A method for designing anti-clutter waveform parameters of pulse Doppler radar
By optimizing the waveform parameters of the pulse Doppler radar, the problem of low target detection probability in radar down-look scenarios was solved, and efficient target detection under clutter and obstruction conditions was achieved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- GUIZHOU AEROSPACE ELECTRONICS TECH CO LTD
- Filing Date
- 2026-03-05
- Publication Date
- 2026-06-09
AI Technical Summary
Existing pulse Doppler radars have a low target detection probability in radar look-down scenarios, and it is difficult to simultaneously eliminate velocity ambiguity, eliminate range ambiguity, and reduce occlusion effects, resulting in a decrease in the probability of target detection.
By calculating the minimum pulse repetition frequency that satisfies velocity ambiguity and the maximum pulse repetition frequency that satisfies range ambiguity, the clutter spectrum characteristics are analyzed, the signal-to-clutter ratio is calculated, the usable range is determined and converted into a gate range, the target effective range segment is calculated, and the anti-clutter waveform parameters are obtained by splicing together, so as to avoid the overlap between the target echo and the clutter area and optimize the receiving range and the transmitting duty cycle.
It improves the target detection probability, ensures that the target echo can still be received completely under the effects of spectrum folding and obstruction, and enhances the radar's target detection capability under radar down-look conditions.
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Figure CN122172126A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of pulse Doppler radar design technology. Background Technology
[0002] Pulse Doppler radar is a radar system that uses the Doppler effect to measure target velocity. It works by transmitting pulse signals and receiving the reflected signals. The waveform design of pulse Doppler radar mainly needs to consider the pulse repetition frequency (PRF), transmit duty cycle, and receive duty cycle of the transmitted signal based on the usage scenario, the target, and the blocking effect.
[0003] Radar applications are primarily categorized into look-up and look-down scenarios. When radar is looking up, the sidelobe clutter is relatively small because the background is usually the sky. When radar is looking down, the sidelobe clutter is larger because it is usually facing the ground or sea surface. In addition to sidelobe clutter, radar generates strong altitude clutter in areas perpendicular to the ground, and strong mainlobe clutter in areas pointed to by the antenna's main lobe beam.
[0004] When the radar's performance parameters are fixed, the radar cross section (RCS) of the target determines the radar's target detection range. The target's velocity direction (head-on or tail-on) determines the position of the target echo in the radar echo spectrum.
[0005] The blocking effect is due to the fact that pulse Doppler radars typically operate in a time-division multiplexing manner, which means that some areas cannot receive target echoes because the radar is transmitting signals.
[0006] The selection of the transmit pulse's pulse frequency (PRF) determines the degree of ambiguity in the radar's velocity and range measurements, as well as its detection capabilities under low-altitude and look-down conditions. The transmit duty cycle primarily determines the radar's effective range and obstruction distance. The receive duty cycle determines the effective range of the target that can be received. Because phased array radars require a certain amount of time to switch from transmit to receive signal mode, the actual receive duty cycle is lower than the transmit duty cycle.
[0007] When designing waveforms, it is necessary to analyze the spectrum of the received coherent pulse signal train so that the target echo can be detected in the spectrum later through signal processing methods. The spectrum of the pulse train is as follows: Figure 1 As shown in the figure. The dashed line in the figure represents the sinc-type envelope of the received pulse train. It is the PRF of the pulse train. This is the carrier frequency of the signal. The mathematical expression for the sinc function here is:
[0008] As can be seen, the spectrum of the pulse train containing the target echo consists of a series of discrete spectral lines that repeat with the sinc function as the envelope and the PRF of the pulse train as the interval.
[0009] When the target is an oncoming target, the carrier frequency Nearby radar echo spectrum such as Figure 2 As shown in the figure. The Doppler frequency shift caused by the mutual motion between the radar and the target is:
[0010] carrier The corresponding wavelength is , It is the speed of the radar platform. It is the angle between the radar velocity vector and the line of sight to the target. It is the target's speed. It is the angle between the target's velocity vector and the line of sight to the target. It is half the width of the clutter region; It is the Doppler frequency shift of the vertical motion component between the radar and the ground; It is the Doppler frequency shift of the radar main lobe half beam relative to the ground motion. It can be seen that the greater the target velocity, the further away the target's Doppler frequency shift is from the clutter region; the smaller the target velocity, the closer the target's Doppler frequency shift is to the edge of the clutter region.
[0011] When the target is a tail-chasing target, the carrier frequency Nearby radar echo spectrum such as Figure 3 As shown, since the radar and target velocity directions are in the same direction, the Doppler frequency shift of the target echo must fall within the clutter region. At this point, due to the presence of sidelobe clutter, elevation line clutter, and main lobe clutter, detecting a tail-chasing target is more difficult than detecting an oncoming target.
[0012] The waveform parameter design of pulse Doppler radar involves designing a suitable pulse train (PRF) after fully evaluating the characteristics of the target and the usage scenario, combined with the performance characteristics of the radar platform.
[0013] For oncoming targets, in order to keep the target's echo away from the clutter region, the transmit pulse's pulse response (PRF) should satisfy the following:
[0014] In radar look-down mode, carrier frequency The sidelobe clutter on the left side mainly originates from the sky behind the platform and is typically weak. At this point, the PRF of the transmitted pulse train only needs to satisfy:
[0015] For a tail-chasing target, since the target will always appear within the clutter region, it is only necessary to ensure that spectral folding does not occur. In this case, the transmit pulse's PRF should satisfy:
[0016] As can be seen, the minimum PRF at this point is only related to the platform's motion speed. related.
[0017] However, if the PRF is too high, it will lead to a decrease in the unambiguous ranging distance. The relationship between the unambiguous ranging distance and the PRF is as follows:
[0018] To avoid transmission leakage, the radar employs time-division multiplexing (TDM). This means that the radar cannot simultaneously transmit and receive signals. Therefore, an obstruction effect exists, and there is a probability that the target echo will not be fully received, resulting in a decrease in target measurement accuracy. This process is as follows: Figure 4 .
[0019] The occlusion process can be represented by the following formula:
[0020] In the formula It is the pulse repetition period (the reciprocal of the PRF). It is the relative speed between the radar and the target. It is the shading period. It is the width of the obstructed area. It is the width of the transparent area. It is the width of the semi-transparent area. It is the transmit pulse width of the transmitted signal. It is the receiving gate width.
[0021] As can be seen, the blocking period is related to the relative velocity between the PRF and the radar target. When the target is known, a larger PRF results in a shorter blocking period. Additionally, a larger pulse transmission duty cycle leads to a wider blocking area.
[0022] When designing the pulse-Doppler radar waveform (PRF), it is necessary to simultaneously consider the absence of velocity ambiguity, the absence of range ambiguity, and minimizing the effects of obstruction. However, in practical applications of radar look-down, it is often impossible to simultaneously address all these factors. The first scenario involves pulse-Doppler radar acquiring target prior information with significant range errors. In this case, the transmitted waveform needs a large unambiguous range to detect the target. The pulse-Doppler response (PRF) of the transmitted waveform should be as small as possible. However, an excessively small PRF can cause spectral folding. The target echo will appear in clutter areas due to this folding, reducing its detection probability.
[0023] The second scenario is that, in order to achieve the maximum target detection range, pulse-Doppler radar should have a transmission duty cycle as large as possible. However, because radar itself is time-division multiplexing, a large transmission duty cycle will result in a greater distance where the signal cannot be received because it is being transmitted, thus reducing the probability of the target being detected.
[0024] Therefore, if the PRF of the pulse train and the transmit and receive duty cycles are selected solely based on the usage scenario, target, and obstruction effect, it may lead to a decrease in the probability of radar targets being detected in actual use. Summary of the Invention
[0025] The purpose of this invention is to provide a method for designing anti-clutter waveform parameters for pulse Doppler radar, which can obtain waveform combinations applicable to different ranges, thereby solving the problem of low radar target detection probability in actual use when using a single waveform parameter.
[0026] To address the aforementioned technical problems, this invention provides a method for designing anti-clutter waveform parameters for pulse Doppler radar, comprising the following steps: S1. Determine the minimum pulse repetition frequency without velocity ambiguity: For radar downward-looking scenarios, calculate the lower limit of the pulse repetition frequency that satisfies velocity ambiguity by combining the motion characteristics of the radar platform and the characteristics of the detected target. ; S2. Calculate the unambiguous parameters: Based on the target's prior range error and the radar receiver duty cycle, calculate the unambiguous maximum range. and the corresponding upper limit of pulse repetition frequency ,in accordance with and The size relationship determines the subsequent design path, such as Then proceed to step S5; S3. Analyze the clutter spectrum characteristics: Calculate the coverage and peak position of main lobe clutter and elevation line clutter in the radar echo spectrum; S4. Calculate the signal-to-clutter ratio: Based on the gain of the transmitting antenna in the direction pointing to the target, the radar cross-section of the target, the distance of the target from the radar, the gain of the transmitting antenna vertically pointing to the ground / sea surface, the height of the ground / sea surface from the radar, and the radar cross-section of the ground / sea clutter, calculate the signal-to-clutter ratio between the target echo power and the peak power of the height line clutter. S5. Determine the usable range: Compare the minimum pulse repetition frequency obtained under the condition of no velocity ambiguity. The maximum pulse repetition frequency that satisfies the error distance of prior information Determine the pulse repetition frequency range that can be used for waveform design. Range of values; S6. Converter gate range: Based on the system sampling frequency Number of gates , pulse repetition frequency range Transform into inclusion Waveform groups of each gate ; S7. Calculate the target effective range segment: Based on the transmitting power of the transmitting antenna and the gain of the transmitting antenna in the direction pointing to the target, calculate the target effective range segment applicable to each transmitting duty cycle segment; S8. Calculate anti-clutter waveform parameters: through waveform groups The receiving interval corresponding to the gate group is calculated based on the target range segment, and then spliced together to obtain the range-gate combination.
[0027] In step S1, the lower limit of the pulse repetition frequency without velocity ambiguity is satisfied. Calculate as follows: , In the formula, The boundary pulse repetition frequency value is calculated as follows: , In the formula, For the speed of the radar platform movement, For the target speed of motion, For radar operating wavelength, It is half the width of the clutter region. The target Doppler frequency shift correlation value.
[0028] In step S2, the maximum distance without distance ambiguity is... and the corresponding upper limit of pulse repetition frequency Calculate as follows: , , In the formula, The speed of electromagnetic wave propagation. For radar reception duty cycle, The distance error is the prior information of the target.
[0029] In step S3, the coverage range of the main lobe clutter in the radar echo spectrum is: The peak position frequency is Calculated as follows: , , , , , , In the formula, For radar velocity vector, The angle between the radar velocity vector and the radar main lobe beam direction. , For radar main lobe beam Half of This refers to the operating wavelength of the radar.
[0030] In step S3, the coverage range of the altitude line clutter in the radar echo spectrum is: The peak position frequency is Calculated as follows: , , , In the formula, For radar velocity vector, The angle between the radar velocity vector and the radar main lobe beam direction. The angle difference between the edge of the radar vertical beam and the vertical line. For the radar's ground-scraping angle, This refers to the operating wavelength of the radar.
[0031] In step S4, the signal-to-clutter ratio of the target echo power to the peak power of the elevation line clutter is... Calculated as follows: , In the formula, The gain of the transmitting antenna in the direction pointing towards the target. The radar cross-section of the target. The distance of the target from the radar. The gain of the transmitting antenna when pointing vertically towards the ground / sea surface. The altitude of the ground / sea surface from the radar. The radar cross-section of ground / sea clutter.
[0032] In step S5, the pulse repetition frequency range that can be used for waveform design The range of values is determined as follows: , In the formula, The minimum pulse repetition frequency obtained under conditions without velocity ambiguity. To satisfy the maximum pulse repetition frequency of the prior information error distance, This represents the width of the height line clutter region in the spectrum to the right of the signal's carrier frequency.
[0033] In step S7, the target effective distance is calculated as follows: , In the formula, This refers to the transmit power of the transmitting antenna. For the launch duty cycle, The gain of the transmitting antenna when pointing vertically towards the ground / sea surface. For radar operating wavelength, Boltzmann's constant, Standard temperature For receiver bandwidth, To detect the signal-to-noise ratio, This refers to the loss of electromagnetic waves during transmission; By analyzing the launch duty cycle The target's effective range segment is calculated by dividing the target into segments.
[0034] The electromagnetic wave loss during transmission Calculate as follows: , In the formula, For radome loss, For signal processing loss, This is due to atmospheric attenuation loss.
[0035] The launch duty cycle Calculate as follows: , In the formula, For the transmission pulse width, For the rising edge timing of the pulse, This represents the total pulse width per cycle.
[0036] Compared to existing technologies, this invention pre-estimates the positions of main lobe clutter and elevation line clutter caused by the ground / sea surface during radar look-down, and avoids overlap between the target echo and high-energy clutter regions after spectral folding during waveform parameter design. This improves the target detection probability when waveform parameters do not meet the condition of no velocity ambiguity. It also takes into account the problem of large range errors in the target's prior information, employing waveform parameters whose receiving interval can completely cover the target and its error range, effectively increasing the probability of target detection. By stitching together the receiving intervals of multiple waveforms, a range-gate combination with minimal obstruction is obtained, solving the problem of periodic signal obstruction caused by time-division multiplexing in traditional pulse Doppler radar.
[0037] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, and in order to make the above and other objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention are described below. Attached Figure Description
[0038] One or more embodiments are illustrated by way of example with reference numerals in the accompanying drawings. These illustrations do not constitute a limitation on the embodiments. Elements with the same reference numerals in the drawings are denoted as similar elements. Unless otherwise stated, the figures in the drawings are not to be limited by scale.
[0039] Figure 1 This is a flowchart illustrating at least one embodiment of the present invention; Figure 2 This is a schematic diagram of the received signal string spectrum; Figure 3 This is a schematic diagram of the spectral components of an oncoming target near the carrier frequency; Figure 4 This is a schematic diagram of the spectral components of a tail-chasing target near the carrier frequency; Figure 5 This is a diagram illustrating the occlusion effect; Figure 6 This is a schematic diagram of the radar look-down velocity model; Figure 7 This is a timing diagram for transmitting pulse trains. Detailed Implementation
[0040] To make the objectives, technical solutions, and advantages of this invention clearer, the embodiments of this invention will be described in detail below with reference to the accompanying drawings. However, those skilled in the art will understand that many technical details are presented in the embodiments of this invention to facilitate a better understanding of this application. However, the technical solutions claimed in this application can be implemented even without these technical details and various variations and modifications based on the following embodiments. The division of the following embodiments is for ease of description and should not constitute any limitation on the specific implementation of this invention. The embodiments can be combined with and referenced by each other without contradiction.
[0041] Example 1 like Figure 1 The method for designing anti-clutter waveform parameters for a pulse Doppler radar, as shown, includes the following steps: S1. Determine the minimum pulse repetition frequency without velocity ambiguity: For radar downward-looking scenarios, calculate the lower limit of the pulse repetition frequency that satisfies velocity ambiguity by combining the motion characteristics of the radar platform and the characteristics of the detected target. ; S2. Calculate the unambiguous parameters: Based on the target's prior range error and the radar receiver duty cycle, calculate the unambiguous maximum range. and the corresponding upper limit of pulse repetition frequency ,in accordance with and The size relationship determines the subsequent design path, such as Then proceed to step S5; S3. Analyze the clutter spectrum characteristics: Calculate the coverage and peak position of main lobe clutter and elevation line clutter in the radar echo spectrum; S4. Calculate the signal-to-clutter ratio: Based on the gain of the transmitting antenna in the direction pointing to the target, the radar cross-section of the target, the distance of the target from the radar, the gain of the transmitting antenna vertically pointing to the ground / sea surface, the height of the ground / sea surface from the radar, and the radar cross-section of the ground / sea clutter, calculate the signal-to-clutter ratio between the target echo power and the peak power of the height line clutter. S5. Determine the usable range: Compare the minimum pulse repetition frequency obtained under the condition of no velocity ambiguity. The maximum pulse repetition frequency that satisfies the error distance of prior information Determine the pulse repetition frequency range that can be used for waveform design. Range of values; S6. Converter gate range: Based on the system sampling frequency Number of gates , pulse repetition frequency range Transform into inclusion Waveform groups of each gate ; S7. Calculate the target effective range segment: Based on the transmitting power of the transmitting antenna and the gain of the transmitting antenna in the direction pointing to the target, calculate the target effective range segment applicable to each transmitting duty cycle segment; S8. Calculate anti-clutter waveform parameters: through waveform groups The receiving interval corresponding to the gate group is calculated based on the target range segment, and then spliced together to obtain the range-gate combination.
[0042] Example 2 Based on Example 1, in step S1, the lower limit of the pulse repetition frequency without velocity ambiguity is satisfied. Calculate as follows: , In the formula, The boundary pulse repetition frequency value is calculated as follows: , In the formula, For the speed of the radar platform movement, For the target speed of motion, For radar operating wavelength, It is half the width of the clutter region. The target Doppler frequency shift correlation value.
[0043] Furthermore, in step S2, the maximum distance without distance ambiguity is... and the corresponding upper limit of pulse repetition frequency Calculate as follows: , , In the formula, The speed of electromagnetic wave propagation. For radar reception duty cycle, The distance error is the prior information of the target.
[0044] Furthermore, in step S3, the coverage range of the main lobe clutter in the radar echo spectrum is: The peak position frequency is Calculated as follows: , , , , , , In the formula, For radar velocity vector, The angle between the radar velocity vector and the radar main lobe beam direction. , For radar main lobe beam Half of This refers to the operating wavelength of the radar.
[0045] Furthermore, in step S3, the coverage range of the altitude clutter in the radar echo spectrum is: The peak position frequency is Calculated as follows: , , , In the formula, For radar velocity vector, The angle between the radar velocity vector and the radar main lobe beam direction. The angle difference between the edge of the radar vertical beam and the vertical line. For the radar's ground-scraping angle, This refers to the operating wavelength of the radar.
[0046] Furthermore, in step S4, the signal-to-clutter ratio of the target echo power to the peak power of the elevation line clutter is... Calculated as follows: , In the formula, The gain of the transmitting antenna in the direction pointing towards the target. The radar cross-section of the target. The distance of the target from the radar. The gain of the transmitting antenna when pointing vertically towards the ground / sea surface. The altitude of the ground / sea surface from the radar. The radar cross-section of ground / sea clutter.
[0047] Furthermore, in step S5, the pulse repetition frequency range that can be used for waveform design The range of values is determined as follows: , In the formula, The minimum pulse repetition frequency obtained under conditions without velocity ambiguity. To satisfy the maximum pulse repetition frequency of the prior information error distance, This represents the width of the height line clutter region in the spectrum to the right of the signal's carrier frequency.
[0048] Example 3 Based on Example 1, in step S7, the target effective distance is calculated as follows: , In the formula, This refers to the transmit power of the transmitting antenna. For the launch duty cycle, The gain of the transmitting antenna when pointing vertically towards the ground / sea surface. For radar operating wavelength, Boltzmann's constant, Standard temperature For receiver bandwidth, To detect the signal-to-noise ratio, This refers to the loss of electromagnetic waves during transmission; By analyzing the launch duty cycle The target's effective range segment is calculated by dividing the target into segments.
[0049] Furthermore, electromagnetic wave loss during transmission. Calculate as follows: , In the formula, For radome loss, For signal processing loss, This is due to atmospheric attenuation loss.
[0050] Furthermore, launch duty cycle Calculate as follows: , In the formula, For the transmission pulse width, For the rising edge timing of the pulse, This represents the total pulse width per cycle.
[0051] Example 4 In conjunction with the above embodiments, the first step is to calculate the minimum PRF of the pulse train that satisfies velocity ambiguity based on the maximum speed of the radar platform, the usage scenario, and the target. PRF stands for Pulse Repetition Frequency.
[0052] Since the clutter noise in the radar spectrum is usually low during upward-looking radar, this invention mainly addresses the downward-looking radar scenario. In this case, formula (4) is used to calculate the boundary PRF value. In order to detect target echoes that fall exactly on the boundary PRF value, Set to:
[0053] The second step is to determine the distance error based on prior information. and receiving duty cycle Calculate the unambiguous range under different launch duty cycles. and its corresponding maximum PRF .for If the condition is met, continue waveform design from step five. Otherwise, continue waveform design from step three.
[0054] To maximize the probability of receiving the target's echo, the maximum unambiguous range is equal to:
[0055] Then, according to the formula:
[0056] The maximum PRF at this point can be calculated. .
[0057] The third step is to estimate the coverage and peak position of the main lobe clutter and height line clutter in the spectrum based on the usage scenario and the characteristics of the target.
[0058] A schematic diagram of the clutter region on the radar spectrum is shown below.Figure 2 , Figure 3 , Figure 4 , Figure 5 As shown. When the radar looks downwards, the velocity model of the radar and the target on the ground / sea surface is as follows. Figure 6 As shown in the figure. Point A is the position where the center of the radar main lobe beam illuminates the ground; points B and C are the positions where the half-width of the radar main lobe beam illuminates the ground, respectively; points D and E are the boundaries that the transmitted pulse can cover when the radar antenna is perpendicularly illuminating the ground. It is the distance corresponding to the width of the transmitted pulse. It is the radius of the echo that illuminates the ground at this moment. It's the radar's ground-grabbing angle; It is the radar main lobe beam Half of it. At this time, the friction angle between the edge B of the radar main lobe half beam and the ground / sea surface is... The angle of friction between edge C and the ground / sea surface is . It is the angle difference between the radar to point D / E and the radar vertical line. and , The relationship between them is:
[0059] In the formula, It refers to the height of the radar platform above the ground.
[0060] The velocity vector of the radar platform in the figure is The target's velocity vector is Blue target vectors represent tail-chasing targets, and red target vectors represent oncoming targets. The deviation angle between the radar velocity vector and the radar main lobe beam direction is... The deviation angle between the target velocity vector and the horizontal direction is If the radar velocity vector Above the target's line of sight, the angle from the radar to point B is: The angle to point C is If the radar velocity vector Below the target's line of sight, the angle from the radar to point B is: The angle to point C is Therefore, the relative velocity between point B on the ground and the radar is:
[0061] The relative velocity between point C on the ground and the radar is:
[0062] The relative speed between the radar and the oncoming target is:
[0063] The relative speed between the radar and the tail-chasing target is:
[0064] The relative velocity of the radar in the vertical direction is:
[0065] The relative velocity between the ground point D / E and the radar is:
[0066] Finally, according to the Doppler effect formula Convert the above velocity values into radar operating wavelengths The Doppler frequency is used to obtain the spectral coverage of the main lobe clutter and the height line clutter. and The function min means taking the smaller of the two values. It is the Doppler frequency corresponding to the radar velocity:
[0067] When the angle between the radar line of sight to point E and the radar line of sight is less than 90°, exist On the right side. At this time, the elevation clutter area is... Width on the right side When the angle between the radar line of sight to point E and the radar line of sight is greater than or equal to 90°, exist On the left. At this time, the elevation clutter area is... Width on the right side .
[0068] The peak position of the main lobe clutter region in the spectrum corresponds to the Doppler frequency of radar illumination point A:
[0069] The peak position of the elevation clutter region corresponds to the Doppler frequency of radar illumination in the vertical direction:
[0070] The fourth step is to calculate the minimum signal-to-clutter ratio (SNR) between the target echo power and the peak power of the height clutter. This is to assess whether the target echo can be detected if spectral folding occurs and the target echo overlaps with the height clutter region.
[0071] The echo power of a radar target can be calculated using radar equations:
[0072] In the formula, It is the transmission power of the transmitting antenna. It is the gain of the transmitting antenna in the direction pointing towards the target. It is the operating wavelength of the antenna. It is the target's RCS. It is the distance of the target from the radar. It refers to the loss of electromagnetic waves during transmission, including radome loss. Signal processing loss Atmospheric attenuation loss The losses are multiplicative: Atmospheric attenuation loss is mainly related to the antenna's operating wavelength. RCS: Radar Cross Section.
[0073] The peak power of height line clutter is equal to:
[0074] In the formula It is the gain of the transmitting antenna when it is pointed vertically towards the ground / sea surface. It is the altitude of the ground / sea surface above the radar. It is the RCS of land / sea clutter. It is the ground / sea surface scattering coefficient With radar effective illumination area The product of:
[0075] Ground / sea surface scattering coefficient It is related to the roughness of the ground / sea surface, the radar irradiation angle, and the radar's operating frequency. The effective illumination area of elevation clutter... for Figure 6 China and Israel A circle with radius . It can be calculated by combining formulas (14) and (15).
[0076] The signal-to-clutter ratio of the target echo power to the peak power of the elevation clutter is equal to... Substituting into formulas (25) and (26), we get:
[0077] As can be seen, the signal-to-noise ratio Mainly related to the antenna gain ratio in different directions RCS ratio of target to clutter and the inverse ratio of the distance from the radar to the target to the distance from the radar to the ground. related.
[0078] The fifth step is to determine the PRF range that can ultimately be used for waveform design. The criterion is to compare the minimum PRF obtained under the condition of no velocity ambiguity. The maximum PRF that satisfies the prior information error distance There are three main scenarios: The range available for waveform design at this time is... .
[0079] It is important to note that the pulse repetition interval (PRI) of the pulse train generated by a real pulse Doppler radar is based on the system sampling frequency. Quantified, that is, the true PRI equals , It is an integer and is called the gate number. Therefore, if in If a suitable number of gates cannot be selected within the specified range, the receiving duty cycle of the waveform calculated in step two can be further increased. This allows for a sufficient number of gates to be used in subsequent calculations.
[0080] 2. and . It is the height line clutter region in the spectrum. The width on the right side. As can be seen from step three, The value of is related to the angle between the radar line of sight to point E and the radar line of sight. The range that can be used for waveform design at this time is... .
[0081] because Pulse Doppler radar exhibits spectral folding. According to step four, the spectral coverage of main lobe clutter and elevation line clutter is... and In subsequent design steps, it is necessary to avoid the folded target echo falling within the main lobe clutter region and the height line clutter region. Additionally, if in If a suitable number of gates cannot be selected within the specified range, the receiving duty cycle of the waveform calculated in step two can be further increased. This allows for a sufficient number of gates to be used in subsequent calculations.
[0082] 3. and The range available for waveform design at this time is... .
[0083] This is because if The designed pulse waveform spectrum will exhibit more severe spectral folding. The height line clutter region will overlap in the spectrum due to folding, leading to a further increase in noise levels within the height line clutter region and a further decrease in the signal-to-noise ratio (SNR) within the spectrum. At this point, it is necessary to further increase the receiving duty cycle of the waveform calculated in step two. Make it larger than .
[0084] If other design specifications, such as the requirement that the dead zone (corresponding to the transmit pulse width + transmit / receive switching time) cannot be too low, result in the receiver duty cycle not being able to be too small, then it can only be handled conventionally. Continue with waveform design. The trade-off is that, due to the failure to meet the distance error requirements of the prior information, the target may not appear within the receiving area of the designed waveform, thus making the target undetectable.
[0085] Step six is to convert the determined PRF range into a gate range.
[0086] Because the PRI of the pulse train generated by a real pulse Doppler radar is based on the system sampling frequency. Quantized, therefore PRF and gate The relationship between them is:
[0087] This relationship can be used to determine the PRF interval obtained in step five. Transform into inclusion Waveform groups of each gate If the number of suitable gates within the interval is insufficient, it can be increased by further increasing the receiving duty cycle of the waveform calculated in step two. This allows for a sufficient number of gates to be used in subsequent calculations.
[0088] Step seven is to calculate the target effective range applicable to that launch duty cycle based on the launch duty cycle.
[0089] The radar equation for the target echo is shown in equation (25). Wherein, the transmit power of the transmitting antenna is... With antenna gain The product of these two values is the antenna's effective isotropic radiated power (EIRP), i.e. Since the actual transmit power is the transmit duty cycle multiplied by the transmit power, formula (25) can be rewritten as:
[0090] The formula for the sensitivity of the echo receiver of pulse Doppler radar is:
[0091] Therefore, substituting into formula (30), we can obtain the formula for the effective range of pulse Doppler radar as follows:
[0092] This formula can be used to calculate the effect of changing the transmit duty cycle while keeping other parameters of the radar system constant. This yields different maximum target effective ranges. Conversely, it allows us to obtain target effective range segments applicable to launch duty cycles ranging from 1% to 40%. The maximum value of each range segment is the maximum target effective range for that corresponding launch duty cycle.
[0093] It should be noted that, in practice, antennas need a certain rise time when transmitting pulse signals. Only then can maximum transmission power be achieved. Therefore, the actual transmission pulse width... equal:
[0094] The transmit duty cycle in formula (32) should be the transmit duty cycle corresponding to the actual transmit pulse width. During waveform design, the actual transmit pulse width needs to be converted to a transmit pulse width including the rise time. .
[0095] Step eight involves combining the determined gate range with the transmit duty cycle applicable to different distance segments to obtain the receiving interval corresponding to the gate combination. Then, the receiving intervals corresponding to different gates are stitched together to obtain a range-gate combination with minimal obstruction.
[0096] Real pulse-Doppler radar systems operate on a time-division multiplexing basis. It takes time for the radar system to switch from transmitting to receiving signals. Therefore, the timing of the pulse train transmitted by the pulse Doppler radar system is as follows: Figure 7 As shown in the figure. Figure (1) shows the transmitted pulse width. (2) is the received pulse width (3) is the send / receive switching time. (4) is the rising edge of the pulse. (5) is the falling edge of the pulse. .
[0097] According to this timing diagram, the transmit duty cycle of the transmit pulse train is:
[0098] The received pulse width is:
[0099] Thus, the signal receiving range of the transmitted pulse is The corresponding distance range is .
[0100] Because pulse Doppler radar systems transmit a series of pulses, not a single pulse, the actual receiving range extends along the range direction. Therefore, the actual receivable range should be: In the formula, It refers to the number of extensions.
[0101] Since the transmit duty cycle is related to the effective range, and the lower the transmit duty cycle, the larger the receiving range, the design is based on using a large transmit duty cycle for long distances and a small transmit duty cycle for short distances.
[0102] Pulse Doppler radar can achieve target ranging capabilities by using linear frequency modulated waveforms and pulse compression techniques. With a fixed system bandwidth, a wider transmitted pulse width results in better pulse compression. Therefore, to balance velocity and ranging capabilities, the transmit duty cycle cannot be too small when designing waveform parameters for pulses used at closer ranges. The specific metric is determined by the system design requirements.
[0103] against To determine the spectral folding pattern, it's necessary to estimate which target velocity ranges will be blocked by main lobe clutter and elevation line clutter regions, based on the target's velocity range and its new position in the spectrum after folding. If blocked regions exist, a new gate waveform for that range should be designed specifically for the blocked target velocity regions, using changes to the waveform PRF to offset the blocked target velocity range from the clutter regions. If no blocked regions exist, no new waveform design is required.
[0104] Therefore, if the target's velocity range is not obstructed by clutter after folding, the final design will still use one range-gate waveform combination. However, if the target's velocity range is obstructed by clutter after folding, the final design will use two or more range-gate waveform combinations. When using the designed waveform set, the radar system needs to determine which range-gate waveform combination to use based on the target's prior velocity information and the target's measured velocity information.
[0105] Example 5 The target of a certain pulse Doppler radar system satisfies the boundary conditions without velocity ambiguity. =300kHz. Follow step one. kHz.
[0106] The system's prior information has a predetermined error of ±60m and a receiving duty cycle of 54%. Therefore, according to step two, its distance-free ambiguity range is determined. m corresponds to the maximum PRF kHz.
[0107] Because at this time Therefore, steps three and four are unnecessary. According to step five, the range available for waveform design is... kHz.
[0108] The sampling frequency of the radar system is 50MHz, so according to step six, the gate range corresponding to the determined PRF interval is 75~166.
[0109] According to step seven, the radar system's maximum effective range against the target is 5.01 km when the transmission duty cycle is 40%. The maximum effective range under different transmission duty cycle conditions is as follows: Table 1. Launch Duty Cycle - Maximum Target Range
[0110] The final step is step eight. The radar system's pulse rising edge consists of 8 gates, and the transmit / receive switching time is also 8 gates. The system design requires a blind zone of 500m. Therefore, the waveform design result for 500m~5000m is as follows: Table 2 Waveform parameter design results
[0111] Example 6 The target of a certain pulse Doppler radar system satisfies the boundary conditions without velocity ambiguity. =300kHz. Follow step one. kHz.
[0112] The system's prior information has a predetermined error of ±200m, a pulse rise time of 8 gates, and a transmit / receive switching time of 8 gates. Following step two, when the actual transmit pulse width is 40%, the receive duty cycle is approximately 55%. At this point, there is no range ambiguity. m corresponds to the maximum PRF kHz; with a true transmit pulse width of 20%, the receive duty cycle is approximately 75%. At this point, there is no range ambiguity. m corresponds to the maximum PRF kHz.
[0113] Because at this time Therefore, continue with steps three and four.
[0114] Following step three, the main lobe clutter and height line clutter cover the spectral regions of [144, 150] kHz and [-21, 42] kHz, respectively. The height line clutter region in the spectrum is... Width on the right side kHz. The peak of the main lobe clutter appears at... At 148.4 kHz, the peak of the elevation line clutter appears The position is 9.8kHz.
[0115] According to step four, the minimum signal-to-clutter ratio (SCR) between the target echo power and the peak power of the elevation clutter is 24 dB. The radar system's detection threshold is 16 dB. Therefore, during waveform design, it is only necessary to ensure that the target echo avoids the main lobe clutter region.
[0116] According to step five, because and Therefore, for a waveform with a transmit pulse width of 40%, the range available for waveform design is [42, 206.25] kHz; for a waveform with a transmit pulse width of 20%, the range available for waveform design is [42, 281.25] kHz.
[0117] According to step six, when the transmit pulse width is 40%, the gate range is [242, 1190]; when the transmit pulse width is 40%, the gate range is [177, 1190].
[0118] According to step seven, the radar system's maximum effective range against the target is 5.01 km when the transmission duty cycle is 40%. The maximum effective range under different transmission duty cycle conditions is as follows: Table 3 Launch Duty Cycle - Maximum Target Range
[0119] The final step is step eight. The radar system's pulse rise time is 8 gates, and the transmit / receive switching time is 8 gates. The system design requires a blind zone of 500m. (The text then abruptly shifts to discussing the boundaries of clutter zones.) 150kHz. The target speed measurement range corresponds to [160, 300]kHz.
[0120] Therefore, the waveform design results for 500m~5000m are as follows: Table 4 Waveform parameter design results Table 1
[0121] The waveform set designed using the table above can meet the error requirements of the prior information. However, due to... Therefore, spectral folding occurs. Since the main lobe clutter range is [144, 150] kHz, and the minimum PRF corresponding to gate = 275 in the table above is 181.82 kHz, which is greater than the maximum value of the clutter range, the main lobe clutter range will not be folded. However, the target velocity measurement range corresponding to [160, 300] kHz will be folded. The folded clutter range and target velocity measurement range are shown in the table below: Table 5 Waveform parameter design results Table 2
[0122] As can be seen, although the target's velocity measurement range is folded at this point, it does not overlap with the main lobe clutter range. Therefore, there is no need to design an additional waveform set.
[0123] Therefore, the present invention: 1. A waveform combination containing multiple waveforms was designed so that the receiving range obtained by splicing multiple waveforms can completely cover the antenna blind zone to the farthest target range. 2. By establishing a velocity model for radar look-down, the calculation methods for the range of main lobe clutter and elevation clutter regions were derived, as well as the calculation method for the peak power of elevation clutter. 3. By avoiding main lobe clutter and height line clutter regions in the waveform design, the target can be detected even if spectral folding occurs; 4. A formula for calculating the minimum signal-to-clutter ratio between the target echo power and the peak power of the elevation clutter was derived. By comparing this ratio with the detection threshold, it helps determine whether the target echo can be allowed to appear within the elevation clutter zone. 5. In addition to the pulse waveform PRF, the transmit duty cycle (receive duty cycle) of the waveform is also incorporated into the design: a) Based on the principle that the larger the transmission duty cycle of the pulse waveform, the farther the effective distance, distance segments corresponding to different transmission duty cycles were planned; b) Based on the principle that a larger receiving duty cycle of a pulse waveform results in a larger receiving range, the unambiguous distance that satisfies the prior information distance error and its corresponding maximum PRF are calculated. The waveform can be changed by adjusting the receiving duty cycle. This allows for gate combinations that can cover the entire range.
[0124] Those skilled in the art will understand that the above embodiments can be modified in form and detail in practical applications without departing from the spirit and scope of the invention.
Claims
1. A method for designing anti-clutter waveform parameters for pulse Doppler radar, characterized in that, Includes the following steps: S1. Determine the minimum pulse repetition frequency without velocity ambiguity: For radar downward-looking scenarios, calculate the lower limit of the pulse repetition frequency that satisfies velocity ambiguity by combining the motion characteristics of the radar platform and the characteristics of the detected target. ; S2. Calculate the unambiguous parameters: Based on the target's prior range error and the radar receiver duty cycle, calculate the unambiguous maximum range. and the corresponding upper limit of pulse repetition frequency ,in accordance with and The size relationship determines the subsequent design path, such as Then proceed to step S5; S3. Analyze the clutter spectrum characteristics: Calculate the coverage and peak position of main lobe clutter and elevation line clutter in the radar echo spectrum; S4. Calculate the signal-to-clutter ratio: Based on the gain of the transmitting antenna in the direction pointing to the target, the radar cross-section of the target, the distance of the target from the radar, the gain of the transmitting antenna vertically pointing to the ground / sea surface, the height of the ground / sea surface from the radar, and the radar cross-section of the ground / sea clutter, calculate the signal-to-clutter ratio between the target echo power and the peak power of the height line clutter. S5. Determine the usable range: Compare the minimum pulse repetition frequency obtained under the condition of no velocity ambiguity. The maximum pulse repetition frequency that satisfies the error distance of prior information Determine the pulse repetition frequency range that can be used for waveform design. Range of values; S6. Converter gate range: Based on the system sampling frequency Number of gates , pulse repetition frequency range Transform into inclusion Waveform groups of each gate ; S7. Calculate the target effective range: Based on the transmitting power of the transmitting antenna and the gain of the transmitting antenna in the direction pointing to the target, calculate the target effective range applicable to each transmitting duty cycle. S8. Calculate anti-clutter waveform parameters: through waveform groups The receiving interval corresponding to the gate group is calculated based on the target range segment, and then spliced together to obtain the range-gate combination.
2. The method for designing anti-clutter waveform parameters for pulse Doppler radar as described in claim 1, characterized in that, In step S1, the lower limit of the pulse repetition frequency without velocity ambiguity is satisfied. Calculate as follows: In the formula, The boundary pulse repetition frequency value is calculated as follows: In the formula, For the speed of the radar platform movement, For the target speed of motion, For radar operating wavelength, It is half the width of the clutter region. The target Doppler frequency shift correlation value.
3. The method for designing anti-clutter waveform parameters for pulse Doppler radar as described in claim 1, characterized in that, In step S2, the maximum distance without distance ambiguity is... and the corresponding upper limit of pulse repetition frequency Calculate as follows: ， ， In the formula, The speed of electromagnetic wave propagation. For radar reception duty cycle, The distance error is the prior information of the target.
4. The method for designing anti-clutter waveform parameters for pulse Doppler radar as described in claim 1, characterized in that, In step S3, the coverage range of the main lobe clutter in the radar echo spectrum is: The peak position frequency is Calculated as follows: ， ， ， ， ， ， In the formula, For radar velocity vector, The angle between the radar velocity vector and the radar main lobe beam direction. , For radar main lobe beam Half of This refers to the operating wavelength of the radar.
5. The method for designing anti-clutter waveform parameters for pulse Doppler radar as described in claim 1, characterized in that, In step S3, the coverage range of the elevation line clutter in the radar echo spectrum is: The peak position frequency is Calculated as follows: ， ， ， In the formula, For radar velocity vector, The angle between the radar velocity vector and the radar main lobe beam direction. The angle difference between the edge of the radar vertical beam and the vertical line. For the radar's ground-scraping angle, This refers to the operating wavelength of the radar.
6. The method for designing anti-clutter waveform parameters for pulse Doppler radar as described in claim 1, characterized in that, In step S4, the signal-to-clutter ratio of the target echo power to the peak power of the altitude clutter is... Calculated as follows: , In the formula, The gain of the transmitting antenna in the direction pointing towards the target. The radar cross-section of the target. The distance of the target from the radar. The gain of the transmitting antenna when pointing vertically towards the ground / sea surface. The altitude of the ground / sea surface from the radar. The radar cross-section of ground / sea clutter.
7. The method for designing anti-clutter waveform parameters for pulse Doppler radar as described in claim 1, characterized in that, In step S5, the pulse repetition frequency range that can be used for waveform design The range of values is determined as follows: ， In the formula, The minimum pulse repetition frequency obtained under conditions without velocity ambiguity. To satisfy the maximum pulse repetition frequency of the prior information error distance, This represents the width of the height line clutter region in the spectrum to the right of the signal's carrier frequency.
8. The method for designing anti-clutter waveform parameters for pulse Doppler radar as described in claim 1, characterized in that, In step S7, the target effective distance is calculated as follows: ， In the formula, This refers to the transmit power of the transmitting antenna. For the launch duty cycle, The gain of the transmitting antenna when pointing vertically towards the ground / sea surface. For radar operating wavelength, Boltzmann's constant, Standard temperature For receiver bandwidth, To detect the signal-to-noise ratio, This refers to the loss of electromagnetic waves during transmission; By analyzing the launch duty cycle The target's effective range segment is calculated by dividing the target into segments.
9. The method for designing anti-clutter waveform parameters for pulse Doppler radar as described in claim 8, characterized in that, The electromagnetic wave loss during transmission Calculate as follows: ， In the formula, For radome loss, For signal processing loss, This is due to atmospheric attenuation loss.
10. The method for designing anti-clutter waveform parameters for pulse Doppler radar as described in claim 8, characterized in that, The launch duty cycle Calculate as follows: In the formula, For the transmission pulse width, For the rising edge timing of the pulse, This represents the total pulse width per cycle.