CN111505633A - Microwave photon distributed radar imaging system and method - Google Patents
Microwave photon distributed radar imaging system and method Download PDFInfo
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- CN111505633A CN111505633A CN202010341233.3A CN202010341233A CN111505633A CN 111505633 A CN111505633 A CN 111505633A CN 202010341233 A CN202010341233 A CN 202010341233A CN 111505633 A CN111505633 A CN 111505633A
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
- G01S13/88—Radar or analogous systems specially adapted for specific applications
- G01S13/89—Radar or analogous systems specially adapted for specific applications for mapping or imaging
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
- G01S7/02—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00
- G01S7/41—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00 using analysis of echo signal for target characterisation; Target signature; Target cross-section
- G01S7/411—Identification of targets based on measurements of radar reflectivity
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Abstract
A distributed radar imaging system, comprising: the central station modulates n paths of optical carriers with different wavelengths by the low-frequency narrow-band linear frequency modulation electric signals, transmits the optical carriers to the transmitting station and the (n-1) receiving stations through optical fibers with different time delays respectively, performs beam combination and parallel deskew processing on echo optical signals from the receiving stations, and performs analog-to-digital conversion, transmission phase delay compensation, frequency domain segmentation and three-dimensional imaging processing on the combined deskew signals; the transmitting station converts the optical carrier radio frequency signal from the central station into a high-frequency broadband linear frequency modulation electric signal for transmission; and the receiving station receives the target echo signal, modulates the optical carrier radio frequency signal from the central station and transmits the optical carrier radio frequency signal back to the central station through the optical fiber. The invention also discloses a microwave photon distributed radar imaging method. The invention applies photon frequency doubling, optical fiber radio frequency transmission and photon parallel deskewing processing technology to the distributed radar, realizes three-dimensional imaging under a one-transmitter-multiple-receiver architecture, reduces the complexity of the system, and improves the distribution capability and the imaging performance of the system.
Description
Technical Field
The invention relates to the field of radar imaging, in particular to a microwave photon distributed radar imaging system and method.
Background
The microwave radar has the remote sensing imaging capability of all-weather, all-weather and high resolution, and plays an indispensable important role in the fields of homeland surveying and mapping, resource exploration, environmental disaster monitoring, regional reconnaissance and the like. With the promotion of scientific and technological development and application, modern radars develop in the directions of high resolution, multiple functions, miniaturization, reconfigurable performance and the like. However, limited by "electronic bottleneck", the electronic technology is difficult to realize the generation, control and processing of broadband signals, and brings great challenges for the traditional radar to realize multiband broadband reconfiguration. In recent years, the photonic technology has become a key technology for illuminating the future of radar by virtue of the characteristics of large bandwidth, low transmission loss, electromagnetic interference resistance, multi-domain multiplexing and the like, and has attracted international attention. The microwave photon radar system and the key technology thereof become a research hotspot at home and abroad, and the photon technology is applied to various links such as signal generation, frequency conversion and frequency doubling, optical fiber transmission, deskew processing, analog-to-digital conversion and the like so as to improve the radar bandwidth and expand the detection baseline and the synthetic aperture, thereby realizing high-resolution two-dimensional imaging and accurate detection.
With the development of microwave photonic radar systems, photonic technology began to expand towards three-dimensional imaging applications. Compared with a two-dimensional image, the three-dimensional image can provide scattering point energy distribution of the target, obtain richer detail information and be more beneficial to target identification. In order to acquire the third dimension information of the target based on the two-dimensional imaging, it is necessary to construct an interference baseline in a direction perpendicular to the two-dimensional imaging plane. A typical method is interferometric inverse synthetic aperture radar (initar), i.e. two antennas are arranged in the third dimension, which is achieved by coherent processing of the received signals. The problems with this approach are: (1) it is difficult to distinguish multiple primary scatter points located in the same range-doppler cell, without third-dimension geometric resolution; (2) the measurement accuracy of the third dimension is improved along with the increase of the base line, but the phase interference quality is also reduced, and the two are in contradiction. In order to solve the above problems, a multi-station distributed radar architecture is proposed, which increases the number of antennas in the third dimension and the length of corresponding base lines compared to the initar, thereby having a geometric resolution capability in the third dimension, and simultaneously improving the coherence among multiple channels. However, the increased number of transmitters and receivers will multiply the system cost and complexity. In addition, the increase of the baseline also brings new challenges to signal coherent processing, and in the existing multi-base electronic radar, after receiving an echo signal of a target, a receiver needs to perform local preprocessing and then transmits the echo signal back to a central station for data fusion, so that the loss of partial information is difficult to avoid. Compared with the traditional electronic technology, the photonic technology has certain advantages in the aspects of generation, processing and transmission of broadband signals. The photon technology is applied to the distributed radar system, so that the existing problems can be hopefully solved, and the imaging detection performance of the system is further improved.
Disclosure of Invention
It is therefore an objective of the claimed invention to provide a microwave photon distributed radar imaging system and method, which are designed to solve at least one of the above problems.
To achieve the above object, as a first aspect of the present invention, there is provided a center station including:
an array of light sources for generating n channels of light with wavelength λ1、λ2、……、λnOptical carrier of (d);
the first optical beam combiner is used for combining the n paths of optical carriers generated by the light source array to obtain an optical carrier group;
the electro-optical modulator is used for modulating the low-frequency narrow-band linear frequency modulation electric signals to the optical carrier group to generate modulated optical signals containing n paths of optical carrier radio-frequency signals;
an optical wavelength division multiplexer for splitting the modulated optical signal according to different carrier wavelengths to obtain n paths of carrier wavelengths respectively of lambda1、λ2、……、λnWherein the optical carrier has a wavelength λ1As an emitted optical signal, carrier wavelengths of lambda2、λ3、……、λnThe (n-1) optical carrier radio frequency signal is used as a reference optical signal;
a second optical beam combiner for respectively setting the carrier wavelengths as λ2、λ3、……、λnThe echo optical signals are combined to obtain combined optical signals;
the photoelectric detector is used for performing photoelectric conversion on the combined beam optical signal generated by the second optical beam combiner to realize parallel deskew processing on the (n-1) path echo signal so as to obtain a combined beam deskew signal;
the analog-to-digital converter is used for performing analog-to-digital conversion on the combined beam deskew signal;
and the digital processor is used for performing digital domain processing on the combined beam deskew signal after analog-to-digital conversion.
As a second aspect of the present invention, there is provided a transmitting station comprising:
the photoelectric detector is used for carrying out photoelectric conversion on the emission light signal from the central station to generate a high-frequency broadband linear frequency modulation electric signal;
and the transmitting antenna is used for transmitting the high-frequency broadband linear frequency modulation electric signal.
As a third aspect of the present invention, there is provided a receiving station, the number of which is (n-1), comprising:
a receiving antenna for receiving an echo signal from a target;
the electro-optical modulator is used for modulating the echo signal received by the receiving antenna to one reference optical signal in (n-1) reference optical signals generated by the central station;
and the optical filter is used for selecting a required frequency component from the optical signal output by the electro-optical modulator to obtain an echo optical signal.
As a fourth aspect of the present invention, there is provided a microwave photon distributed radar imaging system comprising a central station as described above, a transmitting station as described above and (n-1) receiving stations as described above; wherein the central station and the transmitting station are connected by a length of optical fiber, and are used for transmitting the transmitting optical signal generated by the central station to the transmitting station and introducing a time delay tau to the transmitted signal0(ii) a The central station and each receiving station are connected by two sections of optical fibers, wherein one section is used for transmitting one reference optical signal in (n-1) reference optical signals generated by the central station to the receiving station, and different time delays tau are introduced in the transmitted signalsTmAnother section for transmitting the echo optical signal generated by the receiving station to the central station and introducing a delay τ in the transmitted signalRm(ii) a Two between the central station and the receiving stationThe lengths of optical fibre being multiplexed by the same length of optical fibre, i.e. τTm＝τRm。
As a fifth aspect of the present invention, there is provided a microwave photon distributed radar imaging method, including the steps of:
at the central station, the low-frequency narrow-band chirp electric signal is modulated to n paths of signals with the wavelength of lambda1、λ2、……、λn(when i is not less than 1, j is not more than n and i is not equal, lambdai≠λj) Generating a beam of optical carrier group composed of n carriers each having a wavelength of lambda1、λ2、……、λnThe modulated optical signal of the optical carrier radio frequency signal of (a); splitting the modulated optical signal according to different carrier wavelengths; wherein the carrier wavelength is λ1As an emitted optical signal, with a delay of τ0To a launch station; the other (n-1) carrier wave wavelengths are respectively lambda2、λ3、……、λnRespectively pass through (n-1) paths with the time delay of tauT1、τT2、……、τT(n-1)(when i is not less than 1, j is not less than n-1 and i is not equal to j, τ isTi≠τTj) To (n-1) receiving stations;
at a transmitting station, transmitting optical signals from a central station are input to a photoelectric detector, high-frequency broadband linear frequency modulation electric signals are output, and the high-frequency broadband linear frequency modulation electric signals are transmitted through a transmitting antenna;
at each receiving station, each receiving antenna forms an interference baseline in the direction perpendicular to the plane of the target sight line direction and the target movement direction, receives echo signals from the target, and modulates the echo signals to (n-1) paths of carrier waves from the central station respectively with the wavelength of lambda2、λ3、……、λnOn the reference optical signal, the required frequency components are selected by an optical filter to obtain (n-1) paths of carrier wave with the wavelength of lambda respectively2、λ3、……、λnThe echo optical signals are respectively delayed by (n-1) paths by tauR1、τR2、……、τR(n-1)To a central station, said transmission of the echo optical signalThe optical fibre may be multiplexed with said optical fibre carrying the reference optical signal by the same length of optical fibre, i.e. τTm＝τRm；
At the central station, combining the echo optical signals from the (n-1) receiving stations and inputting the combined echo optical signals to a photoelectric detector to realize parallel deskewing of the echo signals and obtain combined deskew signals of the echo signals; performing analog-to-digital conversion on the combined and deskewed signal, performing Fourier transform in a digital domain, compensating the phase caused by envelope delay of the transmitted signal and the residual video phase to obtain a combined distance compressed signal, wherein the transmission delay (tau) of each reference light signal is71、τT2、……、τT(n-1)) Different, the echoes of the targets received by each receiving station are positioned in different frequency ranges of the beam combination distance compressed signals; multiplying the beam combination distance compressed signal by a corresponding function S according to different frequency rangescm(f)＝exp[j4πf(τTm+τRm)]Completing the transmission phase delay compensation, wherein m is 1, 2, … …, n-1, tauTmIs a carrier wave having a wavelength of λm+1The transmission delay, tau, introduced by the transmission of the reference optical signal through the optical fiberRmIs a carrier wave having a wavelength of λm+1The transmission delay introduced by the transmission of the echo optical signal through the optical fiber; carrying out spectrum segmentation on the compensated beam combination distance compressed signals to obtain (n-1) distance compressed signals corresponding to echo signals received by each receiving station; respectively carrying out azimuth compression to obtain (n-1) two-dimensional complex images; and carrying out registration, channel amplitude and phase consistency compensation and third-dimension phase coherence processing on the two-dimensional complex image to finish three-dimensional imaging of the detection target.
Based on the technical scheme, compared with the prior art, the microwave photon distributed radar imaging system and method disclosed by the invention have at least one of the following beneficial effects:
(1) compared with the traditional electronic distributed array radar, the reference signal and the echo signal are transmitted among the central station, the transmitting station and the receiving stations by means of the optical fiber radio frequency transmission technology, the traditional clock signal transmission method is replaced, signal preprocessing is not needed to be carried out on the receiving stations, and the coherence among the echo signals received by the receiving stations is improved, so that the imaging performance of the third dimension is improved, and meanwhile, the structure of the receiving stations is simplified.
(2) Compared with the traditional high-frequency radio-frequency cable transmission, the optical fiber transmission has the characteristics of small loss, long distance, flat gain and the like, is favorable for expanding the distribution range of the antenna array and increasing the length of a base line, thereby expanding the radar detection range and improving the three-dimensional imaging resolution.
(3) By means of the optical fiber radio frequency transmission technology, different time delays are introduced into the reference signals corresponding to the receiving stations, so that the frequency distribution of the echoes subjected to the deskew processing is different, and by means of the wavelength division multiplexing technology, after the optical signals of the echoes are combined, the parallel deskew processing of the multi-channel echo signals can be realized only through one photoelectric detector, and the system cost and the complexity are reduced.
Drawings
FIG. 1 is a schematic structural view of a central station of the present invention;
fig. 2 is a schematic diagram of the structure of the transmitting station of the present invention;
FIG. 3 is a schematic diagram of the structure of the receiving station of the present invention;
FIG. 4 is a schematic structural diagram of a microwave photon distributed radar imaging system of the present invention;
fig. 5 is a schematic structural diagram of a preferred embodiment of the microwave photon distributed radar imaging system of the present invention.
Detailed Description
The invention discloses a microwave photon distributed radar imaging method. The low-frequency narrow-band linear frequency modulation electrical signal is modulated onto a plurality of paths of optical carriers with different wavelengths, the optical carriers are transmitted to a transmitting station and a plurality of receiving stations through optical fibers with different time delays, the optical carriers are transmitted after photon frequency multiplication at the transmitting station, each receiving station antenna forms an interference baseline in the direction perpendicular to the plane where the sight line direction and the movement direction of a detection target are located, simultaneously echoes of the target are received, the optical signals transmitted from the central station are modulated onto the optical signals and transmitted back to the central station through the optical fibers, and after combination, parallel deskew processing is completed through photoelectric conversion. Three-dimensional imaging is realized through distance compression, transmission phase delay compensation, azimuth compression and third-dimension coherent processing of the deskew signals. The invention also discloses a microwave photon distributed radar imaging system. The invention applies photon frequency multiplication, optical fiber radio frequency transmission and photon parallel deskew processing technology to the distributed radar, realizes three-dimensional imaging under a one-transmitter-multiple-receiver architecture, reduces the system cost and complexity, improves the distribution capability of the antenna array and has high three-dimensional imaging precision.
Specifically, as shown in fig. 1, the present invention discloses a central station, which includes: an array of light sources for generating n channels of light with wavelength λ1、λ2、……、λnThe optical carrier of (a); the first optical beam combiner is used for combining the n paths of optical carriers generated by the light source array to obtain an optical carrier group; the electro-optical modulator is used for modulating the low-frequency narrow-band linear frequency modulation electric signals to the optical carrier group to generate modulated optical signals containing n paths of optical carrier radio-frequency signals; an optical wavelength division multiplexer for splitting the modulated optical signal according to different carrier wavelengths to obtain n paths of carrier wavelengths respectively of lambda1、λ2、……、λnWherein the optical carrier has a wavelength λ1As an emitted optical signal, carrier wavelengths of lambda2、λ3、……、λnThe (n-1) optical carrier radio frequency signal is used as a reference optical signal; a second optical beam combiner for respectively setting the carrier wavelengths as λ2、λ3、……、λnThe echo optical signals are combined to obtain combined optical signals; the photoelectric detector is used for performing photoelectric conversion on the combined beam optical signal generated by the second optical beam combiner to realize parallel deskew processing on the (n-1) path echo signal so as to obtain a combined beam deskew signal; the analog-to-digital converter is used for performing analog-to-digital conversion on the combined beam deskew signal; the digital processor is used for carrying out Fourier transform on the combined beam deskew signals after analog-to-digital conversion and compensating phases caused by envelope delay of the transmitted signals and residual video phases to obtain combined beam distance compressed signals; according to the transmission delay introduced by the reference optical signal through optical fiber transmission, the deskew signal of the echo signal of each receiving station receiving target is positioned in different frequency ranges of the beam combination distance compressed signal, and the beam combination distance compressed signal is multiplied by a corresponding function S according to the different frequency rangescm(f)＝exp[j4πf(τTm+τRm)]Completing the transmission phase delay compensation, wherein m is 1, 2, … …, n-1, tauTmIs a carrier wave having a wavelength of λm+1The transmission delay, tau, introduced by the transmission of the reference optical signal through the optical fiberRmIs a carrier wave having a wavelength of λm+1The transmission delay introduced by the transmission of the echo optical signal through the optical fiber; carrying out spectrum segmentation on the compensated beam combination distance compressed signals to obtain (n-1) distance compressed signals corresponding to echo signals received by each receiving station; respectively carrying out azimuth compression to obtain (n-1) two-dimensional complex images; and carrying out registration, channel amplitude and phase consistency compensation and third-dimension phase coherence processing on the two-dimensional complex image to finish the three-dimensional imaging processing of the detection target.
As shown in fig. 2, the present invention discloses a transmitting station comprising a photodetector for performing photoelectric conversion on an emitted optical signal from a central station to generate a high-frequency broadband chirp electrical signal; and the transmitting antenna is used for transmitting the high-frequency broadband linear frequency modulation electric signal.
As shown in fig. 3, the present invention discloses a receiving station, the number of which is (n-1), comprising: a receiving antenna for receiving an echo signal from a target; the electro-optical modulator is used for modulating the echo signal received by the receiving antenna to one reference optical signal in (n-1) reference optical signals generated by the central station; and the optical filter is used for selecting a required frequency component from the optical signal output by the electro-optical modulator to obtain an echo optical signal.
As shown in FIG. 4, the invention discloses a microwave photon distributed radar imaging system, comprising a central station as described above, a transmitting station as described above and (n-1) receiving stations as described above; wherein the central station and the transmitting station are connected by a length of optical fiber, and are used for transmitting the transmitting optical signal generated by the central station to the transmitting station and introducing a time delay tau to the transmitted signal0(ii) a The central station and each receiving station are connected by two sections of optical fibers, wherein one section is used for transmitting one reference optical signal in (n-1) reference optical signals generated by the central station to the receiving station, and different time delays tau are introduced in the transmitted signalsTmAnd the other section is used forTransmitting the echo optical signal generated by the receiving station to a central station and introducing a delay τ in the transmitted signalRm(ii) a The two lengths of optical fibre between the central station and the receiving station may be multiplexed by the same length of optical fibre, i.e. τTm＝τRm。
In order that the objects, technical solutions and advantages of the present invention will become more apparent, the present invention will be further described in detail with reference to the accompanying drawings in conjunction with the following specific embodiments.
The microwave photon distributed radar imaging system of the present invention, as shown in fig. 5, includes: n lasers, 3 optical wavelength division multiplexers, n Mach-Zehnder modulators, 2 photodetectors, 2 optical amplifiers, n-1 optical filters, n low-noise amplifiers, 1 power amplifier, 1 transmitting antenna, n-1 receiving antennas, 1 analog-to-digital converter, 1 digital processor, and (2n-1) sections of optical fibers.
At the central station, n lasers generate n channels of wavelength λ1、λ2、……、λn(when i is not less than 1, j is not more than n and i is not equal to j, lambda isi≠λj) The optical carrier wave is combined by the optical wavelength division multiplexer 1 and input to the Mach-Zehnder modulator 1 working at the minimum bias point, the low-frequency narrow-band linear frequency modulation electric signal is modulated to the optical carrier wave group by the Mach-Zehnder modulator 1 to generate a modulated optical signal containing n paths of optical carrier radio-frequency signals, and the electric field of the modulated optical signal is
Wherein, ω isiIs a wavelength of λiThe angular frequency corresponding to the optical carrier of (a); omegaIF、kIFAnd TpRespectively the central angular frequency, the modulation frequency and the period of the low-frequency narrow-band signal; j. the design is a square1Is a first order Bessel function, βIF＝πVIF/Vπ1Is the modulation factor; vπ1Of Mach-Zehnder modulator 1A half-wave voltage; vIFIs the amplitude of the low frequency narrowband chirp electrical signal. Since the relative amplitude of the higher order modulation sidebands is small, it is ignored here. The modulated optical signal is amplified by an optical amplifier 1, input to an optical wavelength division multiplexer 2, and split according to the difference of carrier wavelengths, wherein the carrier wavelength is lambda1As an emitted light signal, by a delay of τ0Is transmitted to a transmitting station with a carrier wavelength of lambda2、λ3、……、λnRespectively passing through the modulated optical signals with a delay of tauT1、τT2、……、τT(n-1)(when i is not less than 1, j is not less than n-1 and i is not equal to j, τ isTi≠τTi) The optical fiber is transmitted to (n-1) receiving stations to obtain (n-1) paths of reference optical signals, and the electric fields of the reference optical signals are respectively ETj(t-τT(j-1))，j＝2，3，...，n。
At the transmitting station, the modulated optical signal from the central station is input to the photodetector 1, outputting a high-frequency broadband chirped electrical signal, represented as
The signal is amplified by a low noise amplifier 1 and a power amplifier 1 in sequence and then transmitted by a transmitting antenna.
In a receiving station i (i is 1, 2, … …, n-1), a receiving antenna i receives an echo signal of a target, amplifies the echo signal by a low noise amplifier (i +1), modulates the amplified echo signal by a Mach-Zehnder modulator (i +1) operating at an orthogonal bias point to a reference optical signal from a central station, and outputs a signal represented by
Wherein tau isref_i＝τTi-τ0；J0Is a zero order first class Bessel function; tau isecho_iIs the transmission time of the signal from the transmitting antenna to the target and then to the receiving antenna i;
is the modulation factor of the mach-zehnder modulator (i + 1); vπ(i+1)Is the half-wave voltage of the mach-zehnder modulator (i + 1); viIs the amplitude of the echo signal received by the receiving antenna i. In the formula (3), E1、E2、E3、E4、E5And E6Respectively represent different frequency components, are shown as
Wherein, h is 1, 2, l is 3, 4, m is 5, 6. Optical filter i selects frequency component E1And E4Then, an echo optical signal i is obtained with a delay of τRiTo a central station.
At the central station, the echo optical signals from the (n-1) receiving stations are combined by the optical wavelength division multiplexer 3, amplified by the optical amplifier 2 and input to the photoelectric detector 2, so that parallel deskew processing of the echo signals is realized, and combined deskew signals of the echo signals are obtained, which are represented as combined deskew signals
Wherein, Δ τi＝τref_i-τecho_i＝τTi-τ0-τecho_i，τi＝τTi+τRi，fRF＝2fIFAnd kRF＝2kIFFrequency and modulation frequency, V, of the transmitted signalRiCorresponding to the amplitude of the deskew signal of the echo at the receiving station i. As can be seen from equation (5), echo signals received by different receiving stations are processed in parallel and then have a frequency kRFΔτiFrequency of the same and time delay tau of optical fiber transmissionTiProportional to the spatial transmission delay tauecho_iIn inverse proportion. Due to the fibre delay (tau) traversed by the reference optical signal transmitted from the central station to the receiving stationsT1、τT2、……、τT(n+1)) In contrast, the echo deskew signal SRiAlso have different frequencies, so that the signals can be deskewed from the combined beamAnd the signals are distinguished and extracted from the frequency spectrum, so that the parallel deskewing processing of the multi-channel echo is realized. Sampling the beam deskew signal through an analog-to-digital converter, performing Fourier transform in a digital domain through a digital processor, and compensating a phase caused by envelope delay of a transmitted signal and a residual video phase to obtain a beam combination distance compressed signal expressed as
Wherein, Tp′＝Tp-ΔτiAnd f is the fast time frequency. The last two phases of the above formula-2 π kRFΔτiτi-2τfτiIs transmitted by optical fibre with a delay taui＝τTi+τRiThe introduced phase delay, during three-dimensional imaging, can cause azimuthal position errors and deteriorate the phase coherence of the third dimension. Because the echo signal is changed into a sinc function with narrow width after distance compression, the peak value is positioned at f-kRFΔτiTherefore, when the above-mentioned transmission phase delay is compensated, as long as the compensation f is kRFΔτiThe phase of (b) is such that the last two phases of the above equation are written as
Δφ＝-4πfτi. (7)
Multiplying the transmission delay of the beam combination distance compressed signal by the corresponding function S according to the receiving stations corresponding to different frequency rangesci(f)＝exp[j4πcf(τTi+τRi)]Wherein i is 1, 2, … …, n-1, then the transmission phase delay compensation can be completed; the compensated combined beam distance compressed signal is expressed as
Wherein R isref_i＝cτref_i/2＝c(τTi-τ0)/2，RTAnd RRiThe distance of the antenna to the transmitting station and the receiving station i, respectively. Compressing the compensated beam combination distance into a signal IRPerforming spectrum segmentation to obtain connections with each receiving stationReceiving (n-1) distance compressed signals corresponding to the echo signals; then respectively carrying out azimuth compression to obtain (n-1) two-dimensional complex images which are represented as
Wherein f ismIs the Doppler frequency, VTAnd VRiThe radial velocity of the target relative to the transmitting station and the receiving station i, respectively, λ is the center wavelength of the transmitted signal, and the two sinc functions respectively contain the range and doppler information of the detected target. And when the (n-1) receiving antennas form an interference baseline in the direction vertical to the plane where the sight line direction and the movement direction of the detection target are located, performing registration, channel amplitude phase consistency compensation and third-dimension phase coherence processing on the two-dimensional complex image, and thus completing three-dimensional imaging of the detection target.
The above-mentioned embodiments are intended to illustrate the objects, technical solutions and advantages of the present invention in further detail, and it should be understood that the above-mentioned embodiments are only exemplary embodiments of the present invention and are not intended to limit the present invention, and any modifications, equivalents, improvements and the like made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (10)
1. A central station, comprising:
an array of light sources for generating n channels of light with wavelength λ1、λ2、……、λnThe optical carrier of (a);
the first optical beam combiner is used for combining the n paths of optical carriers generated by the light source array to obtain an optical carrier group;
the electro-optical modulator is used for modulating the low-frequency narrow-band linear frequency modulation electric signals to the optical carrier group to generate modulated optical signals containing n paths of optical carrier radio-frequency signals;
an optical wavelength division multiplexer for splitting the modulated optical signal according to different carrier wavelengths to obtain n paths of carrier wavelengths respectively of lambda1、λ2、……、λnWherein the optical carrier has a wavelength λ1As an emitted optical signal, carrier wavelengths of lambda2、λ3、……、λnThe (n-1) optical carrier radio frequency signal is used as a reference optical signal;
a second optical beam combiner for respectively setting the carrier wavelengths as λ2、λ3、……、λnThe echo optical signals are combined to obtain combined optical signals;
the photoelectric detector is used for performing photoelectric conversion on the combined beam optical signal generated by the second optical beam combiner to realize parallel deskew processing on the (n-1) path echo signal so as to obtain a combined beam deskew signal;
the analog-to-digital converter is used for performing analog-to-digital conversion on the combined beam deskew signal;
and the digital processor is used for performing digital domain processing on the combined beam deskew signal after analog-to-digital conversion.
2. The central station of claim 1, wherein the digital processor performs fourier transform on the analog-to-digital converted combined beam deskew signal, compensates for phase due to envelope delay of the transmit signal, and compensates for residual video phase to obtain a combined beam distance compressed signal; according to the transmission delay introduced by the reference optical signal through optical fiber transmission, the deskew signal of the echo signal of each receiving station receiving target is positioned in different frequency ranges of the beam combination distance compressed signal, and the beam combination distance compressed signal is multiplied by a corresponding function S according to the different frequency rangescm(f)＝exp[j4πf(τTm+τRm)]Completing the transmission phase delay compensation, wherein m is 1, 2, … …, n-1, tauTmIs a carrier wave having a wavelength of λm+1The transmission delay, tau, introduced by the transmission of the reference optical signal through the optical fiberRmIs a carrier wave having a wavelength of λm+1The transmission delay introduced by the transmission of the echo optical signal through the optical fiber; carrying out spectrum segmentation on the compensated beam combination distance compressed signals to obtain (n-1) distance compressed signals corresponding to echo signals received by each receiving station; respectively carrying out azimuth compression to obtain (n-1) two-dimensional complex images; registering two-dimensional complex imagesAnd performing amplitude-phase consistency compensation and third-dimension phase coherence processing on the channel to finish three-dimensional imaging processing on the detection target.
3. The hub of claim 1, wherein said electro-optic modulator is a mach-zehnder modulator operating at a minimum bias point and corresponding to a carrier and even-order suppressed double sideband modulation, whereby said high frequency broadband chirp signal has a center frequency and bandwidth that are 2 times greater than said low frequency narrowband chirp signal.
4. A transmitting station, comprising:
the photoelectric detector is used for carrying out photoelectric conversion on the emission light signal from the central station to generate a high-frequency broadband linear frequency modulation electric signal;
and the transmitting antenna is used for transmitting the high-frequency broadband linear frequency modulation electric signal.
5. A receiving station, wherein the number of receiving stations is (n-1), comprising:
a receiving antenna for receiving an echo signal from a target;
the electro-optical modulator is used for modulating the echo signal received by the receiving antenna to one reference optical signal in (n-1) reference optical signals generated by the central station;
and the optical filter is used for selecting a required frequency component from the optical signal output by the electro-optical modulator to obtain an echo optical signal.
6. The receiving station of claim 5, comprising:
the electro-optical modulator of the receiving station is a phase modulator or a Mach-Zehnder modulator working at a quadrature bias point; the optical filter has a passband containing a frequency component of ωm+ωIFAnd ωm-ωIF+ωRFWherein, ω ismThe receiving station receiving the reference optical signal from the central stationCarrier wave length lambdam+1Corresponding angular frequency, ωIFIs the central angular frequency, ω, of the low-frequency narrowband signalRFIs the central angular frequency of the high frequency broadband chirp electrical signal.
7. A microwave photonic distributed radar imaging system comprising a central station according to claims 1-3, a transmitting station according to claim 4 and (n-1) receiving stations according to claims 5-6; wherein the central station and the transmitting station are connected by a length of optical fiber, and are used for transmitting the transmitting optical signal generated by the central station to the transmitting station and introducing a time delay tau to the transmitted signal0(ii) a The central station and each receiving station are connected by two sections of optical fibers, wherein one section is used for transmitting one reference optical signal in (n-1) reference optical signals generated by the central station to the receiving station, and different time delays tau are introduced in the transmitted signalsTmAnother section for transmitting the echo optical signal generated by the receiving station to the central station and introducing a delay τ in the transmitted signalRm(ii) a The two lengths of optical fibre between the central station and the receiving station may be multiplexed by the same length of optical fibre, i.e. τTm＝τRm。
8. A microwave photon distributed radar imaging method is characterized by comprising the following steps:
at the central station, the low-frequency narrow-band chirp electric signal is modulated to n paths of signals with the wavelength of lambda1、λ2、……、λn(when i is not less than 1, j is not more than n and i is not equal to j, lambda isi≠λj) Generating a beam of optical carrier group composed of n carriers each having a wavelength of lambda1、λ2、……、λnThe modulated optical signal of the optical carrier radio frequency signal of (a); splitting the modulated optical signal according to different carrier wavelengths; wherein the carrier wavelength is λ1As an emitted optical signal, with a delay of τ0To a launch station; the other (n-1) carrier wave wavelengths are respectively lambda2、λ3、……、λnOptical carrier radio frequency signalThe signal is used as a reference optical signal and is delayed by tau through (n-1) pathsT1、τT1、τT2、……、τT(n-1)(when i is not less than 1, j is not less than n-1 and i is not equal to j, τ isTi≠τTj) To (n-1) receiving stations;
at a transmitting station, transmitting optical signals from a central station are input to a photoelectric detector, high-frequency broadband linear frequency modulation electric signals are output, and the high-frequency broadband linear frequency modulation electric signals are transmitted through a transmitting antenna;
at each receiving station, each receiving antenna forms an interference baseline in the direction perpendicular to the plane of the target sight line direction and the target movement direction, receives echo signals from the target, and modulates the echo signals to (n-1) paths of carrier waves from the central station respectively with the wavelength of lambda2、λ3、……、λnOn the reference optical signal, the required frequency components are selected by an optical filter to obtain (n-1) paths of carrier wave with the wavelength of lambda respectively2、λ3、……、λnThe echo optical signals are respectively delayed by (n-1) paths by tauR1、τR2、……、τR(n-1)Can be multiplexed with the optical fiber transmitting the reference optical signal by the same optical fiber section, i.e. τTm＝τRm；
At the central station, combining the echo optical signals from the (n-1) receiving stations and inputting the combined echo optical signals to a photoelectric detector to realize parallel deskewing of the echo signals and obtain combined deskew signals of the echo signals; performing analog-to-digital conversion on the combined and deskewed signal, performing Fourier transform in a digital domain, compensating the phase caused by envelope delay of the transmitted signal and the residual video phase to obtain a combined distance compressed signal, wherein the transmission delay (tau) of each reference light signal isT1、τT2、……、τT(n-1)) Different, the echoes of the targets received by each receiving station are positioned in different frequency ranges of the beam combination distance compressed signals; multiplying the beam combination distance compressed signal by a corresponding function S according to different frequency rangescm(f)＝exp[j4πf(τTm+τRm)]Completing the transmission phase delay compensation, wherein m is 1, 2, … …, n-1, tauTmIs a carrier wave having a wavelength of λm+1The transmission delay, tau, introduced by the transmission of the reference optical signal through the optical fiberRmIs a carrier wave having a wavelength of λm+1The transmission delay introduced by the transmission of the echo optical signal through the optical fiber; carrying out spectrum segmentation on the compensated beam combination distance compressed signals to obtain (n-1) distance compressed signals corresponding to echo signals received by each receiving station; respectively carrying out azimuth compression to obtain (n-1) two-dimensional complex images; and carrying out registration, channel amplitude and phase consistency compensation and third-dimension phase coherence processing on the two-dimensional complex image to finish three-dimensional imaging of the detection target.
9. The method according to claim 8, wherein the modulation scheme of the low-frequency narrow-band signal on the n-path optical carrier is carrier and even-order suppressed double-sideband modulation, and the center frequency and the bandwidth of the high-frequency wide-band chirp signal output by the photo detector of the transmitting station obtained by the modulation scheme are both 2 times of the low-frequency narrow-band chirp signal.
10. The method according to claim 8, wherein the echo signal of each receiving station modulates the reference light signal from the central station by phase modulation or intensity modulation; the angular frequency component contained in the optical signal input to the optical filter has ωm±ωIF、ωm+ωIF±ωRF、ωm-ωIF±ωRFEtc. wherein ω ismIs the carrier wavelength lambda of the reference optical signal received by the receiving station from the central stationm+1Corresponding angular frequency, ωIFIs the central angular frequency, ω, of the low-frequency narrowband signalRFIs the central angular frequency of the high frequency broadband chirp electrical signal; the optical filter selects a frequency component of ωm+ωIFAnd ωm-ωIF+ωRF。
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