A lossless echo starboard radar high-resolution wide swath timing design method

Abstract

The application provides a kind of lossless echo spaceborne radar high-resolution wide swath timing design method, zebra chart is drawn using spaceborne radar parameters;The gap between the bands in the zebra chart selects the scene echo limiting area, thereby selecting the pulse repetition frequency range;Randomly select the pulse repetition frequency of each group in the pulse repetition frequency range to form a pulse repetition frequency sequence, and in turn judge whether the distance ambiguity corresponding to the pulse repetition frequency of adjacent two groups is consistent, if not consistent, then according to the pulse repetition frequency from small to large and from large to small, redesign the pulse repetition frequency at the connection of the group pulse repetition frequency sequence to obtain the designed pulse repetition frequency sequence. Through the fine timing design of the pulse repetition frequency sequence, the grouping pulse repetition frequency agile sequence without losing echo is obtained, which still uses the non-uniform undersampling method to ensure the high-resolution wide swath imaging requirements, and at the same time, it does not produce the collision of the transmit-receive timing, ensuring the integrity of the target information. In addition, the design also considers avoiding the influence of the nadir echo, ensuring the subsequent imaging quality.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of radar imaging, and particularly relates to a high-resolution wide-swath time sequence design method for spaceborne radar with intact echoes. BACKGROUND

[0002] With the wide application of spaceborne synthetic aperture radar, the demand for high-resolution wide-swath imaging in the azimuth direction is gradually highlighted. However, high-resolution and wide-swath imaging in the azimuth direction are contradictory due to the limitation of pulse repetition frequency (PRF). According to the Nyquist sampling theorem, high azimuth resolution requires a high pulse repetition frequency, while wide-swath imaging requires a lower pulse repetition frequency. The pulse repetition frequency of the traditional spaceborne radar must follow the Nyquist sampling theorem, and thus cannot meet the requirement of wide-swath imaging. At present, the existing method uses azimuth non-uniform undersampling to solve this problem. The method can break through the limitation of the Nyquist sampling, convert the aliasing caused by undersampling into random noise, and realize high-resolution wide-swath imaging. However, the existing sampling methods such as random sampling, Poisson sampling and grouped random sampling will cause different degrees of disorder of the transmission and reception time sequence caused by the pulse repetition frequency jump. The transmission pulse and the received echo may cross, and thus the echo signal cannot be received, which makes it difficult to collect the echo signal data completely. The existing grouped PRF agile waveform divides the transmission signal into several groups, and the pulse repetition frequency in each group is the same. The repetition frequency of each group is randomly selected within the repetition frequency interval limited by the pulse repetition frequency of the spaceborne radar and the coverage relationship constraint graph (zebra graph). The random non-uniform undersampling in the azimuth direction makes it possible to meet the requirement of high-resolution wide-swath imaging.

[0003] Although the existing grouped PRF agile waveform can ensure that the transmission signal and the echo do not collide in the same group due to the consistent repetition frequency, the echo collision still occurs at the connection between two groups due to the inconsistent repetition frequency, and the problem of transmission and reception collision has not been truly solved. With the increase of the number of echoes and the number of times of random selection of the repetition frequency, the number of echo collisions at the connection between groups also increases, and the number of lost echoes also increases, thereby affecting the final imaging effect. SUMMARY

[0004] In order to solve the above problems in the prior art, the application provides a high-resolution wide-swath time sequence design method for spaceborne radar with intact echoes. The technical problem to be solved by the application is solved by the following technical scheme.

[0005] The application provides a high-resolution wide-swath time sequence design method for spaceborne radar with intact echoes, which comprises the following steps:

[0006] S100, acquiring a plurality of parameters of a spaceborne radar, and drawing a zebra graph according to the plurality of parameters; the zebra graph comprises a plurality of interlaced strips;

[0007] S200, select a scene echo limiting region in the gap between the strips, and use the scene echo limiting region to select the repetition frequency range;

[0008] S300, randomly select the repetition frequencies of each group of pulses within the repetition frequency range to form a repetition frequency sequence, and sequentially determine whether the distance ambiguity number corresponding to the repetition frequency sequences of two adjacent groups is consistent. If they are inconsistent, redesign the repetition frequency at the connection point of the repetition frequency sequence between groups according to the two cases of selecting from small to large and from large to small to obtain the designed repetition frequency sequence.

[0009] Among them, pulses in the same group have the same repetition frequency, while pulses in different groups have randomly selected repetition frequencies.

[0010] Beneficial effects:

[0011] This invention provides a lossless echo-based high-resolution wide-swath timing design method for spaceborne radar. It utilizes spaceborne radar parameters to create a zebra diagram; selects scene echo-limited regions within the gaps between stripes in the zebra diagram to determine the repetition frequency range; randomly selects the repetition frequencies of each pulse group within this range to form a repetition frequency sequence; and sequentially checks whether the range ambiguity numbers corresponding to the repetition frequencies of adjacent groups are consistent. If they are consistent, the repetition frequencies at the connection points between the inter-group repetition frequency sequences are redesigned based on two scenarios: repetition frequencies selected from smallest to largest and from largest to smallest, resulting in the designed repetition frequency sequence. This invention, through meticulous timing design of the repetition frequency sequence, obtains a grouped repetition frequency agile sequence that does not lose echoes. This sequence still employs a non-uniform undersampling method to ensure high-resolution wide-swath imaging requirements while avoiding collisions in transmit and receive timing, thus guaranteeing the integrity of target information. Furthermore, the design also considers avoiding the influence of nadir echoes, ensuring subsequent imaging quality.

[0012] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0013] Figure 1 This is a flowchart illustrating a lossless echo design method for high-resolution wide-swath timing of spaceborne radar provided by the present invention.

[0014] Figure 2 This is a typical coverage map of a spaceborne SAR system provided by the present invention;

[0015] Figure 3 This is a schematic diagram of the transmit and receive timing at the connection point provided by the present invention;

[0016] Figure 4 This is a schematic diagram of the transmit and receive timing at the connection point after the design provided by the present invention;

[0017] Figure 5 This is a schematic diagram of the design process for the repetition frequency sequence provided by the present invention;

[0018] Figure 6 is a timing simulation diagram of a non-designed group PRF agile waveform part;

[0019] Figure 7 is a timing simulation diagram of a group PRF agile waveform part provided by the present application. DETAILED DESCRIPTION

[0020] The present application will be further described below in conjunction with specific embodiments, but the embodiments of the present application are not limited thereto.

[0021] Before introducing the present application, a brief introduction to the technical concept of the present application is given.

[0022] The present application is directed to a space-borne synthetic aperture radar, which is widely used due to its immunity to environmental factors such as illumination and climate. Modern space-borne radars increasingly require high azimuthal resolution and wide imaging, which requires a long receiving time, and thus a low pulse repetition frequency (PRF). However, due to the limitation of the Nyquist sampling theorem, high azimuthal resolution requires a high PRF, thus creating a contradiction. In addition, the selection of PRF is an essential step in the design of a space-borne radar system, and the PRF of a space-borne radar can only be selected within a certain range due to the constraints of a zebra graph, which is an intersection graph formed by the transmitted pulses and the ground echo in the PRF-incident angle two-dimensional plane. The ground echo will cause serious blurring of the image because it is almost specular reflection at the ground, and thus a reasonable PRF needs to be selected to avoid the ground echo. The existing method for solving the high-resolution wide imaging of space-borne radars is to use azimuthal non-uniform undersampling, such as random sampling, Poisson sampling and group random sampling. However, due to the long range of space-borne radars, the scene echo usually arrives after several pulse repetition periods, and if the PRF is changed, the echo signal arriving at this time will not be consistent with the PRF of the transmitted signal, and there may be a collision between the transmitted signal and the echo signal, resulting in the loss of echo signal.

[0023] In view of the technical problems of the prior art, the application continues the method of grouping variable frequency waveform design, the azimuth is still non-uniform undersampling, which can break through the limitation of Nyquist sampling theorem, and a lower pulse repetition frequency can be set to meet the requirement of wide imaging, and the non-uniform undersampling can convert the aliasing term generated by undersampling into irregular noise term, so as to realize high-resolution imaging in the azimuth. First, according to the orbit height, viewing angle and other parameters of the spaceborne radar, a corresponding "zebra picture" is drawn, then according to the width of the target scene and other parameters, a usable pulse repetition frequency interval is selected, and a pulse repetition frequency is randomly selected in the interval as the initial pulse repetition frequency sequence. Then, through timing analysis, the positions where the transmission and reception collide in the sequence are finely designed, which is specifically summarized as follows: the transmission and reception collision only occurs at the position where the pulse repetition frequency changes, when it is judged that the transmission and reception collision will occur in the pulse repetition interval of the pulse, the pulse repetition frequency of the pulse is changed, the basis is that the transmission and reception collision does not occur in the pulse repetition interval of the pulse, and the transmission and reception collision does not occur in the subsequent pulse repetition interval as much as possible, finally, in order to prevent the timing of the subsequent pulses in the group from changing due to the change of the pulse repetition frequency, the timing is aligned, the pulse repetition frequency of the last pulse at the connection is changed, so that the timing of the subsequent pulses is consistent with the timing when the pulse repetition frequency is not changed.

[0024] The technical scheme details of the application are described below.

[0025] In combination with Figure 1 and Figure 5 , the application provides a spaceborne radar high-resolution wide-range timing design method of non-destructive echo, which comprises the following steps:

[0026] S100, obtaining a plurality of parameters of a spaceborne radar, and drawing a zebra picture according to the plurality of parameters; the zebra picture comprises a plurality of interlaced strips;

[0027] The parameters comprise an orbit height, a downward viewing angle and the like.

[0028] When selecting the pulse repetition frequency, the spaceborne radar needs to consider avoiding the limitation of the self subsatellite point echo and the transmitted pulse shielding. The positions of the subsatellite point echo and the transmitted pulse shielding zone are given on a two-dimensional plane determined by the pulse repetition frequency and the signal incidence angle, and these positions cannot fall in the scene area. The subsatellite point echo and the transmitted pulse shielding zone are both shown as interlaced strips on the frequency-repetition-incidence-angle plane, and are also called "zebra picture" because the strips are similar to the stripes on the zebra body. The selection of the observation band position and the pulse repetition frequency in the strip gap can avoid the occurrence of the subsatellite point echo in the echo receiving window and the overlap between the echo receiving window and the transmitted pulse, as shown in the zebra picture of the spaceborne radar frequency selection. Figure 2

[0029] In the spaceborne radar, the pulse repetition frequency needs to be designed according to the coverage map to ensure that the received echo, the transmitted pulse and the subsatellite point echo do not collide.​

[0030] S200, selecting a scene echo limiting area in the gap between the strips, and selecting a PRF range by using the scene echo limiting area;

[0031] S300, randomly selecting PRF of each group of pulses to form a PRF sequence, and sequentially judging whether the distance blurring numbers corresponding to PRFs of adjacent two groups are consistent, if not, re-designing PRF at the connection of the PRF sequence between groups according to the two cases of selecting PRF from small to large and selecting PRF from large to small to obtain a designed PRF sequence;

[0032] Wherein, PRFs of pulses in the same group are the same, and PRFs of pulses in different groups are randomly selected.

[0033] In an optional embodiment of the present application, S200 comprises:

[0034] S210, determining a first parameter selection constraint condition of the single-channel spaceborne radar according to a time sequence relationship of radar transmission and reception.

[0035] The single-channel radar uses the same antenna for transmission and reception, and cannot receive echo signals in the transmission mode. To avoid this problem, according to the time sequence relationship of radar transmission and reception, the parameter selection of the single-channel spaceborne radar needs to meet the first parameter selection constraint condition, which is expressed as:

[0036]

[0037] Wherein, i=0, 1, 2… represents the number of pulses, F p represents the pulse repetition frequency, τ p is the pulse width, R min and R max respectively represent the nearest slant range and the farthest slant range in the target scene, and c is the speed of light.

[0038] S220, determining a second parameter selection constraint condition of the region needing to avoid the subspace point echo area according to the subspace point echo characteristics;

[0039] In addition, the subspace point echo is the echo of the point on the ground closest to the radar, and its energy is large because it is almost specular reflection to the radar, thereby affecting the imaging performance. Therefore, when designing the PRF, the region of the subspace point echo also needs to be avoided, and the selection also needs to meet the second parameter selection constraint condition, which is expressed as:

[0040]

[0041] Wherein, H is the orbit height, k=0, 1, 2… represents the number of pulses, τ d =2τ p represents the time width of the subspace point echo;

[0042] S230, determining a scene echo limit area in the zebra chart by using the first parameter selection constraint and the second parameter selection constraint;

[0043] S240, selecting a range of PRF which has no strip and is closest to the two intersection points by using the boundary of the scene echo limit area and the strip intersection points.

[0044] Reference Figure 2 According to the scene information, the scene echo limit area (black line) is drawn, and the PRF interval which has no transmitting signal (blue line) and no ground echo (red line) is selected as the limit range of random PRF hopping. The existing waveform design of grouping variable PRF is random hopping in the selected range, which can meet the constant PRF in the group and avoid the problems of transceiver collision and ground echo aliasing. However, this design will cause timing disorder and transceiver collision at the connection between groups with different PRF. The range ambiguity number of echo signal is related to the range delay of echo and the PRF of signal, so it can be known that when the PRF changes greatly, the range ambiguity number of the previous group may be inconsistent with that of the next group. In the zebra chart, when the PRF is randomly selected from one interval (green dotted line) to another interval (yellow dotted line), it crosses one transmitting pulse (blue line), and the two PRFs differ by one range ambiguity number. This situation will cause timing disorder at the connection between groups with different PRF. First, the meaning of the connection is defined. The connection between groups refers to the area between the first transmitting signal of the next group and the nearest transmitting signal before the arrival of the scene echo of the signal. Due to the distance ambiguity, when the first transmitting signal of the next group is transmitted, a certain number of scene echoes of the previous group have not arrived, and the number is equal to the range ambiguity number of the previous group PRF, which is set as m1. However, the number of transmitting pulses at the connection is the range ambiguity number m2 of the second group PRF, which leads to the fact that the number of transmitting pulses and the number of scene echoes at the connection cannot be matched one by one, resulting in timing disorder.

[0045] In an optional embodiment of the present application, before S300, the lossless spaceborne radar high-resolution wide swath timing design method further comprises:

[0046] For any two adjacent PRF sequences with inconsistent ambiguity numbers, the overall limit condition for preventing the collision between the transmitting signal of the next group and the scene echo of the previous group at the connection and preventing the aliasing between the ground echo and the scene echo is designed under the conditions that the two PRF sequences are in ascending order or in descending order.

[0047] According to the analysis of the selection process of the repetition frequency range, when the repetition frequency is selected across the interval, the connection will produce a transmission collision. Assuming that the distance ambiguity number m1 of the scene echo under the first group of repetition frequencies is 5, and the distance ambiguity number m2 of the second group is 6, the specific transmission and reception timing at the connection can be specifically shown as Figure 3 , wherein PRT1 and PRT2 represent the pulse repetition periods of the first group and the second group, respectively. It can be known from Figure 3 that m1 echo signals of the first group will arrive in turn at the connection, and m2 transmission signals will be emitted during the period from the first transmission signal of the second group to the first echo signal of the second group. When m1 ≠ m2, timing disorder will occur. When PRT1 > PRT2, the transmission signal at the connection will be closer and closer to the previous echo signal, and the transmission collision problem (red arrow) will occur.

[0048] The repetition period of the pulse about to produce the collision is changed to PRT x1 , so that the subsequent transmission and reception do not produce a collision as much as possible. If a collision will still occur subsequently, the repetition period of the pulse about to produce the collision is changed again until the first echo signal of the second group arrives. It should be noted that when the repetition frequency of some pulses is changed, the subsequent transmission and reception timing will change accordingly. In order to ensure the stability of the timing after the connection, the repetition period PRT y of the last pulse before the connection should be changed again, so that the pulse timing after the connection will not change due to the change of the repetition frequency.

[0049] As an optional embodiment of the application, for the repetition frequency sequence in which the ambiguity numbers of any two adjacent groups are inconsistent, the overall limitation condition for preventing the collision between the transmission signal of the subsequent group and the scene echo of the previous group at the connection and preventing the aliasing between the nadir echo and the scene echo under the two conditions that the two groups of repetition frequency sequences are from small to large or from large to small includes:

[0050] Step a, if the repetition frequencies of the two adjacent groups of repetition frequency sequences are from small to large, a first transmission collision limitation condition for avoiding the collision between the transmission signal of the subsequent group and the scene echo of the previous group at the connection is designed;

[0051] In order to make the subsequent transmission and reception as much as possible without collision, PRT x1 should be as large as possible, but also avoid the collision with the next echo, as shown in Figure 4 , so that the limitation condition for PRT x1 can be obtained, and the first transmission collision limitation condition is obtained and is expressed as:

[0052]

[0053] Step b, design to avoid echo signal repetition frequency change caused by the first transceiver collision restriction condition, so that the latter transmission signal and the corresponding area of the scene echo collision of the second transceiver collision restriction condition;

[0054] Considering the subsequent timing alignment, the pulse repetition frequency in the connection is changed, but the total length of the connection will not change, so the expression of PRT y can be obtained. That is, the repetition period of the last pulse before the connection is changed to PRT y , which is expressed as:

[0055] (m1-2)PRT2+PRT x1 +PRT y =m2·PRT2(4);

[0056] Wherein, the connection will have m1 echo signals of the first group arriving in turn, and m2 transmission signals will be emitted from the first transmission signal of the second group to the first echo signal of the second group;

[0057] The PRT x1 selected according to the above restriction condition can avoid the transceiver collision problem at the connection. However, according to the above formula, the design not only changes the repetition frequency of the pulse at the connection, but also changes the number of pulses at the connection. The connection should have m2+1 pulses, and after the design, it becomes m1+1 pulses. Therefore, in the timing of m2·PRT2 after the connection, there are m2+1 transmission pulses, but the number of echoes is only m1+1. Given that m1 x1 The pulse repetition interval of the echo must contain two transmission signals. Therefore, PRT x1 is further limited, and the second transceiver collision restriction condition is expressed as:

[0058]

[0059] Wherein, PRT x1 is the repetition period of the pulse that will produce collision, PRT1 and PRT2 represent the pulse repetition periods of the first group and the second group respectively, τ p is the pulse width, R min and R max represent the nearest range and the farthest range in the target scene respectively, c is the speed of light, mod(·) is the modulo operation, ΔPRT=|PRT1-PRT2|,

[0060] The intersection of the two ranges is obtained, and a PRT x1From then on, for the problem of transceiver collision, when the repetition frequency is selected from the large interval to the small interval across intervals, the repetition frequency sequence is redesigned according to the method of fine design of waveform timing.

[0061] Step c, if the repetition frequencies of the adjacent two groups of repetition frequency sequences are from large to small, a third transceiver collision restriction condition is designed to avoid the collision between the transmitted signal of the latter group and the scene echo of the former group at the connection;

[0062] Next, the case where the repetition frequency is selected from the large interval to the small interval across intervals is considered. It is assumed that under the first group of repetition frequencies, the distance ambiguity number of the echo is m1=6, and the distance ambiguity number of the second group is m2=5. Similarly, there will be m1 echoes of the first group at the connection, while there should be m2 transmitted signals at the connection, and m1≠m2 will cause timing disorder. When PRT1 x1 , so that the subsequent transceiver does not produce collision as much as possible. If collision will still occur subsequently, the repetition period of the pulse that will collide is changed again until the first echo signal of the second group arrives. In combination with the analysis in the foregoing, when we change the repetition frequency of the pulse, the subsequent transceiver timing will also change. In order to ensure that the timing after the connection is stable, the repetition period PRT y of the last pulse before the connection should be changed again, so that the pulse timing after the connection will not change due to the change of the repetition frequency.

[0063] In order to make the subsequent transceiver timing as much as possible not to produce collision, PRT x1 should be as large as possible, but also to avoid collision with the previous echo signal, therefore, PRT x1 should be limited, that is, the third transceiver collision restriction condition is expressed as:

[0064]

[0065] wherein,

[0066] Considering the alignment of the subsequent timing, the repetition frequency of the pulse in the connection is changed, but the total length of the connection will not change, so the expression of PRT y can be obtained, that is, the repetition period PRT y of the last pulse before the connection is changed to PRT

[0067] (m1-2)PRT2+PRT x1 +PRT y =m2·PRT2(7);

[0068] Step d, design to avoid echo signal frequency change caused by the third transceiver collision restriction condition, so that the latter transmission signal and the receiving signal of the corresponding area collision fourth transceiver collision restriction condition;

[0069] PRT selected according to the above restriction condition x1 The connection transceiver collision problem can be avoided. In line with the foregoing, the design not only changes the frequency of the connection pulse, but also changes the number of connection pulses. The connection should have m2+1 pulses, and after the design, it becomes m1+1 pulses. Thus, in the timing of m2·PRT2 after the connection, there are m2+1 transmission pulses, but the number of echoes is only m1+1. Given that m1>m2, in order to avoid transceiver collision in this area, it is necessary to ensure that the repetition period is PRT x1 The echo and the next echo are received in one PRT2. Thus, the PRT x1 is further limited, that is, the fourth transceiver collision restriction condition is expressed as:

[0070]

[0071] Wherein,

[0072] The intersection of the two ranges is obtained, that is, a PRT x1 which does not produce transceiver collision. From this, for the transceiver collision problem, when the frequency is selected across the interval from the large interval to the small interval, the frequency in the frequency sequence is redesigned according to the waveform timing fine design method.

[0073] From this, the waveform timing fine design for the two cases of transceiver collision problem caused by the selection of frequency across the interval is completed.

[0074] Since the echo path of the sub-satellite point echo is the orbital height, the sub-satellite point echo of the same pulse often arrives one or two pulse repetition intervals earlier than the scene echo, that is, the range ambiguity number of the sub-satellite point echo under the same frequency is usually smaller than that of the scene echo. From Figure 2 It can be seen that when the existing undesigned grouping variable frequency waveform selects two intervals, the two intervals will not be too far apart, the overall scene receiving window will not cross the sub-satellite point echo (red line), and the range ambiguity number of the sub-satellite point echo and the scene echo is usually only 1-2. In this case, the sub-satellite point echo and the scene echo of the undesigned grouping variable frequency waveform can still be one-to-one corresponding at the connection, and generally will not produce aliasing. However, when the pulse frequency at the connection is changed, the timing of the subsequent sub-satellite point echo and the scene echo will change, and aliasing problem may occur.

[0075] Step e, according to the first transceiver collision restriction condition, a first aliasing restriction condition is designed to prevent aliasing of the subspace point echo and the scene echo;

[0076] The first aliasing restriction condition includes a first restriction condition in the case that the subspace point echo arrives one pulse repetition interval in advance and a second restriction condition in the case that the subspace point echo arrives two or more pulse repetition intervals in advance than the scene echo;

[0077] As known from the previous section, the pulse repetition frequency is changed at the connection, which not only affects the subsequent transceiver timing, but also affects the timing of the subsequent subspace point echo and scene echo. Considering the subsequent transceiver timing, this step will analyze the timing of the subspace point echo and the scene echo.

[0078] It is assumed that the subspace point echo always arrives one pulse repetition interval in advance than the scene echo. When the pulse repetition frequency is selected from small to large, the aliasing of the subspace point echo and the scene echo that can occur. Since PRT x1 The timing of the subspace point echo is not considered in the design, so the subsequent subspace point echo and scene echo can be aliased. Therefore, in addition to the restriction of the pulse repetition frequency according to the transceiver timing in the previous section, the pulse repetition frequency needs to be further restricted according to the timing of the subspace point echo and the scene echo. Therefore, PRT x1 A lower limit is set to prevent it from entering the previous scene echo region. The first restriction condition (the lower limit) can be specifically expressed as:

[0079]

[0080] The upper limit is considered below. The upper limit is set to prevent the subspace point echo from being aliased with the subsequent scene echo. However, for the above case, when the subsequent subspace point echo with a repetition period of PRT x1 arrives, the scene echo with a repetition period of PRT x1 has already arrived, the PRT x1 of the pulse gradually increases, and the subsequent scene echo also gradually moves backward, so there is no timing aliasing of the subsequent echo. However, this is only in the case that the subspace point echo arrives one pulse repetition interval in advance. When the subspace point echo arrives more in advance than the scene echo, the timing will change accordingly. It is assumed that the subspace point echo arrives two or more pulse repetition intervals in advance than the scene echo. At this time, because when the subsequent subspace point echo with a repetition period of PRT x1 arrives, the scene echo of the pulse has not arrived, and the timing of the scene echo has not changed, so the subspace point echo can be aliased with the subsequent scene echo because it is too large. The upper and lower limits of PRT x1 are both restricted, that is, the second restriction condition is:

[0081]

[0082] Where m represents the distance ambiguity number of the nadir echo at the second set of repetition frequencies. For the round-down operation, H represents the satellite orbital altitude.

[0083] Finally, consider PRT under transmit and receive timing. x1 By taking the intersection of the constraints, we can obtain the finely designed repetition frequency range when the repetition frequency is selected across intervals from small to large.

[0084] Step f: Design a second aliasing constraint to prevent the nadir point echo from aliasing with the scene echo, based on the third transmit / receive collision constraint.

[0085] Having analyzed the case where the repetition frequency (RF) is chosen from smallest to largest, we will now consider the case where the RF is chosen from largest to smallest. As analyzed in the previous section, when the RF is chosen from largest to smallest, the designed PRT... x1 It is usually smaller than PRT2, and it may cause timing aliasing issues. x1 Both excessively large and excessively small values ​​may cause aliasing with the preceding and following scene echoes. Therefore, upper and lower limits are given to prevent aliasing, i.e., the second aliasing constraint condition is expressed as:

[0086]

[0087] Finally, consider the PRT for transmit and receive timing. x1 By taking the intersection of the constraints, we can obtain the finely designed repetition frequency range when selecting the repetition frequency across the interval from large to small.

[0088] As an optional embodiment of the present invention, combined with Figure 1 and Figure 5 The S300 includes:

[0089] S310, randomly select the repetition frequencies of each group of pulses within the repetition frequency range to form a repetition frequency sequence;

[0090] S320, determine whether the distance ambiguity numbers corresponding to two adjacent sets of repetition frequency sequences are consistent. If they are inconsistent, determine whether the repetition frequency of the two adjacent sets of repetition frequency sequences is from small to large or from large to small.

[0091] S330, if the repetition frequencies of two adjacent sets of repetition frequency sequences are from small to large, then determine the first intersection of the first transmit / receive collision constraint and the first aliasing constraint, redesign the repetition frequency at the connection point of the two adjacent sets of repetition frequency sequences using the first intersection, and design the repetition frequency after the connection point using the second transmit / receive collision constraint to obtain the designed repetition frequency sequence.

[0092] S340, if the repetition frequencies of two adjacent sets of repetition frequency sequences are from large to small, then determine the second intersection of the third transmit / receive collision constraint and the second aliasing constraint, redesign the repetition frequency at the connection point of the two adjacent sets of repetition frequency sequences using the second intersection, and design the repetition frequency after the connection point using the fourth transmit / receive collision constraint to obtain the designed repetition frequency sequence.

[0093] As an optional embodiment of the present invention, S320 includes:

[0094] S331, if the repetition frequencies of two adjacent sets of repetition frequency sequences are from small to large, then determine how many pulse repetition intervals the nadir echo will arrive in advance.

[0095] S332, if the sub-satellite point echo arrives one pulse repetition interval in advance, then by using the intersection of the first transmit / receive collision constraint and the first constraint, the repetition frequency at the connection point of the repetition frequency sequences of the two adjacent groups is designed, and the repetition frequency after the connection point is designed by using the second transmit / receive collision constraint, so as to obtain the designed repetition frequency sequence.

[0096] S333, if the sub-satellite point echo arrives more than one pulse repetition interval in advance, then the intersection of the first transmit / receive collision constraint and the second constraint is used to design the repetition frequency at the connection point of the repetition frequency sequences of the two adjacent groups, and the repetition frequency after the connection point is designed using the second transmit / receive collision constraint, thus obtaining the designed repetition frequency sequence.

[0097] The specific steps of the fine timing design of the grouped variable repetition frequency waveform of the present invention can be described as follows: draw a constraint diagram (zebra diagram) of the pulse repetition frequency and coverage relationship of the spaceborne radar according to the specific parameters of the spaceborne radar orbit; then select the available repetition frequency range according to the specific scene center distance and observation scene width; then, randomly select the repetition frequency of each group of pulses within the range as the initial repetition frequency sequence; sequentially determine whether the repetition frequencies of two adjacent groups cross the interval. If they cross the interval, then according to the two cases of selecting from small to large and from large to small, finely design the pulse repetition frequency at the connection between groups using the different constraint ranges given above, and design a grouped variable repetition frequency repetition frequency sequence that will not produce transmit and receive timing collisions or aliasing of sub-satellite point echoes.

[0098] The experiment simulated a case of inter-group repetition frequency cross-interval selection, where both groups of repetition frequencies each had twenty pulses. Figure 6 It can be seen that a collision occurs between the transmitted signal (red) and the scene echo (blue) at the connection point between groups, causing the echo to be lost. Figure 7 The simulation results show that after the fine design, there will be no transmit / receive collisions, and the nadir echo will not overlap with the scene echo.

[0099] Furthermore, the terms "first", "second", etc. are used only for descriptive purposes and do not connote or imply relative importance. Thus, a feature defined with "first", "second", etc. can implicitly or explicitly include one or more of the features.

[0100] Although the present application has been described in connection with various embodiments thereof, it will be understood that other variations and modifications of the described embodiments can be made by those skilled in the art upon reading the description of the application set forth above. In the claims, the word "comprising" does not exclude other components or steps not mentioned in the claims. The word "a" or "an" preceding an element does not exclude the presence of a plurality of such elements.

[0101] The above description is further to combine the specific preferred embodiments of the present application, and cannot be considered as the specific implementation of the present application is limited to these descriptions. For those skilled in the art, without departing from the concept of the present application, a number of simple deductions or replacements can be made, which should be considered as falling within the scope of protection of the present application.

Claims

1. A spaceborne radar high-resolution wide-swath timing design method without loss of echo, characterized in that, The method comprises the following steps: S100, acquiring a plurality of parameters of a spaceborne radar, and drawing a zebra map according to the plurality of parameters; the zebra map comprises a plurality of interlaced strips; S200, selecting a scene echo limiting area in a gap between the strips, and selecting a pulse repetition frequency (PRF) range by using the scene echo limiting area; S300, randomly selecting a PRF sequence of each group of pulses in the PRF range, and sequentially judging whether distance ambiguities corresponding to adjacent two groups of PRF sequences are consistent; if not, according to the PRF from small to large and from large to small, a PRF at a connection between the groups is redesigned to obtain a designed PRF sequence; wherein PRFs of pulses in the same group are the same, and PRFs of pulses in different groups are randomly selected.

2. The lossless return space-borne radar high strip-width timing design method of claim 1, wherein, S200 comprises the following steps: S210, determining a first parameter selection constraint condition of a single-channel spaceborne radar according to a time sequence relationship of radar transmission and reception; the first parameter selection constraint condition is expressed as: where i = 0, 1, 2… represents the pulse number, F p represents the pulse repetition frequency, τ p is the pulse width, R min and R max respectively represent the nearest and farthest slant ranges in the target scene, and c is the speed of light. S220, determining a second parameter selection constraint condition of a region needing to avoid a subsatellite point echo according to a subsatellite point echo characteristic; the second parameter selection constraint condition is expressed as: where H is the orbital height, k = 0, 1, 2… represents the number of pulses, τ d = 2τ p denotes the time width of the subspace point echo; S230, determining a scene echo limiting area in the zebra map by using the first parameter selection constraint condition and the second parameter selection constraint condition; S240, selecting a PRF range composed of two closest intersection points without a strip by using a boundary of the scene echo limiting area and the intersection points.

3. The lossless return space-borne radar high strip-width timing design method of claim 1, wherein, Before S300, the spaceborne radar high-resolution wide swath time sequence design method further comprises the following steps: for any two adjacent groups of PRF sequences with inconsistent distance ambiguities, designing overall limitation conditions for preventing collision of a rear group of transmission signals and a front group of scene echoes at a connection and for preventing subsatellite point echoes and scene echoes from being mixed in two cases of the two groups of PRF sequences from small to large and from large to small.

4. The space-borne radar high-resolution wide-swath timing design method of claim 3, wherein, The overall limitation conditions for preventing collision of the rear group of transmission signals and the front group of scene echoes at the connection and for preventing the subsatellite point echoes and the scene echoes from being mixed in the two cases of the two groups of PRF sequences from small to large and from large to small comprise the following steps: step a, if the PRFs of the adjacent two groups of PRF sequences are from small to large, designing a first transmission-reception collision limitation condition for avoiding collision of the rear group of transmission signals and the front group of scene echoes at the connection; step b, designing a second transmission-reception collision limitation condition for avoiding change of echo signal PRF caused by the first transmission-reception collision limitation condition, so that the rear group of transmission signals collides with scene echoes of a corresponding region; step c, if the PRFs of the adjacent two groups of PRF sequences are from large to small, designing a third transmission-reception collision limitation condition for avoiding collision of the rear group of transmission signals and the front group of scene echoes at the connection; step d, designing a fourth transmission-reception collision limitation condition for avoiding change of echo signal PRF caused by the third transmission-reception collision limitation condition, so that the rear group of transmission signals collides with reception signals of a corresponding region; step e, designing a first aliasing limitation condition for preventing the subsatellite point echoes and the scene echoes from being mixed according to the first transmission-reception collision limitation condition; The first aliasing restriction condition comprises a first restriction condition in a case where a subspace point echo arrives one pulse repetition interval in advance and a second restriction condition in a case where a subspace point echo arrives two or more pulse repetition intervals in advance than a scene echo. In step f, a second aliasing restriction condition for preventing aliasing of the subspace point echo and the scene echo is designed according to the third transmit-receive collision restriction condition.

5. The spaceborne radar high-resolution wide-swath timing design method of lossless echoes according to claim 4, characterized in that, The first transmit-receive collision restriction condition in step a is expressed as: PRT x1 >PRT1-mod(h1,ΔPRT) The echo signal repetition frequency changes due to the first transceiver collision restriction condition in step b, and the repetition period of the last pulse before the connection is changed to PRT y is represented as: (m1-2)PRT2+PRT x1 +PRT y = m2-PRT2(4); Wherein, at the connection, echo signals of m1 first groups arrive in turn, and during the period from the first transmitted signal of the second group to the first echo signal of the second group, m2 transmitted signals are also sent out. The second transmit-receive collision restriction condition is expressed as: where PRT x1 is the repetition period of the pulses to be generated, PRT1 and PRT2 represent the pulse repetition periods of the first and second groups, respectively, τ p is the pulse width, R min and R max represent the nearest and farthest slant ranges in the target scene, respectively, c is the speed of light, mod(·) is the modulo operation, and ΔPRT = |PRT1 - PRT2|, 6. The space-borne radar high-resolution wide-swath timing design method of claim 5, wherein, The third transmit-receive collision restriction condition in step c is expressed as: PRT x1 <PRT1+mod(h2,ΔPRT)-τ p wherein The echo signal repetition frequency changes due to the third transceiver collision restriction condition in step d, and the repetition period of the last pulse before the connection is changed to PRT y is represented as: (m1-2)PRT2+PRT x1 +PRT y = m2-PRT2(7); The fourth transmit-receive collision restriction condition is expressed as: wherein, 7. The spaceborne radar high-resolution wide-swath timing design method of lossless echoes according to claim 6, characterized in that, The first restriction condition is expressed as: The second restriction condition is expressed as: wherein m represents the range ambiguity of the sub-satellite point echo under the second group of PRFs, H represents the satellite orbital height for the floor operation. The second aliasing restriction condition in step f is expressed as:

8. The lossless return, space-borne radar, high-swath, time-sequenced design method of claim 4, wherein, S300 comprises: S310, randomly selecting a repetition frequency of each group of pulses in the repetition frequency range to form a repetition frequency sequence; S320, judging whether the distance ambiguity numbers corresponding to two adjacent groups of the repetition frequency sequence are consistent, if not, judging whether the repetition frequencies of the two adjacent groups of the repetition frequency sequence are from small to large or from large to small; S330, if the repetition frequencies of the two adjacent groups of the repetition frequency sequence are from small to large, determining a first intersection of the first transmit-receive collision restriction condition and the first aliasing restriction condition, redesigning the repetition frequencies of the two adjacent groups of the repetition frequency sequence at the connection by using the first intersection, and redesigning the repetition frequencies after the connection by using the second transmit-receive collision restriction condition to obtain a designed repetition frequency sequence; S340, if the repetition frequencies of the two adjacent groups of the repetition frequency sequence are from large to small, determining a second intersection of the third transmit-receive collision restriction condition and the second aliasing restriction condition, redesigning the repetition frequencies of the two adjacent groups of the repetition frequency sequence at the connection by using the second intersection, and redesigning the repetition frequencies after the connection by using the fourth transmit-receive collision restriction condition to obtain a designed repetition frequency sequence.

9. The lossless return, space-borne radar, high strip-width timing design method of claim 8, wherein, S320 comprises: S331, if the repetition frequencies of the two adjacent groups of the repetition frequency sequence are from small to large, determining how many pulse repetition intervals in advance the subspace point echo arrives; S332, if the subspace point echo arrives one pulse repetition interval in advance, designing the repetition frequencies of the two adjacent groups of the repetition frequency sequence at the connection by using the intersection of the first transmit-receive collision restriction condition and the first restriction condition, and designing the repetition frequencies after the connection by using the second transmit-receive collision restriction condition to obtain a designed repetition frequency sequence; S333, if the subspace point echo arrives more than one pulse repetition interval in advance, designing the repetition frequencies of the two adjacent groups of the repetition frequency sequence at the connection by using the intersection of the first transmit-receive collision restriction condition and the second restriction condition, and designing the repetition frequencies after the connection by using the second transmit-receive collision restriction condition to obtain a designed repetition frequency sequence.

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