A multi-target three-coordinate detection method based on microwave photon technology

Abstract

A multi-target three-coordinate detection method based on microwave photon technology belongs to the intersection field of microwave photon and radar. The method combines microwave photon technology and radar detection technology, adopts a photon frequency multiplication means to generate a wideband transmitting signal to detect targets, uses a cross-shaped antenna array with a symmetrical structure to receive echoes and performs desquaring processing on the echoes. Symmetry analysis is performed on the frequency of the desquaring signal obtained through the desquaring processing, distance, azimuth and elevation detection information of different targets are distinguished, and distance, azimuth and elevation information of multiple targets are simultaneously detected. The method is not sensitive to laser power fluctuation and modulator bias point drift, and therefore has better stability; the baseline length of the receiving antenna does not have to be less than half a wavelength, and therefore a large-aperture receiving antenna array can be used to obtain higher detection precision; beam scanning is required, and real-time monitoring of a large directional range can be realized.

Description

Technical Field

[0001] This invention proposes a method for detecting the range, azimuth, and elevation angles of multiple targets based on microwave photonics technology. This method belongs to the technical field of microwave photonics and radar intersection. Background Technology

[0002] Radar, one of the most important inventions in 20th-century electronic engineering, uses radio waves to detect targets. Compared to optical and infrared detection methods, radar offers all-weather, all-day, and long-range operation capabilities, finding wide application in both daily life and military fields. Radar needs to detect targets rapidly to pave the way for subsequent long-range early warning, high-precision positioning, and high-resolution imaging, all of which require radar systems with greater instantaneous bandwidth and higher functional integration. Currently, radar systems based on traditional electronic technology face the challenge of "electronic bottlenecks," resulting in limited detection performance, complex system structures, and large sizes. Microwave photonics technology, with its advantages of high bandwidth, resistance to electromagnetic interference, small size, and low transmission loss, can generate and process broadband radar signals in the optical domain, providing an effective means to enhance the performance of radar detection systems.

[0003] When detecting targets, radar systems are required not only to acquire range, azimuth, and elevation information for different targets, but also to have a wide-range directional detection capability to simultaneously detect targets located in various directions. Existing microwave photonic radar detection methods suffer from poor simultaneous multi-target detection capability and a small directional detection range, making them ill-suited for the task of simultaneously detecting range, azimuth, and elevation of multiple targets within a large directional detection range. Summary of the Invention

[0004] To address the limitation of existing microwave photonic radar detection technology in simultaneously measuring the range, azimuth, and elevation angles of multiple targets over a wide directional range, thus hindering its application in practical military and civilian environments, this invention proposes a multi-target range, azimuth, and elevation angle detection method based on microwave photonic technology. This method combines microwave photonic technology with radar detection technology, employing photonic frequency doubling to generate a broadband transmission signal for target detection. A symmetrical cross-shaped antenna array is used to receive the echoes, which are then de-skewed. Symmetry analysis is performed on the frequency of the de-skewed signal to distinguish the range, azimuth, and elevation angle detection information of different targets, enabling simultaneous detection of range, azimuth, and elevation angles of multiple targets.

[0005] The specific technical solution of this invention is as follows:

[0006] A method for detecting the range, azimuth, and elevation angles of multiple targets based on microwave photonics technology, wherein the specific implementation link of the method includes a laser source (LD), a Mach-Zehnder modulator (MZM), a signal source (SG), a first optical coupler (OC1), a front-end photodetector (PD), a front-end power amplifier (PA), a transmitting antenna (PA), a second optical coupler (OC2), a first polarization-multiplexed dual-drive Mach-Zehnder modulator (PDM-DMZM1), a second polarization-multiplexed dual-drive Mach-Zehnder modulator (PDM-DMZM2), an intermediate receiving antenna (RAC), a first x-axis receiving antenna (RAx1), a second x-axis receiving antenna (RAx2), a first y-axis receiving antenna (RAy1), a second y-axis receiving antenna (RAy2), a first polarization controller (PC1), a first polarization beam splitter (PBS1), a second polarization controller (PC2), a second polarization beam splitter (PBS2), a first photodetector (PD1), a second photodetector (PD2), a third photodetector (PD3), a fourth photodetector (PD4), and a signal acquisition and processing module. Both the first polarization-multiplexed dual-drive Mach-Zehnder modulator and the second polarization-multiplexed dual-drive Mach-Zehnder modulator include an upper arm sub-modulator and a lower arm sub-modulator. The distance between the intermediate receiving antenna and the first receiving antenna along the x-axis, the second receiving antenna along the x-axis, the first receiving antenna along the y-axis, and the second receiving antenna along the y-axis is d. The method includes the following steps:

[0007] Step 1: Generate a detection signal with a large instantaneous bandwidth, as follows:

[0008] The continuous optical signal generated by the laser source is input into the Mach-Zehnder modulator as the 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 set so that the Mach-Zehnder modulator operates at the minimum transmission point, suppressing the carrier and even-order sidebands, and retaining only odd-order sidebands.

[0009] Next, the output signal of the Mach-Zehnder modulator is split into two paths using the first optical coupler. One path is input to the pre-photodetector for photoelectric conversion to obtain a second harmonic linear frequency modulated signal.

[0010] Finally, the signal is first amplified by a preamplifier and then transmitted using a transmitting antenna as a radar detection signal.

[0011] Step 2: Detecting the target distance and direction

[0012] The output signal of the Mach-Zehnder modulator is split off by the first optical coupler and input to the second optical coupler. The two optical signals output from the second optical coupler are then input to the first polarization-multiplexed dual-drive Mach-Zehnder modulator and the second polarization-multiplexed dual-drive Mach-Zehnder modulator, respectively, as reference signals. By setting the bias voltages of the first polarization-multiplexed dual-drive Mach-Zehnder modulator and the second polarization-multiplexed dual-drive Mach-Zehnder modulator, both their upper and lower sub-modulators operate at quadrature bias points. The first polarization-multiplexed dual-drive Mach-Zehnder modulator and the second polarization-multiplexed dual-drive Mach-Zehnder modulator each have two drive signals for their upper and lower arm sub-modulators. The drive signal for the upper arm sub-modulator of the first polarization-multiplexed dual-drive Mach-Zehnder modulator is the received echo signal from the central receiving antenna and the first x-axis receiving antenna; the drive signal for the lower arm sub-modulator is the received echo signal from the central receiving antenna and the second x-axis receiving antenna. The drive signal for the upper arm sub-modulator of the second polarization-multiplexed dual-drive Mach-Zehnder modulator is the received echo signal from the central receiving antenna and the first y-axis receiving antenna; the drive signal for the lower arm sub-modulator is the received echo signal from the central receiving antenna and the second y-axis receiving antenna. The output signal of the first polarization-multiplexed dual-drive Mach-Zehnder modulator is polarization demultiplexed using a first polarization controller and a first polarization beam splitter to obtain two output signals with orthogonal polarization directions. After photoelectric conversion by a first photodetector and a second photodetector, the output signals are converted into two electrical signals i1(t) and i2(t). The output signal of the second polarization multiplexed dual-drive Mach-Zehnder modulator is demultiplexed using a second polarization controller and a second polarization beam splitter to obtain two output signals with orthogonal polarization directions. These output signals are then converted by a third and a fourth photodetector, resulting in two electrical signals, i3(t) and i4(t). After acquisition and processing by the signal acquisition and processing module, low-frequency signals related to the target distance, the target echo x-axis angle of arrival, and the target echo y-axis angle of arrival are obtained. Solving for and analyzing the frequency of these low-frequency signals allows for the simultaneous acquisition of the target's distance and the echo's x-axis and y-axis angle of arrival information. Based on the geometric relationship between the angle of arrival, azimuth, and elevation angles, the azimuth and elevation angles of each target are calculated, enabling simultaneous detection of the range, azimuth, and elevation angles of multiple targets.

[0013] The low-frequency signal frequency related to the distance to the nth target and the echo angle of arrival is expressed as follows:

[0014]

[0015] In the formula,

[0016] f x1,n Let be the frequency of the signal obtained after descrambling the nth target echo signal received by the first receiving antenna along the x-axis.

[0017] f x2,n Let be the frequency of the signal obtained after descrambling the nth target echo signal received by the second receiving antenna along the x-axis.

[0018] f C,n Let be the frequency of the signal obtained after descrambling the nth target echo signal received by the intermediate receiving antenna.

[0019] f y1,n Let be the frequency of the signal obtained after descrambling the nth target echo signal received by the first receiving antenna along the y-axis.

[0020] f y2,n Let be the frequency of the signal obtained after descrambling the nth target echo signal received by the second receiving antenna along the y-axis.

[0021] k is the frequency modulation slope of the intermediate frequency linear frequency modulated signal generated by the signal source.

[0022] · indicates multiplication operation,

[0023] n = 1, 2, ..., N, where N is the total number of targets.

[0024] τ x1,n To measure the time delay experienced by a detection signal after it is transmitted by the transmitting antenna, reflected by the nth target, and then transmitted to the first receiving antenna along the x-axis.

[0025] τ x2,n To measure the time delay experienced by the detection signal after it is transmitted by the transmitting antenna, reflected by the nth target, and then transmitted to the second receiving antenna along the x-axis.

[0026] τ C,n To measure the time delay experienced by a detection signal after it is transmitted from the transmitting antenna, reflected by the nth target, and then transmitted to the intermediate receiving antenna.

[0027] τ y1,n To measure the time delay experienced by a detection signal after it is transmitted by the transmitting antenna, reflected by the nth target, and then transmitted to the first receiving antenna along the y-axis,

[0028] τ y2,n To measure the time delay experienced by the detection signal after it is transmitted by the transmitting antenna, reflected by the nth target, and then transmitted to the second receiving antenna along the y-axis,

[0029] The distance R of the nth target n The x-axis arrival angle α of the echo from the nth target n and the y-axis arrival angle β n They are respectively represented as

[0030]

[0031] Where c is the speed of light in air.

[0032] The azimuth angle θ of the nth target n and pitch angle α can be used n and β n They are respectively represented as

[0033]

[0034] At the transmitting end, this invention utilizes a Mach-Zehnder modulator to double the frequency of an intermediate-frequency linear frequency modulated (IF) signal generated by an arbitrary waveform generator, producing an IF signal with a large instantaneous bandwidth, which is then transmitted into free space as a detection signal for target detection. At the receiving end, a receiving antenna array composed of five symmetrically placed antennas (a first receiving antenna along the x-axis, a second receiving antenna along the x-axis, an intermediate receiving antenna, a first receiving antenna along the y-axis, and a second receiving antenna along the y-axis) is used to collectively receive the echo signal reflected from the target. The echo signals received by the first receiving antenna along the x-axis, the second receiving antenna along the x-axis, and the intermediate receiving antenna are used as the driving signal for a first polarization-multiplexed dual-drive Mach-Zehnder modulator. After polarization demultiplexing the output signal of the first polarization-multiplexed dual-drive Mach-Zehnder modulator using a first polarization controller and a first polarization beam splitter, the polarization-demultiplexed optical signal is converted into an electrical signal by a first photodetector and a second photodetector. The echo signals received by the first receiving antenna along the y-axis, the second receiving antenna along the y-axis, and the intermediate receiving antenna are used as the driving signal for a second polarization-multiplexed dual-drive Mach-Zehnder modulator. After demultiplexing the output signal of the second polarization-multiplexed dual-drive Mach-Zehnder modulator using a second polarization controller and a second polarization beamsplitter, the demultiplexed optical signal is converted into an electrical signal by a third and a fourth photodetector. By utilizing the relationship between the echo signals received by different receiving antennas and the relationship between the echo signals and the reference signal, simultaneous detection of the range, x-axis angle of arrival, and y-axis angle of arrival of multiple targets is achieved. Finally, using the geometric relationship between the angle of arrival, azimuth, and elevation angles, the azimuth and elevation angles of each target are calculated, enabling simultaneous detection of the range, azimuth, and elevation angles of multiple targets.

[0035] The beneficial effects of this invention are:

[0036] This invention proposes a multi-target range, azimuth, and elevation detection method based on microwave photonics technology. It combines microwave photonics technology with radar detection technology, utilizing a symmetrical cross-shaped antenna array to receive target echo signals. The target range and direction are detected based on the relationship between the received echo and a reference signal. Different target detection results are distinguished based on the frequency relationship between the deskewing results of echoes received by different antennas, enabling simultaneous detection of multiple targets at range, azimuth, and elevation within a large directional detection range. Compared to existing technologies, this invention significantly improves the effectiveness of microwave photonics-based radar in simultaneous multi-target detection, expands the directional detection range, and makes it more suitable for applications in military and civilian environments.

[0037] Existing microwave photonic orientation detection methods primarily rely on calculating the target orientation based on the phase information of the echo signal or detecting the target orientation through beam scanning in space. When calculating the target orientation based on the phase information of the echo signal, the measurement accuracy is easily affected by laser power fluctuations and modulator bias point drift, leading to a decrease in accuracy. Furthermore, to achieve unambiguous orientation measurement, the antenna baseline length must be less than half the wavelength of the received signal; when the received signal frequency is high and the wavelength is short, an excessively short antenna length also reduces measurement accuracy. When detecting the target orientation through beam scanning in space, the beam scanning range is typically small due to limitations such as antenna impedance matching and the widening of the beamwidth with increasing scanning angle. Moreover, to improve azimuth detection resolution, a very narrow beamwidth is required, resulting in a long time required to scan the entire spatial domain, making real-time detection of multiple targets within a large directional detection range impossible. This invention utilizes the frequency difference between the received echo signal and the reference signal to simultaneously detect the range, azimuth, and elevation angles of multiple targets. It is insensitive to laser power fluctuations and modulator bias point drift, thus exhibiting better stability. The baseline length of the receiving antenna does not need to be less than half a wavelength, allowing the use of large-aperture receiving antenna arrays for higher detection accuracy. The receiving antenna simultaneously receives echo signals from targets in various directions, enabling real-time monitoring of a large directional range of space without beam scanning. Experimental verification shows that this invention can effectively detect multiple targets within an azimuth angle range of 0° to 329.68° and an elevation angle range of 0° to 71.80°, while common microwave photonic beam scanning radar detection systems can only effectively detect multiple targets within an azimuth angle range of 0° to 120° and an elevation angle range of 0° to 60°. Therefore, this invention has a much wider directional detection range. Attached Figure Description

[0038] Figure 1 This is a schematic diagram of the link structure for a multi-target simultaneous ranging and direction finding method based on microwave photonics technology.

[0039] Figure 2 This is a schematic diagram of a cross-shaped antenna array.

[0040] Figure 3 This is a schematic diagram of the target's geometric location. Detailed Implementation

[0041] To address the challenge of existing microwave photonic radar detection technologies in simultaneously measuring the range, azimuth, and elevation angles of multiple targets over a wide directional range, thus hindering their application in practical military and civilian environments, this invention proposes a multi-target range, azimuth, and elevation angle detection method based on microwave photonic technology. This method combines microwave photonic technology with radar detection technology, employing photonic frequency doubling to generate a broadband transmission signal for target detection. A symmetrical cross-shaped antenna array is used to receive the echoes, and the echo deskewing results are analyzed for symmetry. This allows for the differentiation of range, azimuth, and elevation angle detection information for different targets over a wide directional range, ultimately achieving simultaneous range, azimuth, and elevation angle detection for multiple targets.

[0042] The multi-target simultaneous ranging and direction finding method based on microwave photonics technology of the present invention is as follows:

[0043] The continuous optical signal generated by the laser source enters the Mach-Zehnder modulator as the optical carrier. The driving signal of the Mach-Zehnder modulator is generated by the signal source. By adjusting the DC bias voltage, the Mach-Zehnder modulator operates at the minimum transmission point, thereby suppressing the carrier and even-order sidebands while retaining odd-order sidebands. The output signal of the Mach-Zehnder modulator is input to the first optical coupler and split into two paths. One path enters the pre-detector, and after photoelectric conversion by the pre-detector, a frequency-doubled linear frequency modulated signal is obtained. This frequency-doubled linear frequency modulated signal is amplified by the pre-amplifier and transmitted into free space using the transmitting antenna as a radar detection signal. The other path enters the second optical coupler, is split into two paths again, and then input to the first polarization-multiplexed dual-drive Mach-Zehnder modulator and the second polarization-multiplexed dual-drive Mach-Zehnder modulator as reference signals. At the receiving end, a receiving antenna array is formed using five symmetrically placed antennas (first receiving antenna on the x-axis, second receiving antenna on the x-axis, intermediate receiving antenna, first receiving antenna on the y-axis, and second receiving antenna on the y-axis) to jointly receive the echo signal reflected from the target. The echo signals received by the first receiving antenna on the x-axis, second receiving antenna on the x-axis, and intermediate receiving antenna are used as the driving signals for the first polarization-multiplexed dual-drive Mach-Zehnder modulator. After polarization demultiplexing the output signal of the first polarization-multiplexed dual-drive Mach-Zehnder modulator using a first polarization controller and a first polarization beamsplitter, the polarization-demultiplexed optical signal is converted into an electrical signal by a first photodetector and a second photodetector. The echo signals received by the first receiving antenna on the y-axis, second receiving antenna on the y-axis, and intermediate receiving antenna are used as the driving signals for the second polarization-multiplexed dual-drive Mach-Zehnder modulator. After polarization demultiplexing the output signal of the second polarization-multiplexed dual-drive Mach-Zehnder modulator using a second polarization controller and a second polarization beamsplitter, the polarization-demultiplexed optical signal is converted into an electrical signal by a third photodetector and a fourth photodetector. By utilizing the relationships between echo signals received by different receiving antennas and the relationships between echo signals and reference signals, simultaneous detection of the x-axis and y-axis angles of arrival of multiple targets and echoes is achieved. Finally, by utilizing the geometric relationships between the x-axis and y-axis angles of arrival, azimuth, and elevation angles, simultaneous detection of the range, azimuth, and elevation angles of multiple targets is achieved.

[0044] To facilitate public understanding, the invention will be further explained below with reference to the accompanying drawings and mathematical derivations:

[0045] Figure 1This is a schematic diagram of the link structure of the multi-target simultaneous ranging and direction finding method based on microwave photonics technology of the present invention, including a laser source (LD), a Mach-Zehnder modulator (MZM), a signal source (SG), a first optical coupler (OC1), a front-end photodetector (PD), a front-end power amplifier (PA), a transmitting antenna (PA), a second optical coupler (OC2), a first polarization multiplexed dual-drive Mach-Zehnder modulator (PDM-DMZM1), a second polarization multiplexed dual-drive Mach-Zehnder modulator (PDM-DMZM2), an intermediate receiving antenna (RAC), a first x-axis receiving antenna (RAx1), a second x-axis receiving antenna (RAx2), a first y-axis receiving antenna (RAy1), a second y-axis receiving antenna (RAy2), a first polarization controller (PC1), a first polarization beam splitter (PBS1), a second polarization controller (PC2), a second polarization beam splitter (PBS2), a first photodetector (PD1), a second photodetector (PD2), a third photodetector (PD3), a fourth photodetector (PD4), and a signal acquisition and processing module. Both the first polarization-multiplexed dual-drive Mach-Zehnder modulator and the second polarization-multiplexed dual-drive Mach-Zehnder modulator include an upper arm sub-modulator and a lower arm sub-modulator. The distance between the intermediate receiving antenna and the first receiving antenna along the x-axis, the second receiving antenna along the x-axis, the first receiving antenna along the y-axis, and the second receiving antenna along the y-axis is d.

[0046] use Figure 1 The link structure shown illustrates the process of completing a multi-target simultaneous ranging and direction finding method based on microwave photonics technology as follows:

[0047] Step 1: Generate a detection signal with a large instantaneous bandwidth;

[0048] The continuous optical signal generated by the laser source can be expressed as E(t) = E0·exp(j·ω) c ·t), E0 and ω c Here, ∠A represents the amplitude and center angular frequency of the continuous optical signal, · represents multiplication, and j represents the imaginary unit. The continuous optical signal is input to a Mach-Zehnder modulator as its optical carrier. The radio frequency drive signal of the Mach-Zehnder modulator is an intermediate frequency linear frequency modulated signal generated by the signal source, which can be expressed as:

[0049]

[0050] In the formula, V LFM 、T、f LFM Let and k be the amplitude, duration, initial frequency, and modulation slope of the intermediate frequency linear frequency modulated signal, respectively. Let be a rectangular function used to describe the envelope information of the signal, and t represent the time variable. Adjust the DC bias voltage to make the Mach-Zehnder modulator operate at the minimum transmission point, suppressing the carrier and even-order sidebands while retaining only odd-order sidebands. When the amplitude of the intermediate frequency linear frequency modulated signal input to the Mach-Zehnder modulator is less than 200mV, the intermediate frequency linear frequency modulated signal can be considered a small signal. At this time, the output signal of the Mach-Zehnder modulator can be expressed as:

[0051]

[0052] In the formula, J1(m) represents the first-order Bessel function of the first kind, and m in parentheses represents the value of the independent variable of the first-order Bessel function of the first kind. π is the mathematical constant Pi, V LFM V is the amplitude of the intermediate frequency linear frequency modulated signal, and V0 is the half-wave voltage of the Mach-Zehnder modulator.

[0053] Next, the signal is split into two paths using the first optocoupler. One path is input to the pre-detector for photoelectric conversion, yielding a second-harmonic linear frequency modulated signal, which can be expressed as:

[0054]

[0055] Analysis shows that the instantaneous frequency of the linear frequency modulated signal after frequency doubling is related to the time variable t as f T (t)=2·(f LFM +k·t). The second harmonic linear frequency modulated (LFM) signal is amplified by a preamplifier, resulting in a power of 10W. The amplified LFM signal is then transmitted into free space via a transmitting antenna as a radar detection signal.

[0056] Step 2: Detecting the target distance and direction

[0057] The other optical signal output from the first optical coupler is input into the second optical coupler, where it is split into two paths again. These two paths are then input as reference signals to the first polarization-multiplexed dual-drive Mach-Zehnder modulator and the second polarization-multiplexed dual-drive Mach-Zehnder modulator, respectively. A receiving antenna array composed of five symmetrically placed antennas (first receiving antenna on the x-axis, second receiving antenna on the x-axis, intermediate receiving antenna, first receiving antenna on the y-axis, and second receiving antenna on the y-axis) is used to collectively receive the echo signal reflected from the target, such as... Figure 2 As shown.

[0058] like Figure 3 The target shown is located at point P1, R is the distance between the target and the origin, and azimuth angle θ. A For the target radius vector Projection in the xOy plane The angle between the pitch angle and the positive x-axis, θ E for The angles relative to the xOy plane, the x-axis arrival angle α and y-axis arrival angle β of the target echo are respectively The angle between the x-axis and the positive directions of the y-axis. When there are a total of N targets, assume that the x-axis arrival angle of the echo of the nth target is α. n The y-axis reaches an angle of β. n , and τ x1,n , τ x2,n , τ C,n , τ y1,n and τ y2,n Let be the time delays at which the echo of the nth target arrives at the first x-axis receiving antenna, the second x-axis receiving antenna, the intermediate receiving antenna, the first y-axis receiving antenna, and the second y-axis receiving antenna, respectively. Their expressions are as follows:

[0059]

[0060] In the formula R n Let c be the distance information of the nth target, c be the speed of light in air, and d be the spacing between the receiving antennas. Therefore, the received echo signals from the five receiving antennas can be represented as follows:

[0061]

[0062] In the formula S x1 (t) represents the received echo signal from the first receiving antenna along the x-axis, S x2 (t) represents the received echo signal from the second receiving antenna along the x-axis, S C (t) represents the received echo signal from the intermediate receiving antenna, S y1 (t) represents the received echo signal from the first receiving antenna along the y-axis, S y2 (t) represents the received echo signal from the second receiving antenna along the y-axis, and N represents the total number of targets.

[0063] The received echo signals from the intermediate receiving antenna and the first receiving antenna along the x-axis are input as driving signals to the upper arm sub-modulator of the first polarization-multiplexed dual-drive Mach-Zehnder modulator. The received echo signals from the intermediate receiving antenna and the second receiving antenna along the x-axis are input as driving signals to the lower arm sub-modulator of the first polarization-multiplexed dual-drive Mach-Zehnder modulator. The received echo signals from the intermediate receiving antenna and the first receiving antenna along the y-axis are input as driving signals to the upper arm sub-modulator of the second polarization-multiplexed dual-drive Mach-Zehnder modulator. The received echo signals from the intermediate receiving antenna and the second receiving antenna along the y-axis are input as driving signals to the lower arm sub-modulator of the second polarization-multiplexed dual-drive Mach-Zehnder modulator. The amplitudes of the output signals from all five receiving antennas are less than 200mV; therefore, the signals input to the two polarization-multiplexed dual-drive Mach-Zehnder modulators are small signals. Under these small-signal conditions, the output signal of the first polarization-multiplexed dual-drive Mach-Zehnder modulator can be expressed as:

[0064]

[0065] In the formula, This represents a light signal with a polarization direction of x. This represents the optical signal with polarization in the y-direction. The output signal of the second polarization-multiplexed dual-drive Mach-Zehnder modulator can be expressed as:

[0066]

[0067] The output signal of the first polarization-multiplexed dual-drive Mach-Zehnder modulator is demultiplexed using a first polarization controller and a first polarization beamsplitter to obtain two output signals with orthogonal polarization directions. After photoelectric conversion by a first photodetector and a second photodetector, the output signals i1(t) and i2(t) are output. The output signal of the second polarization-multiplexed dual-drive Mach-Zehnder modulator is demultiplexed using a second polarization controller and a second polarization beamsplitter to obtain two output signals with orthogonal polarization directions. After photoelectric conversion by a third photodetector and a fourth photodetector, the output signals i3(t) and i4(t) are output. The output signals i1(t), i2(t), i3(t), and i4(t) are acquired using a signal acquisition and processing module and can be expressed as follows:

[0068]

[0069] Let f1 denote the frequency components of electrical signal i1(t), f2 denote the frequency components of electrical signal i2(t), f3 denote the frequency components of electrical signal i3(t), and f4 denote the frequency components of electrical signal i4(t). The expressions for f1, f2, f3, and f4 can be written as follows:

[0070]

[0071] In the formula, f x1,n f is the frequency of the signal obtained after descrambling the nth target echo signal received by the first receiving antenna along the x-axis. x1,n =2·k·τ x1,n ;f x2,n f is the frequency of the signal obtained after descrambling the nth target echo signal received by the second receiving antenna along the x-axis. x2,n =2·k·τ x2,n ;f C,n f is the frequency of the signal obtained after descrambling the nth target echo signal received by the intermediate receiving antenna. C,n =2·k·τ C,n ;f y1,n f is the frequency of the signal obtained after descrambling the nth target echo signal received by the first receiving antenna along the y-axis. y1,n =2·k·τ y1,n ;f y2,n f is the frequency of the signal obtained after descrambling the nth target echo signal received by the second receiving antenna along the y-axis. y2,n =2·k·τ y2,n N represents the total number of targets. Combining equation (4), it can be determined by the frequency f. x1,n and f x2,n Calculate the x-axis angle of arrival α of the echo from the nth target. n It can be achieved through frequency f y1,n and f y2,n Calculate the y-axis angle of arrival β of the echo from the nth target. n It can be achieved through frequency f C,n and α n Calculate the distance R of the nth target. n

[0072]

[0073] The azimuth angle θ of the nth target n and pitch angle α can be used n and β n They are respectively represented as

[0074]

[0075] Traditional microwave photonics-based detection methods directly calculate the target's range, x-axis angle of arrival (AHA), and y-axis angle of arrival (AHA) from the frequency of the target echo after de-chewing. However, when multiple targets are present, the number of frequency components obtained after de-chewing increases, making the spectral information highly complex. It is often difficult to accurately determine the specific values ​​of the frequency components obtained after de-chewing for each target's echo, thus hindering accurate calculation of the range, AHA, and y-axis angles of arrival for each target using spectral information. This leads to frequent errors in judgment and calculation, making it impossible to effectively detect the range, azimuth, and elevation angles of multiple targets simultaneously. To accurately determine the specific values ​​of the frequency components obtained after de-chewing for each target's echo and calculate the range, azimuth, and elevation angles for each target, this invention employs a symmetrical cross-shaped antenna array to receive the echoes. It combines polarization multiplexing / demultiplexing technology with microwave photonics de-chewing technology to process the received echoes, enabling simultaneous detection of the range, azimuth, and elevation angles of different targets. For the nth target, after de-skewing processing, the resulting de-skewing signal contains two sets of symmetrical frequency components, namely f x1,n and f x2,n Regarding f C,n Symmetry, i.e., f y1,n and f y2,n Regarding f C,n Symmetrical. Where f C,n The overlapping frequency components in the spectra of the four electrical signals i1(t), i2(t), i3(t), and i4(t) appear simultaneously. C,n And regarding the two sets of frequency components that are symmetrical about this frequency, f x1,n f x2,n and f y1,n f y2,n They will appear in the four electrical signals i1(t), i2(t), i3(t) and i4(t) respectively.

[0076] Using polarization multiplexing technology, the echoes from the first and second x-axis receiving antennas are used as driving signals applied to the optical carrier signal in the first polarization multiplexed dual-drive Mach-Zehnder modulator along two defined orthogonal polarization directions. By polarization demultiplexing and photoelectric conversion of the output signal from the first polarization multiplexed dual-drive Mach-Zehnder modulator, the frequency f of the de-angled signal obtained after de-angleing the received echoes from the first and second x-axis receiving antennas can be reduced. x1,n and f x2,nDistinguishing between them is then performed. Simultaneously, the echoes from the first and second y-axis receiving antennas are used as driving signals, applied to the optical carrier signal in the second polarization-multiplexed dual-drive Mach-Zehnder modulator along two defined orthogonal polarization directions. By polarization demultiplexing and photoelectric conversion of the output signal from the second polarization-multiplexed dual-drive Mach-Zehnder modulator, the frequency f of the de-skewed signal obtained after de-skewing the echo signals from the first and second y-axis receiving antennas can be determined. y1,n and f y2,n The frequencies of all de-slant signals of the nth target echo signal are then distinguished. This method is applied to each overlapping frequency component to determine the de-slant frequency of each target echo. Finally, the range, azimuth, and elevation angles of each target are accurately calculated according to equations (9) and (10), enabling simultaneous detection of range, azimuth, and elevation angles of multiple targets.

[0077] In summary, this invention proposes a multi-target range, azimuth, and elevation angle detection method based on microwave photonics technology. It combines microwave photonics technology with radar detection technology, uses photonic frequency doubling to generate broadband transmission signals to detect targets, and uses a cross-shaped antenna array with a symmetrical structure to receive the echoes and perform symmetry analysis on the echo deskewing results. This enables the differentiation of range, azimuth, and elevation angle detection information for different targets, and achieves simultaneous detection of range, azimuth, and elevation angles for multiple targets.

Claims

1. A multi-target three-coordinate detection method based on microwave photonics technology, characterized in that: The specific implementation link of the method includes a laser source (LD), a Mach-Zehnder modulator (MZM), a signal source (SG), a first optical coupler (OC1), a front-end photodetector (PD), a front-end power amplifier, a transmitting antenna, a second optical coupler (OC2), a first polarization-multiplexed dual-drive Mach-Zehnder modulator (PDM-DMZM1), a second polarization-multiplexed dual-drive Mach-Zehnder modulator (PDM-DMZM2), an intermediate receiving antenna (RAC), a first x-axis receiving antenna (RAx1), a second x-axis receiving antenna (RAx2), a first y-axis receiving antenna (RAy1), and a second y-axis receiving antenna (RAy2). 2) A first polarization controller (PC1), a first polarization beam splitter (PBS1), a second polarization controller (PC2), a second polarization beam splitter (PBS2), a first photodetector (PD1), a second photodetector (PD2), a third photodetector (PD3), a fourth photodetector (PD4), and a signal acquisition and processing module; wherein both the first polarization multiplexing dual-drive Mach-Zehnder modulator and the second polarization multiplexing dual-drive Mach-Zehnder modulator include an upper arm sub-modulator and a lower arm sub-modulator; the distance between the intermediate receiving antenna and the first receiving antenna on the x-axis, the second receiving antenna on the x-axis, the first receiving antenna on the y-axis, and the second receiving antenna on the y-axis is d; The continuous optical signal generated by the laser source is input into the Mach-Zehnder modulator as the 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 set so that the Mach-Zehnder modulator operates at the minimum transmission point, suppressing the carrier and even-order sidebands, and retaining only odd-order sidebands. Next, the output signal of the Mach-Zehnder modulator is split into two paths using the first optical coupler. One path is input to the pre-photodetector for photoelectric conversion to obtain a second harmonic linear frequency modulated signal. Finally, the signal is first amplified by a preamplifier and then transmitted using a transmitting antenna as a radar detection signal. Step 2: Detecting the target distance and direction The output signal of the Mach-Zehnder modulator is split off by the first optical coupler and input into the second optical coupler. The two optical signals output from the second optical coupler are respectively input into the first polarization-multiplexed dual-drive Mach-Zehnder modulator and the second polarization-multiplexed dual-drive Mach-Zehnder modulator as reference signals. By setting the bias voltage of the first polarization-multiplexed dual-drive Mach-Zehnder modulator and the second polarization-multiplexed dual-drive Mach-Zehnder modulator, both their upper and lower sub-modulators operate at the quadrature bias point. The upper and lower arms of the first polarization-multiplexed dual-drive Mach-Zehnder modulator and the second polarization-multiplexed dual-drive Mach-Zehnder modulator each have two drive signals. The drive signal of the upper arm sub-modulator of the first polarization-multiplexed dual-drive Mach-Zehnder modulator is the echo signal received by the middle receiving antenna and the first receiving antenna on the x-axis. The driving signal for the lower arm sub-modulator is the received echo signal from the intermediate receiving antenna and the second receiving antenna along the x-axis; the driving signal for the upper arm sub-modulator of the second polarization-multiplexed dual-drive Mach-Zehnder modulator is the received echo signal from the intermediate receiving antenna and the first receiving antenna along the y-axis; the driving signal for the lower arm sub-modulator is the received echo signal from the intermediate receiving antenna and the second receiving antenna along the y-axis; the output signal of the first polarization-multiplexed dual-drive Mach-Zehnder modulator is demultiplexed using a first polarization controller and a first polarization beam splitter to obtain two output signals with orthogonal polarization directions; the output signals are then converted by photoelectric conversion through a first photodetector and a second photodetector, respectively, to output two electrical signals. and The output signal of the second polarization multiplexed dual-drive Mach-Zehnder modulator is demultiplexed using a second polarization controller and a second polarization beam splitter to obtain two output signals with orthogonal polarization directions. These output signals are then converted into two electrical signals by a third photodetector and a fourth photodetector, respectively. and After the four electrical signals are acquired and processed by the signal acquisition and processing module, low-frequency signals related to the target distance, the target echo x-axis angle of arrival, and the target echo y-axis angle of arrival can be obtained. By solving and frequency analysis of the low-frequency signals, the distance and echo x-axis and y-axis angle of arrival of each target can be obtained simultaneously. Based on the geometric relationship between the angle of arrival, azimuth, and elevation angles, the azimuth and elevation angles of each target are calculated, realizing the simultaneous detection of the distance, azimuth, and elevation angles of multiple targets. The low-frequency signal frequencies related to the distance to the nth target and the echo angle of arrival are expressed as follows: ； In the formula, Let be the frequency of the signal obtained after descrambling the nth target echo signal received by the first receiving antenna along the x-axis. Let be the frequency of the signal obtained after descrambling the nth target echo signal received by the second receiving antenna along the x-axis. Let be the frequency of the signal obtained after descrambling the nth target echo signal received by the intermediate receiving antenna. Let be the frequency of the signal obtained after descrambling the nth target echo signal received by the first receiving antenna along the y-axis. Let be the frequency of the signal obtained after descrambling the nth target echo signal received by the second receiving antenna along the y-axis. The frequency modulation slope of the intermediate frequency linear frequency modulated signal generated by the signal source. · indicates multiplication operation, n = 1, 2, ..., N, where N is the total number of targets. To measure the time delay experienced by a detection signal after it is transmitted by the transmitting antenna, reflected by the nth target, and then transmitted to the first receiving antenna along the x-axis. To measure the time delay experienced by the detection signal after it is transmitted by the transmitting antenna, reflected by the nth target, and then transmitted to the second receiving antenna along the x-axis. To measure the time delay experienced by a detection signal after it is transmitted from the transmitting antenna, reflected by the nth target, and then transmitted to the intermediate receiving antenna. To measure the time delay experienced by a detection signal after it is transmitted by the transmitting antenna, reflected by the nth target, and then transmitted to the first receiving antenna along the y-axis, To measure the time delay experienced by the detection signal after it is transmitted by the transmitting antenna, reflected by the nth target, and then transmitted to the second receiving antenna along the y-axis, The distance to the nth target The x-axis angle of arrival of the echo from the nth target and the angle of arrival of the y-axis They are respectively represented as ； in, The speed of light in air; The azimuth angle of the nth target and pitch angle Available and They are respectively represented as ； At the transmitting end, a Mach-Zehnder modulator is used to double the frequency of the intermediate frequency linear frequency modulated (IF) signal generated by an arbitrary waveform generator, producing an IF signal with a large instantaneous bandwidth, which is then transmitted into free space as a detection signal for target detection. At the receiving end, a receiving antenna array composed of five symmetrically placed antennas—a first receiving antenna on the x-axis, a second receiving antenna on the x-axis, an intermediate receiving antenna, a first receiving antenna on the y-axis, and a second receiving antenna on the y-axis—collectively receives the echo signal reflected from the target. The echo signals received by the first receiving antenna on the x-axis, the second receiving antenna on the x-axis, and the intermediate receiving antenna are used as the driving signal for a first polarization-multiplexed dual-drive Mach-Zehnder modulator. After polarization demultiplexing of the output signal of the first polarization-multiplexed dual-drive Mach-Zehnder modulator using a first polarization controller and a first polarization beam splitter, the signal is transmitted through a first photodetector and a second photodetector. The detector converts the polarization-demultiplexed optical signal into an electrical signal; the echo signals received by the first y-axis receiving antenna, the second y-axis receiving antenna, and the intermediate receiving antenna are used as the driving signals for the second polarization-demultiplexed dual-drive Mach-Zehnder modulator; after demultiplexing the output signal of the second polarization-demultiplexed dual-drive Mach-Zehnder modulator using the second polarization controller and the second polarization beam splitter, the polarization-demultiplexed optical signal is converted into an electrical signal by the third photodetector and the fourth photodetector; the relationship between the echo signals received by different receiving antennas and the relationship between the echo signals and the reference signal are used to achieve simultaneous detection of the range of multiple targets and the x-axis and y-axis angles of arrival of the echoes; finally, the geometric relationship between the angle of arrival, azimuth, and elevation angles is used to calculate the azimuth and elevation angles of each target, achieving simultaneous detection of the range, azimuth, and elevation angles of multiple targets.

2. The method according to claim 1, characterized in that: Step 1: Generate a detection signal with a large instantaneous bandwidth; The continuous optical signal generated by the laser source is represented as , and These represent the amplitude and center angular frequency of the continuous optical signal, respectively, with · indicating a multiplication operation. The imaginary unit is represented by a continuous optical signal input to a Mach-Zehnder modulator as its optical carrier. The radio frequency drive signal of the Mach-Zehnder modulator is an intermediate frequency linear frequency modulated signal generated by a signal source, which can be expressed as: ； In the formula, , , and These represent the amplitude, duration, initial frequency, and modulation slope of the intermediate frequency linear frequency modulated signal, respectively. Let be a rectangular function used to describe the envelope information of the signal, and t represent the time variable. Adjust the DC bias voltage to make the Mach-Zehnder modulator operate at the minimum transmission point, suppressing the carrier and even-order sidebands while retaining only odd-order sidebands. When the amplitude of the intermediate frequency linear frequency modulated signal input to the Mach-Zehnder modulator is less than 200 mV, the intermediate frequency linear frequency modulated signal is considered a small signal. At this time, the output signal of the Mach-Zehnder modulator is expressed as: ； In the formula, is The first-order Bessel function of the first kind, where m in parentheses represents the value of the independent variable of the first-order Bessel function of the first kind. , Pi The amplitude of the intermediate frequency linear frequency modulated signal. The half-wave voltage of the Mach-Zehnder modulator; Next, the signal is split into two paths using the first optocoupler. One path is input to the pre-detector for photoelectric conversion, yielding a second-harmonic linear frequency modulated signal, represented as: ； Analysis shows that the instantaneous frequency of the linear frequency modulated signal after frequency doubling is related to the time variable t as follows: The second harmonic linear frequency modulated signal is input into a preamplifier for amplification, and the amplified second harmonic linear frequency modulated signal has a power of 10W. Then, the amplified second harmonic linear frequency modulated signal is transmitted into free space using a transmitting antenna as a radar detection signal. Step 2: Detecting the target distance and direction The other optical signal output from the first optical coupler is input into the second optical coupler, which splits it into two paths again. These two paths are then input into the first polarization multiplexed dual-drive Mach-Zehnder modulator and the second polarization multiplexed dual-drive Mach-Zehnder modulator as reference signals. A receiving antenna array consisting of five symmetrically placed antennas—the first receiving antenna on the x-axis, the second receiving antenna on the x-axis, the intermediate receiving antenna, the first receiving antenna on the y-axis, and the second receiving antenna on the y-axis—is used to receive the echo signal reflected from the target. The target is located at point P1, R is the distance between the target and the origin, and azimuth angle θ A For the target radius vector Projection in the xOy plane The angle between the pitch angle and the positive x-axis, θ E for The angles relative to the xOy plane, the x-axis angle of arrival α and the y-axis angle of arrival β of the target echo are respectively The angle between the x-axis and the positive directions of the y-axis; when there are a total of N targets, assume that the x-axis arrival angle of the echo of the nth target is... The angle reached by the y-axis is ,and , , , and Let be the time delays at which the echo of the nth target arrives at the first x-axis receiving antenna, the second x-axis receiving antenna, the intermediate receiving antenna, the first y-axis receiving antenna, and the second y-axis receiving antenna, respectively. Their expressions are as follows: ； In the formula For the distance information of the nth target, The speed of light in air. Let be the spacing between the receiving antennas; therefore, the received echo signals from the five receiving antennas are represented as follows: ； In the formula The received echo signal is the first receiving antenna along the x-axis. The received echo signal is the second receiving antenna along the x-axis. The received echo signal is from the intermediate receiving antenna. The received echo signal is the first receiving antenna along the y-axis. The received echo signal is the second receiving antenna along the y-axis, and N is the total number of targets. The received echo signals from the intermediate receiving antenna and the first receiving antenna on the x-axis are input into the upper arm sub-modulator of the first polarization multiplexed dual-drive Mach-Zehnder modulator as driving signals, and the received echo signals from the intermediate receiving antenna and the second receiving antenna on the x-axis are input into the lower arm sub-modulator of the first polarization multiplexed dual-drive Mach-Zehnder modulator as driving signals. The received echo signals from the intermediate receiving antenna and the first receiving antenna along the y-axis are input as driving signals to the upper arm sub-modulator of the second polarization-multiplexed dual-drive Mach-Zehnder modulator, and the received echo signals from the intermediate receiving antenna and the second receiving antenna along the y-axis are input as driving signals to the lower arm sub-modulator of the second polarization-multiplexed dual-drive Mach-Zehnder modulator. The amplitudes of the output signals from all five receiving antennas are less than 200 mV, therefore the signals input to the two polarization-multiplexed dual-drive Mach-Zehnder modulators are small signals. Under these small-signal conditions, the output signal of the first polarization-multiplexed dual-drive Mach-Zehnder modulator is expressed as: ； In the formula, This represents a light signal with a polarization direction of x. The optical signal with polarization in the y-direction is represented as: The output signal of the second polarization multiplexed dual-drive Mach-Zehnder modulator is represented as: (7)； The output signal of the first polarization-multiplexed dual-drive Mach-Zehnder modulator is demultiplexed using a first polarization controller and a first polarization beam splitter to obtain two output signals with orthogonal polarization directions. After photoelectric conversion by a first photodetector and a second photodetector, the output signals are output as two electrical signals. and The output signal of the second polarization multiplexed dual-drive Mach-Zehnder modulator is demultiplexed using a second polarization controller and a second polarization beam splitter to obtain two output signals with orthogonal polarization directions. These output signals are then converted into two electrical signals by a third photodetector and a fourth photodetector, respectively. and ; The signal acquisition and processing module is used to acquire the output electrical signals of the four photodetectors. , , and They are represented as follows: ； electrical signal The frequency components in are denoted as , to transmit electrical signals The frequency components in are denoted as , to transmit electrical signals The frequency components in are denoted as , to transmit electrical signals The frequency components in are denoted as ; , , and The expressions are written as follows: ； In the formula, Let be the frequency of the signal obtained after descrambling the nth target echo signal received by the first receiving antenna along the x-axis. ; Let be the frequency of the signal obtained after descrambling the nth target echo signal received by the second receiving antenna along the x-axis. ; Let be the frequency of the signal obtained after descrambling the nth target echo signal received by the intermediate receiving antenna. ; Let be the frequency of the signal obtained after descrambling the nth target echo signal received by the first receiving antenna along the y-axis. ; Let be the frequency of the signal obtained after descrambling the nth target echo signal received by the second receiving antenna along the y-axis. N is the total number of targets; combining equation (4), through frequency and Calculate the x-axis angle of arrival of the echo from the nth target. Through frequency and Calculate the y-axis angle of arrival of the echo from the nth target. Through frequency and Calculate the distance to the nth target. ; ； Azimuth of the nth target and pitch angle use and They are respectively represented as ； A symmetrical cross-shaped antenna array is used to receive echoes. Polarization multiplexing / demultiplexing technology and microwave photonic de-chewing technology are combined to process the received echoes, enabling simultaneous range, azimuth, and elevation angle detection of different targets. For the nth target, the de-chewing signal, after processing, contains two sets of symmetrical frequency components. and about Symmetry, that is and about Symmetry; among which Simultaneously appearing in four electrical signals , , and Therefore, the overlapping frequency components in the spectrum of the four electrical signals are... And the two sets of frequency components that are symmetrical about this frequency, , and , This will appear in four electrical signals respectively. , , and middle; Using polarization multiplexing technology, the echoes from the first and second x-axis receiving antennas are used as driving signals and applied to the optical carrier signal in the first polarization multiplexed dual-drive Mach-Zehnder modulator along two defined orthogonal polarization directions. The output signal of the first polarization multiplexed dual-drive Mach-Zehnder modulator is then polarization demultiplexed and photoelectrically converted. The frequency of the de-angled signal obtained after de-angleing the received echo signals from the first and second x-axis receiving antennas is then determined. and Distinguishing between the two signals; simultaneously, the echoes from the first and second y-axis receiving antennas are used as driving signals loaded onto the optical carrier signal in the second polarization-multiplexed dual-drive Mach-Zehnder modulator along two defined orthogonal polarization directions; the output signal of the second polarization-multiplexed dual-drive Mach-Zehnder modulator is polarization demultiplexed and photoelectrically converted separately, and the frequency of the de-skewed signal obtained after de-skewing the received echo signals from the first and second y-axis receiving antennas is determined. and Distinguish them; finally obtain the frequency of all deslant signals of the nth target echo signal; apply it to each overlapping frequency component to determine the deslant frequency of each target echo; finally, calculate the range, azimuth and elevation angles of each target according to equations (9) and (10) to achieve simultaneous detection of range, azimuth and elevation angles of multiple targets.

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