CN114879218A - Laser and radio frequency composite radar detection method and device - Google Patents
Laser and radio frequency composite radar detection method and device Download PDFInfo
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- 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
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- 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
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- G01S17/48—Active triangulation systems, i.e. using the transmission and reflection of electromagnetic waves other than radio waves
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- G01S17/00—Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
- G01S17/87—Combinations of systems using electromagnetic waves other than radio waves
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- G—PHYSICS
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- 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
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- 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
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Abstract
The invention discloses a laser and radio frequency composite radar detection method. The invention combines the microwave photon radar technology with the laser radar, utilizes a cyclic frequency shift mode to generate a linear frequency modulation optical signal with a large time-width bandwidth product as a laser radar detection optical signal, and multiplexes an echo signal of the laser radar and an electric signal obtained by beat frequency conversion of a reference optical signal to be used as a radio frequency antenna transmission signal, thereby skillfully applying the laser radar and the radio frequency radar to the same system, making up for the deficiency, and leading the radar system to have the advantages of long detection distance, wide range, all-weather and high distance resolution and speed resolution; meanwhile, the system structure is simplified, the use of devices is saved, and the requirement of the system on signal power is reduced. The invention also discloses a laser and radio frequency composite radar detection device. Compared with the prior art, the invention has the advantages of both the microwave photon radar and the laser radar, and has simple system structure and lower realization cost.
Description
Technical Field
The invention belongs to the technical field of radars, and particularly relates to a composite radar detection method combining a laser radar and a radio frequency radar.
Background
The radar can acquire information such as distance, direction, speed and the like of a target by transmitting electromagnetic waves and receiving and processing target echo signals. Due to the capability of detecting the target all day long, all weather and complex environment, the system is widely applied to the fields of traffic monitoring, weather forecasting, resource detection, military guidance, target tracking, battlefield monitoring and the like, and plays an important role in civil use and military.
The detection performance of the radar system is closely related to the characteristics of the emitted waveforms, the larger the radar waveform bandwidth is, the higher the distance resolution is, the larger the time width is, and the longer the detection distance is. With the continuous optimization of radar range resolution and the continuous increase of detection range, the transmitted radar waveform is required to have a large time-wide bandwidth product (TBWP). Therefore, how to generate a radar waveform with a large time-bandwidth product is a major research focus in the current radar field. Conventional radar waveforms are generated primarily by voltage controlled oscillators or in the electrical domain by digital to analog converters (DACs) based on phase or amplitude information of the desired signal. With the rapid development of new technologies, the operating frequency band of radar has been raised to Ka band and W band, and the bandwidth of transmitting signals and receiving signals can reach 40GHz and even 100 GHz. However, the traditional electrical method is limited by clock rate, digital-to-analog conversion rate and the like, the frequency and bandwidth of the generated signal are low, and to generate a high-frequency broadband signal with a bandwidth reaching several GHz to even tens of GHz, multiple times of frequency multiplication and up-conversion processing are required and electromagnetic isolation measures are adopted, so that the power consumption is high, the stability is poor, the structure is complex, and the development requirement of future radars cannot be met.
The microwave photonic technology can generate high-frequency, broadband and tunable broadband signals by virtue of the advantages of high frequency, large bandwidth, reconfigurability, electromagnetic interference resistance and the like without multiple frequency doubling and up-conversion operations, can also realize the generation of high-carrier-frequency and ultra-broadband multipath parallel signals through reasonable design, can effectively overcome the bottlenecks of low central frequency, small bandwidth and the like in the broadband signal generation of the pure electronic technology, and is one of the research hotspots in the field of microwave photonics at present. By utilizing the advantage of abundant optical domain spectrum resources, the frequency, the amplitude and the phase of the signal are manipulated in the optical domain, and the bandwidth of the generated signal can reach dozens of GHz. Therefore, the generation of broadband signals by utilizing the photon technology has great advantages, breaks through the electronic bottleneck, and realizes the inevitable development direction of high-frequency, high-speed and broadband signal generation. The combination of microwave photon technology and a radio frequency radar system to greatly improve the radar detection performance has become a research hotspot, and the microwave photon technologies such as a photoproduction microwave technology, a microwave light delay and phase shift technology, a microwave photon filtering technology, an all-optical sampling quantification technology and the like are applied to different research directions of the traditional radio frequency radar; this type of radar detection system is also known as microwave photonic radar.
In the practical application of radar, the radio frequency radar has the advantages of long detection distance, wide range and the like, is not influenced by rain and snow weather, has the characteristic of all weather, has strong survivability in battlefields, is the most common radar system in military activities at present, but has the resolution limited by signal time width and bandwidth, and is generally inferior to laser radar. Although the lidar is easily affected by rain and snow weather, the lidar has good directivity, strong concealment, strong active interference resistance, high brightness and higher ranging accuracy and resolution, so the lidar is widely applied to the fields of remote sensing, automatic driving and the like. Both laser radar systems and radio frequency radar systems have their own advantages and disadvantages to some extent. Therefore, in practical application, a multifunctional composite radar detection system which is all-weather, wide in detection range, high in resolution, good in directivity and strong in anti-interference capability is needed.
Disclosure of Invention
The technical problem to be solved by the invention is to overcome the defects of the prior art and provide a laser and radio frequency composite radar detection method, which has the advantages of a microwave photon radar and a laser radar, and has the advantages of simple system structure and lower realization cost.
The invention specifically adopts the following technical scheme to solve the technical problems:
a laser and radio frequency composite radar detection method generates two paths of homologous continuous light carriers; frequency shifting is carried out on one path of continuous optical carrier to generate a reference optical signal; for the other path of continuous optical carrier, firstly, carrying out carrier suppression single-sideband modulation on the other path of continuous optical carrier by using a linear frequency modulation electric pulse signal to generate a linear frequency modulation optical pulse signal, and then splicing the generated linear frequency modulation optical pulse signal into a linear frequency modulation optical signal with large time width and large bandwidth through cyclic frequency shift; dividing the linear frequency modulation optical signal into two paths, wherein one path is used as a laser radar detection optical signal to be transmitted to a target, and the other path is subjected to beat frequency with one path of beam splitting signal of the reference optical signal to obtain a double-chirp electric signal S1; coupling the laser radar reflected light signal of the target with the other path of beam splitting signal of the reference light signal, converting the coupled laser radar reflected light signal into an electric signal S2, then dividing the electric signal into two paths, transmitting one path of the electric signal to the target as a radio frequency detection signal of a radio frequency radar, and performing cross-correlation operation on the other path of the electric signal S1 to obtain detection information of the laser radar on the target; and performing cross-correlation operation on the radio frequency radar echo signal S3 of the target and the electric signal S2 to obtain the detection information of the target by the radio frequency radar.
Preferably, the cyclic shift frequency satisfies the following condition:
the pulse width of the linear frequency modulation optical pulse signal is equal to the loop delay of the cyclic frequency shift;
the pulse period of the linear frequency modulation optical pulse signal is integral multiple of the pulse width;
the signal bandwidth of the linear frequency modulation optical pulse signal is equal to the frequency shift frequency of the cyclic frequency shift;
the product of the pulse width of the chirp optical pulse signal and the frequency shift frequency of the cyclic frequency shift is an integer.
Preferably, a double-parallel mach-zehnder modulator operating in a carrier suppression single-sideband modulation mode is used for frequency shifting one path of continuous optical carrier to generate a reference optical signal.
Based on the same inventive concept, the following technical scheme can be obtained:
a laser and radio frequency composite radar detection device, comprising:
the optical carrier module is used for generating two paths of homologous continuous optical carriers;
the reference optical module is used for performing frequency shift on one path of continuous optical carrier to generate a reference optical signal;
the cyclic frequency shift module is used for carrying out carrier suppression single-sideband modulation on the other path of continuous optical carrier by using a linear frequency modulation electric pulse signal to generate a linear frequency modulation optical pulse signal, and then splicing the generated linear frequency modulation optical pulse signal into a linear frequency modulation optical signal with large time width and large bandwidth through cyclic frequency shift;
the transmitting and receiving module is used for dividing the linear frequency modulation optical signal into two paths, wherein one path is used as a laser radar detection optical signal to be transmitted to a target, and the other path is subjected to beat frequency with one path of beam splitting signal of the reference optical signal to obtain a double-chirp electric signal S1; coupling the laser radar reflected light signal of the target with the other path of beam splitting signal of the reference light signal, converting the coupled laser radar reflected light signal into an electric signal S2, then dividing the electric signal into two paths, and using one path as a radio frequency detection signal of a radio frequency radar to transmit the radio frequency detection signal to the target; and the signal processing module is used for performing cross-correlation operation on the other path of electric signal S2 and the electric signal S1 to obtain detection information of the laser radar on the target, and performing cross-correlation operation on the radio frequency radar echo signal S3 and the electric signal S2 of the target to obtain detection information of the radio frequency radar on the target.
Preferably, the cyclic shift frequency satisfies the following condition:
the pulse width of the linear frequency modulation optical pulse signal is equal to the loop delay of the cyclic frequency shift;
the pulse period of the linear frequency modulation optical pulse signal is integral multiple of the pulse width;
the signal bandwidth of the linear frequency modulation optical pulse signal is equal to the frequency shift frequency of the cyclic frequency shift;
the product of the pulse width of the chirp optical pulse signal and the frequency shift frequency of the cyclic frequency shift is an integer.
Preferably, the frequency shift module is a double-parallel mach-zehnder modulator operating in a carrier-suppressed single-sideband modulation mode.
Compared with the prior art, the technical scheme of the invention has the following beneficial effects:
the invention combines the microwave photon radar technology with the laser radar, utilizes a cyclic frequency shift mode to generate a linear frequency modulation optical signal with a large time-width bandwidth product as a laser radar detection optical signal, and multiplexes an echo signal of the laser radar and an electric signal obtained by beat frequency conversion of a reference optical signal to be used as a radio frequency antenna transmission signal, thereby skillfully applying the laser radar and the radio frequency radar to the same system, making up for the deficiency, and leading the radar system to have the advantages of long detection distance, wide range, all-weather and high distance resolution and speed resolution; meanwhile, the system structure is simplified, the use of devices is saved, and the requirement of the system on signal power is reduced.
The invention further adjusts parameters such as pulse width, pulse period, signal bandwidth, loop delay, frequency shift frequency and the like of the linear frequency modulation optical pulse signal in the cyclic frequency shift module to enable the linear frequency modulation optical pulse signal to meet specific requirements, thereby realizing that the generated linear frequency modulation optical signal with large time-width bandwidth product is continuous in time, frequency and phase.
Drawings
FIG. 1 is a schematic structural diagram of an embodiment of a laser and RF composite radar detection apparatus according to the present invention;
FIG. 2 is a schematic diagram of the structure of an optical shift frequency loop in an embodiment;
FIG. 3 is a local oscillator signal time-frequency curve obtained by the photodetector 2 in the embodiment;
FIG. 4 is a time domain waveform simulation of a chirp signal generated by a conventional cyclic frequency shift method;
FIG. 5 is a simulation of a time domain waveform of a chirp generated in an embodiment;
fig. 6 is a cross-correlation result between the echo and the local oscillator signal when the relative delay of the lidar ranging system is 0 and 500ps, respectively, in an embodiment.
Detailed Description
Aiming at the defects of the prior art, the solution idea of the invention is to generate a continuous linear frequency modulation optical signal with large time-bandwidth product on time, frequency and phase particularly based on a cyclic frequency shift principle, use the linear frequency modulation optical signal as a detection optical signal of a laser radar, use an electric signal of a beat frequency of a laser radar echo signal and a reference optical signal as a radio frequency radar emission signal through signal multiplexing, apply the laser radar and the radio frequency radar in the same system, and make up for the shortfall by taking the advantages of long detection distance, wide range and all weather and also considering the advantages of distance resolution and high speed resolution; meanwhile, the system structure can be simplified, the use of devices is saved, and the requirement of the system on signal power is reduced.
The invention provides a laser and radio frequency composite radar detection method, which specifically comprises the following steps:
generating two paths of homologous continuous optical carriers; frequency shifting is carried out on one path of continuous optical carrier to generate a reference optical signal; for the other path of continuous optical carrier, firstly, carrying out carrier suppression single-sideband modulation on the other path of continuous optical carrier by using a linear frequency modulation electric pulse signal to generate a linear frequency modulation optical pulse signal, and then splicing the generated linear frequency modulation optical pulse signal into a linear frequency modulation optical signal with large time width and large bandwidth through cyclic frequency shift; dividing the linear frequency modulation optical signal into two paths, wherein one path is used as a laser radar detection optical signal to be transmitted to a target, and the other path is subjected to beat frequency with one path of beam splitting signal of the reference optical signal to obtain a double-chirp electric signal S1; coupling the laser radar reflected light signal of the target with the other path of beam splitting signal of the reference light signal, converting the coupled laser radar reflected light signal into an electric signal S2, then dividing the electric signal into two paths, transmitting one path of the electric signal to the target as a radio frequency detection signal of a radio frequency radar, and performing cross-correlation operation on the other path of the electric signal S1 to obtain detection information of the laser radar on the target; and performing cross-correlation operation on the radio frequency radar echo signal S3 of the target and the electric signal S2 to obtain the detection information of the target by the radio frequency radar.
The invention provides a laser and radio frequency composite radar detection device, which comprises:
the optical carrier module is used for generating two paths of homologous continuous optical carriers;
the reference optical module is used for performing frequency shift on one path of continuous optical carrier to generate a reference optical signal;
the cyclic frequency shift module is used for carrying out carrier suppression single-sideband modulation on the other path of continuous optical carrier by using a linear frequency modulation electric pulse signal to generate a linear frequency modulation optical pulse signal, and then splicing the generated linear frequency modulation optical pulse signal into a linear frequency modulation optical signal with large time width and large bandwidth through cyclic frequency shift;
the transmitting and receiving module is used for dividing the linear frequency modulation optical signal into two paths, wherein one path is used as a laser radar detection optical signal to be transmitted to a target, and the other path is subjected to beat frequency with one path of beam splitting signal of the reference optical signal to obtain a double-chirp electric signal S1; coupling the laser radar reflected light signal of the target with the other path of beam splitting signal of the reference light signal, converting the coupled laser radar reflected light signal into an electric signal S2, then dividing the electric signal into two paths, and using one path as a radio frequency detection signal of a radio frequency radar to transmit the radio frequency detection signal to the target; and the signal processing module is used for performing cross-correlation operation on the other path of electric signal S2 and the electric signal S1 to obtain detection information of the laser radar on the target, and performing cross-correlation operation on the radio frequency radar echo signal S3 and the electric signal S2 of the target to obtain detection information of the radio frequency radar on the target.
The linear frequency modulation signal (LFM) is a waveform signal commonly used in the current radar system, and the current main methods for generating the linear frequency modulation signal based on the microwave photon technology include a frequency spectrum shaping-frequency-time mapping method, a frequency multiplication method, a light injection semiconductor laser method, a phase modulation method and a time-frequency domain splicing method. The spectrum shaping-frequency-time mapping method is to shape the spectrum of a wide-spectrum light source according to the waveform of a required signal and then map the shape of a frequency domain to a time domain to obtain a desired waveform. The advantages are large bandwidth and tunable; the defects are that the precision of the receiving device is limited, the time width of the generated signal is small, the fineness of the signal waveform is poor, and the radar requirement is difficult to meet. The frequency multiplication method is that a baseband linear frequency modulation signal generated by an electric domain is used for driving an electro-optical modulator, different harmonic sidebands are excited by an electro-optical nonlinear effect, different sidebands are selected for beat frequency, and a signal with the center frequency and the bandwidth being corresponding multiples of the fundamental frequency signal is obtained. Has the advantages of simple structure and easy operation; the disadvantage is the high requirements on the baseband radar waveform generator and the sharp increase in spurs. The light injection semiconductor laser method is based on the principle that the frequency (or wavelength) of a microwave signal obtained by beat frequency between a master laser and a slave laser has a linear relationship with the light injection intensity of the master laser under the condition that the frequency detuning between the master laser and the slave laser is kept unchanged. Its disadvantages are that the phase noise deteriorates exponentially, the spurs increase dramatically, and the efficiency decreases exponentially with the bandwidth and the multiplication factor. The phase modulation method is to introduce quadratic parabolic phase change to a microwave signal by using an optical means to obtain a required chirp signal. The disadvantage is that the time-width bandwidth product of the generated linear frequency modulation signal is small and the requirement is difficult to meet due to the power limitation of the modulator. The time-frequency domain splicing method combines the characteristics of rich optical domain frequency spectrum resources and flexible electric domain signal generation, linear frequency modulation signals are generated through an electric method, and the linear frequency modulation signals with large bandwidth and large time width are obtained by splicing the linear frequency modulation signals in the time-frequency domain after frequency conversion and delay line delay are carried out on the linear frequency modulation signals by using an optical frequency comb. Compared with other methods, the time-frequency domain splicing method has the advantages of large bandwidth, high flexibility, tunable frequency, reconfigurable waveform and the like; the disadvantages are that the phase locking is needed to be carried out on the double optical frequency combs with different frequency intervals, the structure is complex, and the price of the used programmable optical filter is high.
In order to generate a large time-bandwidth product chirp optical signal that is continuous in time, frequency, and particularly phase, the present invention further improves on the basis of the existing cyclic frequency shift method, specifically, the cyclic frequency shift satisfies the following conditions:
the pulse width of the linear frequency modulation optical pulse signal is equal to the loop delay of the cyclic frequency shift;
the pulse period of the linear frequency modulation optical pulse signal is integral multiple of the pulse width;
the signal bandwidth of the linear frequency modulation optical pulse signal is equal to the frequency shift frequency of the cyclic frequency shift;
the product of the pulse width of the chirp optical pulse signal and the frequency shift frequency of the cyclic frequency shift is an integer.
For the public understanding, the technical scheme of the invention is explained in detail by a specific embodiment and the accompanying drawings:
the basic structure of the laser and rf composite radar detection device of the present embodiment is shown in fig. 1. Firstly, a narrow linewidth laser generates a beam of continuous optical carrier which enters an optical coupler 1 and is split into two paths, wherein one path enters a DPMZM (double parallel Mach-Zehnder modulator) 1, the DPMZM1 works in a modulation mode of restraining a single sideband of the carrier to realize the frequency shift of an input optical signal, the frequency shift frequency can be arbitrarily tuned by changing the frequency of an added radio frequency signal, and the optical signal after the frequency shift is used as a reference optical signal; and the other path of optical carrier signal enters an optical switch constructed by cascading a Mach-Zehnder modulator and a filter, a linear frequency modulation electric pulse signal is modulated to the Mach-Zehnder modulator by using an Arbitrary Waveform Generator (AWG), the Mach-Zehnder modulator works at the minimum transmission point to inhibit the carrier and an even number of side bands, and then one of a positive side band and a negative side band of 1 order is selected to be output through the filter, so that the optical switch generates a linear frequency modulation optical pulse signal, and the pulse width and the period of the linear frequency modulation optical pulse signal are consistent with those of the linear frequency modulation electric pulse signal.
Then, the chirp optical pulse signal output from the optical switch is input to a frequency shift loop to be cyclically shifted in frequency. Common devices for shifting the frequency of an optical signal are Acoustic Optical Modulators (AOMs) and dual parallel mach-zehnder modulators. The acousto-optic modulator achieves the frequency shift effect by utilizing the acousto-optic effect to enable the laser to generate the diffraction principle, and has the advantages of high frequency shift precision and good frequency shift effect; the disadvantages are that the amount of frequency shift is severely limited, typically between tens of mhz to hundreds of mhz, by the crystal material, and that its direction of frequency shift is fixed and cannot be altered. The double-parallel Mach-Zehnder modulator excites high-order sidebands by utilizing the modulation of electric light intensity, and achieves the effect of frequency shift by adjusting the phase relation among the sidebands, and has the advantages that the frequency shift frequency can be randomly tuned by changing the frequency of an applied radio frequency signal, and the frequency shift direction can be changed by adjusting bias voltage; the disadvantages are that the variables to be controlled are too many, the bias point is easy to drift, and the suppression to the carrier and the sideband is not large enough. Each of these two methods has advantages and disadvantages.
In the embodiment, a double parallel Mach-Zehnder modulator is selected as a frequency shift device in a frequency shift loop; as shown in fig. 2, the frequency shift loop comprises four parts, namely an optical coupler 6, a double parallel mach-zehnder modulator 2, an optical coupler 7 and an optical amplifier. The following conditions are satisfied by adjusting the parameters: the pulse width of the linear frequency modulation optical pulse signal is equal to the loop delay of the cyclic frequency shift; the pulse period of the linear frequency modulation optical pulse signal is integral multiple of the pulse width; the signal bandwidth of the linear frequency modulation optical pulse signal is equal to the frequency shift frequency of the cyclic frequency shift; the product of the pulse width of the chirp optical pulse signal and the frequency shift frequency of the cyclic frequency shift is an integer. In this case, the output of the frequency shift loop is a linear frequency modulation optical signal with large time width and large bandwidth which is continuously spliced on time, frequency and phase; can be expressed by the formula:
wherein, tau is the pulse width of the chirp optical pulse signal, T L Loop delay, T, for cyclic frequency shift s Is the pulse period, f, of a chirped optical pulse signal s The frequency shift frequency is a cyclic frequency shift, B is the bandwidth of the chirped optical pulse signal, and M, N is a non-zero integer.
Then, the linear frequency modulation optical signal is filtered by an optical filter to remove noise and unnecessary optical sidebands, and then is divided into two paths by a coupler 2, wherein one path enters an optical circulator to serve as a detection optical signal of the laser radar, and the other path serves as a local oscillator signal of the laser radar.
The detection light signal is input into 1 port of the optical circulator, output from 2 ports, and then enter into an optical antenna, and the light in the optical fiber is converted into space light to be emitted. The detection optical signal returns to the original path after detecting the target, the return optical signal is input from the 2 port of the optical circulator through the optical antenna, the optical circulator separates the detection optical signal from the original optical signal, and the return optical signal is output from the 3 port, wherein the return optical signal carries the detection information of the laser radar.
As shown in fig. 1, the present invention multiplexes the echo signal of the laser radar, that is, the echo signal of the laser radar output from the port of the circulator 3 is coupled with one path of the reference optical signal split by the optical coupler 3 and input to the optical coupler 4, and then beat frequency at the position of the photodetector 1 to obtain an electrical signal S2 carrying the detection information of the laser radar, and the chirp electrical signal is input to the transmitting antenna to be transmitted, reflected and received by the target, and the receiving antenna obtains an electrical signal S3 carrying the detection information of the radio frequency radar.
And inputting the other path of reference optical signal branched by the optical coupler 3 and the linear frequency modulation optical local oscillation signal branched by the optical coupler 2 to the optical coupler 5 for coupling, and performing beat frequency at the photoelectric detector 2 to obtain a reference electrical signal S1 detected by the laser radar.
Inputting a reference signal S1 generated by the photoelectric detector 2, an electric signal S2 which is generated by the photoelectric detector 1 and carries laser radar detection information, and an electric signal S3 which is received by a receiving antenna and carries radio frequency radar detection information into a real-time oscilloscope for collection; and performing cross-correlation processing on the S1 and S2 signals to obtain detection information of the laser radar on the target, and performing cross-correlation processing on the S2 and S3 signals to obtain detection information of the radio frequency radar on the target.
For a moving target, when the optical carrier wave split by the optical coupler 1 is not modulated by the double-parallel mach-zehnder modulator 1, the pulse after the cross-correlation processing has only one peak value and only carries the coupling information of the distance and the speed of the target. When the dual parallel mach-zehnder modulator 1 modulates the optical carrier divided by the optical coupler 1 and meets the condition of generating a V-type dual chirp signal (frequency-shifting the optical carrier to a certain frequency in the middle of the chirped optical signal) or an X-type dual chirp signal (modulating and outputting two optical carriers falling on two sides of the chirped optical signal frequency range) by beating the chirped optical signal generated by the cyclic frequency shift module, the pulse signal after the cross-correlation processing contains two peak values, and the target speed information and the target distance information can be obtained through calculation respectively. Therefore, the DPMZM1 should be adjusted so that the output frequency shifted optical signal beats with the chirp optical signal generated by the cyclic frequency shift module to generate a double chirped electrical signal.
Further analysis was carried out in principle below:
one path of optical carrier signal emitted by the laser enters an optical switch realized by a cascade filter of the Mach-Zehnder modulator, and if the optical carrier entering the modulator has an expression E 0 ＝cos(ω 0 t) inputting a chirp s (t) to the modulator by an Arbitrary Waveform Generator (AWG) can be expressed as:
wherein ω is m Is the starting frequency of the signal, τ is the pulse width of the signal, T s P τ is the signal period, k B/4 τ is the chirp rate of the signal, B is the bandwidth, rect x]Is a rectangular window function, specifically:
according to the Mach-Zehnder modulator operating principle, the output can be expressed as:
wherein,
V π is the half-wave voltage, V, of the modulator DC Is a bias voltage, developed by a Bessel series of:
wherein
m＝π/2V π If control V DC Make it
And only small signal modulation is considered, equation (5) can be rewritten as:
the output of the visible modulator has only positive and negative first order sidebands, and after filtering one of the sidebands with an optical filter, equation (6) can be written as:
it can be seen that a chirped optical pulse signal is produced having a pulse width and period which coincide with the pulse width and period of the single frequency pulse signal applied to the modulator.
The other path of signal split by the optical coupler 1 enters a double parallel Mach-Zehnder modulator 1 for modulation, the double parallel Mach-Zehnder modulator is formed by placing two push-pull Mach-Zehnder modulators (MZMs) in parallel, and if the input optical carrier expression is as follows: e a (t)＝Acos(ω 0 t) where ω is 0 The angular frequency of the optical carrier wave and a is the amplitude of the input optical carrier wave, and the output signals are as follows according to the working principle of the double parallel Mach-Zehnder modulator:
wherein, the radio frequency signal amplitude is 2V A Angular frequency of ω, V π Is a half-wave voltage, and is,
the phase difference introduced for the radio frequency signal,
phase difference introduced for three bias voltages, m ═ π V A /2V π Is the modulation factor.
Expanding the formula (8) by a Bessel series:
by controlling three bias voltages
The output signal can be simplified as:
equation (10) shows that the output has only one first-order sideband and one third-order sideband left, and the third-order sideband can be adjusted by 2V radio frequency signal voltage A To make J 1 (m)＞＞J 3 (m) suppressing.
Therefore, by changing the three bias voltages, the phase difference of the radio frequency signal and the output voltage, the single sideband of the carrier can be suppressed, and the output has only one first-order sideband, thereby realizing the frequency shift of the input optical signal, and the frequency shift frequency can be arbitrarily tuned by changing the frequency of the applied radio frequency signal.
Inputting the linear frequency modulation optical pulse output by the optical switch into an optical frequency shift loop for cyclic frequency shift, and enabling the system to meet the requirements
Formula (1). In this case, the output of the cyclic shift module can be expressed as:
equation (11) represents a large time-bandwidth product chirp signal generation with an initial frequency of ω 0 +ω m The bandwidth is PB. It can be seen that the signals are the concatenation in time and frequency of the signals generated by the primary optical switch, and due to τ f s N, so that the phase difference at the splice is
The phase is also illustrated as continuous. This is particularly important compared to current methods: the time-frequency domain splicing method needs to lock the phase of the double optical frequency combs with different frequency intervals, and has high cost and complex structure; the common cyclic frequency shift method can only ensure that the spliced linear frequency modulation signals are continuous in time and frequency, but the phase is not necessarily continuous; the scheme adopted by the invention has great advantages.
Get T s ＝5μs，τ＝500ns，f s ＝1GHz，ω m When the frequency is 2GHz, the time-frequency curve is made through matlab simulation and is shown in fig. 3, and the range of the spliced bandwidth is 2GHz-26GHz, which shows that the scheme generates continuous linear frequency modulation signals in time and frequency through cyclic frequency shift. Meanwhile, the time domain waveforms of the chirp signal generated by the conventional cyclic frequency shift method and the chirp signal generated by the scheme are simulated respectively, and as a result, as shown in fig. 4 and 5, it can be known that the cyclic frequency shift scheme has the advantage of continuous phase compared with the conventional cyclic frequency shift method.
Finally, inputting a reference signal S1 generated by the photoelectric detector 2, an electric signal S2 which is generated by the photoelectric detector 1 and carries laser radar detection information, and an electric signal S3 which is received by a receiving antenna and carries radio frequency radar detection information into a real-time oscilloscope for collection; and performing cross-correlation processing on the S1 and S2 signals to obtain detection information of the laser radar on the target, and performing cross-correlation processing on the S2 and S3 signals to obtain detection information of the radio frequency radar on the target.
In order to verify the effect of the technical scheme of the invention, the distance measuring functions of the laser radar and the radio frequency radar of the laser and radio frequency composite radar detection device are respectively subjected to simulation verification. The simulation of the laser radar is to simulate the distance information of the object detected by the laser radar by adding a light delay method. When the optical delay is 0 and the optical delay is 500ps, respectively, cross-correlation pulse images of the echo signal and the local oscillator signal are made, and the result is shown in fig. 6, and the time coordinates corresponding to the peak values are 500.1ns and 500.6ns, that is, the variation of the loop delay is consistent with the variation of the time coordinates of the peak values of the cross-correlation pulses, so that the ranging capability of the laser radar can be proved.
For the simulation of the radio frequency radar ranging, an electrical delay is added to simulate the distance information of a target object. The verification method is consistent with the laser radar ranging system, and the ranging capability of the system can be verified within a certain error range.
Claims (6)
1. A laser and radio frequency composite radar detection method is characterized in that two paths of homologous continuous light carriers are generated; frequency shifting is carried out on one path of continuous optical carrier to generate a reference optical signal; for the other path of continuous optical carrier, firstly, carrying out carrier suppression single-sideband modulation on the other path of continuous optical carrier by using a linear frequency modulation electric pulse signal to generate a linear frequency modulation optical pulse signal, and then splicing the generated linear frequency modulation optical pulse signal into a linear frequency modulation optical signal with large time width and large bandwidth through cyclic frequency shift; dividing the linear frequency modulation optical signal into two paths, wherein one path is used as a laser radar detection optical signal to be transmitted to a target, and the other path is subjected to beat frequency with one path of beam splitting signal of the reference optical signal to obtain a double-chirp electric signal S1; coupling the laser radar reflected light signal of the target with the other path of beam splitting signal of the reference light signal, converting the coupled laser radar reflected light signal into an electric signal S2, then dividing the electric signal into two paths, transmitting one path of the electric signal to the target as a radio frequency detection signal of a radio frequency radar, and performing cross-correlation operation on the other path of the electric signal S1 to obtain detection information of the laser radar on the target; and performing cross-correlation operation on the radio frequency radar echo signal S3 of the target and the electric signal S2 to obtain the detection information of the target by the radio frequency radar.
2. The laser and radio frequency composite radar detection method of claim 1, wherein the cyclic frequency shift satisfies the following condition:
the pulse width of the linear frequency modulation optical pulse signal is equal to the loop delay of the cyclic frequency shift;
the pulse period of the linear frequency modulation optical pulse signal is integral multiple of the pulse width;
the signal bandwidth of the linear frequency modulation optical pulse signal is equal to the frequency shift frequency of the cyclic frequency shift;
the product of the pulse width of the chirp optical pulse signal and the frequency shift frequency of the cyclic frequency shift is an integer.
3. The laser and radio frequency composite radar detection method of claim 1, wherein a double parallel mach-zehnder modulator operating in a carrier-suppressed single-sideband modulation mode is used to shift a frequency of one of the continuous optical carriers to generate a reference optical signal.
4. A laser and radio frequency composite radar detection device, comprising:
the optical carrier module is used for generating two paths of homologous continuous optical carriers;
the reference optical module is used for performing frequency shift on one path of continuous optical carrier to generate a reference optical signal;
the cyclic frequency shift module is used for carrying out carrier suppression single-sideband modulation on the other path of continuous optical carrier by using a linear frequency modulation electric pulse signal to generate a linear frequency modulation optical pulse signal, and then splicing the generated linear frequency modulation optical pulse signal into a linear frequency modulation optical signal with large time width and large bandwidth through cyclic frequency shift;
the transmitting and receiving module is used for dividing the linear frequency modulation optical signal into two paths, wherein one path is used as a laser radar detection optical signal to be transmitted to a target, and the other path is subjected to beat frequency with one path of beam splitting signal of the reference optical signal to obtain a double-chirp electric signal S1; coupling the laser radar reflected light signal of the target with the other path of beam splitting signal of the reference light signal, converting the coupled laser radar reflected light signal into an electric signal S2, then dividing the electric signal into two paths, and using one path as a radio frequency detection signal of a radio frequency radar to transmit the radio frequency detection signal to the target; and the signal processing module is used for performing cross-correlation operation on the other path of electric signal S2 and the electric signal S1 to obtain detection information of the laser radar on the target, and performing cross-correlation operation on the radio frequency radar echo signal S3 and the electric signal S2 of the target to obtain detection information of the radio frequency radar on the target.
5. The lidar and radio frequency composite radar detection device of claim 4, wherein the cyclic frequency shift satisfies the following condition:
the pulse width of the linear frequency modulation optical pulse signal is equal to the loop delay of the cyclic frequency shift;
the pulse period of the linear frequency modulation optical pulse signal is integral multiple of the pulse width;
the signal bandwidth of the linear frequency modulation optical pulse signal is equal to the frequency shift frequency of the cyclic frequency shift;
the product of the pulse width of the chirp optical pulse signal and the frequency shift frequency of the cyclic frequency shift is an integer.
6. The laser and radio frequency composite radar detection device of claim 4, wherein the frequency shift module is a double parallel Mach-Zehnder modulator operating in a carrier-suppressed single sideband modulation mode.
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| CN117406238A (en) * | 2023-10-09 | 2024-01-16 | 北京交通大学 | Microwave photon dual-mode imaging system |
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| CN117406238A (en) * | 2023-10-09 | 2024-01-16 | 北京交通大学 | Microwave photon dual-mode imaging system |
| CN117406238B (en) * | 2023-10-09 | 2024-05-28 | 北京交通大学 | Microwave photon dual-mode imaging system |
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