CN116626693A - Coherent microwave photon radar detection method and system based on photon frequency multiplication - Google Patents
Coherent microwave photon radar detection method and system based on photon frequency multiplication Download PDFInfo
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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
- G01S17/00—Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
- G01S17/02—Systems using the reflection of electromagnetic waves other than radio waves
- G01S17/06—Systems determining position data of a target
- G01S17/08—Systems determining position data of a target for measuring distance only
- G01S17/10—Systems determining position data of a target for measuring distance only using transmission of interrupted, pulse-modulated waves
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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
- G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
- G01S7/483—Details of pulse systems
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Abstract
The invention discloses a coherent microwave photon radar detection method based on photon frequency multiplication, which comprises the steps of loading a baseband linear sweep frequency signal on an optical carrier signal to obtain a modulated optical signal; dividing the modulated optical signals into two paths, wherein one path of modulated optical signals is subjected to photoelectric conversion and then reflected by a target object to obtain radar echo signals; the other path of modulated optical signals are decomposed through a signal selector, and one of high-order linear sweep frequency sideband signals which are obtained after decomposition and only contain positive sweep frequency sidebands and only contain negative sweep frequency sidebands is used as a reference optical signal, and the other is used as a received optical signal; loading the radar echo signal on the received light signal to obtain a radar received light signal; and performing coherent reception on the reference optical signal and the radar receiving optical signal to obtain a complex intermediate frequency signal to finish detection. The frequency multiplication factor is flexible and adjustable, the system detection precision is high, and the anti-interference performance is excellent. The invention also provides a coherent microwave photon radar detection system based on photon frequency multiplication.
Description
Technical Field
The invention belongs to a radar detection method, and particularly relates to a coherent microwave photon radar detection method and system based on photon frequency multiplication.
Background
Real-time high-precision multifunctional radar detection is one of the main directions of development of modern radar technology, and is widely applied to the military and civil fields. In order to improve the detection precision and real-time performance of the radar, the radar is required to have higher working bandwidth and stronger anti-interference capability, and the signal can be processed and analyzed in real time with high precision.
The literature [ S.Kim, N.Myung, "Wideband linear frequency modulatedwaveform compensation using system predistortion and phase coefficientsextraction method," IEEE Microwave and Wireless Components Letters, vol.17, no.11, pp.808-810,2007 ] discloses that the current bottleneck limit of electronic technology is limited, and potential amplitude/phase nonlinear effects exist when the radio frequency amplification, matching and transmission links bear functions of generating, sampling, processing and the like of broadband signals, so that the development of radars to high-frequency broadband is limited.
Document [ J.Mckiney, "Photonics illuminates the future of radar," Nature, vol.507, no.7492, pp.310-312,2014 ] discloses that optical domain generation, transmission, processing of microwave signals, such as photon mixing, photon sampling, photon true time delay, etc., are beneficial to rapid development of microwave photon technology, and provide new technical support for overcoming the bottleneck problem of traditional radar electronics, improving technical performance, and becoming a key technology of next-generation radars.
Document [ F.Zhang, Q.Guo, Z.Wang, etc., "Photonics-based broadband radarfor high-resolution and real-time inverse synthetic aperture imaging," optics express, vol.25, no.14, pp.16274-16281,2017 ] discloses that techniques such as wideband radar detection signal generation based on photon frequency doubling techniques, and wideband radar echo signal real-time reception processing based on photon mixing techniques have been used in new radar reception techniques.
However, the current radar detection scheme for realizing the generation and the reception of the broadband radar signal based on the photon frequency multiplication technology is limited by the system architecture, which adopts a direct detection technology, and the high signal-to-noise ratio radar signal reception cannot be realized. In addition, the intermediate frequency signal phase information cannot be directly acquired, and compared with coherent detection, the method has no advantage in detection precision.
Although coherent microwave photon radar detection schemes based on photon frequency doubling technology are proposed as in the literature [ Ye X, zhang F, yang Y, et al photonics-based radar withbalanced I/Q de-chirping for interference-supported high-resolution detectionand imaging, 2019,7 (3): 265-272 ], the scheme is limited by structural architecture limitations of the scheme, the frequency doubling factor of the scheme is limited, and the frequency doubling factor cannot be flexibly adjusted.
Disclosure of Invention
The invention provides a coherent microwave photon radar detection method based on photon frequency multiplication, which can enable the frequency multiplication factor of a frequency multiplication radar emission signal to be flexibly adjustable, and has high system detection precision and excellent anti-interference performance.
The specific embodiment of the invention provides a coherent microwave photon radar detection method based on photon frequency multiplication, which comprises the following steps:
loading a baseband linear sweep frequency signal on an optical carrier signal through a photon frequency multiplication unit to obtain a modulated optical signal, wherein the modulated optical signal is a high-order linear sweep frequency sideband signal containing positive and negative sweep frequency sidebands;
dividing the modulated optical signals into two paths, wherein one path of modulated optical signals is converted into frequency multiplication radar emission signals through photoelectric conversion, and the frequency multiplication radar emission signals are reflected by a target object to obtain radar echo signals;
the other path of modulated optical signals are decomposed through a signal selector, and one of high-order linear sweep frequency sideband signals which are obtained through decomposition and only contain positive sweep frequency sidebands and only contain negative sweep frequency sidebands is used as a reference optical signal, and the other one is used as a receiving optical signal;
loading a radar echo signal on a received light signal through an electro-optical modulator to obtain a radar received light signal;
and carrying out coherent reception on the reference optical signal and the radar receiving optical signal to obtain a complex intermediate frequency signal carrying target information, and completing detection.
Further, the frequency is f by a photon frequency multiplier LFM Is loaded on a baseband linear sweep frequency signal with the frequency f c Obtain a modulated optical signal from an optical carrier signal having a frequency f c +Mf LFM Higher order linear swept sideband signal comprising a positive swept sideband and having frequency f c -Nf LFM Is composed of a high-order linear sweep sideband signal containing a negative sweep sideband, wherein M and N are the orders of the sweep sidebands, and M+N is the multiple of photon frequency multiplication.
Further, the frequency f of the baseband linear sweep signal LFM The method comprises the following steps:
f LFM ＝f 0 +kt(0≤t≤T)
wherein f 0 The starting frequency of the baseband chirp signal is that k is the frequency modulation slope, T is the signal period and T is the pulse width.
Further, the one-path modulated optical signal is converted into a frequency multiplication radar transmitting signal through photoelectric conversion, and the method comprises the following steps:
one path of modulated optical signal is subjected to photoelectric conversion to obtain an electric signal, the electric signal is subjected to power amplification to obtain a frequency multiplication radar transmitting signal, and the frequency multiplication radar transmitting signal is transmitted through a transmitting antenna.
Further, after the frequency multiplication radar emission signal meets the reflection of a target object to obtain a radar echo signal, the radar echo signal is subjected to low-noise amplification, and the radar echo signal subjected to low-noise amplification is input into the electro-optical modulator.
Further, the reference optical signal and the radar receiving optical signal are subjected to coherent reception to obtain a complex intermediate frequency signal carrying target information, wherein the complex intermediate frequency signal consists of two paths of orthogonal intermediate frequency signals carrying target information.
Further, after two paths of orthogonal intermediate frequency signals carrying target information are obtained, the two paths of orthogonal intermediate frequency signals are subjected to analog-to-digital conversion to obtain digital signals, and the digital signals are subjected to radar digital signal processing to extract information of a target object.
The specific embodiment of the invention also provides a coherent microwave photon radar detection system based on photon frequency multiplication, which comprises:
a laser source for emitting an optical carrier signal;
the baseband signal source is used for transmitting a baseband linear sweep frequency signal;
the photon frequency doubling unit is used for loading the baseband linear sweep frequency signal on the optical carrier signal to obtain a modulated optical signal, wherein the modulated optical signal is a high-order linear sweep frequency sideband signal containing positive and negative sweep frequency sidebands;
an optical coupler for dividing the modulated optical signal into two paths;
the photoelectric detector is used for converting one path of modulated optical signals into frequency multiplication radar emission signals;
the signal selection unit is used for decomposing the other path of modulated optical signal into a high-order linear sweep frequency side band signal only comprising a positive sweep frequency side band and a high-order linear sweep frequency side band signal only comprising a negative sweep frequency side band through the signal selector, and taking one of the high-order linear sweep frequency side band signal only comprising the positive sweep frequency side band and the high-order linear sweep frequency side band signal only comprising the negative sweep frequency side band as a reference optical signal and the other as a receiving optical signal;
the electro-optical modulator is used for loading a radar echo signal on the received light signal to obtain a radar received light signal, and the radar echo signal is obtained by reflecting a frequency multiplication radar transmitting signal by a target object; and
and the coherent receiving unit carries out coherent receiving on the reference optical signal and the radar receiving optical signal to obtain a complex intermediate frequency signal carrying target information, and detection is completed.
Further, the coherent receiving unit comprises a 90-degree optical coupler and two balanced detectors;
the 90-degree optical coupler is used for introducing 90-degree phase difference into the obtained radar receiving optical signal and the reference optical signal in an optical domain to obtain four paths of composite optical signals;
and the two balanced photoelectric detectors are used for respectively carrying out photoelectric detection on the four paths of composite optical signals output by the 90-degree optical coupler to obtain two paths of orthogonal intermediate frequency signals carrying target information.
Further, the photon frequency doubling unit is a single integrated electro-optical modulator or a multi-device cascading unit, the single integrated electro-optical modulator is a Mach-Zehnder modulator, a double parallel Mach-Zehnder modulator or a polarization multiplexing double parallel Mach-Zehnder modulator, and the multi-device cascading unit is an optical frequency comb generator cascading optical filter, an electro-optical modulator cascading nonlinear optical fiber or an optical filter.
Compared with the prior art, the invention has the beneficial effects that:
the radar echo signal is loaded on the sweep frequency side band obtained by separating the modulated optical signal, and the optical carrier signal is not required to be reserved for receiving the radar echo signal, so that the photon frequency multiplication technology is not limited by carrying out on the optical carrier signal, namely, the loading of the baseband linear sweep frequency signal on the optical carrier signal phase is not limited, and the generation of the broadband radar transmitting signals with different frequency multiplication factors can be realized more flexibly.
The invention realizes the real-time coherent reception of the broadband radar echo signal by the sideband separation and coherent receiving technology of the modulated optical signal, realizes the real-time coherent de-frequency modulation processing of the broadband radar echo signal in the photoelectric domain, can effectively inhibit common mode noise and image interference signals, and improves the radar detection signal to noise ratio.
The signal generating part of the invention, the high-order side band of the modulated optical signal inherits the advantages of high linearity of the baseband linear sweep frequency signal, and the like, and the phase relation between different side bands is fixed, thereby ensuring the performances of linearity, signal-to-noise ratio, and the like of the frequency doubling radar detection signal.
Drawings
FIG. 1 is a flow chart of a method for detecting a coherent microwave photon radar based on photon frequency multiplication according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of a coherent microwave photon radar detection system based on photon frequency multiplication according to an embodiment of the present invention;
FIG. 3 is a schematic diagram of a coherent microwave photon radar detection system based on photon frequency multiplication according to an embodiment;
FIG. 4 is a schematic diagram of signal spectrum and signal generated at a corresponding node by using a photon frequency multiplication coherent microwave photon radar detection method according to an embodiment;
fig. 5 is a schematic structural diagram of a coherent receiving unit according to an embodiment of the present invention.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention. The features of the following examples and embodiments may be combined with each other without any conflict.
Unless otherwise indicated, terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art. In addition, it will be appreciated that terms defined in commonly used dictionaries should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense.
Aiming at the defects of the prior art, the thought of the invention is to generate a wideband and tunable linear frequency modulation radar transmitting signal based on a photon frequency doubling technology, and realize the coherent receiving of a wideband echo signal by a photon coherent receiving method. The radar working parameter of the scheme is flexible and adjustable, the signal processing is real-time and efficient, and the stray resistance is high.
The embodiment of the invention provides a coherent microwave photon radar detection method based on photon frequency multiplication, which is shown in figure 1 and comprises the following steps:
s1, obtaining a modulated optical signal, and loading a baseband linear sweep frequency signal on an optical carrier signal through a photon frequency multiplication unit to obtain the modulated optical signal, wherein the modulated optical signal is a high-order linear sweep frequency sideband signal containing positive and negative sweep frequency sidebands.
In one embodiment, the baseband signal source generates a frequency f LFM The baseband linear sweep frequency signal of (2) is converted into f by a photon frequency multiplier LFM Is loaded on a baseband linear sweep frequency signal with the frequency f c Obtain a modulated optical signal from an optical carrier signal having a frequency f c +Mf LFM Higher order linear swept sideband signal comprising a positive swept sideband and having frequency f c -Nf LFM Comprising a higher order of negative swept sidebandsAnd the linear sweep frequency sideband signal is composed, wherein M and N are multiples of photon frequency multiplication and are positive integers.
In one embodiment, the present invention provides a frequency f of a baseband linear sweep signal LFM The method comprises the following steps:
f LFM ＝f 0 +kt(0≤t≤T)
wherein f 0 The starting frequency of the baseband chirp signal is that k is the frequency modulation slope, T is the signal period and T is the pulse width.
S2, obtaining radar echo signals, dividing the modulated optical signals into two paths, and converting one path of modulated optical signals into frequency (M+N) f through photoelectric conversion LFM The frequency multiplication radar emission signal meets the reflection of a target object to obtain a radar echo signal.
In a specific embodiment, the photon frequency doubling unit is implemented by single integrated electro-optical modulators such as Mach-Zehnder modulators, double parallel Mach-Zehnder modulators, polarization multiplexing double parallel Mach-Zehnder modulators, or multi-device cascading units such as cascading optical filters of optical frequency comb generators, cascading nonlinear optical fibers of electro-optical modulators, optical filters, and the like; the specific frequency multiplication factor (M+N) is determined according to the specific implementation method of the photon frequency multiplication unit.
In a specific embodiment, one path of modulated optical signal is subjected to photoelectric conversion to obtain an electric signal, the electric signal is subjected to power amplification to obtain a frequency multiplication radar transmitting signal, the frequency multiplication radar transmitting signal is transmitted through a transmitting antenna to detect a target object, after the frequency multiplication radar transmitting signal encounters the target object and is reflected to obtain a radar echo signal, the radar echo signal is subjected to low-noise amplification, and the radar echo signal subjected to low-noise amplification is input into an electro-optical modulator.
In a specific embodiment, parameters such as a period, a time width, a bandwidth, a carrier frequency and the like of a frequency multiplication radar transmitting signal provided by the specific embodiment of the invention can be realized by setting parameters such as a period, a time width, a bandwidth, a carrier frequency and the like of a baseband linear sweep signal and a photon frequency multiplication unit frequency multiplication factor (M+N).
S3, obtaining a reference optical signal and a received optical signal, and the other path of modulated optical signal is communicatedThe over-signal selector is decomposed into a frequency f c +Mf LFM Is comprised of only positive swept sideband high order linear swept sideband signal and has frequency f c -Nf LFM Is a high order linear swept sideband signal comprising only a negative swept sideband, the frequency is f c +Mf LFM Is comprised of only positive swept sideband high order linear swept sideband signal and has frequency f c -Nf LFM One of the high-order linear swept sideband signals containing only the negative swept sideband is used as a reference optical signal and the other is used as a receive optical signal.
In one embodiment, the signal selector is an optical filter, a demultiplexer, a beam shaper, or the like, which may implement optical signal filtering.
S4, loading the radar echo signal on the received optical signal through the electro-optical modulator to obtain a radar received optical signal.
In a particular embodiment, the electro-optic modulator is a Mach-Zehnder modulator, a phase modulator, an electro-absorption modulator, a micro-ring modulator, or the like.
S5, carrying out coherent reception on the reference optical signal and the radar receiving optical signal to obtain a complex intermediate frequency signal carrying target information, and completing detection.
In a specific embodiment, the reference optical signal and the radar received optical signal are coherently received to obtain a complex intermediate frequency signal carrying the target information, wherein the complex intermediate frequency signal is composed of two paths of orthogonal intermediate frequency signals carrying the target information.
In a specific embodiment, after two paths of orthogonal intermediate frequency signals carrying target information are obtained, the two paths of orthogonal intermediate frequency signals are subjected to analog-to-digital conversion to obtain digital signals, and the digital signals are subjected to radar digital signal processing to extract the information of the target object.
The embodiment of the invention also provides a coherent microwave photon radar detection system based on photon frequency multiplication, as shown in fig. 2, comprising:
comprising the following steps: the device comprises a laser, a baseband signal source, a photon frequency multiplication unit, an optical coupler, a photoelectric detector, a power amplifier, a transmitting antenna, a Receiving Antenna (RA), a low-noise amplifier, a signal selection unit, an electro-optical modulator, a coherent receiving unit and a signal acquisition and processing unit.
The laser provided by the embodiment of the invention is used for generating the optical carrier signal f C ；
The baseband signal source provided by the embodiment of the invention is used for generating the frequency f LFM Baseband chirp signals of (a);
the photon frequency multiplication unit provided by the embodiment of the invention is used for modulating a baseband linear frequency modulation signal onto an optical carrier signal to obtain a modulated optical signal comprising two high-order linear sweep frequency sidebands;
the optical coupler provided by the embodiment of the invention is used for dividing the modulated optical signal into two paths and sending the two paths of modulated optical signals into the photoelectric detector and the signal selection unit respectively;
the photoelectric detector provided by the embodiment of the invention is used for carrying out photoelectric conversion on one path of modulated optical signals to obtain a frequency multiplication radar emission signal;
the power amplifier and the transmitting antenna provided by the embodiment of the invention are used for carrying out power amplification and signal transmission on the frequency multiplication radar transmitting signal;
the receiving antenna and the low-noise amplifier provided by the embodiment of the invention are used for receiving radar echo signals and amplifying the radar echo signals with low noise;
the signal selection unit provided by the embodiment of the invention is used for dividing another path of modulated optical signal into two high-order linear sweep frequency sideband signals, and sending one path of the two high-order linear sweep frequency sideband signals serving as a reference optical signal to one input end of the coherent receiving unit, and sending the other path of the two high-order linear sweep frequency sideband signals serving as a receiving optical signal to the electro-optical modulator;
the electro-optical modulator provided by the embodiment of the invention is used for modulating the low-noise amplified radar echo signal to a received light signal to obtain a radar received light signal, and sending the radar received light signal to the other input end of the coherent receiving unit;
the coherent receiving unit provided by the embodiment of the invention is used for carrying out coherent detection on a radar received optical signal and a reference optical signal to obtain two paths of orthogonal intermediate frequency signals carrying target information;
the signal acquisition and processing unit provided by the embodiment of the invention is used for carrying out analog-to-digital conversion on two paths of orthogonal intermediate frequency signals and carrying out radar digital signal processing to extract target information.
The coherent receiving unit provided by the embodiment of the invention comprises: the 90-degree optical coupler is used for introducing a 90-degree phase difference between an input radar receiving optical signal and a reference optical signal in an optical domain and outputting four paths of composite optical signals; the two balanced photoelectric detectors are used for respectively carrying out photoelectric detection on four paths of composite optical signals output by the 90-degree optical coupler to obtain two paths of orthogonal intermediate frequency signals carrying target information;
the application process of the coherent microwave photon radar detection system based on photon frequency multiplication provided by the specific embodiment of the invention is as follows: first, at the radar transmitting end, the frequency generated by the baseband signal source is f LFM The baseband linear sweep frequency signal of (2) is loaded to a laser source through a photon frequency doubling unit to generate a frequency f C Generates an optical carrier wave comprising a positive swept sideband f C +Mf LFM And negative sweep sideband f C -Nf LFM Two higher order linear swept sidebands of the modulated optical signal, where M and N are positive integers. The optical coupler divides the modulated optical signal into two paths; one path of modulated optical signal is subjected to photoelectric conversion by a photoelectric detector to obtain a frequency (M+N) f LFM The frequency multiplication radar transmitting signal is amplified by a power amplifier and then transmitted by a transmitting antenna.
At the radar receiving end, radar transmitting signals are reflected by targets to obtain radar echo signals, and the radar echo signals are amplified through a low-noise amplifier after being received by a receiving antenna.
The other path of the modulated optical signal output by the optical coupler provided by the embodiment of the invention is divided into two paths by the signal selector, wherein one path only comprises a positive sweep frequency sideband f C +Mf LFM The other path is a high-order linear sweep frequency sideband signal which only comprises a negative sweep frequency sideband f C -Nf LFM Higher order linear swept sideband signals; one of the two paths of high-order linear sweep frequency sideband signals is used as a reference signal to be sent into a coherent receiving unit, and the other path of high-order linear sweep frequency sideband signals is used as a received light signal to pass throughThe electro-optical modulator receives the radar echo signal amplified by the low-noise amplifier to obtain a radar receiving optical signal; and sending the radar received optical signal into a coherent receiving unit to realize coherent detection with a reference signal, so as to obtain a complex intermediate frequency signal carrying target information. And the signal acquisition and processing unit acquires and processes the intermediate frequency signal, and extracts and obtains detection target information.
For the convenience of public understanding, the following further details of the technical scheme of the present invention are described by a specific example:
examples
The coherent microwave photon radar detection system based on photon frequency multiplication provided in this embodiment, as shown in fig. 3, includes: 1 laser, 1 baseband signal source, 1 double parallel Mach-Zehnder modulator (DPMZM), 1 optical coupler, 1 photo detector, 1 power amplifier, 1 transmitting antenna, 1 receiving antenna, 1 low noise amplifier, 1 wavelength division multiplexer (DWDM), 1 Mach-Zehnder modulator (MZM), 1 coherent receiving unit, 1 signal acquisition and processing unit.
The coherent microwave photon radar detection system based on photon frequency multiplication provided in this embodiment firstly outputs a laser source with a frequency f C The frequency generated by the baseband signal source is f LFM ＝f 0 The baseband linear frequency modulation signal of +kt (T is more than or equal to 0 and less than or equal to T) is modulated on the basis of a double parallel Mach-Zehnder modulator (DPMZM) to obtain a modulated optical signal, wherein f 0 The starting frequency of the baseband chirp signal is that k is the frequency modulation slope, T is the signal period and T is the pulse width.
The embodiment enables the double parallel Mach-Zehnder modulator (DPMZM) to work in a quadruple frequency state by modulating the sub-modulator of the double parallel Mach-Zehnder modulator (DPMZM) and modulating the input bias voltage, thereby outputting a frequency-swept sideband f containing positive frequency at the output end of the double parallel Mach-Zehnder modulator (DPMZM) C +2f LFM And negative sweep sideband f C -2f LFM The spectrum distribution of the obtained modulated optical signals is shown as A in figure 4, and the modulated optical signals are S M (t)：
S M (t)＝A 1 exp[j2π(f C t-2f 0 t-kt 2 ]+A 2 exp[j2π(f C t+2f 0 t+kt 2 ](0≤t≤T)
Wherein A is 1 And A is a 2 The amplitudes of the two sweep sidebands are respectively. The modulated optical signal is divided into two parts by an Optical Coupler (OC), and one path of modulated optical signal is subjected to photoelectric conversion to obtain the frequency of 4f LFM The frequency spectrum distribution of the radar transmission signal is shown as D in fig. 4.
The embodiment of the invention provides a time domain signal S of a radar transmitting signal Tr (t) is:
S Tr (t)＝A Tr exp[j2π(4f 0 t+2kt 2 ](0≤t≤T)
wherein A is Tr The amplitude of the radar transmit signal transmitted for the transmit antenna. The radar transmitting signal is reflected by the target to obtain a radar echo signal, and the radar echo signal is received by a receiving antenna and amplified by a low noise amplifier. If the delay of the radar echo signal relative to the radar emission is tau, the radar echo signal time domain can represent S Rr (t) is:
S Rr (t)＝A Rr exp[j2π(4f 0 (t-τ)+2k(t-τ) 2 ](0≤t≤T)
wherein A is Rr For receiving the amplitude of the radar echo signal received by the antenna.
The other path of modulated optical signal output by the optical coupler is divided into two paths by a demultiplexer, wherein one path only comprises a positive sweep frequency sideband f C +2f LFM The other path is a high-order linear sweep frequency sideband signal which only comprises a negative sweep frequency sideband f C -2f LFM Is a high order linear swept sideband signal.
One of the two paths of high-order linear sweep frequency sideband signals is used as a reference signal to be sent into a coherent receiving unit, and the other path of the high-order linear sweep frequency sideband signals is used as a received light signal to receive a radar echo signal amplified by a low-noise amplifier through an electro-optical modulator to obtain a radarAn optical signal is received. Comprising positive swept frequency sidebands f C +2f LFM The high-order linear sweep frequency sideband signal of (2) is used as a reference signal to be sent into one optical input end of a 90-degree optical coupler in a coherent receiving unit, and only comprises a positive sweep frequency sideband f C +2f LFM The spectral distribution of the higher order linear swept sideband signal is shown in FIG. 4C, time domain signal S M+ (t) is:
S M+ (t)＝A 2 exp[j2π(f C t+2f 0 t+kt 2 ](0≤t≤T)
corresponding to the received optical signal comprising only the negative swept frequency sideband f C -2f LFM The spectral distribution of the higher order linear swept sideband signal is shown in FIG. 4B, time domain signal S M- (t) is:
S M- (t)＝A 1 exp[j2π(f C t-2f 0 t-kt 2 ](0≤t≤T)
the baseband radar echo signal after low noise amplification only comprises a negative sweep frequency sideband f through a Mach-Zehnder modulator pair C -2f LFM And (3) modulating the high-order linear sweep frequency sideband signal to realize the optical domain receiving of the radar echo signal and obtain the radar receiving optical signal. Since only the positive first-order signal of the radar-received optical signal and the positive swept sideband f as the reference optical signal are included C +2f LFM Is close to, differs by an intermediate frequency signal related to target information, so that the following is mainly used for analyzing the positive first-order sideband signal of the radar received light signal, and comprises a negative sweep sideband f C -2f LFM The spectrum distribution of the radar receiving optical signal with the positive first-order modulation sideband is shown as E in fig. 4, and the time domain signal S OR (t) is:
S OR (t)＝A 3 exp[j2π(f C (t-τ)-2f 0 (t-τ)-k(t-τ) 2 ]+A 4 exp[j2π(f C (t-τ)+2f 0 (t-τ)+k(t-τ) 2 ]
wherein A is 3 And A is a 4 The amplitudes of the two sidebands, respectively.
The coherent receiving unit provided in the embodiment of the present invention is shown in fig. 5, and is composed of 1 90-degree optical coupler and 2 balanced detectors (BPD 1 and BPD 2). Sending the radar received optical signal to the other optical input end of the 90-degree optical coupler in the coherent receiving unit, realizing coherent detection with the reference signal, ignoring the parasitic phase, and expressing two orthogonal intermediate frequency electric signals output by the two balanced photoelectric detectors as follows:
i.e. two orthogonal components S of the intermediate frequency signal carrying the target information I (t)、S Q (t) whereinAs the phase information of the intermediate frequency signal, two orthogonal intermediate frequency electric signals correspond to the complex signal form:
S IF (t)＝S I (t)+jS Q (t)＝Aexp[j8πkτt+jφ](0≤t≤T)
a is the amplitude of the intermediate frequency signal, after analog-to-digital conversion of the intermediate frequency signal, the information such as the target distance, the speed, the scattering characteristic and the like can be obtained based on a radar signal processing algorithm, and the frequency spectrum is shown as F in fig. 4, whereinIs the phase of the intermediate frequency signal, f IF Is the frequency of the intermediate frequency signal.
Finally, it should be noted that the above list is only specific embodiments of the present invention. The invention is not limited to the above embodiments, but many variations are possible. All modifications directly derived or suggested to one skilled in the art from the present disclosure should be considered as being within the scope of the present invention.
Claims (10)
1. A coherent microwave photon radar detection method based on photon frequency multiplication is characterized by comprising the following steps:
loading a baseband linear sweep frequency signal on an optical carrier signal through a photon frequency multiplication unit to obtain a modulated optical signal, wherein the modulated optical signal is a high-order linear sweep frequency sideband signal containing positive and negative sweep frequency sidebands;
dividing the modulated optical signals into two paths, wherein one path of modulated optical signals is converted into frequency multiplication radar emission signals through photoelectric conversion, and the frequency multiplication radar emission signals are reflected by a target object to obtain radar echo signals;
the other path of modulated optical signals are decomposed through a signal selector, and one of high-order linear sweep frequency sideband signals which are obtained through decomposition and only contain positive sweep frequency sidebands and only contain negative sweep frequency sidebands is used as a reference optical signal, and the other one is used as a receiving optical signal;
loading a radar echo signal on a received light signal through an electro-optical modulator to obtain a radar received light signal;
and carrying out coherent reception on the reference optical signal and the radar receiving optical signal to obtain a complex intermediate frequency signal carrying target information, and completing detection.
2. The method for detecting a coherent microwave photonic radar based on frequency multiplication of photons according to claim 1, wherein the frequency is f by a photon frequency multiplier LFM Is loaded on a baseband linear sweep frequency signal with the frequency f c Obtain a modulated optical signal from an optical carrier signal having a frequency f c +Mf LFM Higher order linear swept sideband signal comprising a positive swept sideband and having frequency f c -Nf LFM Is composed of a high-order linear sweep sideband signal containing a negative sweep sideband, wherein M and N are the orders of the sweep sidebands, and M+N is the multiple of photon frequency multiplication.
3. The method for detecting a coherent microwave photonic radar based on frequency multiplication of photons according to claim 1, wherein the frequency f of the baseband linear sweep signal LFM The method comprises the following steps:
f LFM ＝f 0 +kt(0≤t≤T)
wherein f 0 The starting frequency of the baseband chirp signal is that k is the frequency modulation slope, T is the signal period and T is the pulse width.
4. The method for detecting the coherent microwave photonic radar based on photon frequency multiplication according to claim 1, wherein one path of modulated optical signal is photoelectrically converted into a frequency-multiplied radar emission signal, and the method comprises the following steps:
one path of modulated optical signal is subjected to photoelectric conversion to obtain an electric signal, the electric signal is subjected to power amplification to obtain a frequency multiplication radar transmitting signal, and the frequency multiplication radar transmitting signal is transmitted through a transmitting antenna.
5. The method for detecting the coherent microwave photonic radar based on photon frequency multiplication according to claim 1, wherein after the frequency multiplication radar emission signal is reflected by a target object to obtain a radar echo signal, the radar echo signal is amplified with low noise, and the radar echo signal amplified with low noise is input into the electro-optical modulator.
6. The method for detecting the coherent microwave photon radar based on photon frequency multiplication according to claim 1, wherein the reference optical signal and the radar receiving optical signal are subjected to coherent reception to obtain a complex intermediate frequency signal carrying target information, and the complex intermediate frequency signal is composed of two paths of orthogonal intermediate frequency signals carrying target information.
7. The method for detecting the coherent microwave photon radar based on photon frequency multiplication according to claim 6, wherein after obtaining two paths of orthogonal intermediate frequency signals carrying target information, the two paths of orthogonal intermediate frequency signals are subjected to analog-to-digital conversion to obtain digital signals, and the digital signals are subjected to radar digital signal processing to extract the information of the target object.
8. A coherent microwave photonic radar detection system based on photon frequency multiplication, comprising:
a laser source for emitting an optical carrier signal;
the baseband signal source is used for transmitting a baseband linear sweep frequency signal;
the photon frequency doubling unit is used for loading the baseband linear sweep frequency signal on the optical carrier signal to obtain a modulated optical signal, wherein the modulated optical signal is a high-order linear sweep frequency sideband signal containing positive and negative sweep frequency sidebands;
an optical coupler for dividing the modulated optical signal into two paths;
the photoelectric detector is used for converting one path of modulated optical signals into frequency multiplication radar emission signals;
the signal selection unit is used for decomposing the other path of modulated optical signal into a high-order linear sweep frequency side band signal only comprising a positive sweep frequency side band and a high-order linear sweep frequency side band signal only comprising a negative sweep frequency side band through the signal selector, and taking one of the high-order linear sweep frequency side band signal only comprising the positive sweep frequency side band and the high-order linear sweep frequency side band signal only comprising the negative sweep frequency side band as a reference optical signal and the other as a receiving optical signal;
the electro-optical modulator is used for loading a radar echo signal on the received light signal to obtain a radar received light signal, and the radar echo signal is obtained by reflecting a frequency multiplication radar transmitting signal by a target object; and
and the coherent receiving unit carries out coherent receiving on the reference optical signal and the radar receiving optical signal to obtain a complex intermediate frequency signal carrying target information, and detection is completed.
9. The coherent microwave photonic radar detection system based on frequency multiplication of photons according to claim 8, wherein the coherent receiving unit comprises a 90 degree optical coupler and two balanced detectors;
the 90-degree optical coupler is used for introducing 90-degree phase difference into the obtained radar receiving optical signal and the reference optical signal in an optical domain to obtain four paths of composite optical signals;
and the two balanced photoelectric detectors are used for respectively carrying out photoelectric detection on the four paths of composite optical signals output by the 90-degree optical coupler to obtain two paths of orthogonal intermediate frequency signals carrying target information.
10. The coherent microwave photon radar detection system based on photon frequency multiplication according to claim 8, wherein the photon frequency multiplication unit is a single integrated electro-optic modulator or a multi-device cascade unit, the single integrated electro-optic modulator is a mach-zehnder modulator, a dual parallel mach-zehnder modulator or a polarization multiplexing dual parallel mach-zehnder modulator, and the multi-device cascade unit is an optical frequency comb generator cascade optical filter, an electro-optic modulator cascade nonlinear optical fiber or an optical filter.
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