A method for frequency diversity-phased array MIMO radar to combat main lobe interference

Abstract

The present invention discloses a method for resisting mainlobe interference in a frequency-diversity phased array MIMO radar, comprising: transmitting orthogonal signals with carrier frequency differences; wherein the equivalent phase reference centers of the K orthogonal signals transmitted by each array element are different; obtaining echo signals received by each array element; performing digital mixing and matched filtering on the echo signal received by the lth array element to obtain a baseband signal of the echo signal of the ith orthogonal signal; determining the covariance matrix of the echo signals received by each array element; and performing robust beamforming on the baseband signals of the echo signals of each orthogonal signal based on the covariance matrix, the steering vector of the echo signal, and a preset uncertainty set of the steering vectors to determine adaptive weight vectors for the N array elements. The present invention creates a certain carrier frequency difference between the orthogonal signals and uses adaptive beamforming based on diagonal loading to suppress deceptive interference, thereby resolving the problems of phased array MIMO radars being unable to resist mainlobe interference and directly resolve range ambiguity.

Description

Technical Field

[0001] The invention belongs to the technical field of radars, and in particular relates to a method for frequency diversity-phased array MIMO radar to resist main lobe interference. Background Art

[0002] MIMO (Multiple Input Multiple Output) radar offers advantages over traditional phased array radar, such as greater degrees of freedom. However, as the array scales, the radar system becomes more complex in terms of waveform design and signal processing. Therefore, many applications combine phased array radar and MIMO technology, resulting in what is known as "phased array MIMO radar." Compared to phased array radar, phased array MIMO radar has a wider transmission pattern, which improves search efficiency. Compared to MIMO radars that transmit orthogonal waveforms, phased array MIMO radars can effectively avoid transmission energy dispersion and reduce signal-to-noise ratio loss.

[0003] However, with the increase in detection targets and the expansion of detection range, phased array MIMO radar faces serious mainlobe interference problems. Therefore, those skilled in the art urgently need to propose a method for phased array MIMO radar to resist mainlobe interference. Summary of the Invention

[0004] In order to solve the above problems existing in the prior art, the present invention provides a frequency diversity-phased array MIMO radar detection method. The technical problem to be solved by the present invention is achieved through the following technical solutions:

[0005] The present invention provides a method for resisting mainlobe interference of a frequency diversity-phased array MIMO radar, which is characterized by being applied to a frequency diversity-phased array MIMO radar, wherein the radar includes N evenly arranged array elements;

[0006] The method for resisting main lobe interference includes:

[0007] Transmitting orthogonal signals with carrier frequency differences; wherein the equivalent phase reference centers of the K orthogonal signals transmitted by each array element are different;

[0008] Obtaining the echo signal received by each array element;

[0009] Perform digital mixing and matched filtering on the echo signal received by the lth array element to obtain the baseband signal of the echo signal of the ith orthogonal signal; where l = 1, 2, ..., N, and i = 1, 2, ..., K;

[0010] Determine the covariance matrix of the echo signal received by each array element;

[0011] Robust beamforming is performed on the baseband signals of the echo signals of each orthogonal signal according to the covariance matrix, the steering vector of the echo signal, and a preset uncertainty set of the steering vector, to determine adaptive weight vectors of N array elements.

[0012] In one embodiment of the present invention, the echo signal received by the lth array element is:

[0013]

[0014] Where, represents the echo signal of the i-th orthogonal signal received by the l-th array element;

[0015]

[0016] Where ξ represents the reflection coefficient of the target, rect{·} represents the pulse function of the transmission signal of the array element, the transmission signal includes K orthogonal signals, t represents the time series, t∈(0,T r ), T r represents the pulse repetition period, T P Indicates the pulse width of the transmitted signal, τ i,l represents the time delay from the time when the lth array element transmits the ith orthogonal signal to the time when it receives the echo signal of the ith orthogonal signal, f i represents the carrier frequency of the i-th orthogonal signal, w i Represents the preset weight corresponding to the i-th orthogonal signal, φ i represents the i-th orthogonal signal, θ represents the angle of the target relative to the radar, a i (θ) represents the steering vector of the i-th orthogonal signal at angle θ, (·) H represents the conjugate transpose.

[0017] In one embodiment of the present invention, the transmit signal of the lth array element is:

[0018]

[0019] Among them, the preset weight matrix w 1l 、w 2l 、…w Kl They represent the preset weights of the 1st, 2nd, ..., Kth orthogonal waveforms transmitted by array element l, Φ1, Φ2, ...Φ K (t) represents the envelope of the 1st, 2nd…Kth orthogonal signals.

[0020] In one embodiment of the present invention, the baseband signal of the echo signal of the i-th orthogonal signal is:

[0021]

[0022] Where * represents convolution, (·) * represents conjugate, Φi represents the envelope of the i-th orthogonal signal, The baseband signal of the echo signal of the i-th orthogonal signal received by the l-th array element.

[0023] In one embodiment of the present invention, robust beamforming is performed on the baseband signals of the echo signals of each orthogonal signal according to the following formula:

[0024]

[0025] stw' H [v(r,θ)+e]≥1

[0026] Where, Represents the covariance matrix of the echo signal received by each array element, r represents the distance between the target and the radar, v(r,θ) represents the steering vector of the target at distance r and angle θ, e represents a preset uncertainty set of the steering vector, and w' represents the adaptive weight vector of N array elements.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] The present invention provides a method for resisting mainlobe interference in a frequency diversity phased array MIMO radar. By ensuring waveform coherence between array elements and transmitting a group of orthogonal signals from the same array element, the carrier frequencies of the orthogonal signals are made to differ to a certain extent. Furthermore, the present invention employs adaptive beamforming based on diagonal loading to suppress deceptive interference, thereby resolving the problem that phased array MIMO radar cannot directly resolve range ambiguity. Compared with existing frequency diversity array parameter estimation methods, the present invention can focus energy on the region of interest, thereby improving the signal-to-noise ratio.

[0029] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a flow chart of a method for frequency diversity-phased array MIMO radar main lobe interference resistance provided by an embodiment of the present invention;

[0031] Figure 2 This is a schematic diagram of a method for frequency diversity-phased array MIMO radar to combat main lobe interference provided by an embodiment of the present invention;

[0032] Figure 3 is a capon estimation diagram of a phased array MIMO radar provided by an embodiment of the present invention;

[0033] Figure 4This is a phased array MIMO time domain pulse pressure diagram provided by an embodiment of the present invention;

[0034] Figure 5 is a spectrum estimation diagram of a frequency diversity-phased array MIMO radar provided by an embodiment of the present invention;

[0035] Figure 6 This is a spectrum estimation diagram after interference suppression of the frequency diversity-phased array MIMO radar provided by an embodiment of the present invention;

[0036] Figure 7 This is a time domain pulse pressure diagram for five orthogonal signals provided by an embodiment of the present invention;

[0037] Figure 8 This is a diagram showing the time-domain pulse compression results of frequency diversity MIMO provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0038] The present invention will be further described in detail below with reference to specific examples, but the embodiments of the present invention are not limited thereto.

[0039] Figure 1 This is a flow chart of a method for frequency diversity-phased array MIMO radar main lobe interference resistance provided by an embodiment of the present invention. Figure 2 This is a schematic diagram of a method for frequency diversity-phased array MIMO radar to resist main lobe interference provided by an embodiment of the present invention. Figure 1-2 The embodiment of the present invention provides a method for resisting mainlobe interference of a frequency diversity-phased array MIMO radar, which is applied to a frequency diversity-phased array MIMO radar, wherein the radar includes N evenly arranged array elements;

[0040] The above-mentioned method for combating main lobe interference includes:

[0041] S1. Transmit orthogonal signals with different carrier frequencies; wherein the equivalent phase reference centers of the K orthogonal signals transmitted by each array element are different;

[0042] S2. Obtain the echo signal received by each array element;

[0043] S3. Perform digital mixing and matched filtering on the echo signals of the K orthogonal signals received by the lth array element to obtain a baseband signal of the echo signal of the ith orthogonal signal; where l = 1, 2, ..., N, and i = 1, 2, ..., K;

[0044] S4. Determine the covariance matrix of the echo signal received by each array element;

[0045] S5. Perform robust beamforming on the baseband signals of the echo signals of each orthogonal signal according to the covariance matrix, the steering vector of the echo signal, and a preset uncertainty set of the steering vector, and determine adaptive weight vectors of N array elements.

[0046] Specifically, the frequency diversity-phased array MIMO radar consists of N evenly spaced elements, with the spacing between two adjacent elements being half a wavelength, and each element transmitting K orthogonal signals:

[0047] Φ(t)=[Φ1(t)exp(j2πf1t),Φ2(t)exp(j2πf2t),…,Φ K (t)exp(j2πf K t)] T

[0048] Among them, Φ1, Φ2, ...Φ K (t) represent the envelopes of the 1st, 2nd…Kth orthogonal signals, f1, f2,…, f K They represent the carrier frequencies of the 1st, 2nd…Kth orthogonal signals respectively, t represents the time series, and the K orthogonal signals transmitted by each array element constitute the transmitted signal of the array element.

[0049] The transmitted signal of the lth array element can be expressed as:

[0050]

[0051] Where t∈(0,T r ), T r represents the pulse repetition period, T P Indicates the pulse width of the transmitted signal and the preset weight matrix w1,…,w K Respectively represent the preset weights corresponding to the i-th orthogonal signal, w 1l 、w 2l 、...w Kl They represent the preset weights of the 1st, 2nd, ..., Kth orthogonal waveforms transmitted by the array element l, rect{·} represents the pulse function of the transmitted signal of the array element, T P Indicates the pulse width of the transmitted signal, f i represents the carrier frequency of the i-th orthogonal signal, Φ i represents the envelope of the i-th orthogonal signal.

[0052] It can be seen that the transmitted signal of N array elements is expressed as:

[0053]

[0054] In the above-mentioned method for frequency diversity-phased array MIMO radar to combat mainlobe interference, the echo signal received by the lth array element can be expressed as:

[0055]

[0056] Where, τ i,lrepresents the time delay from the time when the lth array element transmits the ith orthogonal signal to the time when it receives the echo signal of the ith orthogonal signal, R represents the distance between the first array element and the target, d represents the array element spacing, ξ represents the reflection coefficient of the target, (·) H represents the conjugate transpose, c represents the speed of light, and θ is Figure 2 The angle of the target shown relative to the radar, a i (θ) represents the steering vector of the i-th orthogonal signal at angle θ. Furthermore, a1(θ)=[1exp(j2πf1dsin(θ))…exp(j2πf1(N-1)dsin(θ))] T , a2(θ)=[exp(-j2πf2dsin(θ))1…exp(j2πf2(N-2)dsin(θ))] T ,…,a K (θ)=[exp(-j2πf K (K-1)dsin(θ))…1…exp(j2πf K (NK)dsin(θ))] T .

[0057] Obviously, the echo signal received by the lth array element can be further expressed as:

[0058]

[0059] Where, represents the echo signal of the i-th orthogonal signal received by the l-th array element;

[0060]

[0061] Among them, φ i represents the i-th orthogonal signal, and θ represents the angle of the target relative to the radar.

[0062] In the above step S2, the echo signal y of the K orthogonal signals received by the lth array element is l (t) Perform digital mixing and matched filtering:

[0063]

[0064] Where * represents convolution, (·) * represents conjugation, The baseband signal of the echo signal of the i-th orthogonal signal received by the l-th array element, ρ i represents the amplitude of the i-th orthogonal signal in the echo, β i (t-τ i,l ) represents the main lobe response of the i-th orthogonal signal in the echo after matched filtering.

[0065] Taking the lth array element as an example, its corresponding echo signal can be expressed as follows after digital mixing and matched filtering:

[0066]

[0067] Since it is a narrowband far-field signal, so:

[0068] ρ1=ρ2=…=ρ K =ρ,β1(t-τ 1,l )=β2(t-τ 2,l )=…=β K (t-τ K,l )=β

[0069] therefore Will After substituting, we can get the following formula:

[0070]

[0071] In Δf i,1 When <<f1, Therefore

[0072]

[0073] Optionally, in step S4 above, robust beamforming is performed on the baseband signals of the echo signals of each orthogonal signal according to the following formula:

[0074]

[0075] stw' H [v(r,θ)+e]≥1

[0076] Where, Represents the covariance matrix of the echo signal received by each array element, represents the conjugate of a1(θ), r represents the distance between the target and the radar, v(r,θ) represents the steering vector of the target at distance r and angle θ, e represents the preset uncertainty set of the steering vector, and w' represents the adaptive weight vector of N array elements.

[0077] The above frequency diversity-phased array MIMO radar detection method is further illustrated below through simulation.

[0078] Simulation experiment 1: The array structure used is as follows Figure 2 As shown, the distance between the target and array element 1 is R = 40km, the target angle θ = 30°, the interference distance RJ = 50km, and the target angle θ J =30°,f0=10GHz,fi =10GHz+(i-1)700kHz, i=0...N, N=10, element spacing d=0.015m, pulse repetition period PRF=5kHz, number of snapshots is 200, maximum unambiguous range is 30km, signal-to-noise ratio SNR=5dB, interference-to-noise ratio is 40dB, and range resolution is 10m.

[0079] Figure 3 is a capon estimation diagram of a phased array MIMO radar provided by an embodiment of the present invention, Figure 4 This is a time domain pulse pressure diagram of the phased array MIMO provided by an embodiment of the present invention, such as Figure 3-4 As shown, interference suppression is obviously not possible. Figure 5 is a spectrum estimation diagram of a frequency diversity-phased array MIMO radar provided by an embodiment of the present invention, Figure 6 This is a spectrum estimation diagram of the frequency diversity-phased array MIMO radar after interference suppression provided by an embodiment of the present invention. Figure 5-6 ,Obviously, the frequency diversity - phased array MIMO radar can effectively suppress the ,mainlobe interference. Secondly, due to the introduction of frequency ,diversity, the frequency diversity - phased array MIMO radar can directly resolve the ,range ambiguity, so the spectrum estimation graph also contains the ,range information.

[0080] Simulation experiment 2: The array structure used is as follows Figure 2 As shown, f0 = 11 GHz, f i =11GHz+(i-1)500kHz, i=0...N, N=10, pulse repetition period PRF=5kHz, after down-conversion, channel separation, and matched filtering, the echo received by each array element is beamformed. Figure 7 is a time domain pulse pressure diagram of five orthogonal signals provided by an embodiment of the present invention, Figure 8 FIG is a time domain pulse compression result diagram of frequency diversity MIMO provided by an embodiment of the present invention, such as Figure 7-8 As shown, the frequency diversity-phased array MIMO radar detection method provided by the present invention has a higher signal-to-noise ratio.

[0081] It can be seen from the above embodiments that the beneficial effects of the present invention are:

[0082] The present invention provides a method for resisting mainlobe interference in a frequency diversity phased array MIMO radar. By ensuring waveform coherence between array elements and transmitting a group of orthogonal signals from the same array element, the carrier frequencies of the orthogonal signals are made to differ to a certain extent. Furthermore, the present invention employs adaptive beamforming based on diagonal loading to suppress deceptive interference, thereby resolving the problem that phased array MIMO radar cannot directly resolve range ambiguity. Compared with existing frequency diversity array parameter estimation methods, the present invention can focus energy on the region of interest, thereby improving the signal-to-noise ratio.

[0083] In the description of the present invention, the terms "first" and "second" are used for descriptive purposes only and should not be understood to indicate or imply relative importance or implicitly specify the number of the technical features indicated. Therefore, a feature specified as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, "plurality" means two or more, unless otherwise specifically defined.

[0084] In the description of this specification, the reference terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" mean that the specific features, structures, materials, or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in any appropriate manner in any one or more embodiments or examples. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification.

[0085] Although the present application is described herein in conjunction with various embodiments, in the process of implementing the claimed application, those skilled in the art can understand and implement other changes to the disclosed embodiments by reviewing the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other components or steps, and "a" or "an" does not exclude multiple situations. A single processor or other unit can implement several functions listed in the claims. Certain measures are recorded in different dependent claims, but this does not mean that these measures cannot be combined to produce good results.

[0086] The above is a further detailed description of the present invention in conjunction with specific preferred embodiments, and the specific implementation of the present invention should not be considered to be limited to these descriptions. For those skilled in the art of the present invention, without departing from the concept of the present invention, several simple deductions or substitutions can be made, which should be considered to fall within the scope of protection of the present invention.

Claims

1. A method for frequency diversity-phased array MIMO radar to combat main lobe interference, characterized in that: Applied to a frequency diversity-phased array MIMO radar, the radar comprising N evenly arranged array elements; The method for resisting main lobe interference includes: Transmitting orthogonal signals with carrier frequency differences; wherein the equivalent phase reference centers of the K orthogonal signals transmitted by each array element are different; Obtaining the echo signal received by each array element; Perform digital mixing and matched filtering on the echo signal received by the lth array element to obtain the baseband signal of the echo signal of the ith orthogonal signal; where l = 1, 2, ..., N, and i = 1, 2, ..., K; Determine the covariance matrix of the echo signal received by each array element; performing robust beamforming on baseband signals of the echo signals of each orthogonal signal according to the covariance matrix, the steering vector of the echo signal, and a preset uncertainty set of the steering vector, to determine adaptive weight vectors of N array elements; The echo signal received by the lth array element is: Where, represents the echo signal of the i-th orthogonal signal received by the l-th array element; Where ξ represents the reflection coefficient of the target, rect{·} represents the pulse function of the transmission signal of the array element, the transmission signal includes K orthogonal signals, t represents the time series, t∈(0,T r ), T r represents the pulse repetition period, T P Indicates the pulse width of the transmitted signal, τ i,l represents the time delay from the time when the lth array element transmits the ith orthogonal signal to the time when it receives the echo signal of the ith orthogonal signal, f i represents the carrier frequency of the i-th orthogonal signal, w i Represents the preset weight corresponding to the i-th orthogonal signal, φ i represents the i-th orthogonal signal, θ represents the angle of the target relative to the radar, a i (θ) represents the steering vector of the i-th orthogonal signal at angle θ, (·) H represents the conjugate transpose.

2. The method for frequency diversity-phased array MIMO radar anti-mainlobe interference according to claim 1, characterized in that: The transmitted signal of the lth array element is: Among them, the preset weight matrix w 1l 、w 2l 、...w Kl They represent the preset weights of the 1st, 2nd, ..., Kth orthogonal waveforms transmitted by array element l, Φ1(t), Φ2(t), ...Φ K (t) represents the envelope of the 1st, 2nd…Kth orthogonal signals.

3. The method for frequency diversity-phased array MIMO radar anti-mainlobe interference according to claim 2, characterized in that: The baseband signal of the echo signal of the i-th orthogonal signal is: Where * represents convolution, (·) * represents conjugation, Φ i represents the envelope of the i-th orthogonal signal, The baseband signal of the echo signal of the i-th orthogonal signal received by the l-th array element.

4. The method for frequency diversity-phased array MIMO radar main lobe interference resistance according to claim 3, characterized in that: Robust beamforming is performed on the baseband signals of the echo signals of each orthogonal signal according to the following formula: s.t.w' H [v(r,θ)+e]≥1 Where, Represents the covariance matrix of the echo signal received by each array element, r represents the distance between the target and the radar, v(r,θ) represents the steering vector of the target at distance r and angle θ, e represents a preset uncertainty set of the steering vector, and w' represents the adaptive weight vector of N array elements.

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