CN116626607A - FDA-MIMO radar supporting type interference forwarding method based on phase modulation - Google Patents
FDA-MIMO radar supporting type interference forwarding method based on phase modulation Download PDFInfo
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- 238000000926 separation method Methods 0.000 claims description 4
- 230000002452 interceptive effect Effects 0.000 claims description 2
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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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- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02D—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN INFORMATION AND COMMUNICATION TECHNOLOGIES [ICT], I.E. INFORMATION AND COMMUNICATION TECHNOLOGIES AIMING AT THE REDUCTION OF THEIR OWN ENERGY USE
- Y02D30/00—Reducing energy consumption in communication networks
- Y02D30/70—Reducing energy consumption in communication networks in wireless communication networks
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Abstract
The invention belongs to the technical field of radar interference, and particularly relates to an FDA-MIMO radar supporting type interference forwarding method based on phase modulation. The method of the invention mainly obtains the time difference between the arrival of radar signals at a protection target and the arrival of radar signals at an jammer through a positioning technology, and firstly uses carrier frequency f=f for intercepted FDA-MIMO radar multipath aliased signals 0 Down-converting, separating signals from different transmitting array elements by band-pass filter corresponding to the offset frequency of transmitting array elements, modulating the separated signal components with different phases, and finally modulating carrier signal f 0 Modulating the signal into N parts, respectively carrying out up-conversion on radar offset signals by using the sum of the N parts of carrier signals, and finally, superposing and forwarding the signals so as to achieve the aim of interference on FDA-MIMO radar.
Description
Technical Field
The invention belongs to the technical field of radar interference, and particularly relates to an FDA-MIMO radar supporting type interference forwarding method based on phase modulation.
Background
Based on a common phased array radar, a frequency diversity array multiple-input multiple-output radar (FDA-MIMO) introduces mutually orthogonal transmitting end signals with fixed step frequency, so that a beam forming pattern of an antenna has the characteristic of two-dimensional combination of distance and angle, and the characteristic brings excellent detection performance and main lobe interference resistance to the FDA-MIMO radar. In the aspect of anti-interference, the FDA-MIMO radar can utilize the phase difference between a true target and a false target after the true target and the false target reach a receiving end to inhibit the false target interference entering a radar main lobe. Due to the excellent main lobe interference resistance of FDA-MIMO radar, it has been difficult to formulate an interference scheme for the radar by using traditional means.
For a typical FDA-MIMO radar system, it is assumed that the radar system has M transmitting signal terminals, each transmitting element transmitting a signal differing by a step frequency Δf, the transmitting signal s of the first transmitting terminal 1 The carrier frequency of (t) is set to f 0 And it satisfies f 0 > Δf, signal s transmitted by mth transmitting terminal m Carrier frequency of (t) satisfies f m ＝f 0 +mΔf, where f 0 Is the carrier frequency of the signal and Δf is the step frequency of the signal.
For the conventional supporting interference scenario, the jammer is positioned in a different direction from the protected object, and the jammer is not mounted on the platform of the protected object, as shown in fig. 1. Assume that the protected target is located at r=r 0 ,θ＝θ 0 Where jammers are located at r=r j ,θ＝θ j Where it is located. The radar signal has the following time lengthIs captured by an jammer after the transmission delay of the (a) is completed, and the sum of signals from M transmitting array elements captured by the jammer is subjected to a delay t j Is forwarded and transmitted t j,n Then captured by the nth receiving array element, and the signal is shown as a formula (1).
Wherein A is m (t) represents the envelope of the transmitted signal of the mth transmit element.
After the signal is captured by the radar receiving end, the signal is processed according to the flow shown in fig. 2. The carrier frequency exp (j 2 pi f) of the co-transmitted signal is fed into the analog instrument 0 t) mixing, then sampling the obtained signal to convert it into digital signal, and using different frequencies to make matched filtering. The signal output component obtained by processing the false target signal generated by the accompanying interference is shown as a formula (2).
Wherein χ is j And matching complex coefficients obtained after filtering for the complex envelope signals. The total m X n output signals on or obtained from n receiving array elements of the radar are represented by a vector X as shown in equation (3).
X＝[S 11 ,S 12 ,…,S 1M ,S 21 ,S 22 ,…S 2M ,…,S NM ] T (3)
The above formula can be expressed as formula (4)
Wherein the method comprises the steps ofRepresents the Cronecker product, a (θ) 0 ,r 0 ) To transmit the steering vector, b (θ 0 ,r 0 ) For receiving the steering vector, the following equations (5) and (6) are respectively shown.
In beamforming, FDA-MIMO radar uses vector H (θ 0 ,r 0 ) To filter to obtainThe obtained X is processed, and the expression is shown as a formula (7).
And (3) carrying out normalization processing on the sum of signal components obtained after FDA-MIMO radar filtering, and marking the normalization processing result as W (theta, r), wherein the result represents the average power of radar signals entering a radar receiving array element after target reflection. The expression of W (θ, r) is shown in formula (8).
Wherein the method comprises the steps ofWhen r is j +Δr≠r 0 Or theta j ≠θ 0 Normalized value of signal processing of FDA-MIMO radar W (θ, r)<1, the interference signal is suppressed by the receiving end beam forming technology. It can be seen that it has been difficult to formulate interference schemes for FDA-MIMO radars using conventional means.
Disclosure of Invention
Aiming at the problems, the invention provides an FDA-MIMO radar supporting type interference forwarding method based on phase modulation.
The technical scheme of the invention is as follows:
a supporting type forwarding interference method based on phase modulation comprises the following steps:
s1, using a carrier signal A to a radar multipath aliasing signal received by an jammer dn exp[j2πf 0 (t-t dn )]Down-conversion
S2, filtering the signals through band-pass filters with the center frequency of mDeltaf respectively to obtain offset frequency signals of each transmitting array element.
S3, obtaining the time difference delta t between the arrival of the radar signal at the protection target and the arrival of the radar signal at the jammer through a positioning technology, and then carrying out separation on each obtained signal componentModulating the offset frequency of the mth transmitting array element by phase modulation with different sizes, wherein the phase modulation is that
S4, aiming at all N receiving array elements of a radar receiving end, modulating the up-conversion carrier signals into N parts, superposing the N parts of up-conversion signals, respectively up-converting the radar offset signals mDeltaf by using the N parts of up-conversion signals, and finally superposing and forwarding the signals.
The method has the beneficial effects that the time difference between the arrival of the radar signal at the protection target and the arrival of the radar signal at the jammer is mainly obtained through a positioning technology, and the carrier frequency f=f is firstly used for intercepting the FDA-MIMO radar multipath aliasing signal 0 Down-converting, separating signals from different transmitting array elements by band-pass filter corresponding to the offset frequency of transmitting array elements, modulating the separated signal components with different phases, and finally modulating carrier signal f 0 Modulating the signal into N parts, respectively carrying out up-conversion on radar offset signals mDeltaf by using the N parts of carrier signals, and finally, superposing and forwarding the signals so as to achieve the aim of interference on FDA-MIMO radar.
Drawings
Fig. 1 is a diagram of a supported interference scenario.
Fig. 2 is a signal processing flow of the FDA-MIMO radar receiving end.
Fig. 3 is a flow chart of an jammer modulated signal in a supported jammer scenario.
Fig. 4 is a diagram showing interference effects of a conventional delay forwarding of a supporting type jammer
Fig. 5 is a diagram showing an interference effect of phase modulation and delay retransmission of the supporting type jammer.
Detailed Description
The technical principle and the scheme of the invention are described in detail below with reference to the accompanying drawings and simulation examples:
the invention is divided into four parts, namely radar multipath signal down-conversion, radar signal separation, radar signal phase modulation and up-conversion carrier signal phase modulation. As shown in fig. 3, the specific method of the present invention is as follows:
s1, using a carrier signal A to a radar multipath aliasing signal received by an jammer dn exp[j2πf 0 (t-t dn )]Down-conversion is performed.
The radar multipath aliasing signal received by the jammer is as follows:
and A is a dn exp[j2πf 0 (t-t dn )]The frequency is mixed to obtain a down-converted signal as shown in formula (10).
Wherein X is M,j The subscript M in (t) represents the sum of the M transmit signals and the subscript j represents the j-th jammer. A is that m The envelope of the signal transmitted by the mth transmitting array element is represented, rect () is a rectangular function, and T is the duration of the radar signal pulse. t is t dn For the time difference between the down-converted signal and the radar reference signal, A dn For down-converting the signal amplitude.
S2, filtering signals through M band-pass filters with the center frequency of mΔf, wherein m=0, 1,2 … and M-1, and obtaining offset frequency signals of M transmitting array elements. The offset frequency signal of each transmitting array element is obtained as shown in a formula (11).
S3, obtaining the time difference delta t between the FDA-MIMO radar signal reaching the protected target and the interference machine through a positioning technology, then carrying out different phase modulation on each signal component obtained by separation, and carrying out phase modulation on the offset frequency of the mth transmitting array element, wherein the phase is adjusted to be
The sum of the system positioning time consumption, the modulation signal time consumption and the delay time consumption is recorded as t j ，t j,m ＝t m +Δt，t m The transmission time for the mth transmitting array element to reach the target. As can be seen from the formula (11), the frequency offset mDeltaf of the radar signal after the time delay can generate a phase difference with the magnitude equal toFrom equation (8), it can be known that the additional phase difference of the decoy leads to interference signal suppression by the beamforming technique of the FDA-MIMO radar receiver, so that the frequency offset of each transmitting array element needs to be +.>Wherein the result of phase modulation of the mth signal is shown in formula (12).
S4, aiming at all N receiving array elements of a radar receiving end, an jammer modulates carrier signals needed to be used in up-conversion into N parts, and the sum of the N parts of carrier signals is used for respectively shifting M radar offset signals x m,d (t) up-converting, and then superposing and forwarding the M signals.
In the supporting interference scene, the jammer and the protected target are not at the same angle, and the interference signal reaches the delay vector t of the nth receiving array element of the radar j,n Also different from the delay vector of the real target echo reaching the nth receiving array element of the radar. Although the delays in the delay vectors are small, due to the carrier frequency f of the radar 0 Often large, when these delays are in relation to the radar reference carrier frequency f 0 In combination, the phase characteristics of the interference signal and the phase characteristics of the real target echo are different, so that the interference signal is restrained in beam forming. Thus, in a supported interference scenario, in addition to the step frequency mΔ of the signal to be transmitted to the radar array elementf phase modulation, also requires a reference carrier frequency f for the radar 0 Phase modulation is performed. From equation (1), the phase difference between the false target and the true target due to the radar signal reference frequency isAs shown in formula (13).
As can be seen from the formula (13), the phase difference between the signal of each transmitting array element and the real target echo after being forwarded by the jammer is related to the sequence number n of the receiving array element reached by the signal, so that the reference carrier signal f of a certain transmitting array element cannot be obtained 0 The last fixed phase is modulated. For carrier frequency f 0 The carrier signal used in up-conversion can be modulated into N parts, and the obtained x is superimposed m,up (t) is:
wherein t is up A is the time difference value between the reference clock of the jammer and the reference clock of the radar in up-conversion up For up-converted signal amplitude, l represents the first of the N carrier signals.
By x m,up (t) for M radar offset signals x respectively m,d (t) up-converting, wherein the result of up-converting the mth signal is shown in formula (15).
The jammer superimposes and forwards the M up-converted signals, and the final forwarded signal is shown as a formula (16)
After propagation, signal Y received by nth receiving array element of FDA-MIMO radar receiver M,n And (t) is shown in a formula (17).
Wherein the method comprises the steps ofIs a basic phase term. The signal is processed by the receiving end processing flow shown in fig. 3, and the signal output component obtained after the false target signal generated by the method is processed is shown as a formula (18).
Where χ is the complex coefficient of the complex envelope signal after matched filtering.
The signal vector X of the decoy of the jammer is expressed by a transmit steering vector and a receive steering vector as shown in expression (19).
a(θ 0 ,r 0 )，b(θ 0 ,r 0 ) As shown in the formulas (20) and (21), respectively.
The result W (θ, r) of the FDA-MIMO radar normalization processing is shown in the formula (22) and can be obtained by the formula (8).
When the jammer and the target are in the radar far field, the angle difference between the jammer and the target under the supporting interference generally satisfies delta theta= |theta j -θ 0 |<1 DEG, taking the target distance radar of 300km and the jammer distance target of 3km as an example, the angle difference delta theta apprxeq 0.5 DEG between the jammer and the target at this timeSubstituting the result of the available beamforming, W (θ, r) ≡N 2 >1, therefore, the enemy FDA-MIMO radar cannot suppress spurious signals generated by the jammer.
Simulation example
In the supporting scenario, the supporting interference based on phase modulation and the traditional forwarding interference are simulated and compared, and the simulation and comparison are used for verifying the interference effect of the interference. Parameter setting: FDA-MIMO radar receives and transmits 15 array elements each, and the carrier frequency f of a transmitting end signal 0 =1 GHz, step frequency Δf=1500 Hz, signal pulse width τ=100 us, sampling frequency f s The radar signal carrier frequency wavelength λ=3m, and the spacing between the transmitting array element and the receiving array element is half wavelength, i.e. 1.5m.
The real target is at 200km and 30 degrees from the range radar, and the jammer is at 190km and 35 degrees from the range radar. The signal-to-noise ratio of the real target echo is 20dB, the false target generated by direct delay forwarding is positioned at 210km,220km,230km and 35 degrees, and the signal-to-noise ratio of the false target is 25dB. The decoys generated after delay and phase modulation are also located at 210km,220km,230km,30 degrees, and the signal to noise ratio of the decoys is 25dB. The following simulations compare the power conditions of decoys generated by conventional repeater interference and phase modulation repeater interference designed herein after radar beamforming. Fig. 4 and fig. 5 are an interference effect diagram after conventional delay forwarding and an interference effect diagram after phase modulation and delay forwarding of the supporting type jammer, respectively.
It can be seen from fig. 4 that in the conventional forwarding mode, the three decoys generated at 210km,220km,230km,35 degrees by the jammer are successfully suppressed by the beamforming technique of the FDA-MIMO radar by about 140dB. As can be seen from fig. 5, in the supporting interference scenario, the three decoys generated by the phase-designed forwarding interference at the positions of 210km,220km,230km and 30 degrees are not suppressed by the beam forming level of the FDA-MIMO radar, and the signal strength of the decoys at the radar receiving end is higher than that of the real target echo due to the fact that the signal to noise ratio of the decoys forwarded by the jammer is higher than that of the real target echo, so that the effect of interfering the enemy FDA-MIMO radar is achieved.
Claims (1)
1. A phase modulation-based FDA-MIMO radar supporting type interference forwarding method is used for defining a radar system to have M transmitting array elements aiming at supporting type interference scenes of the FDA-MIMO radar system, signals transmitted by each transmitting array element are different by one stepping frequency delta f, and the carrier frequency of a transmitting signal of the first transmitting array element is f 0 The carrier frequency of the signal transmitted by the m-th transmitting array element is f 0 In the supporting interference scene, the jammer and the protected target are positioned in different directions, and the passing time length of the radar signal is defined asIs captured by an jammer, where r j And theta j The position of an interference machine is represented, subscript j is the number of the interference machine, m represents the m-th transmitting array element, and d is the interval between each transmitting array element of the FDA-MIMO radar; the interference method is characterized by comprising the following steps:
s1, using a carrier signal A to a radar multipath aliasing signal received by an jammer dn exp[j2πf 0 (t-t dn )]Down-conversion is performed:
the radar multipath aliasing signal received by the jammer is as follows:
wherein X is M,j Subscript M in (t) represents the sum of M transmitted signals, subscript j represents the j-th jammer, A m The envelope of the transmitting signal of the mth transmitting array element is represented, T is time, rect () is a rectangular function, and T is the duration of the radar signal pulse;
and A is a dn exp[j2πf 0 (t-t dn )]Mixing to obtain a down-conversion signal:
wherein A is dn For down-converting signal amplitude, t dn Is the time difference between the down-converted signal and the radar reference signal;
s2, filtering the signals through band-pass filters with the center frequency of mDeltaf to obtain offset frequency signals x of M transmitting array elements m,d (t), wherein m=0, 1,2 …, M-1:
s3, obtaining the time difference delta t between the FDA-MIMO radar signal reaching the protected target and the jammer through a positioning technology, and then carrying out different phase modulation on each signal component obtained by separation, so as to eliminate the phase difference between the jammer signal and the protected target signal caused by the stepping frequency mdelta f; the method comprises the following steps: the offset frequencies of M transmitting array elements are respectively phase-modulated, wherein the M-th adjusted phase is as followst j For jammer to radarSum of modulation time of number and jammer delay:
wherein Δt=t j,m -t m ，t j,m The transmission time t of the transmission signal reaching the jammer for the mth transmission array element m The transmission time of the transmission signal of the mth transmission array element reaching the protected target;
s4, aiming at all N receiving array elements of a radar receiving end, an jammer modulates carrier signals needed to be used in up-conversion into N parts, so as to eliminate radar reference carrier frequency f 0 A phase difference between the resulting interfering signal and the protected target signal;
modulating N carrier signals and superposing to obtain x m,up (t) is:
wherein A is up Is the amplitude of the carrier signal, t up For the time difference between the carrier signal and the radar reference signal, l represents the first part of the N parts of carrier signals; reuse of x m,up (t) M radar offset signals x obtained for S3 m,d (t) up-converting the signals respectively, wherein the result of up-converting the mth signal is:
and finally, the M up-conversion signals are overlapped and forwarded by the jammer, and the final signals are as follows:
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