CN114063023A - Device and method for interfering SAR radar - Google Patents
Device and method for interfering SAR radar Download PDFInfo
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- CN114063023A CN114063023A CN202111353494.8A CN202111353494A CN114063023A CN 114063023 A CN114063023 A CN 114063023A CN 202111353494 A CN202111353494 A CN 202111353494A CN 114063023 A CN114063023 A CN 114063023A
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
- G01S7/02—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00
- G01S7/38—Jamming means, e.g. producing false echoes
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
- G01S13/88—Radar or analogous systems specially adapted for specific applications
- G01S13/89—Radar or analogous systems specially adapted for specific applications for mapping or imaging
- G01S13/90—Radar or analogous systems specially adapted for specific applications for mapping or imaging using synthetic aperture techniques, e.g. synthetic aperture radar [SAR] techniques
Abstract
The invention discloses a device for interfering SAR radar, which is arranged beside an area to be protected and comprises: the radar detection unit is used for receiving the SAR radar signal and analyzing and processing the SAR radar signal so as to obtain the SAR radar signal characteristics; and the radar interference unit is used for generating an interference signal according to the SAR radar signal characteristics received by the radar detection unit and transmitting the interference signal to the SAR radar, and the radar interference unit and the radar detection unit are synchronously interconnected through a bidirectional data link. The technical scheme of the invention realizes the protection of the area to be protected by emitting the false echo to generate the false target in the radar image, the emission power of the false echo is not large, the SAR radar imaging the protected area can be coherently interfered, the interference effect is good, and the practicability is strong.
Description
Technical Field
The invention relates to the field of radar interference, in particular to a device and a method for interfering SAR radar.
Background
Due to the long accumulation time (usually tens of seconds) of synthetic aperture radars (SAR for short), the synthetic aperture radars have very high compression gain after pulse compression processing, which enables them to detect targets at very long distances (usually greater than 100 km), and have very high signal-to-noise ratio. Therefore, the interference power required for destroying the detection of the synthetic aperture radar by adopting the conventional interference means is very high, and an effective interference device is difficult to design.
In the prior art, a method of interference is known at present, which includes: the method comprises the steps of emitting incoherent interference such as noise, Continuous Wave (CW) or swept continuous wave in a receiving frequency band of the SAR to be interfered so as to cover a protected key area. This interference requires very high power because the compression gain of synthetic aperture radars is on the order of tens of decibels and, in general, the area to be protected is large, usually several square kilometers, and the effect of incoherent interference is poor.
Another interference method includes: after receiving the signal of the radar, re-transmitting a delay signal (with frequency offset and/or phase offset), for example, using a Digital Radio Frequency Memory (DRFM) system, coherently and repeatedly receiving and transmitting the signal of the SAR radar and a series of replica signals identical to the signal, and distributing the replica signals in a certain frequency band to cover the doppler analysis frequency band of the SAR radar. In this case, the interference power to be generated is also very high, since this is not the case at lateral distances, even though the interference signal can be compressed by the SAR radar matching at radial distances. Furthermore, since the doppler band covered by the SAR radar is unknown, it is necessary to provide high interference power on a higher basis than the SAR band. In other words, the interference is coherent in distance but incoherent in the doppler frequency domain, and it is difficult to achieve the ideal interference effect.
In the prior art, another interference method currently known includes: a signal is retransmitted to repeat the SAR radar transmitted signal, for example, each retransmission using a DRFM and a series of replica signals identical to the signal, which have been pre-calculated for the SAR radar geographical position, the phase value of each pixel in the SAR image, distributed over the frequency band of the SAR radar, and each pulse repetition Period (PRI) is coherent, and then the interference signal is coherent on the range and doppler axes. This technique greatly limits the interference power to be transmitted and requires knowledge of the position of the SAR radar with respect to each location point in the area to be protected from time to time. This information needs to be known in advance and is not possible to obtain unless the observation satellite regularly repeats the orbit under special circumstances. Furthermore, the amount of computation required to determine and generate a series of replica signals in real time makes this solution unfeasible.
Disclosure of Invention
The invention mainly aims to provide a device and a method for interfering SAR (synthetic aperture radar), aiming at realizing the SAR which can interfere coherently to image a protected area by proper transmitting power.
In order to achieve the above object, the present invention discloses a device for interfering an SAR radar, which is arranged beside an area to be protected, and comprises:
the radar detection unit is used for receiving the SAR radar signal and analyzing and processing the SAR radar signal so as to obtain the SAR radar signal characteristics;
and the radar interference unit is used for generating an interference signal according to the SAR radar signal characteristics received by the radar detection unit and transmitting the interference signal to the SAR radar, and the radar interference unit and the radar detection unit are synchronously interconnected through a bidirectional data link.
In one embodiment, the radar detection unit includes:
the receiving module is used for receiving radar signals;
a first processing module; and the SAR signal processing module is used for analyzing and processing the radar signal received by the receiving module to judge whether the radar signal is an SAR radar signal or not, and if the radar signal is the SAR radar signal, the SAR radar signal is analyzed and processed to obtain the moving speed of the SAR radar and the distance between the SAR radar and the area to be protected.
In an embodiment, the receiving module has an antenna which enables wide coverage in azimuth and can be directed.
In an embodiment, the radar jamming unit comprises:
the interference generation module is used for generating an interference signal according to the SAR radar signal characteristics received by the radar detection unit;
and the interference transmitting module is used for transmitting the interference signal generated by the interference generating module.
In addition, in order to achieve the above object, the present invention also discloses a method for interfering the SAR radar, comprising:
receiving a radar signal and judging whether the radar signal belongs to an SAR radar signal;
if so, analyzing and processing the SAR radar signal to obtain SAR radar signal characteristics;
generating an interference signal according to the SAR radar signal characteristics;
the interfering signal is transmitted towards the SAR radar.
In one embodiment, the received radar signal is determined to be a SAR radar signal if at least one of the following conditions is met:
the signal exhibits a constant or periodic modulation during the reoccurrence period; or
The signal exhibits a constant frequency from one pulse to the next or a periodic frequency modulation from one pulse to the next; or
The signal exhibits a constant pulse duration from one pulse to the next; or
The signal exhibits an intra-pulse bandwidth of greater than 50 MHz; or
The signal is free of received signal amplitude modulation associated with rotation of the radar antenna; or
The signal has a constant phase from one pulse to the next; or
The phase of the signal is periodically modulated from one pulse to the next; or
The signal exhibits an identical intra-pulse modulation from one pulse to the next; or
The signal exhibits a periodic modulation of the pulse modulation from one pulse to the next.
In an embodiment, analyzing and processing the SAR radar signal, and acquiring the SAR radar signal feature includes:
acquiring the transmitting frequency or carrier frequency, pulse duration, repetition duration, intra-pulse modulation and corresponding modulation bandwidth, transmitting pulse initial phase and arrival direction of the SAR radar signal;
designing a matched filter according to SAR radar pulse to compress the SAR radar signal;
and obtaining the moving speed of the SAR radar and the distance between the SAR radar and the area to be protected according to pulse compression.
In an embodiment, the pulse compressing the SAR radar signal comprises:
transforming the SAR radar signal from a time domain to a frequency domain by fast Fourier transform;
processing the transformed signal by cross-correlation;
and converting the processed signal from a frequency domain to a time domain through inverse Fourier transform, and then obtaining a compressed pulse.
In an embodiment, the generating the interference signal according to the SAR radar signal characteristics comprises:
the digital signal synthesizer generates a phase sample corresponding to the interference signal according to the moving speed of the SAR radar and the distance between the SAR radar and the area to be protected;
and modulating the received SAR radar signal through the phase sample to generate an interference signal.
In an embodiment, the received radar signal has a receive time and frequency window.
The technical scheme of the invention realizes the protection of the area to be protected by emitting the false echo to generate the false target in the radar image, the emission power of the false echo is not large, the SAR radar imaging the protected area can be coherently interfered, the interference effect is good, and the practicability is strong.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.
FIG. 1a is a first schematic diagram of the operation of the SAR radar jamming device of the present invention;
FIG. 1b is a schematic diagram of the operation of the SAR radar jamming device of the present invention;
FIG. 2 is an antenna pattern of a SAR radar;
FIG. 3 is a schematic diagram of a method of the present invention for jamming SAR radar;
FIG. 4 is a schematic diagram of a time and frequency reconnaissance window of a SAR radar signal;
fig. 5 is a schematic diagram of the SAR equation.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
It should be noted that, if directional indications (such as up, down, left, right, front, and back … …) are involved in the embodiment of the present invention, the directional indications are only used to explain the relative positional relationship between the components, the movement situation, and the like in a specific posture (as shown in the drawing), and if the specific posture is changed, the directional indications are changed accordingly.
In the present invention, unless otherwise expressly stated or limited, the terms "connected," "secured," and the like are to be construed broadly, and for example, "secured" may be a fixed connection, a removable connection, or an integral part; can be mechanically or electrically connected; they may be directly connected or indirectly connected through intervening media, or they may be connected internally or in any other suitable relationship, unless expressly stated otherwise. The specific meanings of the above terms in the present invention can be understood by those skilled in the art according to specific situations.
In addition, if there is a description of "first", "second", etc. in an embodiment of the present invention, the description of "first", "second", etc. is for descriptive purposes only and is not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one such feature. In addition, the meaning of "and/or" appearing throughout includes three juxtapositions, exemplified by "A and/or B" including either A or B or both A and B. In addition, technical solutions between various embodiments may be combined with each other, but must be realized by a person skilled in the art, and when the technical solutions are contradictory or cannot be realized, such a combination should not be considered to exist, and is not within the protection scope of the present invention.
The invention aims to prevent a Synthetic Aperture (SAR) type onboard radar from accurately observing a given place (namely, an area to be protected), and the device and the method for interfering the SAR radar can be realized by shielding the area to be protected to prevent the area to be protected from being seen on an SAR radar image and transmitting false echoes to generate false targets in the SAR radar image.
To this end, the invention provides a method of interfering synthetic aperture radar, said method being configured to transmit a waveform over the accumulation time of the synthetic aperture radar, wherein said is coherent in range and doppler.
In order to achieve this, the invention uses a radar detection unit to predict the doppler frequency and the motion trajectory of the SAR radar signal, based on the waveform of the SAR radar to be interfered, knowing its observation angle over time, in order to predict the phase data of the SAR radar with respect to each point in the area to be protected.
Fig. 1a and 1b show an example of an embodiment for a disturbing SAR radar 10, said area 11 to be protected being for example a sensitive civil or military location, further, the area 11 to be protected may have a fixed size or a variable size, if the area 11 to be protected is of variable size, the inventive device for disturbing SAR radar may modify the area 11 to be protected during the same interference sequence by modifying parameters of various replica signals.
The device for disturbing the SAR radar comprises a plurality of radar detection units 12 and radar interference units, wherein the radar interference units and the radar detection units 12 are arranged together, and the radar detection units 12 are arranged on two sides of the area 11 to be protected so as to surround the area 11 to be protected. The position of the radar detection unit 12 may be selected by taking into account the possible approach trajectory 13 of the SAR radar 10. For example, along a coast or boundary 16, SAR imaging is typically accomplished by moving long distances along a trajectory 13 parallel to the coast or boundary 16. Thus, if the area to be protected 11 is located at the coast or border 16, the radar detection units 12 may be placed on either side of the area to be protected 11 so that they are parallel to the coast or border 16, thus making it parallel to the potential trajectory 13 of the airborne platform on which the SAR radar 10 is mounted (which is attempting to image the area to be protected 11).
According to one embodiment, at least one radar detection unit 12 may be mounted on a mobile device, such as a vehicle, to allow it to move as needed.
In the present embodiment, radar detection unit 12 and radar jamming unit are interconnected by one or more bi-directional data links 18 to allow the exchange of data between these various radar detection units 12 and radar jamming units. Wherein at least one of the data links 18 may be a secure link, preferably all of the links are secure data links. The radar detection unit 12 and the radar jamming unit may be synchronized with each other by means of a GPS clock or any equivalent type of clock means.
In this embodiment, each radar detection unit 12 is equipped with a receiving module for receiving radar signals and a processing module one for analyzing the radar signals to determine the presence of the SAR radar 10 and then estimating the direction of arrival (ideally in two dimensions (azimuth and elevation)) of the SAR radar signal transmission, thereby identifying the characteristics of the SAR signals in both the short term (PRI) and the long term (i.e., PRIs).
In this embodiment, the radar detection unit 12 may be equipped with an antenna that is capable of achieving wide coverage in azimuth (typically on the order of 90 °) and that can be directed (e.g., mechanically directed), and further, a local oscillator may be used to transpose the radar signal received by the antenna to a lower frequency for processing, then digitized by an analog-to-digital converter, and then the main characteristics of the pulse are detected. On this basis, a cross-correlation operation adapted to the SAR signal at each repetition of transmission is calculated.
In this embodiment, the radar jamming unit may detect and identify characteristics of the SAR signal and coherently jam the SAR radar 10 imaging the area to be protected 11 before the SAR radar 10 enters the visible range of the area to be protected 11 and throughout the period in which the SAR radar 10 illuminates the area to be protected 11. To achieve this goal, the SAR signal is jointly executed by several radar detection units 12 providing a high sensitivity radar detection function (for example of the superheterodyne type) mainly for the frequency band (generally the X-band) used by the airborne SAR radar 10. The X-band is known as a radio frequency range of about 10 GHz. The radar detection unit 12 may be provided by a receiver with an instantaneous bandwidth of 500MHz, which is capable of sweeping a frequency band between approximately 8.5GHz and 10.5 GHz, and then by means of a processing module, it is possible to estimate the time of arrival (TOA) of the SAR radar pulse and to estimate the direction of arrival (DOA) of the radar pulse, which information is usually obtained by interferometry and is characterized by a wide coverage in azimuth.
In this embodiment, the first processing module may analyze the SAR radar waveform intercepted by the receiving module, and then obtain intra-pulse parameters of the SAR signal sent by the SAR radar 10 at each repeated transmission. The signal is typically a chirp signal. As described above, the radar detection unit 12 and the radar interference unit have a synchronization and communication means so that they combine the detected information and use it for correlation estimation. For example, the line of sight of the SAR radar 10 generated by at least two different radar detection units 12 around the area 11 to be protected, based on at least two estimates of the pulse direction of arrival and time of arrival. Similarly, we can estimate the position, angle and moving speed of the SAR radar 10 based on the combined information from two radar detection units 12, which two radar detection units 12 can provide radar detection functions around the area to be protected 11.
In this embodiment, the radar interfering unit includes:
the interference generation module is used for generating an interference signal according to the SAR radar signal characteristics received by the radar detection unit;
and the interference transmitting module is used for transmitting the interference signal generated by the interference generating module.
Further, the radar jamming unit comprises a digital radio frequency memory which can copy, delay and dephasing the received radar signal from one PRI to the next PRI by means of the time and phase history associated with the set of pixels of the SAR image.
Furthermore, the radar detection unit 12 also has an intra-pulse analysis function, in which the antenna device with lobe 15 can receive the highest power transmission signal from the SAR radar 10 according to the direction of arrival, and further, the processing module of the radar detection unit 12 has a high sensitivity, which can detect the SAR radar 10, even if the SAR radar 10 irradiates the antenna device of the radar detection unit 12 through the side lobe 21, and the processing module of the detection unit 12 has a high sensitivity, which allows us to predict and implement interference on the SAR radar 10 before the antenna main lobe 14 of the SAR radar 10 irradiates the area 11 to be protected (as shown in fig. 1 a), and during the whole duration of the irradiation of the main lobe 14 on the area 11 to be protected.
In the present exemplary embodiment, the radar detection unit 12 has a temporal evaluation frequency range which is sufficient for measuring the intra-pulse modulation of the SAR radar signal. This requires the radar detection unit 12 to achieve a sufficient signal-to-noise ratio and a sufficient antenna gain. Advantageously, a superheterodyne receiver can achieve this type of processing by requiring a reduction in the instantaneous analysis band and providing high level rejection of out-of-band signals.
Furthermore, the detection sensitivity of the radar detection unit 12 may detect the synthetic aperture radar 10 on the side lobe 21 of its antenna. By way of illustration, fig. 2 gives an example of antenna patterns in a synthetic aperture radar. Considering that the first side lobe 21 is typically located at a level 20dB to 25dB below the main lobe 14, we can choose the sensitivity to be 25dB above the minimum sensitivity required to detect the main lobe of the SAR radar antenna. This sensitivity level can be obtained by techniques known to those skilled in the art, for example, by using a superheterodyne receiver with spectral analysis.
Fig. 3 presents a method of jamming SAR radar according to the present invention.
In step Etp10, the signals received by the radar detection unit 12 are analyzed in order to identify them and to detect the presence of SAR radar signals. The detection and identification of the SAR radar 10 is performed based on a predetermined criterion related to the SAR signal waveform and the illumination distribution of the SAR radar 10. These standards correspond to those typically produced by the synthetic aperture radar 10. For example, an alarm of the presence of the SAR radar 10 may be generated if the following criteria are met:
a pulse signal exists in a search frequency band of a first processing module of the radar detection unit 12;
the signal exhibits a constant or periodic modulation during the reoccurrence period;
the signal exhibits a constant frequency from one pulse to the next or a periodic frequency modulation from one pulse to the next;
the signal exhibits a constant pulse duration from one pulse to the next;
the signal exhibits a wide intra-pulse bandwidth, typically greater than 50 MHz;
this signal corresponds to a certain directional radar, i.e. there is no received signal amplitude modulation associated with the rotation of the radar antenna;
the signal has a constant phase from one pulse to the next (which is most common) or a periodic modulation of the phase from one pulse to the next (this modulation is mainly used for techniques dealing with range ambiguities).
In the present embodiment, the purpose of checking whether all these parameters are present is to avoid activating the radar jamming unit due to a false alarm.
According to an embodiment of the invention, the radar detection unit 12 may also detect the presence of a signal that exhibits a same intra-pulse modulation from one pulse to the next, or a periodic modulation of the pulse modulation from one pulse to the next (which is a possible electronic countermeasure technique or a method of dealing with range ambiguity).
In step Etp20, when the presence of the SAR radar 10 is detected, the processing module of the radar detection unit 12 will determine the signal characteristics transmitted by the synthetic aperture radar 10 in a short time. A short time here refers to a time shorter than the duration of one radar signal repetition. Performing the analysis of the SAR signal over a period having a predetermined duration shorter than the duration of one repetitive transmission of the SAR signal enables us to accurately identify the waveform transmitted by the SAR radar 10 in each repetitive transmission and to predict whether the waveform is constant from between two PRIs, which is the usual case, the duration of the analysis is several tens of milliseconds to several hundreds of milliseconds. In particular, this analysis enables us to identify the transmission frequency or carrier frequency of the radar signal, the pulse duration, the repetition duration, the intra-pulse modulation and the corresponding modulation bandwidth af, the transmission pulse start phase and the direction of arrival.
By means of the modulation bandwidth Δ F of the radar signal, the radial range resolution of the SAR radar, i.e. the size of one elementary pixel in the radar image, can be estimated. The resolution is found by the following formula:
wherein: Δ RdRepresents the radial distance resolution of the radar;
c represents the propagation speed of the radar wave;
Δ F denotes a modulation bandwidth.
In general, the lateral resolution Δ RaEqual to radial resolution Δ Rd。
According to one embodiment, the interference method may include time and frequency windowing in step Etp25 to limit the amount of data of processing module one within a time scout window and a bandwidth corresponding to observed SAR signal characteristics, so that the SAR signal characteristics can be estimated in a short time to select the best-suited reception band for the signal.
With the aid of the illustration of fig. 4, we are enabled to compare an example of a time and frequency scout window with the respective signal spectra as a function of time and as transmitted by the SAR radar 10 and received by the radar detection unit 12. Fig. 41 and 42 show the amplitudes of the pulses 410 of the signals transmitted by the SAR radar 10 and the pulses 420 of the signals received by the radar detection unit 12, respectively. Fig. 43 shows a time reconnaissance window 430 of the receiving module on the radar detection unit 12. These scout windows are periodic and synchronized with the signal received at the receiving module. The time window 430 is synchronized with the pulses 420 received from the radar after the plurality of consecutive pulses 420 were previously received.
Fig. 44 shows the spectral amplitude of the SAR signal emitted by the SAR radar 10. Fig. 45 and 46 show the reception bands 450 and 460 of the radar detection unit 12 before and after detection, respectively.
After detection, the receive frequency band or frequency reconnaissance window 460 of the radar detection unit 12 is tuned to a single frequency band of the SAR signal.
Based on the observed waveform characteristics, step Etp30 is implemented. A first processing module on the radar detection unit 12 calculates a matched filter suitable for the detected SAR signal cross-correlation operation, i.e. suitable for radar pulses, so that it can perform pulse compression on the signal received by the radar detection unit 12, for which purpose the signal is first transformed from the time domain to the frequency domain by means of a fast fourier transform. The resulting signal is then processed by a cross-correlation operation, and then transformed again to convert the signal from the frequency domain to the time domain by an inverse fourier transform. Finally, a compressed pulse is obtained for determining the speed of movement of the airborne SAR radar 10 from one cycle to the next and the distance between the airborne SAR radar 10 and the area 11 to be protected. These parameters will allow the modulation table to be addressed to instruct the generation of phase samples corresponding to the interfering signal by a digital signal synthesizer (direct digital synthesizer, DDS), which phase samples are then produced by the digital signal synthesizer for modulating the received signal, which was previously transposed to a lower frequency and converted from the time domain to the frequency domain. The resulting signal is then converted to the time domain using an inverse fourier transform function and then to an analog signal by means of a digital-to-analog converter. The signal is then converted to a higher frequency in order to bring it to the frequency of the radar, i.e. its original carrier frequency. Finally, the signal is amplified by a High Power Amplifier (HPA)630 before being transmitted through the interfering transmit antenna. The method comprises the following specific steps:
in step Etp40, the short-time cross-correlation operation is used to compress the pulses received by the antenna of radar detection unit 12 over each radar signal transmission cycle. Pulse compression is used here to improve the signal-to-noise ratio of the received signal. Detection of the compressed pulse is such that in range units Δ RdIt becomes possible to acquire the phase in the middle, so that it is possible to learn the doppler history associated with the movement of the radar carrier in the radar detection unit 12 for a long period of time and extract the doppler phase Φ therefromdr(t) and history thereof. This compression pulse will enable us to implement step Etp50, which step Etp50 makes long-term (a duration longer than the duration of one repeated transmission of the SAR signal) iterative periodic measurements of the received signal in order to determine the speed of movement of the SAR radar 10 and the distance between the SAR radar 10 and the area 11 to be protected.
In this embodiment, once the waveform of the SAR radar 10 is analyzed, at least one interference generation module estimates the waveform of the interference signal transmitted by the interference transmission module in step Etp 60.Specifically, referring to fig. 5, a SAR radar 10 is considered, when time t is 0, the SAR radar 10 is located at point o, the ground area 51 is located at point M, and the distance between the SAR radar 10 and point M is D0An included angle between the M point and the motion direction 13 of the airborne SAR radar 10 is theta, and the moving speed of the SAR radar 10 is V. If the conventional SAR equation is considered (which gives the distance history d (t) between the SAR radar 10 and the point M on the ground 51), the following relationship holds:
thus, the transmit-receive phase of each PRI
The following were used:
doppler frequency Fd of direction theta viewed from SAR radar 10rComprises the following steps:
where λ represents a wavelength.
Illumination time T at antenna aperture of SAR radar 10eBandwidth of internal imaging BdComprises the following steps:
thus, the lateral resolution Δ RaAcquisition by the SAR radar 10:
based on the synthetic aperture length L, tooNamely the equivalent length of the SAR antenna and the relations (4) and (5), and deduces the number N of the copy signals to be generated in each range cell covering the whole Doppler frequency banddop：
The rate of change of the doppler phase over time t corresponding to a single path, as seen from the radar detection unit 12, can be expressed as:
the doppler frequency corresponding to a single path is represented at time t as:
the relationship may be expressed in a conventional form corresponding to a chirp signal:
the radio frequency carrier signal intercepted by the antenna of the radar detection unit 12 may be converted into a baseband, i.e. after demodulation by the carrier frequency f:
wherein: τ denotes a short time, i.e., a time of one repetitive emission, a time starting point when one repetitive emission starts;
t represents the long term, i.e. a multiple of the duration of one repetition of the transmission: t is k.Tr；
Δ F represents the modulation bandwidth of the radar signal;
t represents the pulse width of the radar,
a (t) represents the amplitude of the received signal over a long period t;
c represents the propagation velocity of the signal wave.
By applying the previously estimated "short-term" cross-correlation operation, the processing module one of the radar detection unit 12 compresses the signal received during the repeated transmission of the index i according to the propagation delay d (t)/c, so as to extract therefrom a compressed signal rcdr(t), specifically as follows:
according to relation (7):
long term estimation of SAR signals including identification of the initial Doppler frequency Fd in a cross-correlation operation using the following relationshipodr：
Modulation slope of the frequency modulated signal corresponding to SAR:
the analysis is performed within a shorter duration (e.g. more than 100ms) than the illumination time Te of the synthetic aperture radar and is recursively refreshed over time by taking into account a new long-term time origin in each iteration. Considering that the duration for performing the correlation is short, it can be assumed that there is no offset in distance, and the amplitude of the compressed signal can be considered constant during this time, so the cross-correlation operation can be performed using a time-frequency transform, such as the Wigner-Ville transform.
In practice, consider betterShort analysis time and gentle modulation slope, the Doppler frequency can be generally considered constant during the analysis, while a simple Fourier transform enables it to measure the average Doppler frequency Fd of the SAR during the analysisdr。
After estimating the wavelength X and the direction of arrival angle θ of the radar detection unit 12, the average doppler frequency Fd is measureddrSo that it can further deduce therefrom the speed V of the airborne SAR radar 10. Distance D0This may be obtained by combining the detections of the two radar detection units 12, for example by using the difference in angle of arrival or time of arrival of the pulses. From equation (5), the following relationship can be derived:
therefore, the SAR accumulation time T can be derived using the relation (4)eSo as to deduce the spread of the doppler band Bd to be interfered:
the signal r intercepted by the radar detection unit 12 is according to equation (10)dr(τ, t) can be written to baseband, i.e. after demodulation by carrier frequency f, in the form:
will be Δ RdAs radial resolution of SAR radar, Δ RaAs its lateral resolution, d (t) is the current distance from the radar jamming unit to the SAR radar 10. If a given point M' of the zone 11 to be protected is considered, with respect to the radial distance xi＝iΔRdThe radar jamming unit used in the above is offset, where i is an integer. At the same time, by means of the transverse distance yj＝jΔRaWhere j is an integer, the distance D from this point to the SAR radar 10 can be calculatedi，j(t), specifically as follows:
wherein xRAnd yRRespectively, d (t) in the radial and transverse axes.
Finally, the interference signal r generated by the radar interference unit is given in the baseband by the following relationbi，j(τ, t) to cover the point M' at the time defined by the interference pair (t, τ). Wherein t is kTr+ x (k denotes an integer, TrDenotes the time of re-emission, τ denotes the shorter time):
wherein a isi，jIs the desired interference amplitude. Suppose that:
during the short time τ of the re-emission time t, the frequency of the chirp signal is:
by expressing the Fourier transform in a short time and letting Sdr(f τ, t) denotes the radar detection unit 12rdr(tau, t) intercepted messageFourier transform of the numbers, let Sbi，j(fτAnd t) represents an interference signal rb，i，jFourier transform of (τ, t) yields the following equation:
in the Fourier domain, at time t, to be transmitted to cover NdistDistance range and NdopThe interference signal of the complete image in the doppler range is written in the following relation:
in other embodiments, the radar jamming unit further includes a storage table or a modulation table, in which various jamming signals corresponding to various possible trajectories in the carrier wave of the SAR radar 10 to be jammed are recorded in advance. The memory area is addressed to command the generation of a jamming signal to be transmitted, in dependence on radar signal characteristics received by the radar detection unit 12. Thus, the interference signal to be transmitted may also be calculated not in real time, but in a pre-calculated and pre-recorded form selected from a memory area. This has the advantage that non-real-time calculation of the interfering replica signal allows the use of computational means and can significantly reduce processing time.
In the present embodiment, once the interference signal is calculated, in step Etp70, the interference signal is transmitted by the interference transmitting module of the radar interference unit. Depending on the result of the one or more processing modules one of the radar detection unit 12 and the direction of movement of the synthetic aperture radar 10, the radar interfering unit that is angularly closest to the synthetic aperture radar 10 will be activated. As shown in fig. 1b, before the SAR radar 10 is in a position to illuminate the area to be protected 11, the transmission of the interfering signal is performed by pointing the main lobe 17 of the interfering signal transmitting antenna in the direction of the SAR radar 10 and interfering it for the whole time it illuminates the area to be protected 11. To achieve this, the radar jamming unit may be equipped with a directional antenna, which typically has an aperture of a few degrees. The antenna may be kept pointing in the direction of the synthetic aperture radar 10 to be disturbed, for example by mechanical servo control.
Furthermore, the duplicate signal to be transmitted may be periodically subjected to repeated estimation operations in order to continuously optimize the effectiveness of the interference.
In this embodiment, the receiving module of the radar detection unit 12 is an interferometric superheterodyne receiver, which employs a Digital Radio Frequency Memory (DRFM) system.
The above description is only a preferred embodiment of the present invention, and is not intended to limit the scope of the present invention, and all modifications and equivalents of the present invention, which are made by the contents of the present specification and the accompanying drawings, or directly/indirectly applied to other related technical fields, are included in the scope of the present invention.
Claims (10)
1. The utility model provides a device of interference SAR radar, locates to treat by the protection zone, its characterized in that includes: the radar detection unit is used for receiving the SAR radar signal and analyzing and processing the SAR radar signal so as to obtain the SAR radar signal characteristics; and the radar interference unit is used for generating an interference signal according to the SAR radar signal characteristics received by the radar detection unit and transmitting the interference signal to the SAR radar, and the radar interference unit and the radar detection unit are synchronously interconnected through a bidirectional data link.
2. The apparatus that disturbs SAR radars of claim 1, wherein said radar detection unit comprises: the receiving module is used for receiving radar signals; a first processing module; and the SAR signal processing module is used for analyzing and processing the radar signal received by the receiving module to judge whether the radar signal is an SAR radar signal or not, and if the radar signal is the SAR radar signal, the SAR radar signal is analyzed and processed to obtain the moving speed of the SAR radar and the distance between the SAR radar and the area to be protected.
3. The apparatus for jamming SAR radar of claim 2 wherein the receive module has an antenna that can achieve wide coverage in azimuth and can be directional.
4. The apparatus for jamming SAR radar of claim 1, wherein the radar jamming unit comprises: the interference generation module is used for generating an interference signal according to the SAR radar signal characteristics received by the radar detection unit; and the interference transmitting module is used for transmitting the interference signal generated by the interference generating module.
5. A method of jamming a SAR radar, comprising: receiving a radar signal and judging whether the radar signal belongs to an SAR radar signal; if so, analyzing and processing the SAR radar signal to obtain SAR radar signal characteristics; generating an interference signal according to the SAR radar signal characteristics; the interfering signal is transmitted towards the SAR radar.
6. The method for jamming SAR radar of claim 5, wherein the received radar signal is determined to be a SAR radar signal if at least one of the following conditions is met: the signal exhibits a constant or periodic modulation during the reoccurrence period; or the signal exhibits a constant frequency from one pulse to the next or a periodic frequency modulation from one pulse to the next; or the signal exhibits a constant pulse duration from one pulse to the next; or the signal exhibits an intra-pulse bandwidth of greater than 50 MHz; or the signal is absent of received signal amplitude modulation associated with rotation of the radar antenna; or the signal has a constant phase from one pulse to the next; or the phase of the signal is periodically modulated from one pulse to the next; or the signal exhibits an identical intra-pulse modulation from one pulse to the next; or the signal exhibits a periodic modulation of the pulse modulation from one pulse to the next.
7. The method of jamming SAR radar as in claim 5, wherein analyzing SAR radar signals and obtaining SAR radar signal features comprises: acquiring the transmitting frequency or carrier frequency, pulse duration, repetition duration, intra-pulse modulation and corresponding modulation bandwidth, transmitting pulse initial phase and arrival direction of the SAR radar signal; designing a matched filter according to SAR radar pulse to compress the SAR radar signal; and obtaining the moving speed of the SAR radar and the distance between the SAR radar and the area to be protected according to pulse compression.
8. The method of jamming SAR radar of claim 7, wherein the pulse compressing the SAR radar signal comprises: transforming the SAR radar signal from a time domain to a frequency domain by fast Fourier transform; processing the transformed signal by cross-correlation; and converting the processed signal from a frequency domain to a time domain through inverse Fourier transform, and then obtaining a compressed pulse.
9. The method of jamming SAR radar of claim 7, wherein the generating the jamming signal according to SAR radar signal characteristics comprises: the digital signal synthesizer generates a phase sample corresponding to the interference signal according to the moving speed of the SAR radar and the distance between the SAR radar and the area to be protected; and modulating the received SAR radar signal through the phase sample to generate an interference signal.
10. The method of jamming SAR radar of claim 5, wherein the received radar signal has a receive time and frequency window.
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114217274A (en) * | 2022-02-22 | 2022-03-22 | 北京宏锐星通科技有限公司 | Method and device for positioning target of interference synthetic aperture radar |
| CN114740436A (en) * | 2022-06-13 | 2022-07-12 | 北京宏锐星通科技有限公司 | Combined interference method and combined interference device for synthetic aperture radar motion compensation |
| CN115833991A (en) * | 2023-02-22 | 2023-03-21 | 北京航天华腾科技有限公司 | Intelligent interference method for symbiotic radio |
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2021
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114217274A (en) * | 2022-02-22 | 2022-03-22 | 北京宏锐星通科技有限公司 | Method and device for positioning target of interference synthetic aperture radar |
| CN114740436A (en) * | 2022-06-13 | 2022-07-12 | 北京宏锐星通科技有限公司 | Combined interference method and combined interference device for synthetic aperture radar motion compensation |
| CN115833991A (en) * | 2023-02-22 | 2023-03-21 | 北京航天华腾科技有限公司 | Intelligent interference method for symbiotic radio |
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Inventor after: Yu Mingcheng Inventor after: Li Huang Inventor after: Li Jifeng Inventor after: Zhu Wenming Inventor before: Yu Mingcheng Inventor before: Dai Huanyao Inventor before: Li Huang Inventor before: Li Jifeng Inventor before: Zhu Wenming |