Microwave photon single antenna radar radio frequency circulator leakage signal elimination method

Abstract

The application discloses a microwave photon single antenna radar RF circulator leakage signal elimination method, and belongs to the technical field of microwave photon technology.The system used by the method comprises a laser, a Mach-Zehnder modulator, an arbitrary waveform generator, an optical coupler, a first erbium-doped optical fiber amplifier, a second erbium-doped optical fiber amplifier, an electric power amplifier, a radar antenna, a low-noise amplifier, a double-parallel Mach-Zehnder modulator, an electric attenuator, an electric delay line, a first photoelectric detector and a second photoelectric detector of the RF circulator, a low-pass filter and a signal acquisition and processing module.The microwave photon radar is applied to overcome the disadvantages of traditional electronics in bandwidth, volume, weight and electromagnetic interference, and to overcome the interference problem of leakage signals in a single antenna continuous wave radar system.

Description

Technical Field

[0001] This invention belongs to the field of microwave photonics technology, and more specifically, it is a microwave photonics radar ranging system, which is a device for simultaneously ranging and eliminating the leakage signal of the radio frequency circulator in a single-antenna radar system. Background Technology

[0002] Radar is an instrument that uses electromagnetic waves to detect specific targets. With the continuous improvement of digital circuits, semiconductor technology, and circuit integration, radar is developing towards lower cost, lower power consumption, higher precision, and miniaturization. Besides military and aerospace applications, researchers are also extending radar technology to civilian fields, such as autonomous driving, city mapping, and vital signs monitoring. To meet diverse requirements, radar must rapidly and accurately acquire and identify targets in complex environments, day and night. To adapt to this need, radar technology and systems are constantly evolving. However, with the emergence of new detection targets, the electromagnetic properties of the detection environment and the targets themselves are becoming increasingly complex, placing higher demands on the development of modern radar technology and driving it towards larger bandwidth, multiple frequency bands, reconfigurability, and miniaturization.

[0003] However, due to the existence of the "electronic bottleneck," traditional electronic technology struggles to generate high-frequency, broadband, and high-quality signals. Microwave photonics technology, a multidisciplinary new technology, leverages its advantages to generate, process, transmit, and control a variety of complex microwave signals. Compared to traditional electronic technology, microwave photonics technology features large bandwidth, low transmission loss, and resistance to electromagnetic interference. It can generate wide-bandwidth signals in the optical domain and preprocess them to improve radar detection performance.

[0004] Because continuous wave (CFW) radar operates through continuous reception and transmission, its average power equals its peak power, resulting in small size, low interception rate, and no blind spots. CFW radar is widely used due to its ease of implementation, relatively simple structure, small size, light weight, and low cost. However, because CFW radar requires simultaneous transmission and reception, leakage to the receiver becomes significant when using a single antenna or two antennas in close proximity. Excessive leakage can decrease receiver sensitivity and even saturate the receiving front-end equipment. This has become a major obstacle to the development of FMCW radar. Several methods have been explored to address this issue, and many are now available for practical engineering design, including the use of circulators as isolation elements. In monostatic radar, where the transmitter and receiver share a single antenna, circulators are commonly used as isolation devices to separate the transmitted and received signals. Because circulators use anisotropic materials, signals entering from the transmitter can only exit from the antenna, and signals input from the antenna can only output from the receiver. Its working principle is simple, but its isolation performance is not ideal at high frequencies; the isolation of commonly used circulators is usually 25dB. Since the frequency of the leaked signal and the echo is the same, it is difficult to filter using electrical filters. Therefore, radio frequency cancellation technology is crucial for continuous waves from a single antenna. Summary of the Invention

[0005] In view of this, the main objective of this invention is to propose a system for eliminating leakage signals in a single-antenna frequency-doubled ranging radar based on microwave photonics modulation. The application of microwave photonics radar overcomes the disadvantages of traditional electronics in terms of bandwidth, size, weight, and electromagnetic interference, and also overcomes the interference problem of leakage signals in a single-antenna continuous wave radar system.

[0006] The specific technical solution of this invention is as follows:

[0007] A single-antenna radar based on microwave photonics technology simultaneously achieves radio frequency cancellation and frequency doubling ranging. The specific implementation link of the method includes a laser, a Mach-Zehnder modulator (MZM), a dual parallel Mach-Zehnder modulator (DPMZM), an arbitrary waveform generator, an optical coupler (OC), a first erbium-doped fiber amplifier, a second erbium-doped fiber amplifier, an electrical power amplifier, a radar antenna, a low-noise amplifier, a dual parallel Mach-Zehnder modulator, an electrical attenuator, an electrical delay line, an radio frequency circulator, a first photodetector, a second photodetector, a low-pass filter, and a signal acquisition and processing module. The DP-MZM includes an upper arm sub-MZM and a lower arm sub-MZM. The method includes the following steps:

[0008] Step 1: Generate a detection signal with a large instantaneous bandwidth, as follows:

[0009] The optical signal generated by the laser is injected into the Mach-Zehnder modulator (MZM) as an optical carrier. The radio frequency drive signal of the Mach-Zehnder modulator is an intermediate frequency linear frequency modulated signal generated by an arbitrary waveform generator. The DC bias voltage is tuned to make the MZM work at the minimum bias point and suppress the carrier and even-order sidebands.

[0010] Next, the output signal of MZM is split into two paths using a 50:50 coupler OC. One path is injected into the first photodetector for photoelectric conversion to obtain a second harmonic linear frequency modulated signal.

[0011] Finally, the signal is first amplified by a broadband power amplifier, then injected from the input port of the radio frequency circulator and transmitted into free space via the transmitter port to the radar antenna as a radar detection signal.

[0012] Step 2: Detect and suppress leakage signals

[0013] The output signal of the MZM is split off by a 50:50 coupler OC and injected as a reference signal into the dual parallel Mach-Zehnder modulator DP-MZM as its carrier. By tuning the driving voltage of the DP-MZM, both the upper and lower sub-MZMs of the DP-MZM operate at the quadrature bias point. The DP-MZM has two driving signals: the first driving signal is the microwave signal amplified by the first low-noise amplifier at the output of the RF circulator, and the second driving signal is the transmitted signal modulated by the electrical delay line and the electrical attenuator. The output of the DP-MZM is filtered by a low-pass filter and a second photoelectric detector, and then acquired by the signal acquisition and processing module. The low-frequency signal related to the target distance after eliminating self-interference signals can be obtained. Next, the target distance information can be obtained by solving this signal.

[0014] This invention utilizes a Mach-Zehnder modulator (MZM) at the transmitting end to double the frequency of an intermediate-frequency linear frequency modulated (LFM) signal generated by an arbitrary waveform generator, producing an LFM signal with a large instantaneous bandwidth, which is then transmitted into free space as a probe signal. The delayed phase-modulated transmitted signal and the microwave signal at the output of the RF circulator are used as the driving signals for a dual parallel Mach-Zehnder modulator (DP-MZM). Finally, by adjusting the main bias voltage of the dual parallel Mach-Zehnder modulator (DP-MZM), the signals modulated by the sub-MZMs are inverted to cancel each other out. The low-frequency signal related to the target distance after eliminating self-interference signals is then calculated to obtain the target distance information.

[0015] The beneficial effects of this invention are:

[0016] This invention proposes a dual-function system for single-antenna radar ranging and radio frequency cancellation based on microwave photonics technology. It combines microwave photonics cancellation and microwave photonics radar detection methods, utilizing a single radar detection signal to simultaneously achieve target distance measurement and cancel radio frequency self-interference of circulator leakage signals. The detection link constructed using the method described in this invention has a smaller size and lighter weight, making it more suitable for application in military and civilian environments, and it also solves the leakage signal interference problem inherent in single-antenna radar. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the link structure of a single-antenna radar ranging and radio frequency cancellation dual-function system based on microwave photonics modulation.

[0018] Figure 2 (a) Figure 1 Spectrum diagram of point a

[0019] Figure 2 (b) Figure 1 Spectrum diagram of point b

[0020] Figure 2 (c) Figure 1 Spectrum diagram at point c

[0021] Figure 2 (d) Figure 1 Spectrum diagram of point d Detailed Implementation

[0022] To address the issue of leakage signal interference in existing single-antenna radars, which affects detection performance, and the fact that existing detection links are bulky and heavy, hindering their application in military and civilian environments, this invention proposes a dual-function system for single-antenna radar ranging and radio frequency cancellation based on microwave photonics modulation. This system utilizes radar detection signals to simultaneously detect target distance, ultimately achieving radar ranging and circulator leakage signal cancellation.

[0023] The present invention relates to a detection method for a dual-function system of single-antenna radar ranging and radio frequency cancellation based on microwave photonics modulation, the process of which is as follows:

[0024] The optical signal generated by the narrow-linewidth laser enters a Mach-Zehnder modulator (MZM) as its optical carrier. The driving linear frequency modulated (LFM) signal of the MZM is generated by an arbitrary waveform generator. By tuning the DC bias voltage, the MZM is brought to its minimum operating state, thereby suppressing the carrier and the positive and negative first-order sidebands. The output signal of the MZM is amplified by an erbium-doped fiber amplifier (EDFA) and then injected into a 50:50 coupler to split it into two paths. One path enters a first photodetector, where it beats to obtain a frequency-doubled LFM signal. This frequency-doubled LFM signal is amplified by a broadband amplifier and then injected into an RF circulator before being transmitted into free space by a radar antenna as a radar detection signal. The other path is injected as a reference signal into a dual parallel Mach-Zehnder modulator (DP-MZM) as its carrier. The two driving signals of the DP-MZM are the microwave signal amplified by a first low-noise amplifier at the output of the RF circulator and the transmitted signal modulated by an electrical delay line and an electrical attenuator. The output of the DP-MZM is amplified by an erbium-doped fiber amplifier (EDFA), then low-pass filtered and photodetected. The signal is then acquired by a signal acquisition and processing module to obtain a distance-dependent low-frequency signal. Next, the distance to the target can be obtained by solving this signal.

[0025] To facilitate public understanding, the invention will be further explained below with reference to the accompanying drawings and mathematical derivations:

[0026] Figure 1 This is a schematic diagram of the link structure of a single-antenna radar ranging and radio frequency cancellation dual-function system based on microwave photonics modulation. It includes a laser, a Mach-Zehnder modulator (MZM), a dual parallel Mach-Zehnder modulator (DPMZM), an arbitrary waveform generator, an optical coupler (OC), a first erbium-doped fiber amplifier, a second erbium-doped fiber amplifier, an electrical power amplifier, a radar antenna, a low-noise amplifier, the dual parallel Mach-Zehnder modulator, an electrical attenuator, an electrical delay line, an radio frequency circulator, a first photodetector, a second photodetector, a low-pass filter, and a signal acquisition and processing module.

[0027] use Figure 1 The link structure shown illustrates the process of completing a non-cooperative target spatial location detection method based on microwave photonics technology as follows:

[0028] Step 1: Generate a detection signal with a large instantaneous bandwidth;

[0029] The optical signal generated by the continuous wave laser can be expressed as E(t) = E0exp(jωt). m t), where E0 and ω mLet represent the amplitude and center angular frequency of the optical signal, respectively, with j representing the imaginary unit. The optical signal is injected into a Mach-Zehnder modulator (MZM), serving as the modulated optical carrier. The intermediate frequency linear frequency modulated signal generated by the arbitrary waveform generator is used as the radio frequency drive signal for the MZM, expressed as:

[0030]

[0031] In the formula, V LFM f0, T, and k represent the amplitude, initial frequency, duration, and modulation slope of the intermediate frequency linear frequency modulated signal, respectively; and where... Let be a rectangular function, representing the envelope information of the signal; by adjusting the DC bias voltage to make the Mach-Zehnder modulator (MZM) operate at the minimum bias point, the carrier and even-order sidebands can be suppressed to obtain odd-order sidebands, as shown in Figure a. Therefore, the output signal of the MZM is expressed as:

[0032]

[0033] J n (m0) is a Bessel function of the first kind, where the value of n represents the order of the sideband, and J0(m0) represents the carrier amplitude, J1(m0) represents the positive first-order sideband amplitude, J -1 (m0) represents the amplitude of the negative first-order sideband. Here, m0 is the modulation coefficient of the MZM, i.e., m0 = πV LFM / V π1 V π1 This is the half-wave voltage of the Mach-Zehnder modulator MZM;

[0034] Next, the output signal is split into two paths using a 50:50 coupler. One path is injected into the first photodetector for photoelectric conversion and beat frequency generation, resulting in a second harmonic linear frequency modulated signal, as shown in Figure b. This signal can be represented as follows:

[0035]

[0036] The instantaneous frequency of the linear frequency modulated signal after frequency multiplication is f. LFM (t)=2(f0+kt); The frequency-doubled signal is injected into the power amplifier for amplification, transmitted from the input port of the RF circulator to the RF circulator, and then transmitted to free space by the radar antenna through the transmit port as a radar detection signal;

[0037] Step 2: Distance detection and suppression of RF circulator leakage signals

[0038] Another optical signal output from the OC is injected into the dual parallel Mach-Zehnder modulator DP-MZM at the receiver as a reference signal; after the signal is incident into the DP-MZM, the power is equally divided and enters the upper and lower sub-phase modulators MZM.

[0039] The radar antenna receives the echo signal from the target, which is transmitted from the transmitter port of the RF circulator to the output port. Due to insufficient isolation of the RF circulator, the signal output at the output port includes not only the echo signal received by the radar antenna but also a leakage signal that leaks directly from the input port to the output port. The echo signal V SOI (t) and leakage signal V Si (t) can be expressed as follows:

[0040] V SOI (t)=V SOI cos[4πf0(t+τ)+2πk(t+τ) 2 (4)

[0041] V Si (t)=V Si cos[4πf0(t+τ')+2πk(t+τ') 2 (5)

[0042] In the formula V SOI and V Si Let V represent the amplitudes of the echo signal and the leakage signal, respectively, and let τ and τ' represent the delays experienced by the echo signal and the leakage signal, respectively; here, the echo signal V SOI (t) and leakage signal V Si (t) is input as one modulation signal to the DPMZM for modulation. By splitting the modulated frequency-multiplying signal into one channel and then delaying and phase-modulating it, the reference signal V can be obtained. Sr (t), and input this signal into another MZM as a modulation signal, where the reference signal V is... Sr (t) is represented as

[0043] V Sr (t)=V Sr cos[4πf0(t'+μ)+2πk(t'+μ) 2 (6)

[0044] In the formula V Sr Let represent the amplitude of the reference signal, t' represent the delay experienced by the reference signal, and μ represent the delay introduced by the electrical delay line. By adjusting the two sub-MZMs of the dual parallel MAZM modulator to operate at the quadrature propagation point and the main bias voltage to operate at the minimum propagation point, the inversion between the reference signal and the self-interference signal is achieved, as shown in Figure c. Then, the output of the DPMZM can be expressed as...

[0045]

[0046] Where, m SOI =πV SOI / V π ,m Si =πV Si / V π ,m Sr＝ πV Sr / V π θ represents the modulation depth of the echo signal, interference signal, and reference signal, respectively, and θ represents the optical phase shift caused by the DC bias applied to the DPMZM master bias point.

[0047] As can be seen from equation (7), to eliminate Si, the amplitudes and delays of Sr and Si at the DPMZM must be consistent. Simultaneously, the signal phase must be adjusted by regulating the main bias voltage, thereby achieving phase inversion. Therefore, the following conditions must be met.

[0048]

[0049] After satisfying condition (8), the output optical signal of the DPMZM can be expressed as:

[0050]

[0051] By using a filter to select the signal related to f0+kt and f0+kt+2kτ, as shown in Figure d, and then using a photodetector to perform beat frequency analysis, the intermediate frequency signal related to the target distance information is obtained. The frequency of this signal is Δf=2kτ. Therefore, the target distance information can be calculated.

[0052]

[0053] In the formula, c represents the speed of light; B = kt is the bandwidth of the signal.

[0054] In summary, this invention proposes a dual-function system for single-antenna radar ranging and radio frequency cancellation based on microwave photonics technology. It combines microwave photonics cancellation and microwave photonics radar detection methods, utilizing a single radar antenna and a radio frequency circulator to simultaneously detect target distance and cancel radio frequency leakage signals from the circulator. This solves the problem of radio frequency circulator leakage signal interference inherent in single-antenna radar systems.

Claims

1. A radio frequency circulator leakage signal cancellation system for microwave photonic single-antenna radar, characterized in that, The system includes: A laser (1) is used to provide continuous probe light for the Mach-Zehnder modulator (3); An arbitrary waveform generator (2) is used to provide a modulation signal, a linear frequency modulation signal, for the Mach-Zehnder modulator (3); A Mach-Zehnder modulator (3) modulates the input light from the laser (1) with a linear frequency modulation signal loaded by an arbitrary waveform generator (2) and outputs an odd-order modulated light signal. —The first erbium-doped fiber amplifier (4) is used to amplify the optical signal modulated by the Mach-Zehnder modulator (3); A first photodetector (5) is used to perform photoelectric conversion on the optical signal amplified by the first erbium-doped fiber amplifier (4) to obtain a second harmonic signal; —Electrical amplifier (6) is used to increase the power of the frequency-doubled electrical signal obtained by photoelectric conversion of the first photodetector (5); A radio frequency circulator (7) transmits the frequency-doubled signal amplified by the electric amplifier (6) to the radar antenna (8) for transmission, and at the same time transmits the echo signal received by the radar antenna (8) to the low noise amplifier (9). —The radar antenna (8) transmits the frequency-doubled signal transmitted from the radio frequency circulator (7) into free space and receives the echo signal of the target being detected; —The low-noise amplifier (9) amplifies the signal output by the radio frequency circulator (7), including the echo signal received by the radio frequency circulator (7) and the leakage signal of the radio frequency circulator (7); A dual parallel Mach-Zehnder modulator (10) is used to modulate the optical signal from the Mach-Zehnder modulator (3), the signal from the first photodetector (5) whose power is adjusted by the electrical attenuator (11) and then delayed and phase-modulated by the electrical delay line (12), and the received signal amplified by the low noise amplifier (9) are used as the modulated radio frequency signal. The leakage signal elimination and the deskewing modulation of the received echo signal are realized at the dual parallel Mach-Zehnder modulator (10). —Electrical attenuator (11) adjusts the amplitude of the optical signal output by the Mach-Zehnder modulator (3) to match the conditions for eliminating leakage signals; —Electrical delay line (12) adjusts the phase of the optical signal output by the Mach-Zehnder modulator (3) to match the conditions for eliminating leakage signals; A filter (13) is used to select the desired frequency signal in the optical signal modulated by the line Mach-Zehnder modulator (10); —The second erbium-doped fiber amplifier (14) is used to amplify the optical signal selected by the filter (13); A second photodetector (15) is used to convert the optical signal obtained by the filter (13) into an electrical signal to obtain the distance information of the target; Step 1: Generate a detection signal with a large instantaneous bandwidth; The optical signal generated by the continuous wave laser is represented as: , among them and Let represent the amplitude and center angular frequency of the optical signal, respectively, with j representing the imaginary unit. The optical signal is injected into a Mach-Zehnder modulator (MZM), serving as the modulated optical carrier. The intermediate frequency linear frequency modulated signal generated by the arbitrary waveform generator is used as the radio frequency drive signal for the MZM, expressed as: (1)； In the formula, , , and These represent the amplitude, initial frequency, duration, and modulation slope of the intermediate frequency linear frequency modulated signal, respectively; and where... Let be a rectangular function, representing the envelope information of the signal; by adjusting the DC bias voltage to make the Mach-Zehnder modulator (MZM) operate at the minimum bias point, suppressing the carrier and even-order sidebands to obtain odd-order sidebands, the output signal of the MZM is expressed as: (2)； J n (m0) is a Bessel function of the first kind, where the value of n represents the order of the sideband, and J0(m0) represents the carrier amplitude, J1(m0) represents the positive first-order sideband amplitude, J -1 (m0) represents the magnitude of the negative first-order sideband; here The modulation coefficients of MZM, i.e. ,in This is the half-wave voltage of the Mach-Zehnder modulator MZM; Next, a 50:50 coupler is used to split the output signal into two paths. One path is injected into the first photodetector for photoelectric conversion and beat frequency modulation, resulting in a second harmonic linear frequency modulated signal, denoted as... (3)； The instantaneous frequency of the linear frequency modulated signal after frequency multiplication is The frequency-doubled signal is injected into the power amplifier for amplification, transmitted from the input port of the radio frequency circulator to the radio frequency circulator, and then transmitted from the transmitter port to the radar antenna into free space as a radar detection signal. Step 2: Distance detection and suppression of RF circulator leakage signals The other optical signal output from the coupler is injected into the dual parallel Mach-Zehnder modulator DP-MZM at the receiver as a reference signal; after the signal is incident into the DP-MZM, the power is equally divided and enters the upper and lower sub-phase modulators MZM. The radar antenna receives the echo signal from the target, which is transmitted from the transmitter port of the RF circulator to the output port. Due to insufficient isolation of the RF circulator, the signal output at the output port includes not only the echo signal received by the radar antenna but also a leakage signal that leaks directly from the input port to the output port. The echo signal V SOI (t) and leakage signal V Si (t), respectively denoted as （4）； （5）； In the formula V SOI and V Si Let V represent the amplitudes of the echo signal and the leakage signal, respectively, and let τ and τ' represent the delays experienced by the echo signal and the leakage signal, respectively; here, the echo signal V SOI (t) and leakage signal V Si (t) is input as one modulation signal to the DPMZM for modulation. The reference signal V is obtained by splitting the modulated frequency-multiplied signal, delaying and phase-modulating it. Sr (t), and input this signal into another MZM as a modulation signal, where the reference signal V is... Sr (t) is represented as （6）； In the formula V Sr Let represent the amplitude of the reference signal, t' represent the delay experienced by the reference signal, and μ represent the delay introduced by the electrical delay line. The two sub-MZMs of the dual parallel MAZM are adjusted to operate at the quadrature propagation point, and the main bias voltage operates at the minimum propagation point to achieve phase inversion between the reference signal and the self-interference signal. The output of the DPMZM is expressed as... （7）； Where, m SOI = πV SOI / V π ,m Si = πV Si / V π ,m Sr= πV Sr / V π These represent the modulation depths of the echo signal, interference signal, and reference signal, respectively, and θ represents the optical phase shift caused by the DC bias applied to the DPMZM master bias point. As can be seen from equation (7), to eliminate Si, the amplitudes and delays of Sr and Si at the DPMZM must be consistent. Simultaneously, the signal phase must be adjusted by regulating the main bias voltage, thereby achieving phase inversion. Therefore, the following conditions must be met. （8）； After satisfying condition (8), the output optical signal of DPMZM is expressed as follows: （9）； By using a filter to select the signal related to f0+kt and f0+kt+2kτ, and then using a photodetector to perform beat frequency analysis, an intermediate frequency signal related to the target distance information is obtained, with the frequency of this signal being Δf=2kτ. The target distance information can then be calculated. (10)； In the formula, c represents the speed of light; This represents the bandwidth of the signal.

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