CN114879218A - Laser and radio frequency composite radar detection method and device - Google Patents

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

Laser and radio frequency composite radar detection method and device

technical field

The invention belongs to the technical field of radar, and in particular relates to a composite radar detection method combining laser radar and radio frequency radar.

Background technique

The radar can obtain the distance, direction, speed and other information of the target by emitting electromagnetic waves and receiving and processing the target echo signal. Because of its ability to detect targets in all-day, all-weather and complex environments, it is widely used in traffic monitoring, weather forecasting, resource detection, military guidance, target tracking, battlefield surveillance and other fields, and plays an important role in both civilian and military applications. effect.

The detection performance of a radar system is closely related to the characteristics of its emission waveform. The larger the radar waveform bandwidth, the higher the range resolution, the larger the time width, and the longer the detection distance. With the continuous optimization of radar range resolution and the continuous improvement of detection range, the transmitted radar waveform is required to have a large time-width-bandwidth product (TBWP). Therefore, how to generate radar waveforms with large time-width-bandwidth products is the current research focus in the field of radar. Traditional radar waveforms are mainly generated by voltage-controlled oscillators or digital-to-analog converters (DACs) in the electrical domain, based on the phase or amplitude information of the desired signal. With the rapid development of new technologies, the working frequency band of radar has risen to Ka-band and W-band, and the bandwidth of transmitting and receiving signals can reach 40GHz or even 100GHz. However, the traditional electrical method is limited by the clock rate and the digital-to-analog conversion rate, and the frequency and bandwidth of the generated signal are low. To generate a high-frequency broadband signal with a bandwidth of several GHz or even tens of GHz, multiple frequency doubling and Up-conversion processing and electromagnetic isolation measures are adopted, which have high power consumption, poor stability and complex structure, which cannot meet the development needs of future radars.

With the advantages of high frequency, large bandwidth, reconfigurability, and anti-electromagnetic interference, microwave photonic technology can generate high-frequency, wide-band, and tunable wide-band signals without multiple frequency doubling and up-conversion operations. It can realize the generation of high carrier frequency and ultra-wideband multi-channel parallel signals, and can effectively overcome the bottlenecks of low center frequency and small bandwidth faced by pure electronic technology to generate broadband signals. It is one of the current research hotspots in the field of microwave photonics. Taking advantage of the abundant spectral resources in the optical domain, the frequency, amplitude and phase of the signal are manipulated in the optical domain, and the resulting signal bandwidth can be as high as tens of GHz. Therefore, the use of photonic technology to generate broadband signals has great advantages, and it is an inevitable development direction to break through the electronic bottleneck and achieve high-frequency, high-speed, and broadband signal generation. The combination of microwave photonic technology and radio frequency radar system to greatly improve the detection performance of radar has become a research hotspot. Microwave photonic technology such as photo-generated microwave technology, microwave optical delay and phase shifting technology, microwave photon filtering technology and all-optical sampling quantization technology has emerged. The technology is applied to different research directions of traditional RF radar; this type of radar detection system is also known as microwave photonic radar.

In the practical application of radar, radio frequency radar has the advantages of long detection distance and wide range, and is not affected by rain and snow weather, has all-weather characteristics, and has strong survivability in the battlefield. It is the most commonly used radar system in military activities. However, its resolution is limited by signal time width and bandwidth, and is generally inferior to lidar. Although Lidar is easily affected by rain and snow weather, it has good directionality, strong concealment, strong anti-active interference, high brightness and higher ranging accuracy and resolution, so it is widely used in remote sensing, automatic driving and many other areas. Both lidar systems and radio frequency radar systems have their own advantages and disadvantages to a certain extent. Therefore, a multifunctional composite radar detection system that can take into account all weather, wide detection range, high resolution, good directionality and strong anti-interference ability is required in practical applications.

SUMMARY OF THE INVENTION

The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art and provide a laser and radio frequency composite radar detection method, which combines the advantages of microwave photonic radar and laser radar, and has a simple system structure and low implementation cost.

The present invention specifically adopts the following technical solutions to solve the above-mentioned technical problems:

A laser and radio frequency composite radar detection method generates two continuous optical carriers of the same source; shifts the frequency of one continuous optical carrier to generate a reference optical signal; It performs carrier-suppressed single-sideband modulation to generate a chirp optical pulse signal, and then splices the generated chirp optical pulse signal into a large time-width and large-bandwidth chirp optical signal through cyclic frequency shifting; The signal is divided into two channels, one channel is sent to the target as the detection optical signal of the laser radar, and the other channel is beat frequency with the one channel splitting signal of the reference optical signal to obtain a double-chirp electrical signal S1; The other beam splitting signal of the reference optical signal is coupled and converted into an electrical signal S2, and then divided into two paths, one of which is used as a radio frequency detection signal of the radio frequency radar to be transmitted to the target, and the other path is interacted with the electrical signal S1. Correlation operation is performed to obtain the detection information of the target by the lidar;

Preferably, the cyclic frequency shift meets the following conditions:

The pulse width of the chirp optical pulse signal is equal to the loop delay of the cyclic frequency shift;

The pulse period of the chirp optical pulse signal is an integer multiple of the pulse width;

The signal bandwidth of the chirp 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, one of the continuous optical carriers is frequency-shifted by using a dual-parallel Mach-Zehnder modulator operating in a carrier-suppressed single-sideband modulation mode to generate a reference optical signal.

Based on the same inventive concept, the following technical solutions can also be obtained:

A laser and radio frequency composite radar detection device, comprising:

Optical carrier module, used to generate two continuous optical carriers of the same source;

The reference optical module is used to frequency shift one of the continuous optical carriers to generate a reference optical signal;

The cyclic frequency shift module is used to perform carrier suppression single sideband modulation on another continuous optical carrier with a linear frequency modulation electrical pulse signal to generate a linear frequency modulation optical pulse signal. The pulse signal is spliced into a linear frequency modulation optical signal with large time width and large bandwidth;

The transmitting and receiving module is used to divide the linear frequency modulated optical signal into two channels, one channel is used as the laser radar detection optical signal to transmit to the target, and the other channel and the one channel splitting signal of the reference optical signal are beat frequency to obtain a double chirp signal. Electrical signal S1; couple the target's laser radar reflected optical signal with another beam splitting signal of the reference optical signal and convert it into an electrical signal S2, then divide it into two channels, and use one of them as the radio frequency detection of the radio frequency radar The signal is transmitted to the target; the signal processing module is used to perform a cross-correlation operation with another electrical signal S2 and the electrical signal S1 to obtain the detection information of the target by the lidar, and conduct the target's RF radar echo signal S3 with the electrical signal S2. The cross-correlation operation is used to obtain the detection information of the target by the radio frequency radar.

Preferably, the cyclic frequency shift meets the following conditions:

The pulse width of the chirp optical pulse signal is equal to the loop delay of the cyclic frequency shift;

The pulse period of the chirp optical pulse signal is an integer multiple of the pulse width;

The signal bandwidth of the chirp 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 shifting module is a dual-parallel Mach-Zehnder modulator operating in a carrier-suppressed single-sideband modulation mode.

Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

The invention combines the microwave photonic radar technology with the laser radar, uses the cyclic frequency shifting method to generate a linear frequency modulated optical signal with a large time-width bandwidth product as the laser radar detection optical signal, and multiplexes the echo signal of the laser radar and the reference optical signal to beat the The electrical signal converted from the frequency is used as the radio frequency antenna to transmit the signal, so that the lidar and the radio frequency radar are skillfully applied in the same system. At the same time, it also simplifies the system structure, saves the use of devices, and reduces the system's requirements for signal power.

The invention further adjusts the pulse width, pulse period, signal bandwidth, loop delay, frequency shifting frequency and other parameters of the linear frequency modulated optical pulse signal in the cyclic frequency shifting module to meet specific requirements, thereby realizing the generated large-time broadband The wide-product chirp optical signal is continuous in time, frequency and phase. Compared with the existing time-frequency domain splicing method and cyclic frequency shifting method, the required cost is lower, the structure is simpler, and the tunability is better.

Description of drawings

FIG. 1 is a schematic structural principle diagram of a specific embodiment of a laser and radio frequency composite radar detection device of the present invention;

2 is a schematic diagram of the structural principle of an optical frequency shift loop in a specific embodiment;

Fig. 3 is the time-frequency curve of the local oscillator signal from the beat frequency of the photodetector 2 in the specific embodiment;

Fig. 4 is the chirp signal time domain waveform simulation that the existing cyclic frequency shift method produces;

5 is a simulation of the time-domain waveform of the chirp signal generated in the specific embodiment;

FIG. 6 is a cross-correlation result between the echo and the local oscillator signal when the relative delays of the lidar ranging system are 0 and 500ps respectively in the specific embodiment.

Detailed ways

In view of the deficiencies of the prior art, the solution of the present invention is to generate a continuous linear frequency modulation optical signal with a large time-width bandwidth product in time, frequency, especially phase, based on the principle of cyclic frequency shifting, which is used as the detection optical signal of the lidar, And through signal multiplexing, the electrical signal of the lidar echo signal and the beat frequency of the reference optical signal is used as the radio frequency radar transmit signal, and the lidar and radio frequency radar are applied in the same system, so that the radar system has long detection distance, The wide range and all-weather characteristics also take into account the advantages of high range resolution and speed resolution; at the same time, it can also simplify the system structure, save the use of components, and reduce the system's requirements for signal power.

The laser and radio frequency composite radar detection method proposed by the present invention specifically includes the following steps:

Generate two continuous optical carriers of the same source; shift the frequency of one continuous optical carrier to generate a reference optical signal; for the other continuous optical carrier, first perform carrier suppression SSB modulation on the other continuous optical carrier with a linear frequency modulated electrical pulse signal to generate Linear frequency modulation optical pulse signal, and then splicing the generated linear frequency modulation optical pulse signal into a large time width and large bandwidth linear frequency modulation optical signal through cyclic frequency shifting; the linear frequency modulation optical signal is divided into two channels, and one channel is used as a lidar The detection optical signal is transmitted to the target, and the other channel and the reference optical signal are beat frequency to obtain a double-chirp electrical signal S1; the target's laser radar reflected optical signal and the other beam splitting of the reference optical signal are split. The signal is coupled and converted into an electrical signal S2, and then it is divided into two channels, one of which is used as the radio frequency detection signal of the radio frequency radar to transmit to the target, and the other channel is cross-correlated with the electrical signal S1 to obtain the detection of the target by the lidar. information; the radio frequency radar echo signal S3 of the target and the electrical signal S2 are cross-correlated to obtain the detection information of the target by the radio frequency radar.

The laser and radio frequency composite radar detection device proposed by the present invention includes:

Optical carrier module, used to generate two continuous optical carriers of the same source;

The reference optical module is used to frequency shift one of the continuous optical carriers to generate a reference optical signal;

The cyclic frequency shift module is used to perform carrier suppression single sideband modulation on another continuous optical carrier with a linear frequency modulation electrical pulse signal to generate a linear frequency modulation optical pulse signal. The pulse signal is spliced into a linear frequency modulation optical signal with large time width and large bandwidth;

The transmitting and receiving module is used to divide the linear frequency modulated optical signal into two channels, one channel is used as the laser radar detection optical signal to transmit to the target, and the other channel and the one channel splitting signal of the reference optical signal are beat frequency to obtain a double chirp signal. Electrical signal S1; couple the target's laser radar reflected optical signal with another beam splitting signal of the reference optical signal and convert it into an electrical signal S2, then divide it into two channels, and use one of them as the radio frequency detection of the radio frequency radar The signal is transmitted to the target; the signal processing module is used to perform a cross-correlation operation with another electrical signal S2 and the electrical signal S1 to obtain the detection information of the target by the lidar, and conduct the target's RF radar echo signal S3 with the electrical signal S2. The cross-correlation operation is used to obtain the detection information of the target by the radio frequency radar.

The linear frequency modulation signal (LFM) is a commonly used waveform signal in the current radar system. At present, the main methods of generating the linear frequency modulation signal based on the microwave photonic technology include the spectrum shaping-frequency-time mapping method, the frequency doubling method, the optical injection semiconductor laser method, and the phase modulation method. , time-frequency domain splicing method. The spectrum shaping-frequency-time mapping method is to shape the spectrum of a broad-spectrum light source according to the waveform of the desired signal, and then map the shape of the frequency domain to the time domain to obtain the desired waveform. The advantage is that the bandwidth is large and tunable; the disadvantage is that due to the limitation of device accuracy, the time width of the generated signal is small, and the precision of the signal waveform is very poor, which is difficult to meet the needs of radar. The frequency doubling method is to use the baseband chirp signal generated in the electrical domain to drive the electro-optical modulator. Different harmonic sidebands are excited by the electro-optical nonlinear effect, and the beat frequencies of different sidebands are selected to obtain the center frequency and bandwidth corresponding to the fundamental frequency signal multiples of the signal. The advantage is that the structure is simple and easy to operate; the disadvantage is that the baseband radar waveform generator has high requirements and the spurious increases sharply. The optical injection semiconductor laser method is based on the frequency (or wavelength) of the microwave signal obtained from the beat frequency between the master and slave lasers and the optical injection of the master laser under the condition that the frequency detuning between the master laser and the slave laser remains unchanged. The principle of the linear relationship of intensity. Its disadvantages are that phase noise deteriorates exponentially, spurs increase dramatically, and efficiency decreases exponentially with bandwidth and multiplication factor. The phase modulation method uses optical means to introduce a quadratic parabolic phase change to the microwave signal to obtain the desired chirp signal. The disadvantage is that limited by the power of the modulator, the time-width-bandwidth product of the generated chirp signal is small, which is difficult to meet the demand. The time-frequency domain splicing method combines the characteristics of abundant spectral resources in the optical domain and flexible signal generation in the electrical domain. The linear frequency modulation signal is generated by the electrical method, and the frequency conversion and delay line delay are used to obtain the splicing in the time-frequency domain. Large bandwidth, large time width chirp signal. Compared with other methods, the time-frequency domain splicing method has the advantages of large bandwidth, high flexibility, frequency tunability, and waveform reconfiguration. Programmable optical filters are expensive.

In order to generate a continuous chirp optical signal with a large time-width bandwidth product in time, frequency, especially phase, the present invention further improves the existing cyclic frequency shifting method, specifically, making the cyclic frequency shifting satisfy the following conditions :

The pulse width of the chirp optical pulse signal is equal to the loop delay of the cyclic frequency shift;

The pulse period of the chirp optical pulse signal is an integer multiple of the pulse width;

The signal bandwidth of the chirp 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 order to facilitate the public's understanding, the technical solutions of the present invention will be described in detail below through a specific embodiment and in conjunction with the accompanying drawings:

The basic structure of the laser and radio frequency composite radar detection device of this embodiment is shown in FIG. 1 . First, a beam of continuous optical carrier is generated by a narrow linewidth laser and enters into the optical coupler 1, which is split into two paths, one of which enters the DPMZM (Dual Parallel Mach-Zehnder Modulator) 1. By making the DPMZM1 work in the suppression The carrier single sideband modulation mode realizes the frequency shift of the input optical signal. The frequency shift frequency can be adjusted arbitrarily by changing the frequency of the added RF signal, and the frequency shifted optical signal is used as the reference optical signal; the other optical carrier signal enters the In the optical switch constructed by cascading Mach-Zehnder modulators and filters, an arbitrary waveform generator (AWG) is used to modulate a linear frequency modulated electrical pulse signal for the Mach-Zehnder modulator, and the Mach-Zehnder modulator works at a minimum The transmission point suppresses the carrier and the even-numbered sidebands, and then selects one of the positive and negative first-order sidebands to output through the filter, so that the optical switch generates a chirp optical pulse signal, and the pulse width and period of the chirp optical pulse signal are Consistent with the linear frequency modulated electrical pulse signal.

Next, the linear frequency modulated optical pulse signal output by the optical switch is input into the frequency shifting loop to perform cyclic frequency shifting. Common devices for frequency-shifting optical signals include acousto-optic modulators (AOMs) and dual parallel Mach-Zehnder modulators. The acousto-optic modulator uses the principle of acousto-optic effect to make the laser diffract to achieve the effect of frequency shifting. The advantage is that the frequency shifting precision is high and the frequency shifting effect is good; Between tens of megahertz and hundreds of megahertz, and its frequency shift direction is fixed and cannot be changed. The double-parallel Mach-Zehnder modulator uses electro-optical intensity modulation to excite high-order sidebands, and achieves the effect of frequency shifting by adjusting the phase relationship between the sidebands. Tuning, and the frequency shift direction can be changed by adjusting the bias voltage; the disadvantage is that there are too many variables to be controlled, the bias point is easy to drift, and the carrier and sideband suppression is not large enough. Both methods have advantages and disadvantages.

In this embodiment, a double-parallel Mach-Zehnder modulator is selected as the frequency-shifting device in the frequency-shifting loop; as shown in FIG. 2, the frequency-shifting loop includes an optical coupler 6, a double-parallel Mach-Zehnder modulator 2, an optical Coupler 7, optical amplifier four parts. By adjusting the parameters, the following conditions are satisfied: the pulse width of the chirp optical pulse signal is equal to the loop delay of the cyclic frequency shift; the pulse period of the chirp optical pulse signal is an integer multiple of the pulse width; the chirp The signal bandwidth of the 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-shifting loop is a chirp optical signal with large time width and large bandwidth that is continuously spliced in time, frequency and phase; it can be expressed as:

Among them, τ is the pulse width of the chirp optical pulse signal, _TL is the loop delay of the cyclic frequency shift, T _s is the pulse period of the chirp optical pulse signal, f _s is the frequency shift frequency of the cyclic frequency shift, and B is the Bandwidth of the chirp optical pulse signal, M and N are non-zero integers.

Then, through the optical filter, the noise and unnecessary optical sidebands in the linear frequency modulated optical signal are filtered out, and then it is divided into two paths through the coupler 2, one of which enters the optical circulator as the detection optical signal of the lidar, The other one is used as the local oscillator signal of the lidar.

The detection optical signal is input to port 1 of the optical circulator, output by port 2, and then enters an optical antenna, and the light in the optical fiber is converted into space light and emitted. After the detection optical signal detects the target, it returns to the original path. The return optical signal is input from the 2 port of the optical circulator through the optical antenna. The optical circulator separates it from the original optical signal, and the return optical signal is output at the 3 port. The return optical signal That is, it carries the detection information of the lidar.

As shown in FIG. 1 , the present invention multiplexes the echo signal of the laser radar, that is, the laser radar echo signal output by the circulator 3 port is coupled with a reference optical signal branched by the optical coupler 3 and is input into the optical coupler 4 , Beat the frequency at the photodetector 1 to obtain the electrical signal S2 carrying the detection information of the laser radar, input the linear frequency modulation electrical signal to the transmitting antenna and transmit it. Electrical signal S3.

Input the other reference optical signal branched by the optical coupler 3 and the chirp optical local oscillator signal branched by the optical coupler 2 to the optical coupler 5 for coupling, and beat the frequency at the photodetector 2 to obtain the laser radar detection signal. Reference electrical signal S1.

The reference signal S1 generated by the photodetector 2, the electrical signal S2 generated by the photodetector 1 that carries the detection information of the laser radar, and the electrical signal S3 that carries the detection information of the radio frequency radar received by the receiving antenna are input into the real-time oscilloscope for collection; S1, After the cross-correlation processing of the S2 signal, the detection information of the target by the laser radar can be obtained. After the cross-correlation processing of the S2 and S3 signals, the detection information of the target by the radio frequency radar can be obtained.

For a moving target, when the dual-parallel Mach-Zehnder modulator 1 does not modulate the optical carrier branched by the optical coupler 1, the pulse after cross-correlation processing has only one peak value, which only carries the distance and speed of the target. Coupling information. When the dual-parallel Mach-Zehnder modulator 1 modulates the optical carrier branched by the optical coupler 1, and meets the beat frequency of the linear frequency modulated optical signal generated by the cyclic frequency shifting module, a V-shaped double chirp signal is generated (the optical carrier When the frequency is shifted to a certain frequency in the middle of the chirp optical signal) or the X-type double chirp signal (the modulation output is two optical carriers that fall on both sides of the frequency range of the chirp optical signal), after cross-correlation processing The pulse signal contains two peaks, and after calculation, the speed information and distance information of the target can be obtained respectively. Therefore, a double-chirp electrical signal should be generated by adjusting the frequency-shifted optical signal output by the DPMZM1 and the beat frequency of the linear frequency-modulated optical signal generated by the cyclic frequency-shifting module.

The principle is further analyzed as follows:

One optical carrier signal from the laser enters the optical switch realized by the Mach-Zehnder modulator cascade filter. If the optical carrier entering the modulator is expressed as E ₀ =cos(ω ₀ t), use an arbitrary waveform generator ( AWG) inputting a chirp s(t) to the modulator can be expressed as:

where ω _m is the starting frequency of the signal, τ is the pulse width of the signal, T _s =Pτ is the signal period, k=B/4τ is the chirp rate of the signal, B is the bandwidth, and rect[x] is a rectangular window function ,Specifically:

According to the working principle of Mach-Zehnder modulator, the output can be expressed as:

V_π是调制器的半波电压，V_DC是偏置电压，用贝塞尔级数展开得：in,

V _π is the half-wave voltage of the modulator, and V _DC is the bias voltage, expanded by Bessel series:

m＝π/2V_π，若控制V_DC使

并且只考虑小信号调制，那么式(5)可以被改写为：in

m=π/2V _π , if V _DC is controlled to make

And only consider small signal modulation, then equation (5) can be rewritten as:

It can be seen that the output of the modulator has only positive and negative first-order sidebands, and after filtering out one of the sidebands with an optical filter, equation (6) can be written as:

It can be seen that a linear frequency modulated optical pulse signal is generated, and its pulse width and period are consistent with the pulse width and period of the single frequency pulse signal applied to the modulator.

The other signal from the optocoupler 1 enters the dual parallel Mach-Zehnder modulator 1 for modulation. The dual-parallel Mach-Zehnder modulator is composed of two push-pull Mach-Zehnder modulators (MZM) placed in parallel. If the input optical carrier expression is: E _a (t)=Acos(ω ₀ t), where ω ₀ is the angular frequency of the optical carrier, and A is the amplitude of the input optical carrier, according to the working principle of the dual parallel Mach-Zehnder modulator It can be seen that the output signal is:

为射频信号引入的相位差，

为三个偏置电压引入的相位差，m＝πV_A/2V_π为调制系数。Among them, the RF signal amplitude is 2V _A , the angular frequency is ω, V _π is the half-wave voltage,

The phase difference introduced for the RF signal,

The phase difference introduced for the three bias voltages, m=πV _A /2V _π is the modulation coefficient.

Expand formula (8) with Bessel series to get:

输出信号可化简为：By controlling the three bias voltages, the

The output signal can be simplified to:

Equation (10) shows that there is only one first-order sideband and one third-order sideband left in the output, and the third-order sideband can be suppressed by adjusting the RF signal voltage 2V _A to make J ₁ (m) >> J ₃ (m) .

Therefore, by changing the three bias voltages and the phase difference of the RF signal and the output voltage, the carrier single sideband can be suppressed, so that 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 adjusted It can be tuned arbitrarily by changing the frequency of the applied RF signal.

The linear frequency modulated optical pulse output by the optical switch is input into the optical frequency shifting loop for cyclic frequency shifting, and the system meets the

Formula 1). In this case, the output of the cyclic frequency shifting block can be expressed as:

说明相位也是连续的。这一点是尤其重要的，相较于目前方法：时频域拼接法需要对不同频率间隔的双光频梳进行相位锁定，成本高、结构复杂；常见的循环移频法通常只能保证拼接产生的线性调频信号在时间和频率上是连续的，而相位并不一定连续；本发明所采用的方案具有很大优势。Equation (11) represents the generation of an optical FM signal with a large time-width-bandwidth product, its starting frequency is ω ₀ +ω _m , and the bandwidth is PB. It can be seen that the signal is the time and frequency splicing of the signal generated by the original optical switch, and since τf _s =N, the phase difference at the splicing is

Note that the phase is also continuous. This is especially important, compared with the current method: the time-frequency domain splicing method requires phase locking of dual optical frequency combs with different frequency intervals, which is costly and complicated in structure; the common cyclic frequency shifting method usually only guarantees that the splicing produces The chirp signal is continuous in time and frequency, but the phase is not necessarily continuous; the scheme adopted in the present invention has great advantages.

When T _s = 5μs, τ = 500ns, f _s = 1GHz, and ω _m = 2GHz, the time-frequency curve is obtained through matlab simulation as shown in Figure 3. The bandwidth range after splicing is 2GHz-26GHz, indicating that this scheme has Cyclic frequency shifting produces a chirp signal that is continuous in time and frequency. At the same time, the time-domain waveforms of the linear frequency modulation signal generated by the existing cyclic frequency shifting method and the linear frequency modulation signal generated by this scheme are simulated respectively. The results are shown in Figure 4 and Figure 5. The cyclic frequency shifting method has the advantage of phase continuity.

Finally, the reference signal S1 generated by the photodetector 2, the electrical signal S2 generated by the photodetector 1 that carries the detection information of the laser radar, and the electrical signal S3 that carries the detection information of the radio frequency radar received by the receiving antenna are input into the real-time oscilloscope for collection; S1 After the cross-correlation processing of the S2 and S2 signals, the detection information of the target by the laser radar can be obtained. After the cross-correlation processing of the S2 and S3 signals, the detection information of the target by the radio frequency radar can be obtained.

In order to verify the effect of the technical solution of the present invention, the ranging functions of the laser radar and the radio frequency radar of the laser and radio frequency composite radar detection device of the present invention are simulated and verified respectively. The simulation of lidar is to use the method of adding an optical delay to simulate the distance information of the object detected by lidar. When the optical delay is 0 and the optical delay is 500ps, the cross-correlation pulse image of the echo signal and the local oscillator signal is made. The results are shown in Figure 6. The time coordinates corresponding to the peak values are 500.1ns and 500.6ns, respectively. That is to say, the variation of the loop delay is the same as the variation of the time coordinate of the peak value of the cross-correlation pulse. Therefore, the ranging capability of the lidar can be proved.

For the simulation of RF radar ranging, an electrical delay is added to simulate the distance information of the target object. The verification method is consistent with the lidar ranging system, and the results are within a certain error range, which can also verify the ranging capability of the system.

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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