skewing receiving technology to effectively reduce the requirements for ADC sampling rate, which is expected to further improve radar resolution and reduce the difficulty and cost of implementing the receiver system.

[0097] (3) The receiver architecture proposed in the present disclosure is implemented using microwave photonic technology, which can give full play to the advantages of broadband and rich multiplexing resources of photonic technology, thereby further improving the working bandwidth of the receiver and providing the possibility of further improving the radar resolution. It can also effectively reduce the number of devices required for system implementation and greatly simplify the system structure.

[0098] The present disclosure proposes a photon-assisted de-slanting receiving system and imaging method for an azimuth multi-antenna high-resolution wide-band imaging radar. In order to make the purpose, technical solution and advantages of the present disclosure more clear, the present disclosure is further described in detail below in combination with specific implementation examples and with reference to the accompanying drawings.

[0099] Specifically, Figure 3 As shown, the optical reference signal source generates an optical carrier E modulated by the nth laser. n The frequency on is f ref , the modulation frequency is k, and the period is T ref The linear frequency modulated continuous wave signal, the generated signal can be expressed as:

[0100]

[0101] Wherein, m represents the (m-1)th periodic reference signal generated in one radar transmission and reception cycle.

[0102] The generated optical reference signal is input into the multi-channel delay unit and divided into N channels by the optical wavelength division multiplexer. After passing through the optical fiber delay line, different delay amounts are added to each optical reference signal. The nth optical reference signal can be expressed as:

[0103]

[0104] Among them, τ n The delay introduced by the nth reference signal.

[0105] The delayed optical reference signal is combined by the optical wavelength division multiplexer and sent to the optical beam splitter. After the optical beam splitter performs equal power splitting, the optical reference signal is sent to the dual-polarization electro-optical modulator to mix with the echo after the polarization state of the optical reference signal is adjusted to an angle of 45° with the slow axis by the polarization controller. The echo is expressed as:

[0106]

[0107] Among them, f e is the center frequency of the radar transmitting signal, τ r is the round-trip delay from the target to the radar. The mixed signal is split by the polarization beam splitter to obtain an optical signal modulated by the echo received by one of the antenna array elements. After the optical signal is demultiplexed by the wavelength division multiplexer, the echo modulated optical signal of the nth de-slanted channel is obtained, and input into the photoelectric detector to complete the mixing process and convert it into an electrical signal. The output nth de-slanted channel signal can be expressed as:

[0108]

[0109] The mixed signal includes the difference frequency and sum frequency components of the echo and the reference signal, wherein the difference frequency component contains an effective de-skewing signal.

[0110] In order to ensure that the distance resolution determined by the bandwidth of the transmitted signal can be obtained, it is necessary to ensure that the envelope of a single echo pulse completely coincides with the envelope of one of the periodic signals of the reference signal, so it is necessary to satisfy 0≤τ r -mT ref -τ n ≤T ref -T e , the corresponding de-sloped signal frequency f dechirp Satisfy f e -f ref -k(T ref -T e )≤f dechirp ≤f e -f ref Therefore, after the mixed signal passes through the electrical filter, only the frequency that satisfies f e -f ref -k(T ref -T e )≤f dechirp ≤f e -f ref The signal, other frequency components such as sum frequency and difference frequency are suppressed. After passing through the filter, the de-sloped signal is digitized by ADC to obtain a digital de-sloped signal, which is then processed in a digital signal processor. The processing algorithm flow chart is shown in Figure 4 shown.

[0111] The filtered de-skewed signal can be expressed as:

[0112]

[0113] The filtered de-slanted signal is subjected to fast-time Fourier transform (FT), and the FT-treated signal is sorted in the time sequence of the transmitted pulses to obtain a two-dimensional signal in the range-slow time domain, which can be expressed as:

[0114]

[0115] Among them, the echo delay is a function of the slow time η and is expressed as τ r (η).

[0116] Perform RVP, envelope tilt and system-related phase correction on the signal after FFT. Since the de-skewed signal after FFT is equivalent to the pulse pressure result of the de-skewed signal, the pulse pressure obtains a very narrow sinc function corresponding to the target distance, with a peak value at f r = k(mT ref +τ n -τ r (η))+f e -f ref Therefore, phase compensation can be performed only on the peak point, and the compensated signal can be expressed as:

[0117] S(f r ,η)=T e sinc{T e [f r -f e +f ref -k(mT ref +τ n -τ r (η))]}exp(-j2πf e τ r (η)) (7)

[0118] In high-resolution wideband applications, in order to achieve a large range width, the pulse repetition frequency (PRF) is generally relatively small, resulting in Doppler ambiguity. The present disclosure will reconstruct the Doppler spectrum by using the echoes received by multiple antennas in azimuth to achieve the purpose of suppressing azimuth Doppler ambiguity. Figure 2 As shown in the figure, the interval between adjacent antenna elements is d, and element 1 is used as the reference element. The distance between the pth antenna element and the reference element is (p-1)d. Assuming that the shortest slant distance between the reference element and the target is R0 and the platform movement speed is v, the instantaneous slant distance between the reference element and the target can be expressed as The instantaneous slant range between the pth array element and the target can be expressed as The first array element is the reference array element itself, so d1 = 0. The delay between the radar signal being transmitted by the reference array element and the echo being received by the pth antenna array element is τ pr (η)=(R ref (η)+R p (η)) / c, so the signal of the pth antenna element after phase compensation can be expressed as:

[0119]

[0120] Where A(f r , p, η) is the envelope of the signal, and the exponential term is the Doppler term in the azimuth direction. p , so A(f r ,p,η)≈A(f r ,1,η+d p / (2v)). Therefore, from formula (8), we can know that the signal of the pth antenna element can be regarded as the reference element signal delayed by d in the slow time. p / (2v), and the phase difference is a constant exp[-j(πf e d p 2 ) / (2cR0)]. Therefore, by performing slow time FT on the two-dimensional signals in the range-slow time domain after phase correction of each antenna, the Doppler spectrum of the received signal of each antenna can be obtained. The Doppler response of the pth antenna array element is:

[0121]

[0122] Among them, f d is the Doppler frequency, A s,ref (f d ) is the Doppler response of the reference array element, and A s,1 (f d )=A s,ref (f d ).

[0123] The Doppler response transfer function between the pth antenna element and the reference element is defined as:

[0124]

[0125] Assume that U is the unambiguous Doppler spectrum received by the reference array element. According to equations (9) and (10), the relationship between the aliased Doppler spectrum received by each antenna array element and U can be expressed as:

[0126]

[0127] Where L represents the Doppler aliasing number. Therefore, by obtaining the inverse matrix of the transfer matrix in equation (11), and then multiplying it by the matrix composed of the aliased Doppler spectra received by each antenna array element, the solution of the linear equation group represented by the above matrix can be obtained, and the alias-free Doppler spectrum U can be obtained.

[0128] The unambiguous range Doppler spectrum after Doppler ambiguity resolution can be processed by two-dimensional imaging using traditional radar algorithms suitable for de-slanted signals (including but not limited to RD algorithm and ωk algorithm) to obtain two-dimensional image segments with different reference signal periods m corresponding to different observation distances. The image distances can be stitched upward using the reference signal period m as a sequence number to obtain a complete high-resolution wide-swath SAR imaging result.

[0129] The present invention utilizes a photon-assisted de-slant reception method to process broadband signals with a low-speed ADC, which is beneficial to further improving the radar resolution; utilizes optical wavelength division multiplexing and polarization multiplexing technology to simplify the system structure, making it easier to build a multi-antenna, multi-channel system; integrates azimuth multi-antenna technology with photon-assisted de-slant reception technology, and extends the de-slant reception technology to high-resolution wide-band imaging radar applications.

[0130] The above description is only a preferred embodiment of the present disclosure and an explanation of the technical principles used. Those skilled in the art should understand that the scope of the invention involved in the present disclosure is not limited to the technical solution formed by a specific combination of the above technical features, but should also cover other technical solutions formed by any combination of the above technical features or their equivalent features without departing from the inventive concept. For example, the above features are replaced with the technical features with similar functions disclosed in the present disclosure (but not limited to) by each other.

Claims

1. A photon-assisted de-slant receiving system for azimuth multi-antenna high-resolution wide-band imaging radar. in, include: Multiple antenna elements, photon-assisted de-skewing receiving module, and digital signal processor; The multiple antenna array elements are arranged along the moving direction of the synthetic aperture radar platform and are respectively used to receive echo signals reflected by the target; The antenna array elements correspond to the photon-assisted de-skewing receiving modules, and each photon-assisted de-skewing receiving module is used to process echo signals received by one or two antenna array elements; The photon-assisted de-skewing receiving module comprises: an optical reference signal source, a multi-channel delay unit, a mixing filter unit and an analog-to-digital converter; wherein, The optical reference signal source is used to generate an optically carried linear frequency modulation signal; The multi-channel delay unit is used to divide the optical linear frequency modulation signal generated by the optical reference signal source into multiple identical reference signals, and delay the multiple identical reference signals for different times respectively; The mixing and filtering unit is used to mix the echo signal received by the antenna array element with the optical reference signal after multi-path delay and filter to select the de-skewed signal at the target frequency; The analog-to-digital converter is used to convert the de-skewed signal into a digital signal; The digital signal processor is used to perform relevant radar algorithm processing on the digital signal after analog-to-digital conversion; Wherein, the optical reference signal source comprises: a plurality of lasers, an optical wavelength division multiplexer, an electrical signal source and an electro-optical modulator; The multiple laser signals generated by the multiple lasers enter the optical wavelength division multiplexer, and the optical wavelength division multiplexer combines the multiple laser signals to form an optical carrier; The electrical signal source generates an intermediate frequency reference signal, and the electro-optical modulator modulates the intermediate frequency reference signal onto the optical carrier to obtain optical linear frequency modulation signals at different optical wavelengths; The mixing and filtering unit comprises: A polarization controller, a dual-polarization electro-optical modulator, a polarization beam splitter, two optical wavelength division multiplexers, a plurality of photodetectors, and a plurality of electrical filters; wherein, The polarization controller is used to control the polarization direction of the optical reference signal so that it is input into the dual-polarization electro-optical modulator in a preset polarization state; The dual-polarization electro-optical modulator is used to modulate the echo signals received by any two antenna array elements onto the optical reference signals with orthogonal polarizations to obtain the echo modulated optical signals with orthogonal polarizations; The polarization beam splitter performs polarization demultiplexing on the echo modulated optical signal with orthogonal polarizations, that is, splits the signal into two independent echo modulated optical signals according to the polarization directions; The optical wavelength division multiplexer performs wavelength division multiplexing on the echo modulated optical signal after polarization demultiplexing, that is, splits the echo modulated optical signal at different optical wavelengths into different optical paths; The photoelectric detector performs photoelectric conversion on the echo modulated optical signal after wavelength division multiplexing, thereby obtaining an electrical signal after de-skew processing; The electric filter filters each de-skewed electric signal to obtain a de-skewed signal at a target frequency.

2. The system according to claim 1, in, The multi-channel delay unit includes: two optical wavelength division multiplexers and multiple optical fiber delay lines; wherein, The two optical wavelength division multiplexers are respectively arranged at the input end and the output end of the optical fiber delay line. The wavelength division multiplexer at the input end is used to branch the optical reference signals at different optical wavelengths to different optical fiber delay lines; the wavelength division multiplexer at the output end is used to combine the delayed optical reference signals into one path; The multiple optical fiber delay lines respectively delay the optical reference signals at different optical wavelengths in different ways.

3. The system according to claim 1, in, The photon-assisted de-skewing receiving module further comprises: The optical beam splitter is used to split the output signal of the multi-channel delay unit into multiple paths and then input the signals into the mixing and filtering unit.

4. A method for azimuth multi-antenna high-resolution wide-band radar imaging processing based on de-slant reception, The following steps are involved: Acquire a de-slanted signal corresponding to each antenna array element within a repetition period of multiple continuous transmission pulses of the radar; the de-slanted signal is obtained by using the azimuth multi-antenna high-resolution wide-band imaging radar photon-assisted de-slanted receiving system according to any one of claims 1 to 3; For each antenna array element in each transmission pulse repetition period, based on the duration window of the delayed optical reference signal corresponding to the de-skew signal [ t n , t n + mT ref ] segmenting the de-skewed signal in the time domain; Preprocessing each segment of the de-skewing signal; The de-skewed signals of the preprocessed segments are sorted and spliced ​​according to the delay amounts of the corresponding optical reference signals, so as to obtain a one-dimensional range pulse pressure result of the target in a wide-bandwidth scenario within each transmission pulse repetition period of each antenna array element; For each antenna array element, the one-dimensional distance pulse compression results within the repetition period of multiple consecutive transmission pulses are arranged according to the azimuth slow time to obtain a data matrix of the distance and azimuth slow time corresponding to each antenna array element; Perform azimuth fast Fourier transform on the data matrix of distance and azimuth slow time corresponding to each antenna array element to obtain the distance and Doppler data matrix; A two-dimensional imaging result of the target is obtained based on the distance and the Doppler data matrix.

5. The method according to claim 4, in, Preprocessing each segment of the de-skewing signal after segmentation includes: Performing a fast Fourier transform on each segment of the de-skewed signal; Filtering the de-skewing signal after the fast Fourier transform using a digital filter to filter out spurious signals outside the target frequency; Performing envelope tilting and RVP phase compensation on the de-skewed signal after filtering; The relative distance between the target and the radar is obtained based on the frequency of the de-skewed signal after envelope skew and RVP phase compensation and the corresponding time delay of the optical reference signal.

6. The method according to claim 4 or 5, in, A two-dimensional imaging result of the target is obtained based on the distance and Doppler data matrix, including: Determine the fixed phase difference and the linear phase difference between the distance and Doppler data matrix of the antenna array element and the distance and Doppler data matrix of the reference array element; constructing a transfer matrix using the fixed phase difference and the linear phase difference; Reconstructing the distance and Doppler data of all the antenna array elements based on the transfer matrix to obtain unambiguous distance and Doppler data; The unambiguous range and Doppler data are processed using a radar imaging algorithm to obtain a two-dimensional imaging result of the target.

Images