Radar super-resolution method based on transient polarization response

Abstract

This invention discloses a radar super-resolution method based on transient polarization response, comprising: transmitting a narrowband single-carrier signal with a single polarization direction, and applying the narrowband single-carrier signal to two targets with different polarization scattering characteristics; receiving echo signals based on H and V dual-polarized antennas; weighting the echo signals from the H and V polarization channels of the H and V dual-polarized antennas to synthesize equal-amplitude, anti-phase target echoes, thereby decoupling the echoes from the two targets; and using an edge threshold detector method based on the equal-amplitude, anti-phase target echoes to achieve super-resolution and range estimation of the two targets. This invention is applied to the field of polarimetric radar target super-resolution technology, achieving decoupling between range resolution and signal bandwidth. High range resolution can be obtained by increasing the device bandwidth, eliminating the dependence of range resolution on signal bandwidth, and has significant engineering application value in the field of polarimetric radar target super-resolution.

Description

Technical Field

[0001] This invention belongs to the field of polarimetric radar target super-resolution technology, and relates to a radar super-resolution method based on transient polarimetric response, specifically a polarimetric super-resolution method that utilizes transient echo information. Background Technology

[0002] Radar echoes of extended targets can generally be divided into two parts: a steady-state segment and a transient segment. The transient segment refers to the establishment and disappearance segments of the echo, corresponding to the leading and trailing edges of the echo, and includes the entire process of the echoes from each scattering center of the target being superimposed (or disappearing) sequentially. Currently, scholars have conducted a large amount of research based on the steady-state segment of the echo. In fact, the transient segment of the target echo contains rich target information, and its echo characteristics are closely related to factors such as the waveform of the transmitted signal, the number and location of the target scattering centers, the equipment bandwidth, and the SNR (Signal-to-noise ratio). However, the transient segment of the echo has not received sufficient attention. Polarization is another dimension of measurement information for electromagnetic waves besides amplitude, frequency, and phase. Polarization information contains the phase relationship between each polarization channel, and joint processing of each polarization channel can obtain richer and deeper target characteristics. In particular, the concept of "polarization domain zoom" indicates that by adjusting the transmit and receive polarization states, the radar's ability to acquire target information can be enhanced, achieving range super-resolution. Therefore, the information gain of polarization in the transient echo segment is also worth exploring in depth. This invention mainly focuses on the super-resolution potential of polarization in the transient echo segment. Summary of the Invention

[0003] To address the shortcomings of the existing technologies, this invention provides a polarization super-resolution method utilizing transient echo information. Classical resolution theory states that radar range resolution is inversely proportional to signal bandwidth, meaning that a large signal bandwidth is a prerequisite for achieving high range resolution. This invention achieves polarization super-resolution by utilizing transient echo information. Based on narrowband dual-target echoes, it uses the polarization information of electromagnetic waves to weightedly synthesize "equal amplitude and anti-phase" target echoes, canceling the steady-state segment of the echoes and highlighting the transient segment, thereby decoupling the two target echoes. Furthermore, it utilizes the transient echo information to achieve super-resolution and range estimation for both targets, demonstrating that increasing equipment bandwidth can still improve range resolution.

[0004] To achieve the above objectives, the present invention provides a radar super-resolution method based on transient polarization response, comprising the following steps:

[0005] Step 1: Transmit a narrowband single-carrier frequency signal with a single polarization direction, and apply the narrowband single-carrier frequency signal to two targets with different polarization scattering characteristics;

[0006] Step 2: Receive echo signals based on H and V dual-polarized antennas, wherein the echo signals are the result of coherent superposition of the echoes from two targets;

[0007] Step 3: Weight the echo signals from the H and V polarization channels in the H and V dual-polarization antennas to synthesize equal-amplitude, phase-inverted target echoes, thereby decoupling the two target echoes.

[0008] Step 4: Based on the target echoes with equal amplitude and opposite phase, use the edge threshold detector method to achieve super-resolution and distance estimation of the two targets.

[0009] In one embodiment, in step 1, both targets are point targets.

[0010] In one embodiment, step 3 includes:

[0011] Select the steady-state echo of the H-polarization channel and the steady-state echo of the V-polarization channel corresponding to the selected time;

[0012] The steady-state echo of the H-polarized channel and the steady-state echo of the V-polarized channel are weighted based on the weights to obtain the average value of the steady-state echo after weighting the steady-state echo of the H-polarized channel and the steady-state echo of the V-polarized channel.

[0013] Using the weights as control parameters and minimizing the average echo value of the steady-state segment as the objective, the optimal weights are calculated.

[0014] The echo signal of the entire H-polarized channel and the echo signal of the entire V-polarized channel are weighted based on the optimal weight to obtain the target echo with equal amplitude and opposite phase.

[0015] In one embodiment, the steady-state echo average value is specifically:

[0016]

[0017] in, N is the weighted average of the steady-state echoes from the H-polarized channel and the V-polarized channel. s H represents the number of sampling points for the selected steady-state echo. sj (t) and V sj (t) represents the echo signal at the j-th sampling point in the steady-state segment of the H and V polarization channels, respectively, and k represents the echo signal at k. w Z is the weight. sj (t) represents the echo signal at the j-th sampling point after weighting the echo in the steady-state segment;

[0018] Using the aforementioned weights as control parameters, minimizing the average echo value in the steady-state segment is...

[0019] In one embodiment, in step 4, the distance resolution between the two targets is:

[0020]

[0021] Where ΔR′ is the distance resolution, c is the speed of light, and T e B represents the rise / fall time of the echo pulse. r For device bandwidth

[0022] In one embodiment, in step 4, the distance between the two targets is estimated as follows:

[0023]

[0024]

[0025] in, These are the distance estimates for the two targets, where c is the speed of light and τ is the distance between them. w t is the pulse width of the transmitted signal. p1 t p2 t p3 t p4 These are the four intersection points of the edge threshold detector and the echo, t p1 With t p3 t corresponds to the arrival and end times of the first target echo, respectively. p2 With t p4 These correspond to the arrival and end times of the second target echo, respectively.

[0026] Compared with the prior art, the present invention has the following beneficial technical effects:

[0027] The radar super-resolution method based on transient polarization response proposed in this invention, based on the narrowband dual-target echo, utilizes the polarization information of electromagnetic waves to weightedly synthesize "equal amplitude and anti-phase" target echoes, canceling the steady-state segment of the echo and highlighting the transient segment of the echo, thus achieving decoupling of range resolution and signal bandwidth. High range resolution can still be obtained by increasing the device bandwidth, thus getting rid of the dependence of range resolution on signal bandwidth. It has great engineering application value in the field of polarization radar target super-resolution. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0029] Figure 1 This is a flowchart of the radar super-resolution method based on transient polarization response in an embodiment of the present invention;

[0030] Figure 2 This is a schematic diagram of the echo of two targets after passing through a band-limited device in an embodiment of the present invention;

[0031] Figure 3 This is a schematic diagram of the distance estimation between two targets in an embodiment of the present invention;

[0032] Figure 4 This is a schematic diagram of the model used in the actual experiment in this embodiment of the invention;

[0033] Figure 5 This is a flowchart of the experimental scheme in an embodiment of the present invention;

[0034] Figure 6 This is a schematic diagram of the measured experimental results in an embodiment of the present invention.

[0035] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0036] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0037] Furthermore, the technical solutions of the various embodiments of the present invention can be combined with each other, but only if they are feasible for those skilled in the art. If the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention.

[0038] like Figure 1 The above illustrates a radar super-resolution method based on transient polarization response disclosed in this embodiment, which specifically includes the following steps:

[0039] Step 1: Transmit a narrowband single-carrier signal with a single polarization direction and apply the narrowband single-carrier signal to two targets with different polarization scattering characteristics. Here, the two targets refer to point targets, which can be abstracted as a PSM (PolarizationScatteringMatrix). According to the point scattering model, the target echo obtained at this time can be represented as the result of the coherent superposition of the echoes of the two point targets.

[0040] Step 2: Receive the echo signal based on the H and V dual-polarized antenna. The echo signal is the result of the coherent superposition of the echoes of the two targets. Receive the target echo signal through the H and V dual-polarized antenna. Compared with single-channel reception, richer target information can be obtained.

[0041] Step 3: Weight the echo signals of the H and V polarization channels in the H and V dual polarization antennas to synthesize the target echo with equal amplitude and opposite phase. Based on the target echo with equal amplitude and opposite phase, the steady-state segment of the echo is canceled out, and the transient segment is highlighted, thus achieving decoupling of the two target echoes. This provides the prerequisite for target super-resolution.

[0042] Step 4: Based on the equal-amplitude, out-of-phase target echoes, the edge threshold detector method is used to achieve super-resolution and range estimation for the two targets. The edge threshold detector, evolved from the leading-edge threshold detector, simultaneously focuses on both the leading and trailing edges of the pulse, and is an approximate rectangular pulse delay estimation method. Because this method directly operates on the magnitude of the receiver output, it is an incoherent method. By achieving decoupling of the two target echoes, this method can directly yield the range estimates for the two targets.

[0043] In step 1, the ideal single-carrier rectangular transmit pulse can be represented as:

[0044]

[0045] Among them, A t τ is the amplitude of the transmitted signal. w Let f be the pulse width of the transmitted signal, f0 be the carrier frequency of the transmitted signal, t be the time variable, j be the imaginary unit, and rect(·) represent the rectangular envelope of the ideal transmitted signal, defined as:

[0046]

[0047] After the transmitted signal is applied to two point targets, the target echo signals are obtained. However, during the transmission and reception process, the actual signal transceiver equipment is limited by bandwidth. The characteristics of the echo signal received by the receiver ultimately depend on the minimum equipment bandwidth during transmission and reception, which is denoted as B. r A band-limited device is essentially a bandpass filter. Assuming the window function I(f) of this filter is rectangular, it can be expressed as:

[0048]

[0049] Where f0 is the carrier frequency of the transmitted signal, which is also the center frequency of the filter, and f is the frequency variable.

[0050] After inverse Fourier transform, the time-domain response i(t) of the rectangular window function I(f) is obtained, expressed as:

[0051]

[0052] Where sinc(·) is the Sinker function, expressed as sin(x) / x.

[0053] The target echo after passing through the band-limited device can be represented as the time-domain convolution result of the ideal echo and i(t). After orthogonal demodulation and normalization, this echo is represented as:

[0054]

[0055] in, and These represent the amplitudes of the echoes from the two target points. and These represent the phases of the echoes from the two targets, comprising both the target's phase and the echo delay. and These represent the phase and echo delay of the two targets, respectively, and * is the convolution operator.

[0056] It can be seen that after passing through the band-limited device, the envelope of the rectangular pulse signal becomes the convolution of rect(·) and the Sinc function sinc(·), which will cause the pulse to produce rising / falling edges.

[0057] Analysis shows that the rise / fall times of the echo pulse are mainly determined by the distance between the first zeros of the sinc(·) function, expressed as:

[0058]

[0059] This indicates that the rise / fall time of the echo pulse is inversely proportional to the device bandwidth.

[0060] For ease of representation, the convolution of rect(·) with the Sinker function sinc(·) can be approximated as a trapezoid, denoted as trap(·,T). e ), which is defined in the same way as rect(·).

[0061] The echoes from two targets passing through the band-limited device are plotted as a schematic diagram, such as... Figure 2 As shown. Figure 2In the image, parts ①-③ of the echo together form the leading edge of the echo, where ① and ③ are the rising edges of the echo, marking the arrival of the first and second target echoes; ② is the quasi-steady-state segment containing only the first target echo; part ④ is the steady-state segment of the echo; parts ⑤-⑦ of the echo together form the trailing edge of the echo, where ⑤ and ⑦ are the falling edges of the echo, marking the end of the first and second target echoes; ⑥ is the quasi-steady-state segment containing only the second target echo. It is worth noting that when the amplitude of the steady-state segment of the echo is lower than that of parts ② or ⑥, parts ③ and ⑤ of the echo will correspondingly change to falling edges and rising edges.

[0062] Considering the polarization properties of electromagnetic waves, equation (5) can be expressed as:

[0063]

[0064] in, h T and h R For the transmit and receive polarization vectors, (·) T For matrix transpose, S i Let be the polarization scattering matrix of the i-th point target. Let be the average amplitude of the target echo of target i. Let be the average phase of the target echo of target i.

[0065] Polarization is characterized using Jones vectors, and the polarization state vector is written as:

[0066]

[0067] Where (γ,φ) is the polarization phase descriptor, with γ∈[0,π / 2] being the polarization angle and φ∈[-π,π) being the phase angle. Then h T =h(γ) T ,φ T ), h R =h(γ) R ,φ R S i It can be represented as:

[0068]

[0069] in, These are the four elements of the PSM. Under monostatic radar conditions, the polarization scattering matrix is ​​reciprocal, i.e.

[0070] In step 2, using an H / V dual-polarized antenna to receive the target echo provides richer target information compared to single-channel reception. Analysis shows that if an H / V dual-polarized antenna is used... T Polarized emission signal, h RBy polarizing the receiver echo, the target echo as shown in equation (7) can be obtained. Taking the magnitude of equation (7) and squaring it, the time-domain waveform of the echo can be obtained, expressed as:

[0071]

[0072] in, g1 and g2 are the echo amplitude modulation coefficients obtained by the two targets under the current transmit and receive polarization states, respectively. The phase difference between the echoes from the two targets is, i.e.

[0073] Analysis using equation (10) shows that when the polarization scattering characteristics of the two targets are different (i.e., S1 ≠ S2), changing h T and h R The relative amplitude and phase relationship between g1 and g2 can be adjusted, thereby changing the time-domain waveform y(t) over a wide range. Since most practical antennas are H-polarized and V-polarized, when using an H / V dual-polarized antenna to receive target echoes, the echoes from the two channels can be weighted by a certain weight, which can also achieve the purpose of changing the echo time-domain waveform y(t).

[0074] In step 3, as shown in equation (10), by adjusting the relative amplitude and phase relationship of g1 and g2, when the echoes from the two targets are "equal in amplitude and out of phase", steady-state segment of the echo ( Figure 2 Part ④ in the text is canceled out, and the transient segment (including the leading edge and trailing edge) is cancelled out. Figure 2 Parts ①-③ and ⑤-⑦ in the diagram are highlighted. Analysis shows that the leading edge of the two target echoes corresponds to the echo of the first target, and the trailing edge corresponds to the echo of the second target. Both are independent target echoes, and there is no coherent superposition (or coupling) of the echoes. Therefore, the decoupling of the two target echoes is achieved, which is a prerequisite for achieving resolution.

[0075] Since the steady-state segment of the echo generally accounts for the majority of the echo, this embodiment selects the steady-state echo segments of the H and V channels corresponding to two time points and weights them as follows:

[0076]

[0077] in, It is the weighted steady-state echo average, N s H represents the number of sampling points for the selected steady-state echo. sj (t) and V sj (t) represents the echo signal at the j-th sampling point in the steady-state segment of the H and V polarization channels, respectively, and k represents the echo signal at k. w Z is the weight. sj (t) represents the echo signal at the j-th sampling point after weighting the echo in the steady-state segment.

[0078] The result of the weight calculation is denoted as Then use By weighting the entire echo, the target echo with "equal amplitude and opposite phase" can be obtained.

[0079] In step 4, after obtaining the "equal amplitude and opposite phase" target echo, the range resolution can be determined by the rise / fall time T of the pulse. e Defined as follows: as long as the distance between two targets is greater than T e The corresponding distance allows for the differentiation of two targets. The distance resolution at this point is expressed as:

[0080]

[0081] Where c is the speed of light.

[0082] Equation (12) shows that the distance resolution is inversely proportional to the device bandwidth, that is, increasing the device bandwidth can improve the distance resolution.

[0083] Without pulse compression, the target distance can be estimated by detecting the leading and trailing edges of the pulse. This is called the edge (including leading and trailing edges) threshold detector method. This method is only applicable to cases with high echo SNR.

[0084] Assuming the time delay estimate is t0 when there is no noise, and the noise entering the band-limited device is WGN (White Gaussian Noise), the error δt of the time delay estimate and the noise amplitude at t0 have the following approximate relationship based on the edge threshold detector method:

[0085]

[0086] Among them, A r Let n(t0) be the amplitude of the echo, and n(t0) be the amplitude deviation caused by noise.

[0087] When the echo SNR is high, the deviation of the time delay estimation is very small, and the mean square error of the time delay estimation is E{(δt)}. 2} can be used as the variance of the estimator's delay error, i.e.:

[0088]

[0089] Where, σ w 2 Let χ be the variance of the noise, and let SNR be the echo; Equation (14) is the mean square error bound.

[0090] Through theoretical derivation, we can obtain:

[0091]

[0092] in, Echo delay estimate when there is noise variance The target distance estimate under the same conditions The variance of the target distance can be obtained through the above equation (15).

[0093] refer to Figure 3 The distances between two targets can be estimated using the intersection points of the edge threshold detector and the echo. It's easy to see that intersection points 1 and 3 correspond to the arrival and end times of the first target's echo, respectively, with a time difference of one pulse width. Intersection points 2 and 4 correspond to the arrival and end times of the second target's echo, respectively, with a time difference of one pulse width. Therefore, the estimated distances between the two targets can be expressed as follows:

[0094]

[0095]

[0096] in, Let τ be the distance estimate between the two targets. w t is the pulse width of the transmitted signal. p1 t p2 t p3 t p4 These are the four intersection points of the edge threshold detector and the echo, t p1 With t p3 t corresponds to the arrival and end times of the first target echo, respectively. p2 With t p4 These correspond to the arrival and end times of the second target echo, respectively.

[0097] The effectiveness of the radar super-resolution method based on transient polarization response in this embodiment will be further verified and explained below with specific experimental results.

[0098] The targets selected were two basic scatterers: a right-angled dihedral and a right-angled trihedral. Each face of the scatterer was a square with side lengths of 0.3m and 0.4m, respectively. The dihedral was placed in front, followed by the trihedral, because its RCS (Radar Cross-section) is larger. The dihedral was rotated by a certain angle to ensure a difference in their polarization scattering characteristics. The experimental scenario was abstracted into a model, such as... Figure 4 As shown. Figure 4In the diagram, ① is the transmitting antenna, and ② is the receiving antenna; the transmitting and receiving antennas are separate. The transmitting antenna emits H-polarized electromagnetic waves, and the echoes are received by H- and V-polarized antennas. Measurements taken with a laser rangefinder show x0 = 0.5m, x1 = 2.7m, and x2 = 5.2m.

[0099] Experimental protocol as follows Figure 5 As shown, a single-carrier rectangular pulse with H polarization is first generated by computer simulation at a frequency of 720MHz and a pulse width of 2µs. This pulse is then radiated into free space at a frequency of 9.35GHz via an AWG (Arbitrary Waveform Generator) 5014C, an up-converter, and a dual-polarized horn antenna. The electromagnetic wave is reflected by two targets, and the echoes are simultaneously received by H and V dual-polarized horn antennas. After down-conversion, intermediate frequency conditioning, and sampling with an oscilloscope, an echo signal with an intermediate frequency of 720MHz and a sampling rate of 10GHz is obtained. Finally, echo analysis is performed.

[0100] By measuring the rise / fall time T of the target echo e The device bandwidth B can be obtained. r An approximation of T. However, note that the obtained T... e The measured value is after taking the modulus and needs to be corrected according to its edge characteristics. The corrected value is the complete rise / fall time T. e ≈17.5ns. From equation (6), we get B. r ≈114MHz, therefore ΔR′=2.625m. It should be noted that when using the threshold detector method to estimate the target distance, the maximum distance estimation error caused by the distance resolution remains within 0.5 times the distance resolution, regardless of changes in the detection threshold. Therefore, the allowable error range for target distance estimation can be expressed as:

[0101]

[0102] Where i = {1, 2}, R i Let be the true distance value of the i-th target.

[0103] By weighting the measured echo using the method provided in this embodiment, a target echo with "equal amplitude and opposite phase" can be obtained, such as... Figure 6 As shown. Figure 6 This indicates that by weighting the echoes, the steady-state segment of the echo is canceled out, while the transient segment is highlighted. This shows that the transient segment of the echo does exist, and it can be assumed that the steady-state segment of the echo contains only noise. Calculations show that the measured SNRs of the leading and trailing edges of the echo are 6.2 dB and 7.0 dB, respectively. Calculated using equation (18), under these experimental conditions, the maximum permissible error for estimating the target distance based on the leading and trailing edges of the echo is ±1.3125 m.

[0104] Figure 6 This indicates that there were two instances where the noise amplitude exceeded the detector threshold, due to the SNR of only 6-7 dB at the leading and trailing edges of the echo. Since these two noise points are located in the steady-state region of the echo, they do not actually affect the distance estimation of the two targets. Further increasing the echo SNR can effectively avoid this situation. The distance estimates of the two targets obtained from the measured data have already been obtained... Figure 6 As indicated by the data, the analysis shows that all four distance estimates are within the error tolerance range defined by equation (18). The experimental results fully demonstrate the effectiveness of this invention.

[0105] The above description is merely a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural transformations made using the contents of the present invention's specification and drawings under the inventive concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A radar super-resolution method based on transient polarization response, characterized in that, Includes the following steps: Step 1: Transmit a narrowband single-carrier frequency signal with a single polarization direction, and apply the narrowband single-carrier frequency signal to two targets with different polarization scattering characteristics; Step 2: Receive echo signals based on H and V dual-polarized antennas, wherein the echo signals are the result of coherent superposition of the echoes from two targets; Step 3 involves weighting the echo signals from the H and V polarization channels of the H and V dual-polarization antenna to synthesize equal-amplitude, out-of-phase target echoes, thereby decoupling the two target echoes. This includes: Select the steady-state echo of the H-polarization channel and the steady-state echo of the V-polarization channel corresponding to the selected time; The steady-state echo of the H-polarized channel and the steady-state echo of the V-polarized channel are weighted based on the weights to obtain the average value of the steady-state echo after weighting the steady-state echo of the H-polarized channel and the steady-state echo of the V-polarized channel. Using the weights as control parameters and minimizing the average echo value of the steady-state segment as the objective, the optimal weights are calculated. The echo signal of the entire H-polarized channel and the echo signal of the entire V-polarized channel are weighted based on the optimal weights to obtain the target echo with equal amplitude and opposite phase. Step 4: Based on the target echoes with equal amplitude and opposite phase, use the edge threshold detector method to achieve super-resolution and distance estimation of the two targets.

2. The radar super-resolution method based on transient polarization response according to claim 1, characterized in that, In step 1, both targets are point targets.

3. The radar super-resolution method based on transient polarization response according to claim 1 or 2, characterized in that, The average echo value in the steady-state segment is specifically: in, The average steady-state echo value is the weighted average of the steady-state echo values ​​from the H-polarization channel and the V-polarization channel. The number of sampling points for the selected steady-state echo. and These are the steady-state segments of the H and V polarization channels, respectively. j Echo signal at each sampling point For weights, The weighted echo after steady-state segment j Echo signals from each sampling point; Using the aforementioned weights as control parameters, minimizing the average echo value in the steady-state segment is... .

4. The radar super-resolution method based on transient polarization response according to claim 1 or 2, characterized in that, In step 4, the distance resolution between the two targets is: in, For distance resolution, c At the speed of light, The rise / fall time of the echo pulse. This refers to the device bandwidth.

5. The radar super-resolution method based on transient polarization response according to claim 1 or 2, characterized in that, In step 4, the distance between the two targets is estimated as follows: in, , These are distance estimates for the two targets. c At the speed of light, The pulse width of the transmitted signal. , , , These are the four intersection points of the edge threshold detector and the echo. and These correspond to the arrival and end times of the first target echo, respectively. and These correspond to the arrival and end times of the second target echo, respectively.

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