Broadband radar receiver based on photon time stretching

Abstract

A novel broadband radar receiver based on photonic time-stretching technology includes a broadband light source, a first dispersion module, an optical filtering module, an electro-optic modulation module, a receiving antenna module, a second dispersion module, an optical power divider module, a first photoelectric conversion module, a first analog-to-digital conversion module, a first digital signal processing module, a third dispersion module, a second photoelectric conversion module, a second analog-to-digital conversion module, and a second digital signal processing module. This radar receiver uses photonic time-stretching technology to perform real-time detection, reception, and matched filtering of the echo signal from the target. Leveraging the ultra-high speed and large bandwidth advantages of photonic time-stretching technology, it simplifies the original digital DSP processing, significantly improving signal processing speed and providing a feasible solution for real-time signal processing. This system receives microwave signals in the photonics domain, offering advantages such as high bandwidth and low noise performance. Its operating frequency is reconfigurable, making it widely applicable in ultra-wideband radar, digital communication, and other information technology fields.

Description

TECHNICAL FIELD

[0001] The present application relates to photonic information processing, in particular, a wideband radar receiver based on photonic time-stretch technology. BACKGROUND

[0002] After decades of development, modern radar systems have multiple functions, multiple frequency bands and digitalization, and the new generation of radar systems are developing towards wideband, integration, miniaturization and reconfigurable characteristics. The detection means of modern radar systems has been expanded to multiple forms such as microwaves, infrared light, laser and the like, and the additional functions implemented include search, identification, tracking, imaging and classification.

[0003] The increase of radar signal bandwidth not only directly increases the detection resolution, but also facilitates the integration of multiple functions of the radar system. At present, the channelization scheme is mainly used for the reception of wideband signals in radar systems, that is, a plurality of narrowband systems are used to sample the wideband signals, so as to reduce the performance requirements of the sampling system. With the increase of signal bandwidth, the number of channels increases exponentially, and interference such as spurs and noise is inevitably introduced, which seriously affects the detection performance of the radar system and limits the development of radar multi-function integration. The effective combination of microwave photonics technology and radar technology can greatly improve the bandwidth and frequency band of radar transmission signals, and greatly improve the distance resolution and multi-function integration capability of the radar, by taking advantage of the characteristics that the frequency and bandwidth of light waves are much higher than those of microwaves, and by converting light waves into microwaves.

[0004] As a device for detecting high-altitude and high-speed moving targets, the radar must be able to receive and process the echo signal in real time in order to accurately detect the target and obtain the effective position of the target. However, the traditional photonic time-stretch-based scheme needs to combine wavelength division multiplexing or time division multiplexing to receive the signal in segments, and finally splice the signals in the time domain to obtain the complete radar echo signal. This process faces the problem of whether the flatness of the receiving aperture of each channel is consistent. The non-flatness of each channel will cause nonlinear distortion of the signal. In addition, in the splicing process, the problem of whether the phase of the signal time domain segment is continuous is faced. If the phase of the signal is not continuous, the "spliced" signal is still multiple signals, rather than a complete signal. The above problems will cause the resolution of the recovered signal after matched filtering to be unable to reach the resolution corresponding to the transmitted signal, which seriously limits the performance of the radar. SUMMARY

[0005] The present application aims at the deficiencies of the prior art and the processing requirements of future radar signal multi-function and integration, and proposes a new type of wideband radar receiver based on two-way different stretching multiple photon time stretching technology.Based on the advantage of processing wideband radio frequency signals by photon time stretching technology, the signal processing is carried out in the analog domain by using two-way different stretching multiple photon time stretching technology, the frequency band and bandwidth of the echo signal are compressed by multiple times, and the ranging and one-dimensional image imaging functions of the target to be measured are realized by using the matching filter technology.In addition, by using the advantages of super high speed and large bandwidth of the photon time stretching technology, the original DSP processing process in the digital domain is simplified, the signal processing speed is greatly improved, and a feasible scheme for real-time signal processing is provided.

[0006] The technical scheme of the present application is as follows:

[0007] A new type of wideband radar receiver based on photon time stretching technology, characterized in that it comprises a wide spectrum light source, a first dispersion module, an optical filter module, an electro-optical modulation module, a receiving antenna module, a second dispersion module, an optical power division module, a first photoelectric conversion module, a first analog-digital conversion module, a first digital signal processing module, a third dispersion module, a second photoelectric conversion module, a second analog-digital conversion module and a second digital signal processing module.

[0008] The period of femtosecond optical pulse of the wide spectrum light source is T R , after the first dispersion module with dispersion amount βps / nm and the optical filter module with bandwidth T R / βnm, the femtosecond pulse of the wide spectrum light source is expanded to an optical pulse with time length T R , the time length of the optical pulse is equal to the period of the optical pulse, the duty cycle is 100%, and the receiving aperture (i.e. the time length of the pulse) formed by the expanded optical pulses of different periods can cover the entire time domain, and the receiving aperture of the kth period can be expressed as [T d +kT R ,T d +(k+1)T R ].

[0009] The receiving antenna module is used for receiving the radio frequency echo signal reflected by the target to be measured and transmitting it to the electro-optical modulation module, the expanded optical pulse is transmitted to the electro-optical modulation module and is modulated by the radio frequency echo signal.Setting the radio frequency echo signal as r(t), the time length as T S , and the delay relative to the reference clock as T d +kT R +t d , the time domain range of this signal can be expressed as [T d +kT R +t d ,T d+kT R +t d +T S ], when satisfying t d +T S <T R Under certain conditions, the signal can be completely received by the receiving aperture of the k-th period.

[0010] After the modulated optical pulse signal passes through the second dispersion module, the pulse signal is further broadened due to the dispersion effect. Let the dispersion of the second dispersion module be (M-1)βps / nm, then the duration of the broadened optical pulse is MT. R At this point, the receiving aperture of the k-th cycle can be expressed as [kT] R +MT d ,(k+M)T R +MT d ], T d The delay caused by the dispersion effect of the longer wavelength of the broadband optical pulse means that the reference clock time becomes MT. d This inevitably leads to the receiving aperture of the k-th cycle overlapping with the receiving apertures of the (k+1)th, ..., (k+(M-1))th cycles in the time domain. At this point, the time domain range of the modulated signal is [kT]. R +MT d +Mt d ,kT R +MT d +M(t d +T S If the signal appears in the stretched overlapping interval [(k+1)T], R +MT d ,(k+M)T R +MT d Within [T], it will be impossible to infer whether the signal before stretching was modulated within [T]. d +kT R ,T d +(k+1)T R Although the above derivation is based on the premise that the signal is completely received by the receiving aperture of the k-th cycle, in practice we can only obtain the time-domain position of the finally stretched signal. This is essentially because the pulse obtained through matched filtering has a delay difference kT relative to the reference clock. R +Mt d Includes k and t d These two variables cause a "temporal ambiguity" problem, which can be seen in the following diagram. Figure 2 The green part represents the overlap between the receiving aperture of the k-th cycle and the receiving aperture of subsequent cycles.

[0011] To solve for k and td The two variables are divided into two paths by the optical power division module, introduce two different stretching factors of photon time stretching, one path is transmitted to the first digital signal processing module through the first photoelectric conversion module and the first analog-digital conversion module in turn, and the pulse compression is performed on the radio frequency signal with the stretching factor M; the other path is transmitted to the second digital signal processing module through the third dispersion module with the dispersion amount of (N-M) βps / nm, the second photoelectric conversion module and the second analog-digital conversion module in turn, and the pulse compression is performed on the radio frequency signal with the stretching factor N. After N times of time stretching, the time domain range of the modulated signal is [kT R +NT d +Nt d ,kT R +NT d +N(t d +T S )]. Since the stretching starting points of different receiving apertures are different, the time domain positions before signal stretching can be deduced according to the pulse compression results of two different stretching factors at this time. Similarly, the delay difference kT R +Nt d of the pulse relative to the reference clock can be obtained after the matched filtering processing. The following equation group is solved:

[0012]

[0013] Wherein, C M and C N are constants, which can be obtained by matched filtering, and the delay t d of the target to be measured relative to the reference clock can be obtained by the above equation. The position information of the target can be obtained by calculating (T d +kT R +t d )c / 2.

[0014] The wide spectrum light source can be implemented by but not limited to a distributed feedback laser, a passive mode-locked laser, an active mode-locked laser, a tunable laser or a modulation frequency comb, etc.

[0015] The optical filtering module is used to filter out the spectrum of a specific wavelength range, and has the ability of tunability. Spatial optical filter, fiber grating filter, waveguide, etc. can be used but not limited to.

[0016] The optical power division module can be implemented by but not limited to a crystal waveguide polarization beam splitter, a silicon-based nanowire optical waveguide polarization beam splitter or a micro-nano optical fiber polarization beam splitter.

[0017] The electro-optical modulation module can adopt, but is not limited to, a lithium niobate electro-optical modulator, a polymer electro-optical modulator, a silicon-based integrated electro-optical modulator, an acousto-optic modulator or a spatial light modulator. The modulation mode adopts, but is not limited to, a carrier-suppressed double-sideband modulation, a carrier-suppressed single-sideband modulation, a phase modulation or an intensity modulation. The photoelectric conversion module is used for converting the modulated optical pulse signal into an electrical signal, and generating a time-domain bandwidth-expanded compressed received microwave signal. The photoelectric conversion module can be realized by adopting, but is not limited to, a PIN tube or an APD tube.

[0018] The analog-to-digital conversion module can adopt, but is not limited to, an electrical analog-to-digital converter or an optical analog-to-digital converter.

[0019] The data processing module is used for processing the collected data, and can adopt, but is not limited to, a digital signal processor or computer software.

[0020] The receiving antenna module can adopt, but is not limited to, a horn antenna, a microstrip antenna, a phased array antenna and the like, and can be realized in combination with, but is not limited to, a type A and type B complementary symmetrical power amplification circuit and a power BJT.

[0021] Compared with the prior art, the present application has the following advantages:

[0022] 1. The frequency and bandwidth of the wideband high-frequency signal returned by the target to be measured are compressed by a factor of the photon time stretching technology, the compressed narrowband signal is pulse compressed in real time by the matched filtering of the digital signal processing module, and then the target distance and one-dimensional image information are obtained. In the analog domain, the time stretching technology can reduce the frequency band and bandwidth of the radar echo signal, can greatly reduce the signal sampling and one-dimensional image imaging processing difficulty of the digital back end, and greatly improves the timeliness of the radar receiver to receive the signal.

[0023] 2. The photon time stretching processing technology with two different stretching multiples can eliminate the problem that the adjacent processing windows overlap due to the continuous widening of the optical pulse by the second dispersion module when the processing window duty cycle is equal to 100% after the wide-spectrum light source is widened by the first dispersion module.

[0024] 3. The present application has the advantages of high bandwidth and low noise performance in the field of photonics for receiving microwave signals, and the working frequency is reconfigurable, which can be widely used in the fields of ultra-wideband radar, digital communication and the like. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 The present application is a new type of wideband radar receiver system architecture based on photon time stretching technology.

[0026] Figure 2 The present application is a radar receiver receiving mode schematic diagram.

[0027] Figure 3 For the specific implementation case of the present application, to characterize the time delay difference of the signal after stretching treatment relative to the reference signal, Figure a is the pulse compression result of a group of simulated echo signals after photon time stretching treatment with a stretching factor of 3, and Figure b is the pulse compression result of the same group of simulated echo signals after photon time stretching treatment with a stretching factor of 4. DETAILED DESCRIPTION

[0028] A specific embodiment of the present application is given below in combination with the drawings. The present embodiment is implemented on the premise of the technical solution of the present application, and a detailed implementation manner and process are given, but the protection scope of the present application is not limited to the following embodiment.

[0029] The present embodiment refers to Figure 1 , Figure 2 and Figure 3 , the wideband radar receiver system based on the time stretching technology of two different stretching factors includes a wide spectrum light source 1, a first dispersion module 2, an optical filtering module 3, an electro-optical modulation module 4, a receiving antenna module 5, a second dispersion module 6, an optical power splitting module 7, a first photoelectric conversion module 8, a first analog-digital conversion module 9, a first digital signal processing module 10, a third dispersion module 11, a second photoelectric conversion module 12, a second analog-digital conversion module 13, and a second digital signal processing module 14.

[0030] The wide spectrum light source 1 generates a wide spectrum ultrashort pulse with a certain repetition frequency. After passing through the first dispersion module 2, the optical pulse is stretched into a chirped optical pulse in the time domain due to the group velocity dispersion effect, that is, the components of different wavelengths propagate at different speeds in the optical fiber. After passing through the optical filtering module 3, only a specific range of spectrum is retained, and a virtual time receiving window is formed within a specific time range, as shown in Figure 2 The time length of the receiving aperture is adjusted by adjusting the bandwidth of the optical filtering module 3 and the dispersion amount of the first dispersion module 2, and the time length of the receiving aperture is close to the repetition period of the output optical pulse of the wide spectrum light source 1. The radio frequency echo signal reflected by the target to be measured passes through the receiving antenna module 5, is modulated onto the optical pulse by the electro-optical modulation module 4, is further broadened after passing through the second dispersion module 6, and is then split into two paths by the optical power splitting module 7 for photon time stretching with different stretching factors.

[0031] Suppose the femtosecond optical pulse period of the wide spectrum light source is T R= 10 ns, the femtosecond pulse of the wide spectrum light source is stretched into a light pulse with a time length of 10 ns after passing through a first dispersion module with a dispersion amount of 1000 ps / nm and a light filtering module with a bandwidth of 10 nm, the time length of the light pulse is equal to the period of the light pulse, and the duty cycle is 100%. The receiving aperture formed by the light pulses of different periods (i.e., the time length of the pulse) can cover the entire time domain, and the receiving aperture of the kth period can be represented as [10k, 10(k+1)] ns.

[0032] The receiving antenna module is used to receive the radio frequency echo signal reflected by the target to be measured and transmit to the electro-optical modulation module. The above-mentioned stretched light pulse is transmitted to the electro-optical modulation module and modulated by the radio frequency echo signal. Assuming that the radio frequency echo signal is r(t), the time length is 4 ns, and the delay corresponding to the reference clock is (10k+t d ) ns. The time domain range of this signal can be represented as [10k+t d , 10k+t d +4] ns. Under the condition that t d +4 < 10 is satisfied, the signal can be completely received by the receiving aperture of the kth period.

[0033] The modulated light pulse signal passes through the second dispersion module, and due to the dispersion effect, the pulse signal is further stretched. Assuming that the dispersion amount of the second dispersion module is 3000 ps / nm, the time length of the stretched light pulse is 4T R at this time. The receiving aperture of the kth period can be represented as [10k+4T d , 10(k+4)+4T d ] ns, and T d is the delay of the long wavelength of the wide spectrum light pulse due to the dispersion effect, which inevitably leads to the overlap of the receiving aperture of the kth period with the receiving apertures of the subsequent k+1th, …, k+(M-1)th periods in the time domain. At this time, the time domain range of the modulated signal is [10k+4T d +4t d , 10k+4T d +4(t d +4)] ns. If the signal appears in [(k+1)10+4t r , (k+4)10+4t r ] ns, it cannot be determined whether the signal before stretching is modulated in [10k, 10(k+1)]. Although the above derivation process is based on the complete reception of the signal by the receiving aperture of the kth period, in practice, we can only obtain the time domain position of the signal after stretching, and cannot know the time domain position of the signal after being modulated by the electro-optical modulation module, so the "time ambiguity" problem occurs.

[0034] To address this issue, the optical pulse signal is split into two paths by the aforementioned optical power divider module, introducing two photon time stretching paths with different stretching factors. One path sequentially passes through the first photoelectric conversion module and the first analog-to-digital conversion module before being transmitted to the first digital signal processing module, where the RF signal with a stretching factor of 4 undergoes pulse compression. The other path sequentially passes through the third dispersion module with a dispersion factor of 2000 ps / nm, the second photoelectric conversion module, and the second analog-to-digital conversion module before being transmitted to the second digital signal processing module, where the RF signal with a stretching factor of 3 undergoes pulse compression. After a 3x time stretch, the time domain range of the modulated signal is [10k+3T]. d +3t d 10k+3T d +3(t d +4)]ns. At this point, the time domain position of the signal before stretching can be inferred from the compression results of the two pulses with different stretching factors. Assume that the delay difference between the pulse obtained after matched filtering and the reference clock is C. M =18ns, C N =16ns, by solving the system of equations

[0035]

[0036] You can get t d =2ns, the actual target distance relative to the reference target is (T d +kT R +t d c / 2 = 1.8m. To verify more complex scenarios, we simulated a set of echo signals with delays relative to the reference signal set to 5ns, 10ns, 12ns, and 15ns, respectively. Taking simulations with 3x and 4x photon time stretching as examples, ... Figure 3 The image shows the pulses obtained after the stretched signal is processed by matched filtering. Relative to the reference pulse, the delay differences of the pulses after 3x stretching are 10ns, 15ns, 16ns, and 25ns, respectively; and the delay differences of the pulses after 4x stretching are 10ns, 18ns, 20ns, and 30ns, respectively. Using the above equations, the delay differences of the original echo signals of each target under test relative to the reference signal can be calculated to be 5ns, 10ns, 12ns, and 15ns, respectively. This verifies that the above scheme can solve the problem of the inability to recover the original signal delay difference caused by the overlap of adjacent receiving apertures.

[0037] The application carries out real-time detection and reception on echo signals of a target to be measured by a photon time stretching technology and carries out matched filtering processing, so that distance and one-dimensional image of the target are obtained, and the application has the advantages of high bandwidth and low noise performance, and the working frequency is reconfigurable, and can be widely used in the fields of ultra-wideband radar, digital communication and other information technology fields.

Claims

1. A wideband radar receiver based on photon time stretching, characterized by, The system comprises a wide spectrum light source (1), a first dispersion module (2), a light filtering module (3), an electro-optical modulation module (4), a receiving antenna module (5), a second dispersion module (6), an optical power splitting module (7), a first photoelectric conversion module (8), a first analog-digital conversion module (9), a first digital signal processing module (10), a third dispersion module (11), a second photoelectric conversion module (12), a second analog-digital conversion module (13) and a second digital signal processing module (14). The receiving antenna module (5) is used for receiving the radio frequency echo signal reflected by the target to be measured and transmitting the radio frequency echo signal to the electro-optical modulation module (4); the wide spectrum light source (1) generates wide spectrum ultrashort pulses, which are stretched into chirped light pulses in the time domain after the first dispersion module (2); the chirped light pulses are filtered by the light filtering module (3) and then transmitted to the electro-optical modulation module (4) and modulated by the radio frequency echo signal. The modulated light pulse signal is further broadened by the second dispersion module (6) and then split into two paths by the optical power splitting module (7). The modulated optical pulse signal is transmitted to the first digital signal processing module (10) after the first photoelectric conversion module (8) and the first analog-digital conversion module (9) in sequence, and the radio frequency signal with the stretching multiple M is pulse compressed, at this time, the time domain range of the modulated signal is wherein, is the repetition period of the wide spectrum optical pulse, is the delay of the long wavelength of the wide spectrum optical pulse due to the dispersion effect, is the delay of the echo signal of the target to be measured relative to the reference signal, k is the kth period, is the time length; Another modulated optical pulse signal is transmitted to the second digital signal processing module (14) after sequentially passing through the third dispersion module (11), the second photoelectric conversion module (12) and the second analog-digital conversion module (13), and pulse compression is performed on the radio frequency signal with a stretching multiple of N, at this time, the time domain range of the modulated signal is , and N≠M. The dispersion amount of the first dispersion module (2) is The dispersion amount of the second dispersion module (6) is The dispersion amount of the third dispersion module (11) is It is ensured that the stretching multiple N of the second path is not equal to the stretching multiple M of the first path, i.e. N≠M, so that the first and second digital signal processing modules can jointly calculate the original time delay information of the echo signal from the same target based on the processing results of two different stretching multiples, to eliminate time ambiguity.

2. The photonic time-stretched wideband radar receiver of claim 1, wherein, Let the radio frequency echo signal be , the time length is , the reference clock is the time when the echo signal of the reference target is modulated on the receiving aperture of the photon stretching system, and it is assumed that the receiving aperture where the echo signal of the reference target is modulated is the 0th cycle receiving aperture, the delay relative to the reference clock is , the time domain range of the radio frequency echo signal is expressed as , wherein is the delay of the long wavelength of the wide spectrum light pulse due to the dispersion effect, is the repetition period of the wide spectrum light pulse, is the delay of the echo signal of the target to be measured relative to the echo signal of the reference target, is the time length of the echo signal of the target to be measured; When the radio frequency echo signal is received completely by the receiving aperture of the kth period of the photonic time stretch system; Let the dispersion of the second dispersion module (6) be , the time length of the stretched optical pulse be , the receiving aperture of the kth period be , the time of the reference clock be , the receiving aperture of the kth period overlap with the receiving aperture of the k+1th, …, k+(M-1)th period in time domain; the time domain range of the modulated signal be , the time domain range of the modulated signal be after N times of time stretching. The time length of the virtual time receiving window is adjusted by solving the following equation group: wherein, and is a constant, the echo signal of the scattering point after the photon time stretching processing is relative to the delay of the reference signal, and is obtained by the matched filtering. The delay of the target to be measured relative to the reference clock can be obtained by the above equation , and the position information of the target can be obtained by calculating , wherein c is the speed of light.

3. A novel wideband radar receiver based on photonic time-stretch technique as claimed in claim 1, wherein, The time length of the virtual time receiving window is adjusted by adjusting the bandwidth of the light filtering module (3) and the dispersion amount of the first dispersion module (2), and the time length of the receiving aperture is close to the repetition period of the output light pulse of the wide spectrum light source (1).

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