An array beamforming-based interferometric passive microwave imaging system and method

Abstract

The present application relates to the field of passive microwave millimeter wave imaging detection, and particularly relates to an interferometric passive microwave imaging system and method based on array beam forming, wherein the array beam forming comprises phased array beam forming and digital beam forming, and the data after array beam forming will be used to complete imaging detection by the interferometric passive microwave imaging method. A plurality of antenna units form a phased subarray, and the phased array beams formed by all the phased subarrays are directed in the same direction. A plurality of phased subarrays form a digital subarray, and the digital subarray generates digital beams within the phased array beam pointing range. A plurality of digital subarrays form an interference array, each digital subarray acts as a unit to participate in the interferometric correlation operation of the interference array, and the interference array completes the interferometric passive microwave imaging within the digital beam range.

Description

Technical Field

[0001] This invention relates to the field of microwave passive imaging detection, and in particular to an interferometric passive microwave imaging system and method based on array beamforming. Background Technology

[0002] Beamforming technology based on antenna arrays is a common method in antenna design. Depending on the beamforming method, it can be divided into phased array beamforming based on analog phase shifter networks and digital beamforming based on digital phase shifters. Phased array beamforming uses analog phase shifters to shift the signal of each element, and then sums all the signals in the phased array to form a sum beam. Digital beamforming samples the signal of each element to form a digital signal, and then uses digital phase shifters and digital adders to form a digital sum beam signal. (Reference: H. Steyskal. Digital Beamforming Antennas: An Introduction[J]. Microw. Journal, vol.30, pp.107-110, Jan.1986.)

[0003] Interferometric passive microwave imaging is a commonly used imaging and detection method in radio astronomy and satellite remote sensing. This technique utilizes multiple synchronously receiving units to form an interferometric array. Each receiving unit participates in pairwise correlation operations within the interferometric array as an interferometric unit, achieving effective coverage observation in the spatial frequency domain. Then, spatial imaging detection is completed through image inversion based on the inverse Fourier operator. (See Reference 1: Han Donghao, “Research on Rotating Circular Array Synthetic Aperture Microwave Radiometer System” [D]. University of Chinese Academy of Sciences, 2012.)

[0004] The advantages of interferometric passive microwave imaging technology are its high aperture sparsity ratio, meaning that high spatial resolution can be achieved with a relatively small number of antenna elements through optimized array design. The disadvantages are low observation sensitivity and high computational complexity in interferometric operations. Antenna array-based beamforming technology offers the advantage of forming flexible, multi-beam orientation without sacrificing sensitivity, but suffers from a large number of antenna elements and a low aperture sparsity ratio. Among these, phased array beamforming has a simple structure but its beamforming effect is fixed and difficult to adjust, while digital beamforming has a complex structure but allows for flexible variation in the number and shape of the formed beams. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of low sensitivity and complex calculation in interferometric passive microwave imaging technology, and the shortcomings of large number of antenna elements and low aperture sparsity ratio in array beamforming technology. An interferometric passive microwave imaging system and method based on array beamforming is proposed.

[0006] This invention proposes an interferometric passive microwave imaging system based on array beamforming.

[0007] The system includes an interferometric array, which includes P digital subarrays, each of which includes N phased subarrays; each phased subarray includes M antenna elements.

[0008] The N phased array subarrays form phased array beams pointing in the same direction through a phased array beamforming method; each digital subarray generates a digital beam within the pointing range of the phased array beam, and each digital subarray participates in the interferometric correlation operation of the interferometric array as an interferometric unit, completing interferometric passive microwave imaging within the range of the digital beam.

[0009] As an improvement to the above technical solution, each of the phased subarrays forms a phased array beam using a phased array beamforming method; the system forms a total of P×N phased array beams, and the P×N phased array beams point in the same direction.

[0010] The system completes the scanning of the entire observation area by configuring phased array beamforming parameters and controlling the direction of the phased array beams.

[0011] As an improvement to the above technical solution, each of the digital subarrays generates Q digital beams using a digital array beamforming method; the P digital subarrays form P×Q digital beams; the P×Q digital beams are divided into Q groups, each group containing P digital beams, and the P digital beams in each group come from the P digital subarrays respectively, and the beam directions of the P digital beams within the group are the same; the Q groups of digital beams have a total of Q digital beam directions, and all digital beam directions are within the phased array beam range;

[0012] The system controls the digital beam pointing to scan within the phased array beam region by configuring digital subarray beamforming parameters, thereby suppressing field-of-view aliasing in interferometric passive microwave imaging.

[0013] As an improvement to the above technical solution, the interferometric array performs interferometric correlation operations within each group of the Q-group digital beams. The interferometric correlation operations of each group complete the interferometric passive microwave imaging within the pointing range of that group of digital beams; the Q-group interferometric passive microwave imaging constitutes a complete interferometric passive microwave imaging.

[0014] As one of the improvements to the above technical solution, the antenna elements in the phased subarray and the phased subarray in the digital subarray are arranged in an equally spaced array.

[0015] As an improvement to the above technical solution, the arrangement principle of the P digital subarrays included in the interference array is to achieve effective coverage of the spatial frequency domain; the effective coverage of the spatial frequency domain specifically includes:

[0016] Take the array centers of P number subarrays, and let the coordinate set be A = {(x p / λ,y p / λ)|1≤p≤P}, where p is the p-th numerical subarray, (x p ,y p ) represents the center coordinates of the p-th digital subarray, and λ represents the observation wavelength;

[0017] The spacing d between horizontally adjacent digital subarrays i ,satisfy Where, d u =(x p -x p-1 ) / λ;x p x p-1 θ represents the x-coordinates of the p-th and (p-1)-th horizontally adjacent numerical subarrays, respectively; x The lateral field of view for interferometric passive microwave imaging;

[0018] The spacing d between vertically adjacent digital subarrays v ,satisfy Where d v =(y p -y p-1 ) / λ;y p y p-1 θ represents the ordinates of the p-th and (p-1)-th vertically adjacent numerical subarrays, respectively. y The longitudinal field of view for interferometric passive microwave imaging.

[0019] This invention also proposes an interferometric passive microwave imaging method based on array beamforming, implemented based on one of the above-described systems, the method comprising:

[0020] Multiple antenna elements are arranged to form a phased subarray, then multiple phased subarrays are arranged to form a digital subarray, and finally multiple digital subarrays are arranged to form an interferometric array. The phased subarrays are then used to form a phased array beam using phased array beamforming to complete the scanning of the overall observation area. The digital subarrays are then used to form a digital beam using digital beamforming to scan within the phased array beam area, suppressing field-of-view aliasing in interferometric passive microwave imaging. Finally, interferometric correlation operations are performed within the interferometric array to complete the interferometric passive microwave imaging.

[0021] As an improvement to the above technical solution, the method includes the following steps:

[0022] First, P×N phased array beams are formed using a phased array beamforming method, with the P×N phased array beams pointing in the same direction; and by configuring the phased array beamforming parameters, the direction of the phased array beams is controlled to complete the scanning of the entire observation area.

[0023] Then, P × Q digital beams are formed using P digital subarrays through a digital array beamforming method. The P × Q digital beams are divided into Q groups, each group containing P digital beams from the P digital subarrays, and the beam directions of the P digital beams in each group are the same. The Q groups of digital beams have a total of Q digital beam directions. All digital beam directions are located within the phased array beam range. By configuring the digital subarray beamforming parameters, the digital beam directions are controlled to scan within the phased array beam region, suppressing field-of-view aliasing in interferometric passive microwave imaging.

[0024] Finally, interferometric correlation operations are performed within each group of the Q-group digital beams of the interferometric array. Each digital subarray participates in the interferometric correlation operation of each group as an interferometric unit. The interferometric correlation operation of each group completes the interferometric passive microwave imaging within the pointing range of that group of digital beams. The Q-group interferometric passive microwave imaging constitutes a complete interferometric passive microwave imaging.

[0025] This invention implements an interferometric passive microwave imaging system based on array beamforming. Array beamforming includes phased array beamforming and digital beamforming. The data from the array beamforming is then used for imaging detection using an interferometric passive microwave imaging method. Multiple antenna elements constitute a phased array subarray, with all phased array subarrays generating phased array beams that point in the same direction. Multiple phased array subarrays also constitute a digital subarray, generating digital beams within the pointing range of the phased array beams. Multiple digital subarrays form an interferometric array, with each digital subarray participating as a unit in the interferometric correlation calculations of the interferometric array. The interferometric array completes interferometric passive microwave imaging within the digital beam range. The advantages of this system are: reduced antenna element count, increased aperture sparsity ratio, improved detection sensitivity, and reduced complexity of interferometric correlation calculations. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of an interferometric passive microwave imaging system based on array beamforming according to the present invention.

[0027] Figure 2 This is a schematic diagram of the beamforming result of the phased subarray;

[0028] Figure 3 This is a schematic diagram of the beamforming results of the first group of digital subarrays;

[0029] Figure 4 This is a schematic diagram of the beamforming results of the second group of digital subarrays;

[0030] Figure 5 This is a schematic diagram of the results of interferometric passive microwave dual-point source imaging based on array beamforming.

[0031] Attached Figure Labels

[0032] 1. Antenna element; 2. Phased array; 3. Digital subarray; 4. Interferometer array Detailed Implementation

[0033] The technical solutions provided by the present invention are further illustrated below with reference to embodiments. The description of exemplary embodiments is merely for illustrative purposes and is by no means a limitation on the present invention or its application or use.

[0034] This invention relates to the field of passive microwave and millimeter-wave imaging detection, and particularly to an interferometric passive microwave imaging system based on array beamforming. The array beamforming includes phased array beamforming and digital beamforming. The data from the array beamforming is then used to perform imaging detection using an interferometric passive microwave imaging method. Multiple antenna elements constitute a phased array subarray, with all phased array subarrays pointing in the same direction. Multiple phased array subarrays also constitute a digital subarray, which generates a digital beam within the pointing range of the phased array beam. Multiple digital subarrays form an interferometric array, with each digital subarray participating as a unit in the interferometric correlation calculations of the interferometric array. The interferometric array performs interferometric passive microwave imaging within the digital beam range.

[0035] Example 1

[0036] like Figure 1 The diagram shown is a schematic representation of the interferometric passive microwave imaging system based on array beamforming, according to Embodiment 1 of the present invention. Antenna elements are arranged at equal intervals to form a phased subarray, and the phased subarrays are arranged at equal intervals to form a digital subarray. (It should be noted that the arrangement of antenna elements and phased subarrays is not limited to equal intervals. In fact, those skilled in the art can choose other arrangement rules according to the actual situation or target settings, thereby achieving the design of antenna elements → phased subarray → digital subarray → interferometric subarray.)

[0037] Specifically, this invention proposes an interferometric passive microwave imaging system based on array beamforming. The system includes: a phased array 2 composed of M antenna elements 1, with all phased array subarrays 2 forming phased array beams pointing in the same direction; a digital subarray 3 composed of N phased array subarrays 2, with the digital subarray 3 generating digital beams within the pointing range of the phased array beams; and an interferometric array 4 composed of P digital subarrays 3, with each digital subarray 3 participating as an interferometric unit in the interferometric correlation operation of the interferometric array 4. The interferometric array 4 completes interferometric passive microwave imaging within the range of the digital beams.

[0038] The interferometric array 4 comprises P×N phased array subarrays 2. P represents the number of digital subarrays 3 in the interferometric array, and N represents the number of phased array subarrays 2 within a single digital subarray 3. Each phased array subarray 2 forms a phased array beam, and the P×N phased array beams point in the same direction. The beam pointing can be configured by adjusting the phase shift parameters of the phased array subarrays to scan the entire observation area.

[0039] The interferometric array 4 comprises P digital subarrays 3, each forming Q digital beams. These P × Q digital beams can be divided into Q groups, each group containing P digital beams originating from the P digital subarrays 3, with all P beams within a group pointing in the same direction. The Q groups of digital beams have a total of Q beam directions, all of which are located within the phased array beam area. The digital beam direction can be configured by adjusting the digital phase-shifting parameters of the digital subarrays 3 to scan the phased array beam region.

[0040] The interferometric array 4 comprises Q groups of digital beams formed by P digital beam subarrays. Interferometric correlation operations are performed within each of the Q groups of digital beams, with each digital beam subarray participating in the interferometric correlation operation as an interferometric unit. The interferometric correlation operation of each group completes interferometric passive microwave imaging within the pointing range of that group of digital beams.

[0041] The interferometric array 4, comprising P digital beam subarrays, can achieve effective coverage of the spatial frequency domain: Taking the array center of the P digital beam subarrays, the coordinate set is A = {(x...} p / λ,y p / λ)|1≤p≤P}, where (x p ,y p Let λ be the center coordinates of the p-th digital beam subarray, and λ be the observation wavelength. The spacing d between horizontally adjacent digital beam subarrays... u =(x p -x p-1 ) / λ, have Where x p x p-1 θ represents the x-coordinate of the horizontally adjacent digital beam subarrays. x The lateral field of view for interferometric passive microwave imaging is denoted by d. The longitudinal spacing d between adjacent digital beam subarrays is also denoted by d. v =(y p -y p-1 ) / λ, have Where y p y p-1 θ represents the ordinate of the vertically adjacent digital beam subarrays. y The longitudinal field of view for interferometric passive microwave imaging.

[0042] Example 2

[0043] This invention proposes an interferometric passive microwave imaging method based on array beamforming, implemented using the aforementioned system. The method includes the following steps:

[0044] First, P×N phased array subarrays 2 are used to form P×N phased array beams using a phased array beamforming method. The P×N phased array beams point in the same direction. Then, by configuring the phased array beamforming parameters, the direction of the phased array beams is controlled to complete the scanning of the entire observation area.

[0045] Then, P × Q digital beams are formed using P digital subarrays 3 through a digital array beamforming method. The P × Q digital beams are divided into Q groups, each group containing P digital beams from the P digital subarrays 3 respectively, and the beam directions of the P digital beams in each group are the same; the Q groups of digital beams have a total of Q digital beam directions; all digital beam directions are located within the phased array beam range; and by configuring the digital subarray beamforming parameters, the digital beam directions are controlled to scan within the phased array beam region, suppressing the field-of-view aliasing of interferometric passive microwave imaging;

[0046] Finally, interferometric correlation operations are performed within each group of the Q-group digital beams of the interferometric array 4. Each digital subarray participates in the interferometric correlation operation of each group as an interferometric unit. The interferometric correlation operation of each group completes the interferometric passive microwave imaging within the pointing range of the digital beams of that group. The Q-group interferometric passive microwave imaging constitutes a complete interferometric passive microwave imaging.

[0047] The embodiments shown in this invention are illustrated with reference to... Figure 1 The diagram illustrates an array design schematic of an interferometric passive microwave imaging system based on array beamforming. In this embodiment, the antenna element 1 has a spacing of λ / 2, where λ is the detection wavelength. A phased array 2 is composed of M = 4 antenna elements 1, with all phased array subarrays 2 forming a consistent phased array beam. A digital subarray 3 is composed of N = 16 phased array subarrays 2, generating a digital beam within the phased array beam pointing range. An interferometric array 4 is composed of P = 7 digital subarrays 3, with each digital subarray 3 acting as an interferometric unit participating in the interferometric correlation operation of the interferometric array 4. The interferometric array 4 completes interferometric passive microwave imaging within the digital beam range. This embodiment uses a T-shaped interferometric array with a rectangular spatial frequency coverage area and an angular resolution of 6.75°. Compared to traditional imaging techniques, it achieves higher spatial resolution with fewer antennas and improves the aperture sparsity ratio.

[0048] In this embodiment, the interferometric array 4 comprises P×N = 112 phased array subarrays 2. Each phased array subarray 2 contains M = 4 antenna elements 1, and each antenna element 1 serves as a unit of a phased array subarray 2. The phased array subarrays 2 form a phased array beam using a phased array beamforming method. The 112 phased array beams point in the same direction. The beam pointing can be configured by adjusting the phased array beamforming parameters to scan the entire observation area. When the phased array beamforming parameters are configured to point towards the center of the observation area, the phased array beamforming result is as follows: Figure 2 As shown in the figure, the coordinates (ζ, η) are the direction cosine coordinates of the array beam of the phased subarray, and the Z-axis is the antenna gain.

[0049] In this embodiment, the interferometric array 4 comprises P = 7 digital subarrays 3. Each digital subarray 3 contains N = 1 phased array subarrays 2, and each phased array subarray 2, as a unit of a digital subarray 3, forms Q = 2 digital beams using a digital array beamforming method. The P × Q = 14 digital beams can be divided into Q = 2 groups, each group containing P = 7 digital beams, originating from the 7 digital subarrays 3 respectively, and the beam pointing of the 7 digital beams within each group is the same. The 2 groups of digital beams have a total of 2 digital beam pointing directions, all of which are located within the phased array beam range. The digital beam pointing can be configured by setting digital beamforming parameters to scan the phased array beam region. When the first group of digital beamforming parameters is configured to point towards the center of the observation area, the beamforming result of the first group of digital subarrays is as follows. Figure 3 As shown. When the second group of digital beamforming parameters is configured to point at (30°, 30°), the beamforming result of the second group of digital subarrays is as follows. Figure 4 As shown. Figure 3 , 4 The coordinates (ζ, η) represent the direction cosine coordinates of the array beam of the digital subarray, and the Z-axis represents the antenna gain. The array beam uses the digital subarray as the basic interferometric unit, and with a relatively large number of 448 antenna elements, there are still only 7 interferometric elements, which reduces the complexity of the system's interferometric correlation calculations.

[0050] In this embodiment, the interferometric array 4 comprises P=7 digital subarrays 3 forming Q=2 groups of digital beams. Interferometric correlation operations are performed within each group, with each digital subarray 3 participating as an interferometric unit in the interferometric correlation operation of each group. A total of 2 groups of interferometric correlation operations are completed, and the interferometric correlation operation of each group completes interferometric passive microwave imaging within the pointing range of that group of digital beams.

[0051] In this embodiment, the interferometric array comprises P=7 digital subarrays arranged in a T-shape, with the horizontal spacing d between adjacent digital beam subarrays. u =4λ, the lateral field of view θ of interferometric passive microwave imaging x =7°, there is The spacing d between adjacent digital beam subarrays in the longitudinal direction v =4λ, longitudinal field of view θ of interferometric passive microwave imaging y =7°, there is Assuming the imaging target is a dual-point source scene located at the center of the field of view and at an azimuth of (30°, 30°), the interferometric passive microwave imaging result based on array beamforming is as follows: Figure 5 As shown in the figure, the coordinates (ζ, η) represent the direction cosine coordinates of the brightness temperature target. The values ​​in the legend represent the brightness temperature intensity. The brightness temperature intensity value retrieved from the dual point sources is affected not only by the brightness temperature intensity of the point sources themselves but also by the phased array beam and the digital beam pointing. Under the limited resolution of this embodiment, the point source azimuth detection is relatively accurate, and the brightness temperature intensity is reasonable. In this embodiment, multiple beams generated by the digital subarray are used to simultaneously image two point source targets distributed at the center of the field of view in space and at an azimuth of (30°, 30°). Compared with existing interferometric imaging techniques, this invention can convert the target into an image by adjusting the array beamforming parameters and simultaneously image the key areas of interest in the spatial domain with relatively low interferometric computational complexity, thus improving detection sensitivity.

[0052] As can be seen from the above detailed description of the present invention, the system of the present invention reduces the number of antenna elements and improves the detection sensitivity, and the method of the present invention reduces the complexity of interferometric correlation calculations.

[0053] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to the embodiments, those skilled in the art should understand that modifications or equivalent substitutions to the technical solutions of the present invention do not depart from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. An array beamforming-based interferometric passive microwave imaging system, characterized in that, the system comprises an interference array (4), the interference array (4) comprising P digital subarrays (3), each of the digital subarrays (3) comprising N phased subarrays (2); each of the phased subarrays (2) comprising M antenna units (1); wherein the interference array (4) is T-shaped; the N phased subarrays (2) form phased array beams pointing in the same direction through phased array beamforming; each digital subarray (3) generates digital beams within the phased array beam pointing range, and at the same time each digital subarray (3) participates in the interferometric correlation operation of the interference array (4) as a unit to complete interferometric passive microwave imaging within the digital beam range; each of the digital subarrays (3) generates Q digital beams through digital array beamforming; the P digital subarrays (3) form P×Q digital beams; the P×Q digital beams are divided into Q groups, each group containing P digital beams, and the P digital beams in each group come from the P digital subarrays (3) respectively, and the P digital beams in each group have the same beam pointing direction; the Q groups of digital beams have Q digital beam pointing directions, and all the digital beam pointing directions are located within the phased array beam range; the system controls the digital beam pointing direction to scan within the phased array beam range by configuring digital subarray beamforming parameters to suppress the field of view aliasing of interferometric passive microwave imaging.

2. The array beamforming based interferometric passive microwave imaging system of claim 1, wherein, Each of the phased subarrays (2) forms a phased array beam through phased array beamforming; the system forms P×N phased array beams, and the P×N phased array beams have the same pointing direction; the system controls the phased array beam pointing direction to complete the scanning of the overall observation area by configuring phased array beamforming parameters.

3. The array beamforming based interferometric passive microwave imaging system of claim 1, wherein, The interference array (4) performs interferometric correlation operation in each group of the Q groups of digital beams, and the interferometric correlation operation of each group completes the interferometric passive microwave imaging within the digital beam pointing range of the group; the Q groups of interferometric passive microwave imaging constitute complete interferometric passive microwave imaging.

4. The array beamforming based interferometric passive microwave imaging system according to one of claims 1 to 3, characterized in that The arrangement of the antenna units (1) in the phased subarrays (2) and the phased subarrays (2) in the digital subarrays (3) is an equidistant array arrangement.

5. The array beamforming based interferometric passive microwave imaging system according to one of claims 1 to 3, characterized in that The arrangement principle of the P digital subarrays (3) included in the interference array (4) is to complete effective coverage of the spatial frequency domain; the effective coverage of the spatial frequency domain specifically includes: Take the array center of P digital sub-arrays (3), the coordinate set is A = {(x p ,y p / λ)|1≤p≤P}, wherein, p is the pth digital sub-array (3), (x p ,y p ) is the array center coordinate of the pth digital sub-array (3), and λ is an observation wavelength; The distance d of the transversely adjacent digital subarrays (3) u satisfies where d u = (x p -x p-1 ) / λ; x p , x p-1 are the abscissas of the pth and (p-1)th transversely adjacent digital subarrays (3) respectively; θ x is the horizontal field of view of the interferometric passive microwave imaging. The distance d of the longitudinal adjacent digital sub-arrays (3) v satisfies where d v = (y p - y p-1 ) / λ; y p , y p-1 are the longitudinal coordinates of the pth and (p-1)th longitudinal adjacent digital sub-arrays (3), respectively, and θ y is the longitudinal field of view angle of the interferometric passive microwave imaging.

6. An array beamforming-based interferometric passive microwave imaging method, implemented based on the system of any one of claims 1-5, the method comprising: The multiple antenna units (1) are arranged to form phased subarrays (2), the multiple phased subarrays (2) are arranged to form digital subarrays (3), and the multiple digital subarrays (3) are arranged to form an interference array (4); the phased subarrays (2) are used to form phased array beams by the phased array beam forming method to complete the scanning of the overall observation area; the digital subarrays (3) are used to form digital beams by the digital beam forming method to complete the scanning in the phased array beam area to suppress the field of view aliasing of the interferometric passive microwave imaging; and finally, the interferometric correlation operation is performed in the interference array (4) to complete the interferometric passive microwave imaging.

7. The array beamforming based interferometric passive microwave imaging method of claim 6, characterized in that, The method comprises the following steps: First, P×N phased subarrays (2) are used to form P×N phased array beams by the phased array beam forming method, the P×N phased array beams are directed in the same direction, and the phased array beam direction is controlled by configuring the phased subarray beam forming parameters to complete the scanning of the overall observation area; Then, P digital subarrays (3) are used to form P×Q digital beams by the digital array beam forming method, the P×Q digital beams are divided into Q groups, each group contains P digital beams from the P digital subarrays (3), and the beam directions of the P digital beams in each group are the same; the Q groups of digital beams refer to the Q digital beam directions; all the digital beam directions are located in the phased array beam range; the digital beam directions are controlled by configuring the digital subarray beam forming parameters to complete the scanning in the phased array beam area to suppress the field of view aliasing of the interferometric passive microwave imaging; Finally, the interferometric correlation operation is performed in each group of the Q groups of digital beams of the interference array (4), each digital subarray participates in the interferometric correlation operation of each group as an interference unit, and the interferometric correlation operation of each group completes the interferometric passive microwave imaging in the beam direction range of the group; the Q groups of interferometric passive microwave imaging constitute the complete interferometric passive microwave imaging.

Images