Target measurement method based on low-altitude radar three pulses

Abstract

The invention belongs to the technical field of radars, and particularly relates to a target measurement method based on low-altitude radar three pulses, which comprises the following steps of: designing a three-pulse composite signal, adopting a wide, narrow and middle three-pulse composite signal form, transmitting the three-pulse composite signal by a radar through a transmitter, receiving echoes through a receiver, and outputting the echoes; a three-pulse composite echo signal from a low-altitude target is obtained; performing orthogonal digital down-conversion processing on the three-pulse composite echo signal to obtain a three-pulse composite baseband signal; performing pulse compression processing on the three-pulse composite baseband signal to obtain a three-pulse composite signal after energy accumulation; performing distance splicing processing on the three-pulse composite signal after energy accumulation to obtain a spliced three-pulse composite signal; and performing low-altitude moving target detection (MTD) processing on the spliced three-pulse composite signal to obtain the distance and the speed of a low-altitude moving target. The method has the capability of far and near distance detection, and is suitable for a low-altitude detection radar system and other multifunctional radar platforms.

Description

Technical Field

[0001] The invention belongs to the technical field of radar, and in particular relates to a target measurement method based on low-altitude radar three pulses. Background Art

[0002] With the operational deployment of new penetration weapons such as reconnaissance and strike drones and stealth cruise missiles, traditional air defense systems face severe challenges from ultra-low-altitude blind spot threats. Against this backdrop, developing low-altitude defense radar systems with multi-source fusion detection capabilities has become a key technological breakthrough for countries to enhance their battlefield situational awareness.

[0003] The range measurement performance of a radar system is positively correlated with the transmitted signal bandwidth: the wider the signal bandwidth, the better the range measurement accuracy and resolution. Velocity measurement performance, on the other hand, depends on the signal's time-width parameter: the longer the time-width, the better the velocity measurement accuracy and resolution. Traditional pulse radars are limited to single-frequency rectangular pulse waveforms with a time-bandwidth product of approximately 1. This inherent characteristic creates a mutual constraint between the system's time-width and bandwidth selection, making it difficult to optimize both range and velocity measurement performance. In contrast, linear frequency modulation (LFM) signals, by introducing secondary phase modulation, achieve independent control of time-width and bandwidth. Their large time-bandwidth product effectively overcomes the performance bottleneck of traditional radars and significantly enhances the system's multi-dimensional detection capabilities.

[0004] However, traditional single-line frequency-modulated pulse signal radars typically increase the transmit pulse duration to achieve higher transmit energy to improve target detection range. This design approach has inherent technical limitations: as the pulse duration increases, the radar's blind spot in range measurement also increases. Summary of the Invention

[0005] The purpose of the present invention is to provide a target measurement method based on low-altitude radar three-pulse to solve the problem that radar in the prior art cannot have both short-range and long-range detection capabilities.

[0006] The present invention achieves the above-mentioned purpose through the following technical solutions:

[0007] Step 1: Three-pulse composite signal design, using wide, narrow, and medium three-pulse composite signal forms. The radar transmits the three-pulse composite signal through the transmitter and receives the echo through the receiver to obtain the three-pulse composite echo signal from the low-altitude target.

[0008] Step 2: performing orthogonal digital down-conversion processing on the three-pulse composite echo signal to obtain a three-pulse composite baseband signal; the three-pulse composite baseband signal retains the amplitude and phase information of the original signal.

[0009] Step three: performing pulse compression processing on the three-pulse composite baseband signal to obtain a three-pulse composite signal after energy accumulation; wherein the signal after pulse compression processing contains the distance information of the detection target.

[0010] Step 4: performing distance splicing processing on the three-pulse composite signal after energy accumulation to obtain a spliced three-pulse composite signal; wherein the distance splicing includes wide pulse effective distance, narrow pulse effective distance, and medium pulse effective distance splicing.

[0011] Step 5: Perform low-altitude moving target detection (MTD) processing on the spliced three-pulse composite signal to obtain the distance and speed of the low-altitude moving target.

[0012] Furthermore, the wide, narrow, and medium pulses in the three-pulse composite signal described in step 1 all utilize linear frequency modulation (LFM) pulse signals. These signals include the wide pulse duration T1, center frequency F1, and frequency modulation slope K1; the narrow pulse duration T2, center frequency F2, and frequency modulation slope K2; the medium pulse duration T3, center frequency F3, and frequency modulation slope K3; and a pulse bandwidth B (all three pulses have the same bandwidth). The three-pulse composite echo signal includes information such as the distance R from the target to the radar and the target's velocity V relative to the radar.

[0013] Furthermore, in step 2, orthogonal digital down-conversion is performed on the three-pulse composite echo signal to obtain a baseband signal, including:

[0014] Perform digital down-conversion processing on the three-pulse composite echo signal respectively, and mix the three pulse echo signals with the F1 intermediate frequency signal, the F2 intermediate frequency signal, and the F3 intermediate frequency signal respectively, that is, multiply the wide, narrow, and medium pulse signals with the two orthogonal local oscillator signals respectively to obtain the mixed output. Multiply one channel by cos(2πF i t) down-converted to zero intermediate frequency, with the same phase as the original signal; the other one is multiplied by sin(2πF i t) down-convert to zero intermediate frequency, which is orthogonal to the phase of the original signal. The mathematical expression of the mixing output is:

[0015]

[0016] Where t represents time, j represents imaginary unit, and i=1, 2, and 3 represent the serial numbers of wide, narrow, and medium pulses respectively. i (t) represents the echo signals of the three pulses, F i Represents three intermediate frequency signals.

[0017] The mixed output signal is low-pass filtered. Each of the three pulse channels uses a 128-order FIR low-pass filter with a cutoff frequency of 5 MHz. The filter uses a Hamming window design with a stopband attenuation of ≥ 60 dB. The filter removes the high-frequency components after mixing and retains the baseband signal.

[0018] Furthermore, in step three, pulse compression processing is performed on the three-pulse composite baseband signal, including:

[0019] Perform a Fast Fourier Transform (FFT) on the baseband signals of the wide, narrow, and medium pulses and convert them to the frequency domain. Perform a complex multiplication of the FFT result with the pre-stored matched filter frequency domain coefficients (generated by FFT of the conjugate time domain waveform of the transmitted signal). The expression is:

[0020]

[0021] P i (f) = B i (f) H i (f) i=1, 2, 3

[0022] Where f represents frequency, b i (t) is the baseband signal of the wide, narrow and medium pulses, H i (f) is the pre-stored matched filter frequency domain coefficient, P i (f) represents the frequency domain signal after multiplication.

[0023] Perform inverse FFT on the multiplied frequency domain signal to obtain the time domain pulse signal after energy accumulation. The expression is:

[0024]

[0025] Furthermore, in step 4, distance splicing processing is performed on the three-pulse composite signal after energy accumulation, including:

[0026] Calculate the measurement blind zone R of wide pulses b , because the radar transmitter cannot receive pulses during the time period of transmitting pulses, there is a blind zone in the wide pulse where the target cannot be measured. The expression is:

[0027]

[0028] Where C represents the speed of light and T1 represents the pulse duration of the wide pulse.

[0029] The segmented ranging performance is optimized, and the distance segments are divided based on the measurement blind area, including: short-range segment, transition segment, medium-long-range segment, and long-range segment.

[0030] Furthermore, in step 5, low-altitude moving target detection (MTD) processing is performed on the spliced three-pulse composite signal, including:

[0031] Doppler filter bank construction and interference suppression: Based on the FIR transverse filter bank architecture, N Doppler filters are configured to cover the complete unambiguous speed measurement range. The m-th tap weight of the k-th filter in the filter bank is:

[0032] W mk =e -j2π(m-1)k / N (m=1,...,N; k=0,1,...,N-1)

[0033] Among them, each filter corresponds to a specific Doppler frequency response, and the spectrum separation of moving targets and stationary objects is achieved by adjusting the k value.

[0034] FFT High-Efficiency Mode: Performs FFT operations on the same-range gate data of N pulses in the slow-time dimension, equivalently generating a Doppler filter bank. This significantly reduces the amount of computation, improves real-time performance, and reduces hardware resource usage.

[0035] The beneficial effects of the present invention are:

[0036] The present invention provides a target measurement method based on low-altitude radar three-pulse, which constructs a multi-scale distance coverage mechanism by collaboratively modulating the time-frequency parameters of wide pulses, narrow pulses and medium pulses. Specifically, the wide pulse adopts a large time-width-bandwidth product design to achieve high-gain detection of long-range targets; the narrow pulse ensures high-resolution ranging accuracy of short-range targets; and the medium pulse fills the detection blind spot in the mid-range transition area. The received echo signal is sequentially subjected to orthogonal digital down-conversion, frequency domain pulse compression, range splicing and moving target detection (MTD) processing, combined with frequency domain matched filtering and coherent accumulation algorithm to accurately extract the Doppler velocity and radial distance information of the target. Through the collaborative processing of multi-mode signals under the composite pulse system, the ranging blind spot of the traditional single pulse waveform is effectively eliminated, and seamless coverage of target detection in the near and far full range domain is achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 A schematic flow chart of a target measurement method using a low-altitude radar triple pulse according to an embodiment of the present invention;

[0038] Figure 2 A simulation diagram of a three-pulse composite signal provided in an embodiment of the present application;

[0039] Figure 3 This is a simulation diagram of the wide pulse provided in the embodiment of the present application after digital down-conversion processing;

[0040] Figure 4 This is a simulation diagram of the narrow pulse provided in the embodiment of the present application after digital down-conversion processing;

[0041] Figure 5 This is a simulation diagram of the medium pulse provided in the embodiment of the present application after digital down-conversion processing;

[0042] Figure 6 This is a simulation diagram of the wide pulse provided in the embodiment of the present application after pulse compression processing;

[0043] Figure 7 This is a simulation diagram of the narrow pulse provided in the embodiment of the present application after pulse compression processing;

[0044] Figure 8 This is a simulation diagram of the pulse after pulse compression processing provided in the embodiment of the present application;

[0045] Figure 9 This is a simulation diagram of the composite pulse provided in the embodiment of the present application after distance splicing processing;

[0046] Figure 10 This is a simulation diagram of the composite pulse provided in an embodiment of the present application after being processed by moving target detection (MTD); DETAILED DESCRIPTION

[0047] In order to enable those skilled in the art to better understand the present invention, the present application is further described in detail below in conjunction with the accompanying drawings. The following specific embodiments are only used to further illustrate the present application and are not to be construed as limiting the scope of protection of the present application. Those skilled in the art may make some non-essential improvements and adjustments to the present application based on the above application content.

[0048] like Figure 1 As shown, this embodiment provides a target measurement method based on low-altitude radar three-pulse, the method comprising the following steps:

[0049] Step 1: Design a three-pulse signal, using a wide, narrow, and medium three-pulse composite signal. The radar transmits the three-pulse composite signal through a transmitter and receives the echo through a receiver to obtain a three-pulse composite echo signal from a low-altitude target.

[0050] The following is a detailed description of step one:

[0051] The wide, narrow, and medium pulses in the three-pulse composite signal all use linear frequency modulation (LFM) pulse signals. These include the wide pulse duration T1, center frequency F1, and frequency modulation slope K1; the narrow pulse duration T2, center frequency F2, and frequency modulation slope K2; the medium pulse duration T3, center frequency F3, and frequency modulation slope K3; and the pulse bandwidth B (all three pulses have the same bandwidth). The echo signal includes information such as the target-to-radar distance R and the target's relative velocity V.

[0052] The linear frequency modulation wide, narrow and medium pulse expressions are:

[0053]

[0054] The frequency modulation slopes are K1=B / T1, K2=B / T2, and K3=B / T3. represents the rectangular pulse envelope, and its expression is:

[0055]

[0056] The sum of wide, narrow and medium pulses is a composite signal, which is expressed as:

[0057] s(t)=s1(t)+s2(t)+s3(t), (0≤t≤T1+T2+T3)

[0058] Assuming the target's distance is R, the time delay from the radar transmitting the signal to hitting the target and then receiving the echo signal is τ = 2R / c, where c is the speed of light. Therefore, the echo signal received by the radar can be expressed as:

[0059]

[0060] Step 2: performing orthogonal digital down-conversion processing on the three-pulse composite echo signal to obtain a three-pulse composite baseband signal; the three-pulse composite baseband signal retains the amplitude and phase information of the original signal, making subsequent processing easier;

[0061] The following is a detailed description of step 2:

[0062] Perform digital down-conversion processing on the three-pulse composite echo signal respectively, and mix the three pulse echo signals with the F1 intermediate frequency signal, the F2 intermediate frequency signal, and the F3 intermediate frequency signal respectively, that is, multiply the wide, narrow, and medium pulse signals with the two orthogonal local oscillator signals respectively to obtain the mixed output. Multiply one channel by cos(2πF i t) down-converted to zero intermediate frequency, with the same phase as the original signal; the other one is multiplied by sin(2πF i t) down-convert to zero intermediate frequency, which is orthogonal to the phase of the original signal. The mathematical expression of the mixing output is:

[0063]

[0064] Where t represents time, j represents imaginary unit, and i=1, 2, and 3 represent the serial numbers of wide, narrow, and medium pulses respectively. i (t) represents the echo signals of the three pulses, F i Represents three intermediate frequency signals.

[0065] The mixed output signal is low-pass filtered. The three pulse channels use a 128-order FIR low-pass filter with a cutoff frequency of 5 MHz. The filter uses a Hamming window design with a stopband attenuation of ≥ 60 dB. The filter removes the high-frequency components after mixing and retains the baseband signal.

[0066] y i (t) is the output after mixing, y i The real and imaginary parts of (t) correspond to the I-path and Q-path signals respectively. The expressions for I and Q are:

[0067] y iI (t) = r i (t)cos(2πF i t)

[0068]

[0069] y iQ (t) = -r i (t)sin(2πF i t)

[0070]

[0071] in, is the amplitude of the echo signal, is the phase of the echo signal. Use a low-pass filter to filter out the 4πF i Components, get I and Q baseband signals, the expression is:

[0072]

[0073] Step 3: performing pulse compression processing on the three-pulse composite baseband signal to obtain a three-pulse composite signal after energy accumulation; wherein the signal after pulse compression processing contains the distance information of the detected target;

[0074] The following is a detailed description of step three:

[0075] Perform a Fast Fourier Transform (FFT) on each of the three-pulse composite baseband signals and convert them to the frequency domain. Perform a complex multiplication of the FFT result with the pre-stored matched filter frequency domain coefficients (generated by FFT of the conjugate time domain waveform of the transmitted signal). The expression is:

[0076]

[0077] P i (f) = B i (f) H i (f) i=1, 2, 3

[0078] Where f represents frequency, b i (t) is the baseband signal of the wide, narrow and medium pulses, H i (f) is the pre-stored matched filter frequency domain coefficient, P i (f) represents the frequency domain signal after multiplication.

[0079] The impulse response of the matched filter h i (t) is defined as the conjugate time-inverse waveform of the radar transmission signal, that is: h i (t) = s i * (t). Its physical meaning includes:

[0080] (1) Conjugate operation: Compensates for phase distortion in signal propagation and ensures maximum coherence matching between the echo signal and the filter.

[0081] (2) Time reversal operation: align the signal’s time domain energy distribution so that the filtered output forms a peak at the target delay.

[0082] For h i (t) Perform Fourier transform to obtain the frequency domain coefficients of the matched filter:

[0083]

[0084] The matched filter maximizes the output signal-to-noise ratio (SNR), with a peak power equal to 2Es / N0 times the input signal energy (Es is the signal energy, and N0 is the noise power spectral density). The matched filter coefficient H(f) is individually designed for different pulse types (wide / narrow / medium), suppressing pulse compression sidelobes and adapting to the SNR requirements of each range.

[0085] Perform inverse FFT on the multiplied frequency domain signal to obtain the time domain pulse signal after energy accumulation, which is expressed as:

[0086]

[0087] Step 4: performing distance splicing processing on the three-pulse composite signal after energy accumulation to obtain a spliced three-pulse composite signal; wherein the distance splicing includes splicing of wide pulse effective distance, narrow pulse effective distance, and medium pulse effective distance;

[0088] The following is a detailed description of step four:

[0089] Specifically, performing distance splicing processing on the three-pulse composite signal after energy accumulation includes:

[0090] Calculate the measurement blind zone R of wide pulses b, because the radar transmitter cannot receive pulses during the time period of transmitting pulses, there is a blind zone in the wide pulse where the target cannot be measured. The expression is:

[0091]

[0092] Where C represents the speed of light and T1 represents the pulse duration of the wide pulse.

[0093] The segmented ranging performance is optimized, and the distance segments are divided based on the measurement blind area, including: short-range segment, transition segment, medium-long-range segment, and long-range segment.

[0094] By introducing relevant parameters, the measurement blind area R of the wide pulse can be obtained. b =1800m. The distance segments are specifically divided as follows:

[0095] (a) Short range (<1800m): The target is within the range of the narrow pulse and the distance is measured using the narrow pulse.

[0096] (b) Transition section (1800m-2000m): The narrow pulse echo signal is cut off by the filter after the splicing point. The energy of the wide pulse after the splicing point is too low to generate an effective peak through pulse compression. The measurement is switched to the medium pulse to ensure ranging continuity.

[0097] (c) Medium- to long-range (2000-3600 m): The target is within the wide pulse range. However, only the portion of the wide pulse echo after the splicing point is received within this range, while the portion before the splicing point is intercepted. The wide pulse cannot fully accumulate energy during pulse compression, and there is a mismatch, but it is sufficient for target detection.

[0098] (d) Long-range segment (>3600m): The wide pulse receives the echo signal completely, and the energy is fully accumulated after matched filtering, so the ranging accuracy reaches the theoretical limit.

[0099] Step 5: Performing low-altitude moving target detection (MTD) processing on the spliced three-pulse composite signal to obtain the distance and speed of the low-altitude moving target;

[0100] The following is a detailed description of step five:

[0101] Specifically, performing low-altitude moving target detection (MTD) processing on the spliced three-pulse composite signal includes:

[0102] Doppler filter bank construction and interference suppression: Based on the FIR transverse filter bank architecture, N Doppler filters are configured to cover the complete unambiguous speed measurement range. The m-th tap weight of the k-th filter in the filter bank is:

[0103] W mk =e-j2π(m-1)k / N (m=1,...,N; k=0,1,...,N-1)

[0104] Among them, each filter corresponds to a specific Doppler frequency response, and the spectrum separation of moving targets and stationary objects is achieved by adjusting the k value.

[0105] FFT High-Efficiency Mode: Performs FFT operations on the same-range gate data of N pulses in the slow-time dimension, equivalently generating a Doppler filter bank. This significantly reduces the amount of computation, improves real-time performance, and reduces hardware resource usage.

[0106] The signal x[m,n] after distance splicing (m is the pulse number, n is the distance index) is input into the filter bank along the slow time dimension (m axis); the output of the kth filter is:

[0107]

[0108] Static clutter (zero Doppler frequency) is suppressed by filter 0, and the energy of the moving target is highlighted in the corresponding k-value filter channel, so the target speed can be obtained. Perform FFT operation on N pulse data x[0,n],x[1,n],…,x[N-1,n] of the same range gate n:

[0109]

[0110] It can be seen that the FFT output G k [n] and the filter bank output g k [n] is equivalent, but the computational complexity is increased from O(N 2 ) is reduced to O(NlogN).

[0111] In order to further illustrate the advantages of the present invention, the following will combine the process simulation of target detection based on the above target detection method.

[0112] Figure 2 Figures 2 and 3 show the time and frequency domain simulations of a linear frequency modulated multi-pulse system. The simulation parameters are: frequency modulation frequency Fc = 100 MHz, bandwidth B = 10 MHz, wide pulse width T1 = 12 µs, carrier frequency F1 = 15 MHz, narrow pulse width T2 = 1 µs, carrier frequency F2 = 26 MHz, medium pulse width T3 = 2 µs, carrier frequency F3 = 37 MHz. The pulse repetition period Tp = 60 µs. The amplitudes of both the transmitted and echo signals are 1. The simulation considers only Gaussian white noise and excludes other clutter.

[0113] The simulation graph shows that the three-pulse composite signal is essentially composed of three linear frequency-modulated pulses separated in the frequency domain and with different pulse widths. The wide pulses utilize a large time-bandwidth product design, resulting in an in-band energy concentration of ≥95%, and a spectrum that approaches an ideal rectangular distribution. However, due to their shorter duration, the energy of narrow and medium pulses is lower than that of wide pulses. Furthermore, due to their smaller time-bandwidth product, the in-band energy is less concentrated, resulting in a less rectangular spectrum.

[0114] Figures 3 to 5 They are the simulated waveforms of wide pulse, narrow pulse and medium pulse after digital down-conversion processing. Although the intermediate frequencies of linear frequency modulation wide, narrow and medium pulses are different, the bandwidth is 10MHz. After digital down-conversion (zero intermediate frequency processing), the frequency band range is -5-5MHz. The spectrum shape is the same as Figure 2 Stay consistent.

[0115] Figures 6 to 8 The simulated waveforms for a wide pulse, a narrow pulse, and a medium pulse after pulse compression processing are shown. The horizontal axis represents distance, and the vertical axis represents signal amplitude. After pulse compression, the signal peaks, and the peak position corresponds to the target delay τ. The distance R is then inferred from τ = 2R / c to obtain the target distance. Three targets were selected for this simulation, at distances of 5000m, 1000m, and 1900m, corresponding to the measurement ranges for wide, narrow, and medium pulses, respectively. As can be seen from the results, the simulation results are all within ±1m of accuracy.

[0116] The simulated waveform of the wide pulse after pulse compression processing produces an inconspicuous peak near 1903.5m. This is because the energy of the wide pulse after the splicing point is too low to generate an effective peak through pulse compression.

[0117] Figure 9 This is the simulated waveform after the composite pulses are spliced at different distances. The spliced waveform has peaks at 1000.5m, 1899m, and 4999.5m, representing the distances of the three targets, with an error within ±1m. Comparison shows that the peak at 4999.5m is the highest. This is because the wide pulse has a longer duration and relatively higher energy, resulting in the best measurement results.

[0118] Figure 10 This is a simulation diagram of a composite pulse after moving target detection (MTD) processing. The X-axis represents distance, the Y-axis represents velocity, and the Z-axis represents signal amplitude. The speeds of the three targets selected for this simulation are -5 m / s, -10 m / s, and 10 m / s, respectively. As can be seen from the figure, the distances and velocities corresponding to the target coordinates are consistent with the target parameters set in the simulation. The errors in both distance and velocity measurements are within reasonable limits, demonstrating that the measurement method and process are correct and feasible.

[0119] According to the performance simulation cases provided by the present invention and the simulation results, the signal processing method of the present invention has the following significant advantages:

[0120] (1) Elimination of ranging blind spots and continuous coverage of the entire distance segment

[0121] Through the composite modulation of wide, narrow and medium pulses and dynamic distance splicing technology, the ranging blind spot problem of the traditional single pulse system is completely solved:

[0122] Short-range segment (<1800m): Utilizing the high-resolution characteristics of narrow pulses, ranging accuracy is achieved to ≤1m (target error in simulation cases is ±1m);

[0123] Transition section (1800m-2000m): Medium pulses are used to fill the blind zone, eliminating the ranging blank area around 1800m in traditional solutions.

[0124] Medium and long distances (2000m-3600m): Measurement is performed using wide pulse echoes that are not fully received.

[0125] Long-range segment (>3600m): After matched filtering, the complete wide pulse echo has an energy accumulation efficiency of ≥95%, and the signal-to-noise ratio is improved by 12dB.

[0126] (2) Breakthroughs in resource efficiency and real-time performance

[0127] Efficient implementation of FFT-MTD: Slow time dimension FFT operation reduces computational complexity from O(N 2 ) is reduced to O(NlogN). Single-frame processing delay is ≤ 3.5ms (traditional FIR solution is 12ms);

[0128] The specific implementation methods listed in this specification are only used to illustrate the core technical concept of this application and do not constitute a limitation on the scope of protection. Any person skilled in the art can still make adaptive adjustments to the technical solutions recorded in the embodiments or perform equivalent replacements for specific technical features based on the reference to the embodiments of this application. Such derivative changes or element replacements of technical solutions should be deemed to fall within the scope of protection of the patent right of this application as long as they do not deviate from the innovative principles and technical boundaries defined in the claims of this application.

Claims

1. A target measurement method based on low-altitude radar three-pulse, characterized in that: The method comprises: Step 1: Design a three-pulse composite signal, using a wide, narrow, and medium three-pulse composite signal. The radar transmits the three-pulse composite signal through a transmitter and receives the echo through a receiver to obtain a three-pulse composite echo signal from a low-altitude target. Step 2: performing orthogonal digital down-conversion processing on the three-pulse composite echo signal to obtain a three-pulse composite baseband signal; the three-pulse composite baseband signal retains the amplitude and phase information of the original signal; Step 3: performing pulse compression processing on the three-pulse composite baseband signal to obtain a three-pulse composite signal after energy accumulation; wherein the signal after pulse compression processing contains the distance information of the detected target; Step 4: performing distance splicing processing on the three-pulse composite signal after energy accumulation to obtain a spliced three-pulse composite signal; wherein the distance splicing includes splicing of wide pulse effective distance, narrow pulse effective distance, and medium pulse effective distance; Step 5: Perform low-altitude moving target detection (MTD) processing on the spliced three-pulse composite signal to obtain the distance and speed of the low-altitude moving target.

2. A target measurement method based on low-altitude radar three-pulse according to claim 1, characterized in that, The wide, narrow, and medium pulses in the three-pulse composite signal all utilize linear frequency modulation (LFM) pulse signals. These signals include the wide pulse duration T1, center frequency F1, and frequency modulation slope K1; the narrow pulse duration T2, center frequency F2, and frequency modulation slope K2; the medium pulse duration T3, center frequency F3, and frequency modulation slope K3; and a pulse bandwidth B (all three pulses have the same bandwidth). The three-pulse composite echo signal includes information such as the target-to-radar range R and the target's relative velocity V.

3. A target measurement method based on low-altitude radar three-pulse according to claim 2, characterized in that, Performing orthogonal digital down-conversion processing on the three-pulse composite echo signal to obtain a three-pulse composite baseband signal, including: Perform digital down-conversion processing on the three-pulse composite echo signal, and mix the three pulse echo signals with the F1 intermediate frequency signal, the F2 intermediate frequency signal, and the F3 intermediate frequency signal, that is, multiply the wide, narrow, and medium pulse signals with the two orthogonal local oscillator signals to obtain the mixed output. Down-converted to zero intermediate frequency, the same phase as the original signal; the other multiplied by Down-converted to zero intermediate frequency, which is orthogonal to the original signal phase. The mathematical expression of the mixing output is: ； in Indicates time, represents the imaginary unit, They represent the serial numbers of the three types of pulses: wide, narrow, and medium. Represents the echo signals of three pulses, Represents three intermediate frequency signals; The mixed output signal is low-pass filtered, using a 5MHz FIR low-pass filter for each of the three pulse channels. The filter order is 128, using a Hamming window design with a stopband attenuation of ≥60dB. This filter removes the high-frequency components of the mixed signal while retaining the baseband signal.

4. The target measurement method based on low-altitude radar three-pulse according to claim 3 is characterized in that: Performing pulse compression processing on the three-pulse composite baseband signal to obtain a three-pulse composite signal after energy accumulation, including: Perform a Fast Fourier Transform (FFT) on the baseband signals of the wide, narrow, and medium pulses and convert them to the frequency domain. Perform a complex multiplication of the FFT result with the pre-stored matched filter frequency domain coefficients (generated by FFT of the conjugate time domain waveform of the transmitted signal). The expression is: ； ； in Indicates frequency, are the baseband signals of the wide, narrow and medium pulses, is the pre-stored matched filter frequency domain coefficient, represents the frequency domain signal after multiplication; Perform inverse FFT on the multiplied frequency domain signal to obtain the time domain pulse signal after energy accumulation. The expression is:

5. The target measurement method based on low-altitude radar three-pulse according to claim 4 is characterized in that: Performing distance splicing processing on the three-pulse composite signal after energy accumulation, including: Calculating the measurement blind zone of wide pulses , because the radar transmitter cannot receive pulses during the time period of transmitting pulses, there is a blind zone in the wide pulse where the target cannot be measured. The expression is: ； Where C represents the speed of light, T1 represents the pulse duration of the wide pulse; The segmented ranging performance is optimized, and the distance segments are divided based on the measurement blind area, including: short-range segment, transition segment, medium-long-range segment, and long-range segment.

6. The target measurement method based on low-altitude radar three-pulse according to claim 5 is characterized in that: Performing low-altitude moving target detection (MTD) processing on the spliced three-pulse composite signal to obtain the range and speed of the low-altitude moving target, including: Doppler filter bank construction and interference suppression: Based on the FIR transverse filter bank architecture, N Doppler filters are configured to cover the complete unambiguous speed measurement range. The m-th tap weight of the k-th filter in the filter bank is: ； Among them, each filter corresponds to a specific Doppler frequency response, and the spectrum separation of moving targets and stationary objects is achieved by adjusting the k value; FFT high-efficiency mode: Performs FFT operations on the same-range gate data of N pulses in the slow time dimension, equivalently generating a Doppler filter bank, significantly reducing the amount of calculation, improving real-time performance, and reducing hardware resource usage.

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