A broadband LFM signal array beamforming method and system

Abstract

The invention discloses a broadband LFM signal array beamforming method and system thereof, belonging to the technical field of radar signal processing. The method comprises: antenna array elements of M channels receive radar echoes and receive the same mixing signal sent from the same digital frequency synthesizer; digitally mix the radar echo and the mixing signal of the first channel, filter out high-frequency components, and perform AD sampling on the mixing signal as a reference signal; digitally mix the mixing signal and the radar echo of the mth channel, perform low-pass filtering, and perform AD sampling to obtain a sampled signal m; input a mixing compensation signal into the mth channel, perform secondary digital mixing on the sampled signal m and the mixing compensation signal to obtain a secondary mixing signal m; apply a delay signal to each secondary mixing signal m to perform delay compensation, so that the output signal of the mth channel is equal to the reference signal; and accumulate the output signals of the M channels to obtain a de-skewed array beam.

Description

Technical Field

[0001] The present invention belongs to radar signal processing technology, and in particular relates to a broadband LFM signal array beamforming method and system thereof. Background Art

[0002] Phased array radars use broadband LFM signals to achieve high-resolution range profiles of targets. When performing wide-angle scanning of the observed target, the distances between the array elements of the phased array's M channels and the observed target vary due to the proportional relationship between the antenna array's physical size (i.e., aperture) and wavelength. This difference causes deviations in the time it takes for the signal to reach each element, a phenomenon known as the aperture transit effect (aperture transit time refers to the time it takes for a signal to propagate from one element in the array to the adjacent element). When the radar signal bandwidth is wide, this time delay causes signals of different frequency components to experience different phase changes, thereby distorting the signal's spectrum and causing "spatial dispersion." This means that beams of different frequency components point in different directions, affecting the beam's focusing and directional performance, and thus, the accurate acquisition of a high-resolution range profile of the observed target. Summary of the Invention

[0003] In response to the above-mentioned deficiencies in the prior art, the present invention provides a broadband LFM signal array beamforming method and system, which solves the problem that when the bandwidth of existing radar signals is wide, the signal spectrum is distorted, resulting in poor beam focusing and directionality.

[0004] In order to achieve the above-mentioned object of the invention, the technical solution adopted by the present invention is:

[0005] In a first aspect, a broadband LFM signal array beamforming method is provided, comprising the steps of:

[0006] S1. The antenna array elements of the M channels of the phased array radar receive radar echoes of the broadband LFM radar transmission signal reflected by the observation target, and receive the same mixed signal sent from the same digital frequency synthesizer;

[0007] S2. Digitally mix the radar echo of the first channel and the mixed signal and filter out high-frequency components to obtain a mixed signal. Then, perform AD sampling on the mixed signal as a reference signal.

[0008] S3. Digitally mix the mixed signal of the mth channel and the radar echo and perform low-pass filtering to obtain a first-order mixed signal m, and then perform AD sampling to obtain a sampled signal m, 2≤m≤M;

[0009] S4, based on the reference signal, input the mixing compensation signal to the mth channel, perform secondary digital mixing on the sampling signal m and the mixing compensation signal to obtain a secondary mixing signal m,

[0010] S5. Apply a delay signal to each secondary mixing signal m to perform delay compensation, so that the output signal of the mth channel is equal to the reference signal;

[0011] S6. Accumulate the output signals of the M channels to obtain a de-skewed array beam.

[0012] Furthermore, the expression of the radar echo is:

[0013]

[0014] Among them, x1(t) is the radar echo received by the first channel; x m (t) is the radar echo received by the mth channel; f0 is the signal carrier frequency; t is time; t0 is the echo delay; μ is the frequency modulation slope; T is the pulse width; τ is the signal delay; rect(.) is the rectangular function;

[0015] The expression of the mixing signal is:

[0016]

[0017] Among them, s ref1 (t) is the mixing signal; t r is the time delay calculated based on the estimated distance of the phased array radar to the observed target.

[0018] Furthermore, the expression of the mixing signal of the first channel is:

[0019]

[0020] Where z1(t) is the mixing signal of the first channel; f1 and ψ1 are the signal frequency and phase of the first channel respectively;

[0021] The expression of the reference signal is:

[0022]

[0023] Where x1(n) is the digital reference signal; j is the complex number n=1,2,3…is the time variable after digital sampling; T s is the sampling period.

[0024] Furthermore, the expression of the first-level mixing signal m is:

[0025]

[0026] f′ m =μ(t r -t0)-μ(m-1)τ=f1-μ(m-1)τ

[0027]

[0028] Among them, z m (t) is the first-order mixing signal m; f′ m and ψ′ m are the signal frequency and phase of the mth channel after one mixing.

[0029] Furthermore, the expression of the mixing compensation signal input to the mth channel is:

[0030]

[0031] Among them, s′ refm (t) is the mixing compensation signal input to the mth channel; e is the natural logarithm; j is the complex number

[0032] The expression of the secondary mixing signal m is:

[0033]

[0034] f m =f1,ψ m =ψ1-2πμ(t r -t0)(m-1)τ

[0035] Where x′ m (n) is the secondary mixing signal m; f m and ψ m are the signal frequency and phase of the mth channel after secondary mixing; n=1, 2, 3... are the time variables after digital sampling; T s is the sampling period.

[0036] Furthermore, the expressions for calculating the echo delay and signal delay are:

[0037]

[0038] Where θ is the incident angle of the radar echo; d is the equivalent spacing between two adjacent channels; λ is the wavelength; R is the estimated distance of the phased array radar to the observed target; and c is the speed of light.

[0039] Furthermore, the first to M channels are digitally mixed at the analog video end according to the mixing signal; and the second to M channels are digitally mixed twice at the digital processing end.

[0040] In a second aspect, a broadband LFM signal array beamforming system is provided, comprising:

[0041] A digital frequency synthesizer is used to send the same mixed frequency signal to the antenna array elements of M channels of the phased array radar;

[0042] The first channel includes an antenna array element for receiving a radar echo of a broadband LFM radar transmission signal reflected by an observation target, a first mixer for digitally mixing the received radar echo and a mixing signal, a filter for filtering out high-frequency components in the mixing signal to obtain the mixing signal, and an AD sampler for performing AD sampling on the filtered mixing signal as a reference signal;

[0043] Channels 2 to 3 include antenna array elements for receiving radar echoes of broadband LFM radar transmission signals reflected by an observation target, a first mixer for digitally mixing a mixing signal and the radar echo, a filter for removing a low-pass filter from the mixing signal to obtain a first-order mixing signal m, an AD sampler for performing AD sampling on the filtered first-order mixing signal m to obtain a sampled signal m, a second mixer for receiving a mixing compensation signal input based on a reference signal and performing secondary digital mixing on the sampled signal m and the mixing compensation signal to obtain a second-order mixing signal m, and a delay compensation filter for applying a delay signal to the second-order mixing signal m for delay compensation so that its output signal is equal to the reference signal;

[0044] The beamformer is used to accumulate the output signals of the M channels to obtain a de-skewed array beam.

[0045] The beneficial effects of the present invention are as follows: in the array beamforming method, this solution performs mixing based on the same mixing signal from the same DDS device; then, a secondary mixing method is used to make the frequency of each channel consistent; finally, delay compensation is used to make each channel output a signal with the same frequency and phase. This solution combines beams by means of two mixing steps, which can effectively remove the influence of different time delays on LFM waves caused by different path differences in different channels, so that the radar receiving beams are all correctly pointed and are not affected by the aperture transition effect within the sub-array, and the de-skewing effect is good.

[0046] In addition, when performing mixing, this solution performs the first mixing based on the same mixing signal from the same DDS device, and the second mixing is digital mixing, which is processed in the digital segment. No additional chips are required, only a few lines of code are needed. That is, this solution uses one component to generate mixing signals for multiple channels, which can solve the problems of high design and power consumption costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 Flowchart of the broadband LFM signal array beamforming method.

[0048] Figure 2The schematic diagram of the broadband LFM signal array beamforming system is shown in Figure 2.

[0049] Figure 3 is the array pattern when the elevation angle is 0°.

[0050] Figure 4 It is the array pattern when the elevation angle is 5°.

[0051] Figure 5 is the array pattern when the elevation angle is 10°.

[0052] Figure 6 The beam patterns obtained by this method are at different azimuth and elevation angles. DETAILED DESCRIPTION

[0053] The specific embodiments of the present invention are described below to facilitate understanding of the present invention by those skilled in the art. However, it should be clear that the present invention is not limited to the scope of the specific embodiments. For those skilled in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the appended claims, these changes are obvious, and all inventions and creations utilizing the concepts of the present invention are protected.

[0054] refer to Figure 1 , Figure 1 FIG. 4 shows a flow chart of a broadband LFM signal array beamforming method; FIG. Figure 1 As shown, the method S includes steps S1 to S6.

[0055] In step S1, antenna array elements of M channels of the phased array radar receive radar echoes of broadband LFM radar transmission signals reflected by an observation target, and receive the same mixed signal sent from the same digital frequency synthesizer;

[0056] During implementation, the optimal radar echo expression of this scheme is:

[0057]

[0058] Among them, x1(t) is the radar echo received by the first channel; x m (t) is the radar echo received by the mth channel; f0 is the signal carrier frequency; t is time; t0 is the echo delay; μ is the frequency modulation slope; T is the pulse width; τ is the signal delay; rect(.) is the rectangular window function;

[0059] The expression of the mixing signal is:

[0060]

[0061] Among them, s ref1 (t) is the mixing signal; tr is the time delay calculated based on the estimated distance of the phased array radar to the observed target.

[0062] In step S2, the radar echo of the first channel and the mixed signal are digitally mixed and the high-frequency components are filtered out to obtain a mixed signal, which is then AD sampled as a reference signal;

[0063] During implementation, the preferred expression of the mixing signal of the first channel of this solution is:

[0064]

[0065] Where z1(t) is the mixing signal of the first channel; f1 and ψ1 are the signal frequency and phase of the first channel respectively;

[0066] The expression of the reference signal is:

[0067]

[0068] Where x1(n) is the digital reference signal; j is the complex number n=1,2,3…is the time variable after digital sampling; T s is the sampling period.

[0069] In step S3, the mixed signal of the mth channel and the radar echo are digitally mixed and low-pass filtered to obtain a first-order mixed signal m, which is then AD sampled to obtain a sampled signal m, 2≤m≤M;

[0070] The expression of the first-order mixing signal m is:

[0071]

[0072] f′ m =μ(t r -t0)-μ(m-1)τ=f1-μ(m-1)τ

[0073]

[0074] Among them, z m (t) is the first-order mixing signal m; f′ m and ψ′ m are the signal frequency and phase of the mth channel after one mixing.

[0075] In step S4, the reference signal is used as a reference, and a mixing compensation signal is input to the mth channel. The sampling signal m is digitally mixed with the mixing compensation signal twice to obtain a secondary mixing signal m.

[0076] The expression of the mixing compensation signal input to the mth channel is:

[0077]

[0078] Among them, s′ refm (t) is the mixing compensation signal input to the mth channel; e is the natural logarithm; j is the complex number

[0079] The expression of the secondary mixing signal m is:

[0080]

[0081] f m =f1,ψ m =ψ1-2πμ(t r -t0)(m-1)τ

[0082] Where x′ m (n) is the secondary mixing signal m; f m and ψ m are the signal frequency and phase of the mth channel after secondary mixing; n=1, 2, 3... are the time variables after digital sampling; T s is the sampling period.

[0083] In step S5, a delay signal is applied to each secondary mixing signal m to perform delay compensation, so that the output signal of the mth channel is equal to the reference signal, that is, x m (n) = x1(n).

[0084] In step S6, the output signals of the M channels are accumulated to obtain a de-skewed array beam.

[0085] The expressions for calculating echo delay and signal delay are:

[0086]

[0087] Where θ is the incident angle of the radar echo; d is the equivalent spacing between two adjacent channels; λ is the wavelength; R is the estimated distance of the phased array radar to the observed target; and c is the speed of light.

[0088] In this solution, the 1st to Mth channels are digitally mixed at the analog video end according to the mixing signal; the 2nd to Mth channels are digitally mixed twice at the digital processing end.

[0089] like Figure 2 As shown, the present solution also provides a broadband LFM signal array beamforming system, which includes:

[0090] A digital frequency synthesizer is used to send the same mixed frequency signal to the antenna array elements of M channels of the phased array radar;

[0091] The first channel includes an antenna array element for receiving a radar echo of a broadband LFM radar transmission signal reflected by an observation target, a first mixer for digitally mixing the received radar echo and a mixing signal, a filter for filtering out high-frequency components in the mixing signal to obtain the mixing signal, and an AD sampler for performing AD sampling on the filtered mixing signal as a reference signal;

[0092] Channels 2 to 3 include antenna array elements for receiving radar echoes of broadband LFM radar transmission signals reflected by an observation target, a first mixer for digitally mixing a mixing signal and the radar echo, a filter for removing a low-pass filter from the mixing signal to obtain a first-order mixing signal m, an AD sampler for performing AD sampling on the filtered first-order mixing signal m to obtain a sampled signal m, a second mixer for receiving a mixing compensation signal input based on a reference signal and performing secondary digital mixing on the sampled signal m and the mixing compensation signal to obtain a second-order mixing signal m, and a delay compensation filter for applying a delay signal to the second-order mixing signal m for delay compensation so that its output signal is equal to the reference signal;

[0093] The beamformer is used to accumulate the output signals of the M channels to obtain a de-skewed array beam.

[0094] The following is a simulation to illustrate the de-skewing effect of the broadband LFM signal array beamforming method of this scheme:

[0095] The simulation conditions are set as: f0 = 10GHz, bandwidth B = 1GHz, number of array elements M = 64, and the radar system is simulated at different elevation angles (0°, 5°, 10°) at a fixed azimuth angle. Figure 3-Figure 5 As shown, the horizontal axis is the elevation angle at different angles, and the vertical axis is the normalized direction diagram, which reflects the distribution of the signal at different elevation angles.

[0096] by Figure 3 For example, the signal is strong in the direction of 0° elevation angle and extremely weak in other directions, and the radar receiving beam is accurately pointed. Figure 4 、 Figure 5 Similarly, due to the aperture transition effect, without frequency mixing, the radar receive beam will have deviations in its pointing direction, which is more pronounced at large angles. However, this method, through frequency mixing and other processing, ensures that the radar receive beam is correctly pointed, unaffected by the aperture transition effect within the subarray, and achieves excellent de-skewing effects.

[0097] exist Figure 6, which shows the beam patterns obtained by the method of this scheme at different azimuth and elevation angles, with the horizontal coordinates being the azimuth and elevation angles respectively; the black box in the figure corresponds to an azimuth angle of 20° and an elevation angle of 5°. From this point, it can be seen that even at a larger angle (20°), no obvious aperture crossing effect is found, indicating that the beamforming method of this scheme can obtain an accurate radiation pattern of the radar system.

Claims

1. A broadband LFM signal array beamforming method, characterized in that: Including steps: S1. The antenna array elements of the M channels of the phased array radar receive radar echoes of the broadband LFM radar transmission signal reflected by the observation target, and receive the same mixed signal sent from the same digital frequency synthesizer; S2. Digitally mix the radar echo of the first channel and the mixed signal and filter out high-frequency components to obtain a mixed signal. Then, perform AD sampling on the mixed signal as a reference signal. S3. Digitally mix the mixed signal of the mth channel and the radar echo and perform low-pass filtering to obtain a first-order mixed signal m, and then perform AD sampling to obtain a sampled signal m, 2≤m≤M; S4, using the reference signal as a reference, inputting a mixing compensation signal into the mth channel, performing a secondary digital mixing on the sampled signal m and the mixing compensation signal to obtain a secondary mixing signal m; S5. Apply a delay signal to each secondary mixing signal m to perform delay compensation, so that the output signal of the mth channel is equal to the reference signal; S6. Accumulate the output signals of the M channels to obtain a de-skewed array beam.

2. The broadband LFM signal array beamforming method according to claim 1, wherein: The expression of the radar echo is: Among them, x1(t) is the radar echo received by the first channel; x m (t) is the radar echo received by the mth channel; f0 is the signal carrier frequency; t is time; t0 is the echo delay; μ is the frequency modulation slope; T is the pulse width; τ is the signal delay; rect(.) is the rectangular window function; The expression of the mixing signal is: Among them, S ref1 (t) is the mixing signal; t r is the time delay calculated based on the estimated distance of the phased array radar to the observed target.

3. The broadband LFM signal array beamforming method according to claim 2, wherein: The expression of the mixed signal of the first channel is: Where z1(t) is the mixing signal of the first channel; f1 and ψ1 are the signal frequency and phase of the first channel respectively; The expression of the reference signal is: Where x1(n) is the digital reference signal; j is the complex number n=1,2,3…is the time variable after digital sampling; T s is the sampling period.

4. The broadband LFM signal array beamforming method according to claim 2, wherein: The expression of the first-order mixing signal m is: f′ m =μ(t r -t0)-μ(m-1)τ=f1-μ(m-1)τ Among them, z m (t) is the first-order mixing signal m; f′ m and ψ′ m are the signal frequency and phase of the mth channel after one mixing.

5. The broadband LFM signal array beamforming method according to claim 4, characterized in that: The expression of the mixing compensation signal input to the mth channel is: Among them, s′ refm (t) is the mixing compensation signal input to the mth channel; e is the natural logarithm; j is the complex number The expression of the secondary mixing signal m is: f m =f1,ψ m =Ψ1-2pm(t r -t0)(m-1)τ Among them, x' m (n) is the secondary mixing signal m; f m and ψ m are the signal frequency and phase of the mth channel after secondary mixing; n=1, 2, 3... are the time variables after digital sampling; T s is the sampling period.

6. The broadband LFM signal array beamforming method according to any one of claims 2 to 5, characterized in that: The expressions for calculating echo delay and signal delay are: Where θ is the incident angle of the radar echo; d is the equivalent spacing between two adjacent channels; λ is the wavelength; R is the estimated distance of the phased array radar to the observed target; and c is the speed of light.

7. The broadband LFM signal array beamforming method according to any one of claims 2 to 5, characterized in that: The first to M channels are digitally mixed at the analog video end according to the mixing signal; the second to M channels are digitally mixed twice at the digital processing end.

8. A broadband LFM signal array beamforming system, characterized in that: include: A digital frequency synthesizer is used to send the same mixed frequency signal to the antenna array elements of M channels of the phased array radar; The first channel includes an antenna array element for receiving a radar echo of a broadband LFM radar transmission signal reflected by an observation target, a first mixer for digitally mixing the received radar echo and a mixing signal, a filter for filtering out high-frequency components in the mixing signal to obtain the mixing signal, and an AD sampler for performing AD sampling on the filtered mixing signal as a reference signal; Channels 2 to 3 include antenna array elements for receiving radar echoes of broadband LFM radar transmission signals reflected by an observation target, a first mixer for digitally mixing a mixing signal and the radar echo, a filter for removing a low-pass filter from the mixing signal to obtain a first-order mixing signal m, an AD sampler for performing AD sampling on the filtered first-order mixing signal m to obtain a sampled signal m, a second mixer for receiving a mixing compensation signal input based on a reference signal and performing secondary digital mixing on the sampled signal m and the mixing compensation signal to obtain a second-order mixing signal m, and a delay compensation filter for applying a delay signal to the second-order mixing signal m for delay compensation so that its output signal is equal to the reference signal; The beamformer is used to accumulate the output signals of the M channels to obtain a de-skewed array beam.

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