CN110471040B - Inverse synthetic aperture radar interference method based on FDA antenna - Google Patents

Inverse synthetic aperture radar interference method based on FDA antenna Download PDF

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CN110471040B
CN110471040B CN201910777774.8A CN201910777774A CN110471040B CN 110471040 B CN110471040 B CN 110471040B CN 201910777774 A CN201910777774 A CN 201910777774A CN 110471040 B CN110471040 B CN 110471040B
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宗竹林
黄栎冰
黄丽梅
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University of Electronic Science and Technology of China
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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
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Abstract

The invention belongs to the technical field of radar interference countermeasure, and relates to an inverse synthetic aperture radar interference method based on an FDA antenna. The method of the invention is based on the phased array antenna, the frequency control array adds a frequency increment which is far smaller than the working carrier frequency to the transmitting signal on the adjacent array elements, and the accompanying type interference machine carrying the frequency control array antenna transmits the interference signal to the protected target and then scatters the interference signal to the ISAR receiver through the target.

Description

Inverse synthetic aperture radar interference method based on FDA antenna
Technical Field
The invention belongs to the technical field of radar interference countermeasure, and relates to an inverse synthetic aperture radar interference method based on an FDA antenna.
Background
Inverse Synthetic Aperture Radar (ISAR) has the ability to detect and identify non-cooperative moving targets at all times, all weather, and in a long distance, and has a high imaging resolution, so that it plays an increasingly important role in the military field, particularly in the aspects of aerial target identification, reverse guidance, and the like. At present, electronic interference and interference resistance of ISAR become research hotspots in the fields of ISAR and electronic countermeasure. Interference with ISAR is largely divided into two categories: compression and spoofing. The suppression type interference mainly utilizes Gaussian white noise to generate an interference signal, and the mode requires that the transmitting power of an interference machine is large and the interference is easy to eliminate through matched filtering. The deceptive jamming is to firstly receive the signal transmitted by the radar of the other party and then to transmit the signal through signal processing. The existing deception jamming technology generates a plurality of jamming targets, and simultaneously, the calculation amount is also greatly increased, so that the jamming efficiency is reduced.
Frequency-controlled array (FDA) radar was first proposed and applied for us patent by Antonik and Wicks in 2006. Once this concept has been developed, it has gained wide attention in national defense research units in the united states because it can generate distance dependent beams. The frequency control array transmits coherent signals like a phased array radar, and only through adding small frequency deviation (relative carrier frequency) control, the frequency center of signals radiated by each array element is deviated, but the main frequency components of the signals are overlapped. Therefore, the frequency control array still belongs to the phased array category, and can be regarded as an expansion of the phased array.
Disclosure of Invention
In order to solve the problem of low interference efficiency of the traditional deception jamming method, the invention provides a frequency control array new system-based antenna jamming ISAR imaging method. On the basis of a phased array antenna, a frequency control array adds a frequency increment which is far smaller than a working carrier frequency to a transmitting signal on an adjacent array element, an accompanying type interference machine carrying the frequency control array antenna transmits the interference signal to a protected target, the interference signal is scattered to an ISAR receiver through the target, after matching and filtering, a plurality of false targets containing true target information can be generated in the distance direction, and therefore the ISAR imaging system cannot judge the true positions of the targets.
The Frequency control array (FDA) used in the present invention is different from the phased array antenna and the mechanical scanning antenna in that: the carrier frequencies of signals transmitted by each array element of the phased array antenna are the same, the beam direction is controlled through a phase shifter system, and the spatial domain scanning of the beams can be realized by adjusting the phase shift amount of the phase shifter; the carrier frequencies of signals transmitted by each array element of the mechanical scanning antenna are also the same, and airspace scanning is realized through a servo motor; the carrier frequency of the signal transmitted by each array element of the FDA is different, and a frequency increment much smaller than the operating carrier frequency is added to the transmitted signal on the adjacent array element. The uniform linear array composed of N array elements outputs images of N positions completely superposed through matched filtering because the transmitting signals are completely the same. Each array element of the frequency control array has a tiny frequency offset, so that N images cannot be overlapped, and a plurality of false target effects are generated. And the frequency offset between the array elements is changed, the distance between the decoys is changed, the number of the antenna array elements is increased, and the number of the decoys is also increased. This interference only affects the imaging of the ISAR in the range direction, i.e. only a number of false targets will appear in the range direction and no false targets will appear in the azimuth direction.
In order to solve the technical problem, the technical scheme adopted by the invention comprises the following steps:
a. and establishing a frequency control array jammer geometric model and an inverse synthetic aperture radar jamming geometric model.
b. The jammer samples and stores the signal transmitted by the inverse synthetic aperture radar and forwards the signal to the protected air target through the frequency control array antenna to form an interference signal.
c. And performing de-chirp (Dechirp) processing on the frequency control array interference signal received by the inverse synthetic aperture radar to obtain an interference pattern.
Specifically, in step a, we assume that the antenna geometric model of the frequency-controlled array is as shown in fig. 1. The frequency control array consists of a uniform linear arrayThe array element number is N, the array element spacing is d, and a linear micro frequency offset delta f is applied between the transmitting signals of the adjacent array elements. If the first array element is taken as the reference array element, the transmitted signal is f 0 The carrier frequency is a chirp signal, the signal transmitted by the kth array element is expressed as:
Figure BDA0002175625640000021
wherein
Figure BDA0002175625640000022
T p Is the width of the pulse or pulses,
Figure BDA0002175625640000023
is the distance modulation frequency, the subscript r represents the distance direction, B r Is the distance signal bandwidth, f k ＝f 0 And + k delta f, k is 0,1, …, and N-1 is the carrier frequency of the k-th array element transmission signal. The most remarkable characteristic of the frequency control array is that the frequency increment applied between adjacent array elements is small, and the frequency increment delta f taken by people is far smaller than the carrier frequency f of a reference array element 0 . Therefore, for an array of N array elements, in order to avoid uncorrelation of the transmitted signal between the individual array elements, the frequency increment must satisfy the following constraint:
Figure BDA0002175625640000031
it can be seen that the constraint of the frequency increment Δ f is associated with the carrier frequency f 0 And the number N of array elements.
In the specific step a, it is assumed that an ISAR interference model is as shown in fig. 2: the inverse synthetic aperture radar is positioned on the ground, an aerial target can be regarded as a rotary table model, and the distance vector of the inverse synthetic aperture radar reaching the frequency control array antenna is R RJ The distance vector of the frequency control array antenna reaching the protected target in the air is R J The distance vector of the inverse synthetic aperture radar reaching the protected target in the air is R R 。
The total propagation time of the inverse synthetic aperture radar transmission signal forwarded by the frequency-controlled array jammer to the radar receiver via the aerial protected target and then scattered is
Figure BDA0002175625640000032
Wherein subscript i denotes the ith scattering point on the airborne target, | · | | non | E Representing the Euclidean norm, r i Representing the distance vector, theta, from the i-th scattering point on the object to the center of rotation of the object i ＝θ i0 +ωt a The rotation angle of the ith scattering point on the target relative to the rotation center within the radar irradiation time, omega is the rotation angular velocity of the target, t a For slow time, c is the speed of light.
In the specific step b, we assume that the FDA antenna is mounted on a satellite-borne jammer platform, and the expression that the interfering signal transmitted by the FDA antenna is scattered to the ISAR receiver via a protected target to form an interfering signal (for convenience of analysis, only the interfering echo signal is considered here to ignore the echo signal transmitted by a normal ISAR) is:
Figure BDA0002175625640000033
wherein: t is t r For fast times, the subscript r represents the distance direction, the subscript a represents the azimuth direction, ξ i And K is the scattering coefficient of the ith scattering point and the number of the target scattering points.
Specifically, in the step c, the ISAR Dechirp algorithm (Dechirp) based on FDA interference includes the following steps. And performing frequency mixing processing, residual video phase item compensation, distance Fourier transformation and azimuth Fourier transformation on the echo data.
Firstly, echo data is subjected to frequency mixing processing and residual video phase compensation, and the expression is as follows:
Figure BDA0002175625640000041
wherein R is i (t a )＝Δt i ×c，R ref For solving reference distance vectors of chirp processing, Δ R i (t a )＝2||R ref || E -R i (t a ) And K is the number of target scattering points.
The echo signal is transformed to a fast time frequency domain-a slow time domain through range-to-Fourier transform, and the echo signal is also called a high-resolution range image, and the expression is as follows:
Figure BDA0002175625640000042
wherein: f. of r Is a fast time signal frequency domain variable. According to
Figure BDA0002175625640000043
The expression of high resolution range image in the range-slow time domain is as follows:
Figure BDA0002175625640000044
then, performing azimuth Fourier transform, namely performing azimuth Fourier transform on the high-resolution range profile in the range-slow time domain, and obtaining an expression of echo data in the range-Doppler domain as follows:
Figure BDA0002175625640000045
wherein T is a For the inverse synthetic aperture radar observation time,
Figure BDA0002175625640000051
indicating the doppler frequency of the ith scattering point. After the above process, the ISAR interference result is output. It can be seen from the above formula that the number of decoys is related to the number of array elements N, and the distance between decoys is related to the frequency increment Δ f. Decoys may only appear in the range direction independent of the azimuth direction.
From the transmit signal of the frequency controlled array, it can be known that: when Δ f is equal to 0, the carrier frequencies of the signals transmitted by all the array elements of the frequency control array are all equal, and the frequency control array becomes a phased array. As can be seen from the frequency-controlled array imaging expression: the phased array cannot generate interference effect on airborne SAR imaging. The specific simulation results are shown in fig. 4.
Compared with the prior deception jamming technology, the method has the advantages that the jamming efficiency is improved, and meanwhile, a plurality of jamming targets with controllable positions and quantities can be generated.
Drawings
Fig. 1 is a schematic diagram of an FDA antenna transmit array;
FIG. 2 is a diagram of an ISAR deceptive interference model;
FIG. 3 is a diagram of an aerial target model;
FIG. 4 is a diagram of a 7-array element phased array antenna interference ISAR point target imaging;
FIG. 5 is a diagram of 7-element FDA antenna interference ISAR imaging;
FIG. 6 is an ISAR imaging diagram of 7-element unequal interval frequency offset FDA antenna interference;
fig. 7 is an image diagram of 15 array elements FDA antenna interference ISAR.
Detailed Description
The effectiveness of the invention is illustrated below with reference to the figures and simulation examples.
According to the signal model of the invention, Matlab (a computer algorithm language) is used for simulation verification, and the specific simulation parameters are as follows:
setting system parameters: radiation source frequency f of first array element of frequency control array antenna 0 10GHz, frequency increment delta f is 8MHz, array element interval d is lambda/2, array element number N is 7, and signal bandwidth B r 1GHz, pulse width T p 20us, pulse repetition frequency PRF 1kHz, target rotation angular velocity ω 0.06rad/s, coherence imaging time T a 0.25s, radar-to-air target distance R R || E 50km, jammer to target distance | | | R J || E 30km, the ground angle α of the ground of the bipartite is 0 °, the ISAR resolution is 0.15m × 0.97m, the observation scene is 800m × 400m, and the aerial target size is 19m × 20 m.
FIG. 3 is a diagram of an aerial target model. Figure 4 is a phased array antenna interference ISAR imaging result. Fig. 5 is the result of the constituent FDA antenna interference ISAR for 7 elements. FIG. 6 shows the imaging result of FAD antenna interference ISAR composed of 7 non-equidistant frequency offset array elements. Fig. 7 shows the result of the imaging of the FDA antenna interference ISAR with 15 array elements. As can be seen from fig. 4, 5 and 7, the interference mechanism composed by FDA causes good interference to ISAR imaging, and the number of decoys increases by increasing the number of array elements. As can be seen from a comparison of fig. 5 and 6, by varying the magnitude of the frequency offset, the spacing between decoys also varies.

Claims (2)

1. An inverse synthetic aperture radar jamming method based on an FDA antenna is characterized by comprising the following steps:
s1, establishing an FDA jammer geometric model and an inverse synthetic aperture radar jamming geometric model, specifically: the frequency control array consists of a uniform linear array, the number of array elements is N, the spacing between the array elements is d, and a linear micro frequency offset delta f is applied between the transmitting signals of the adjacent array elements; the inverse synthetic aperture radar is positioned on the ground, an aerial target is regarded as a rotary table model, and the distance vector of the inverse synthetic aperture radar reaching the frequency control array antenna is R RJ The distance vector of the frequency control array antenna reaching the protected target in the air is R J The distance vector of the inverse synthetic aperture radar reaching the protected target in the air is R R ；
S2, the jammer samples and stores the signals transmitted by the inverse synthetic aperture radar and forwards the signals to a protected aerial target through an FDA antenna to form interference signals, the FDA antenna is enabled to be carried on a flight accompanying jammer platform, and the transmitted interference signals are scattered to the inverse synthetic aperture radar receiver through the protected target to form interference signals:
Figure FDA0003671479680000011
wherein, t r For fast times, the subscript r denotes the distance, t a For azimuth slow time, subscript a denotes azimuth, ξ i Is the ithThe scattering coefficient of the scattering points, K is the number of the target scattering points,
Figure FDA0003671479680000012
||·|| E representing the Euclidean norm, r i Representing the distance vector, theta, from the i-th scattering point on the object to the center of rotation of the object i The rotation angle of the ith scattering point on the target relative to the rotation center within the radar irradiation time is shown, alpha represents a bistatic angle formed by the jammer and the radar relative to the target, and c is the speed of light;
and S3, performing de-chirp processing on the frequency control array interference signal received by the inverse synthetic aperture radar to obtain an interference pattern.
2. The method of claim 1, wherein the specific method for performing the de-chirp processing in step S3 is as follows:
s31, performing frequency mixing processing on echo data and compensating a residual video phase term, wherein the expression is as follows:
Figure FDA0003671479680000021
wherein R is i (t a )＝△t i ×c，△R i (t a )＝2||R ref || E -R i (t a )，R ref Reference distance vector, T, for de-chirp processing p Is the width of the pulse or pulses,
Figure FDA0003671479680000022
is the distance modulation frequency, the subscript r represents the distance direction, B r Is the distance direction signal bandwidth, K is the number of target scattering points, Δ f is the frequency increment and
Figure FDA0003671479680000023
f 0 is the carrier frequency of the reference array element, and the parameter j represents a complex number;
s32, transforming the echo signal obtained in step S31 into a fast time frequency domain-a slow time domain by distance fourier transform, and defining the transformed echo signal as a high-resolution range profile:
Figure FDA0003671479680000024
wherein f is r Is the frequency domain variation of the fast time signal, d is the array element spacing, is composed of
Figure FDA0003671479680000025
The expression for obtaining a high resolution range image in the range-slow time domain is:
Figure FDA0003671479680000026
wherein B is r ＝T p K r Is the signal bandwidth.
S33, performing azimuth Fourier transform, namely performing azimuth Fourier transform on the high-resolution range profile in the range-slow time domain, and obtaining an expression of echo data in the range-Doppler domain, wherein the expression is as follows:
Figure FDA0003671479680000027
sin c[T a (f a -f i_D )]
wherein T is a For the inverse synthetic aperture radar observation time,
Figure FDA0003671479680000031
indicating the doppler frequency of the ith scattering point.
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