An FDA deblurring imaging method based on joint design of array elements and inter-array frequency offset

Abstract

The present application relates to the technical field of radar signal processing, aiming at the target positioning and imaging ambiguity caused by the distance-angle coupling of the traditional frequency diversity array beam pattern, and the problem that more array elements are needed for random frequency offset to remove ambiguity, a FDA structure based on joint design of intra-array frequency offset and inter-array frequency offset is proposed, the transmission energy is focused on the expected distance-angle area to realize distance-angle decoupling, and by increasing the number of intra-array frequency increments, the number of array elements is increased to improve the target ambiguity-free limit, the number of frequency increments is increased from N of the traditional FDA to, the order of magnitude of the ambiguity-free limit can be greatly increased, and the tolerance of the target ambiguity-free limit is greater. By optimizing the parameters of the array element and inter-array frequency offset design, the de-ambiguous imaging can be realized without complex imaging algorithm.

Description

Technical Field

[0001] This invention relates to the field of radar signal processing technology, specifically a method for unblurring imaging based on a frequency diverse array (FDA) jointly designed with array elements and inter-array frequency offset. Background Technology

[0002] Compared to traditional phased arrays, frequency diversity arrays can generate range-angle dependent beam patterns, making them highly promising for suppressing range-dependent interference and clutter, and for synthetic aperture radar imaging. However, because the range and angle of the transmitted beam pattern of a traditional frequency diversity array are both dependent and coupled, a series of range-angle combinations exist to match the echo of a single target, causing ambiguity in target localization and imaging.

[0003] One method for decoupling using linear frequency increments is double-sideband FDA, which involves transmitting positive and negative frequency increments within the array. However, this method is limited to decoupling from a single target; for multi-target imaging, it produces false targets, making it impossible to identify the true target, and still results in target localization and imaging blurring. One method for removing FDA imaging blur is randomized FDA, where the frequency increment on each element of the FDA is an independently and identically distributed random number. This can achieve both range and azimuth decoupling of the transmitted beam and removal of target imaging blur. However, using random frequency increments to solve the target blur problem cannot achieve reliable decoupling when the number of array elements is small. Summary of the Invention

[0004] This invention addresses the target localization and imaging ambiguity caused by range-angle coupling in traditional frequency diversity array beammaps. Instead of using random frequency offsets to de-ambiguate, which requires a large number of array elements, this invention proposes a FDA structure based on a joint design of intra-element and inter-element frequency offsets. This structure focuses the transmitted energy into the desired range-angle region to achieve range-angle decoupling. Furthermore, by increasing the number of intra-element frequency increments, it enables unambiguous target imaging with a smaller number of array elements.

[0005] This invention is achieved through the following technical solution:

[0006] In the FDA structure based on the joint design of array elements and inter-array frequency offset, it consists of N array elements arranged linearly with equal spacing. Each array element emits M sets of signals with different frequency offsets. The frequency offset between array elements is designed linearly or nonlinearly to focus the transmitted energy in the desired range-angle region to achieve range-angle decoupling and realize target blur removal imaging.

[0007] This invention discloses a FDA deblurring imaging method based on the joint design of array elements and inter-array frequency offset, comprising the following steps:

[0008] Step 1: Construct a frequency diversity array (FDA) based on the joint design of array elements and inter-array frequency offset. It consists of N array elements arranged linearly with equal spacing, where N is a positive integer and the spacing between array elements is d, where d is generally half the wavelength of the transmitted signal. The N array elements transmit N narrowband signals with different frequencies.

[0009] Step 2: After the modulators of N array elements modulate the N narrowband signals respectively, each array element generates M sets of signals with different frequency increments. The frequency of the m-th signal of the n-th array element is:

[0010] f mn =f0+Δf mn (1)

[0011] Where f0 is the initial carrier frequency of the array, i.e., the center frequency of the signal transmitted by the 0th element. The 0th element is set as the reference element, Δf mn Let f be the m-th frequency increment on the n-th array element, where n∈{1,2,...N, m∈{1,2,...,M}, and Δf is the frequency increment, satisfying NΔf<<f0.

[0012] The modulation signal expression s corresponding to the nth array element n (t) is:

[0013]

[0014] Step 3: The N array element transmitting antennas respectively transmit signals containing M sets of frequency increments from within these N array elements. The transmitted signals are:

[0015]

[0016] Step 4: The receiving antennas of N array elements receive the echo signal reflected back from the target;

[0017] Step 5: After the echo signals received by the receiving array elements are filtered by a filter, all signals are simultaneously weighted and summed, and the modulus is calculated to obtain the range-angle decoupled beam pattern. For a far-field target, let the distance from the first array element to the target be R0, and the angle between R0 and the perpendicular line to the array arrangement direction be θ. Then the time delay for the nth array element to receive the echo signal is:

[0018]

[0019] Where c is the propagation speed of electromagnetic waves in space, and d is the distance between each array element;

[0020] The range-angle decoupled beam pattern function is then:

[0021]

[0022] Step 6: Use the Back Projection (BP) imaging algorithm to complete the target deblurring imaging.

[0023] Compared with the prior art, the present invention has the following characteristics:

[0024] 1. When the frequency diversity array transmit beam pattern of the FDA model of this invention is a superposition of multiple "S"-shaped curves, the transmitted energy can be focused on the desired range-angle region to achieve range-angle decoupling.

[0025] 2. When imaging multiple targets using double-sideband FDA, the target position may become blurred. Existing technologies achieve deblurring imaging by improving the imaging algorithm. However, this invention achieves deblurring imaging without complex imaging algorithms by optimizing the parameters of array elements and inter-array frequency offset design.

[0026] 3. The method of the present invention improves the target ambiguity limit by increasing the number of frequency increments within the array element without increasing the number of array elements. The number of frequency increments increases from N in the traditional FDA to N×M, which can greatly increase the order of magnitude of ambiguity and has a greater tolerance for target ambiguity. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the FDA structure designed based on the joint design of array elements and inter-array frequency offset.

[0028] Figure 2 This is a simulation diagram of the range-angle decoupled beamforming of the FDA, which is based on the joint design of array elements and inter-array frequency offset.

[0029] Figure 3 The original scene diagram for the two targets.

[0030] Figure 4 A simulation image of the double-band FDA with blurred target location imaging;

[0031] Figure 5 This is a simulation diagram of the FDA's deblurring imaging of two targets designed for this invention. Detailed Implementation

[0032] The present invention will be further described below with reference to the accompanying drawings and embodiments, but this is not intended to limit the scope of the invention.

[0033] Example

[0034] FDA structures based on the joint design of array elements and inter-array frequency offsets, such as Figure 1As shown, a virtual array element is set at the corresponding position of the array and used as a reference array element. The distance and angle of the target are set relative to the reference array element. The interval between array elements is N, where N is generally 1 / 2 wavelength of the transmitted signal. Each array element transmits M groups of signals with different frequency offsets.

[0035] The frequency of the m-th signal emitted by the nth element is f0 + Δf mn Where f0 is the initial carrier frequency of the array, i.e., the center frequency of the signal transmitted by the 0th element. The 0th element is set as the reference element, Δf mn It is the m-th frequency increment on the n-th array element, where n∈{1,2,...,N} and m∈{1,2,...,M}. Δf is the frequency increment and must satisfy NΔf<<f0. It consists of N array elements arranged linearly with equal spacing, where N is a positive integer.

[0036] A FDA deblurring imaging method based on the joint design of array elements and inter-array frequency offset includes the following steps: Step 1, constructing a frequency diversity array based on the joint design of array elements and inter-array frequency offset, consisting of N array elements arranged linearly with equal spacing, where N is a positive integer, the spacing between array elements is d, where d is generally 1 / 2 wavelength of the transmitted signal, and the N array elements transmit N narrowband signals with different frequencies.

[0037] Step 2: After the modulators of N array elements modulate the N narrowband signals respectively, each array element generates M sets of signals with different frequency increments. The frequency of the m-th signal of the n-th array element is:

[0038] f mn =f0+Δf mn (1)

[0039] Where f0 is the initial carrier frequency of the array, i.e., the center frequency of the signal transmitted by the 0th element. The 0th element is set as the reference element, Δf mn It is the m-th frequency increment on the n-th array element. m∈{1,2,...,M}, Δf is the frequency increment, and it must satisfy NΔf<<f0.

[0040] The modulation signal expression s corresponding to the nth array element n (t) is:

[0041]

[0042] Step 3: The N array element transmitting antennas respectively transmit signals containing M sets of frequency increments from within these N array elements. The transmitted signals are:

[0043]

[0044] Step 4: The receiving antennas of N array elements receive the echo signal reflected back from the target;

[0045] Step 5: After the echo signals received by the receiving array elements are filtered by a filter, all signals are simultaneously weighted and summed, and the modulus is calculated to obtain the range-angle decoupled beam pattern. For a far-field target, let the distance from the first array element to the target be R0, and the angle between R0 and the perpendicular line to the array arrangement direction be θ. Then the time delay for the nth array element to receive the echo signal is:

[0046]

[0047] Where c is the speed of electromagnetic wave propagation in space, and d is the distance between each array element.

[0048] The range-angle decoupled beam pattern function is then:

[0049]

[0050] Step 6: Use the Back Projection (BP) imaging algorithm to complete the target deblurring imaging.

[0051] Simulation Experiment

[0052] Simulation diagram of FDA range-angle decoupled beamforming based on joint design of array elements and inter-array frequency offset, as shown below. Figure 2 As shown, the simulation parameters are: N = 18, f0 = 10G, Δf = 300K, d = λ0 / 2. In the experiment, the element frequency offset and inter-array frequency offset of the embodiment are designed to have a linear relationship, that is, the element frequency offset Δf n = n·Δf, inter-array frequency offset Δf m =m·Δf, then Δf mn =n·m·Δf, where the maximum amplitude in the figure is the intersection of multiple curves. The beam is focused on the bright spot, achieving distance-angle decoupling, which allows the distance and angle of the target to be determined.

[0053] Figure 3 The original scene for imaging two targets is located at (-10°, 2000m) and (10°, 2000m). The range (R) of the imaging scene is (1970m~2030m), and the angle (θ) of the imaging scene is (-30°~30°).

[0054] Figure 4 The method for imaging two targets directly using linear increments of positive and negative frequencies for double-sideband FDA (Factor-Oriented Detector) can image the targets, but it produces two false targets, resulting in blurred targets and making it impossible to determine the true target's location. In contrast, the FDA designed using the method of this invention... Figure 5As shown, multiple different frequency offsets are emitted within the array to directly image two targets, avoiding the generation of false targets and achieving de-blurring imaging.

Claims

1. A FDA-based deblurring imaging method based on the joint design of array elements and inter-array frequency offset, comprising the following steps: Step 1: Construct a frequency diversity array (FDA) based on the joint design of array elements and inter-array frequency offset. It consists of N array elements arranged linearly with equal spacing, where N is a positive integer and the spacing between array elements is d, where d is generally half the wavelength of the transmitted signal. The N array elements transmit N narrowband signals with different frequencies. Step 2: After the modulators of N array elements modulate the N narrowband signals respectively, each array element generates M sets of signals with different frequency increments. The frequency of the m-th signal of the n-th array element is: f mn =f0+Δf mn (1) in, f0 is the initial carrier frequency of the array, i.e., the center frequency of the signal transmitted by the 0th element. The 0th element is set as the reference element. Δf mn Let f be the m-th frequency increment on the n-th array element, where n∈{1,2,...,N} and m∈{1,2,...,M}, and Δf is the frequency increment, satisfying NΔf<<f0. The modulation signal expression s corresponding to the nth array element n (t) is: Step 3: The N array element transmitting antennas respectively transmit signals containing M sets of frequency increments from within these N array elements. The transmitted signals are: Step 4: The receiving antennas of N array elements receive the echo signal reflected back from the target; Step 5: After the echo signals received by the receiving array elements are filtered by a filter, all signals are simultaneously weighted and summed, and the modulus is calculated to obtain the range-angle decoupled beam pattern. For a far-field target, let the distance from the first array element to the target be R0, and the angle between R0 and the perpendicular line to the array arrangement direction be θ. Then the time delay for the nth array element to receive the echo signal is: Where c is the propagation speed of electromagnetic waves in space, and d is the distance between each array element; The range-angle decoupled beam pattern function is then: Step 6: Use the back projection imaging algorithm to complete the target deblurring imaging.

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