Large-spacing sparse phased array antenna based on low-profile Maxwell fisheye lens

Abstract

This invention discloses a large-pitch sparse phased array antenna based on a low-profile Maxwell fisheye lens, belonging to the field of microwave antenna technology. The phased array antenna consists of periodically arranged lens antenna elements, each including a Maxwell fisheye lens, a metal cavity, and five microstrip patch antennas. The Maxwell fisheye lens has a cylindrical structure, composed of several concentric nested layers of circular lenses with gradually increasing radii from top to bottom. The phased array antenna of this invention achieves a sparsity of 72.4%, enabling ±43° scanning, with a sidelobe level less than -7.4dB. Compared to a full-array antenna with half-wavelength arrangement of the same aperture, it significantly reduces the cost of the phased array system, with a gain loss of less than 2dB and a zero-degree gain higher than that of a full-array antenna, thus reducing system cost while maintaining the radiation characteristics of the array antenna.

Description

Technical Field

[0001] This invention belongs to the field of microwave antenna technology, specifically relating to a sparse phased array antenna based on large-spacing grating lobe suppression using a Maxwell fisheye lens. Background Technology

[0002] With the iterative updates of modern communication technologies, phased array antenna technology, due to its electronically scanned characteristics, is widely used in various communication systems, such as radars and base stations. However, the high cost of phased array systems increases the overall cost of radar systems, with T / R components accounting for 60% to 80% of the total cost. Therefore, reducing the number of T / R components while maintaining radiation characteristics is one of the current hot research directions for low-cost phased arrays. However, reducing the number of T / R components by increasing the spacing can lead to problems such as grating lobe formation and array antenna gain loss. Therefore, researching large-spacing, low-cost, sparse phased array antenna technology that maintains good radiation characteristics is particularly important.

[0003] Patent document CN113851833A (application number CN202111220999.7) discloses a grating lobe suppression wide-angle scanning phased array antenna based on pattern reconfigurable subarray technology. This antenna consists of several periodically arranged subarrays with an element spacing of 1λ in the y-direction and 0.5λ in the x-direction. By aligning the subarray patterns with the array factor patterns at null points, it achieves ±50° scanning in the xoz plane and ±30° scanning in the yoz plane within the frequency band, suppressing grating lobes to below -8.6dB. This eliminates grating lobes caused by large-pitch arrays. However, this method leads to gain loss in the array antenna, and the scanning angle is limited in the large-pitch direction. Furthermore, the multi-layer structure and complex feed network design of the subarrays also affect the antenna fabrication difficulty and operational stability.

[0004] Patent document CN112803174A (application number CN202110104425.7) discloses a large-pitch phased array based on a null-scanning antenna and a grating lobe suppression method. This antenna is also composed of a multi-layer structure with an element spacing of 0.8λ. It uses a null alignment method to suppress grating lobes caused by the large-pitch arrangement, achieving ±55° scanning. However, this multi-layer structure is complex, difficult to manufacture, and has limited operational stability. Furthermore, the element spacing is only increased to 0.8λ, and the number of T / R components can only be reduced to a limited extent, thus failing to significantly reduce the cost of the phased array antenna system.

[0005] Patent document CN111985145A (application number CN201910423768.2) discloses a method for suppressing grating lobes in a large-pitch phased array antenna. This method uses a genetic optimization algorithm to optimize the position information of the antenna elements, achieving grating lobe suppression below -8dB. However, this method makes the design of the back-end RF circuitry, T / R components, and power divider circuit of the phased array antenna system extremely complex, increasing the overall complexity of the antenna system design and making it unsuitable for practical industrial production.

[0006] Patent document CN114678688A (application number CN202210418800.X) discloses a novel low-cost phased array feeding network composed of multiple single-layer C-BFNs, ultimately achieving a 56% reduction in phase shifters. However, this method suffers from significant energy loss, and the scanning angle is limited by the element spacing. When the element spacing is not less than 0.5λ, the antenna scanning angle will be less than 30°.

[0007] Patent document CN114421178A (application number CN202210336470.X) discloses a Luneburg lens phased array antenna, which uses Luneburg lenses for beam deflection. By switching different feed sources, beam deflection at different angles can be achieved. This method can improve gain and extend the scanning angle, but the scanning accuracy is limited. In addition, the Luneburg lens has a high profile, and sometimes the antenna array needs to be designed in an arc shape and fed close to the edge of the lens, which poses a certain obstacle to practical industrial applications.

[0008] The two main problems currently encountered with large-pitch antenna arrays are: 1. grating lobe suppression and 2. gain loss. Therefore, research on low-cost phased array antennas should pay attention to the following points: 1. Suppressing grating lobes caused by large-pitch arrays; 2. Reducing gain loss and maintaining basic stability of radiation characteristics; 3. The antenna structure should be as simple as possible to ensure the stability of the antenna during operation. Summary of the Invention

[0009] This invention addresses the shortcomings mentioned in the above technical background by proposing a large-spacing sparse phased array antenna based on a low-profile Maxwell fisheye lens.

[0010] The technical solution adopted in this invention is as follows:

[0011] A large-spacing sparse phased array antenna based on a low-profile Maxwell fisheye lens, the phased array antenna being composed of M×N (M and N are arbitrary positive integers) periodically arranged lens antenna elements, characterized in that the center distance between the lens antenna elements is (>1λ), where λ is the free space wavelength corresponding to the operating center frequency.

[0012] The lens antenna unit includes a low-profile Maxwell fisheye lens, a metal cavity, and five microstrip patch antennas.

[0013] The low-profile Maxwell fisheye lens has a cylindrical structure, consisting of K layers of concentric nested circular lenses with gradually increasing radii from top to bottom. The topmost lens is a circular thin sheet, while the other lenses are circular thin sheets with a circular groove hollowed out in the center. The dielectric constant of each lens layer decreases sequentially from top to bottom.

[0014] The five microstrip patch antennas are arranged in one dimension, with the two side microstrip patch antennas serving as dummy elements and the three middle microstrip patch antennas serving as radiating elements, controlling the working mode of the excitation source and realizing pattern reconstruction.

[0015] The metal cavity is composed of a square metal fence and a floor; the low-profile Maxwell fisheye lens is located inside the metal cavity, and the microstrip patch antenna is nested on the floor of the metal cavity.

[0016] Furthermore, in the low-profile Maxwell fisheye lens, four arc-shaped sections are cut off on the outer side of the bottom layer lens, and the four cut surfaces are parallel to the four faces of the square metal fence, which helps to block energy from accumulating at the lens edge and improve the overall gain effect.

[0017] The lens antenna uses a simple microstrip patch antenna as the feed source for the lens. An RF switch selects the microstrip patch antenna to be excited, thereby controlling the antenna's radiation direction. Microstrip patch antenna 11 radiates in the positive angular direction, microstrip patch antenna 12 radiates in the normal direction, and microstrip patch antenna 13 radiates in the negative angular direction. During operation, each antenna element has exactly one active patch antenna. When the array scans from 0° to ±10°, microstrip patch antennas 12 of each element are excited simultaneously; when the array scans from 10° to 43°, microstrip patch antennas 11 of each element are excited simultaneously; and when the array scans from -10° to -43°, microstrip patch antennas 13 of each element are excited simultaneously. This effectively suppresses the grating lobes generated by the 1.82λ large-pitch array during scanning from 0° to ±43°.

[0018] The innovation of this invention is:

[0019] (1) This invention proposes a large-spacing sparse phased array antenna based on a low-profile Maxwell fisheye lens, which suppresses the grating lobes that appear during wide-angle scanning of the large-spacing sparse array. The antenna element spacing is 1.82λ, and scanning from 0° to ±43° is achieved within the antenna frequency band. The SLL is kept below -7.4dB, effectively suppressing the grating lobes.

[0020] (2) This invention proposes a large-spacing sparse phased array antenna based on a low-profile Maxwell fisheye lens, which saves the number of T / R components and reduces the cost of phased array radar. Compared with a half-wavelength full array, it achieves a sparsity of 72.4% and saves 21 T / R components (29 are required for a full array).

[0021] (3) This invention proposes a large-spacing sparse phased array antenna based on a low-profile Maxwell fisheye lens, which compensates for the gain loss caused by the sparse array. The zero-degree gain is 20.6dB, which is higher than the 0° gain of 19.5dB when the array is full. It suppresses grating lobes while reducing gain loss and maintaining the radiation characteristics of the antenna.

[0022] (4) This invention proposes a large-spacing sparse phased array antenna based on a low-profile Maxwell fisheye lens. The profile is only 0.286λ, which is much lower than the profile height of various lens antennas. The antenna has a planar structure and is more suitable for practical industrial applications compared with other arc-shaped lens antennas. Attached Figure Description

[0023] Figure 1 This is a cross-sectional view of the antenna element described in this invention;

[0024] Figure 2 This is a layered diagram of the antenna unit structure described in this invention;

[0025] Figure 3 This is a top view of the microstrip antenna portion of the antenna unit described in this invention;

[0026] Figure 4 This is a top view of the antenna element described in this invention;

[0027] Figure 5 This is a top view of the phased array antenna described in this invention;

[0028] Figure 6 These are the S-parameter curves of the array and antenna unit described in this invention;

[0029] Figure 7 This is the beam scanning angle pattern of the large-pitch phased array described in this invention.

[0030] Explanation of reference numerals: 1. Low-profile Maxwell fisheye lens, 2. Metal cavity, 3. Microstrip patch antenna, 4. First layer lens, 5. Second layer lens, 6. Third layer lens, 7. Fourth layer lens, 8. Fifth layer lens, 9. Sixth layer lens, 10. First microstrip patch antenna, 11. Second microstrip patch antenna, 12. Third microstrip patch antenna, 13. Fourth microstrip patch antenna, 14. Fifth microstrip patch antenna, A. Antenna element. Detailed Implementation

[0031] The present invention will now be further described in conjunction with the accompanying drawings and specific embodiments.

[0032] Antenna examples of the present invention Figure 1 As shown, this unit is a low-profile Maxwell fisheye lens antenna. The microstrip patch antenna at the bottom is the feed source of the Maxwell fisheye lens. The bandwidth of the lens antenna is the bandwidth of the feed microstrip antenna. Different types of feed antennas can be replaced according to the requirements of different frequency bandwidths. In this embodiment, the simplest and most effective microstrip patch antenna with an operating frequency band of 4.02GHz to 4.13GHz is used as an example to illustrate the technical solution of the present invention in detail.

[0033] The Maxwell fisheye lens in this embodiment is as follows: Figure 4 As shown, the low-profile Maxwell fisheye lens adopts a low-profile cylindrical nested structure, consisting of six concentric nested circular lenses with gradually increasing radii from top to bottom. The topmost lens is a circular thin sheet, while the other lenses are circular thin sheets with a circular groove hollowed out in the center. From the first to the sixth lens, the dielectric constants are 4, 3.5, 3, 2.5, 2, and 1.5, respectively; the radii are 19.5 mm, 29.9 mm, 29.43 mm, 48.75 mm, 57.2 mm, and 65 mm, respectively; and the heights are 5.25 mm, 7.7 mm, 10.15 mm, 12.425 mm, 14.15 mm, and 16.275 mm, respectively. Compared with various lens antennas currently available, this invention can significantly reduce the antenna's profile height, and the feed antenna is arranged in a planar structure, eliminating the need for an arc-shaped distribution.

[0034] like Figure 3 As shown, five microstrip patch antennas are arranged in one dimension. The microstrip patch antennas on both sides serve as dummy elements, while the three microstrip patch antennas in the middle serve as radiating elements. The lens antenna is excited by the bottom microstrip patch antenna. The patch antennas operate in the frequency band of 4.02 GHz to 4.13 GHz. When the phased array is working, each lens antenna element has one and only one radiating element. After exciting the radiating element, the electromagnetic wave is refracted by multiple layers of lenses with different media to achieve angle deflection. Then, the array is electrically scanned to achieve beam scanning. When performing a positive angle scan, the second microstrip patch antenna 11 is excited; when performing a normal direction scan, the third microstrip patch element 12 is excited; and when performing a negative angle scan, the fourth microstrip patch antenna 13 is excited. The first microstrip patch antenna 10 and the fifth microstrip patch antenna 14 are dummy antennas. Their function is to adjust the coupling of the three radiating elements and optimize the radiation pattern of the lens element. They are not excited.

[0035] like Figure 2As shown, the Maxwell fisheye lens and the microstrip antenna element are connected by a metal cavity with a side length of 134.8 mm (the size of the lens antenna element, i.e., the center distance of the array elements), which is approximately 1.82λ. The metal cavity can reduce the coupling radiation effect of the surrounding antennas.

[0036] The large-pitch sparse phased array antenna based on a low-profile Maxwell fisheye lens proposed in this invention is as follows: Figure 5 As shown, Unit A is the aforementioned lens antenna unit. The array consists of 24 of the aforementioned lens antenna units, with an element spacing of 1.82λ. It belongs to the ultra-large spacing phased array antenna, and the array size is 404.5mm × 1079.5mm.

[0037] Figure 6 The S-parameter curves of the array antenna and the lens antenna element are shown. The antenna array operates in the 4.02GHz to 4.13GHz frequency band, which is the same as the operating frequency band of the microstrip patch antenna, and the matching effect is good. The phased array antenna proposed in this invention can replace the bottom feed antenna according to different polarization requirements, bandwidth requirements, and frequency requirements. The example shown in this invention uses the simplest and most effective microstrip patch element as the lens feed.

[0038] Figure 7 This invention presents a beam scanning pattern for a large-pitch sparse phased array antenna based on a low-profile Maxwell fisheye lens. The phased array antenna can achieve angular scanning from 0° to ±43°, with a sparsity ratio (SLL) of less than 7.4dB. A phased array antenna with a half-wavelength pitch arrangement of the same aperture requires 29 T / R components, while this invention requires only 8 T / R components of the same aperture, achieving a sparsity ratio as high as 72.4%, as shown in Table 1. Compared with a full array with a half-wavelength pitch arrangement, the gain loss of the phased array antenna proposed in this invention is less than 2dB. Furthermore, the zero-degree gain of the phased array antenna proposed in this invention is higher than the actual gain of the antenna when it is fully deployed, effectively maintaining the antenna's radiation characteristics and overcoming several shortcomings of sparse arrays mentioned in the background.

[0039] Table 1 Comparison data between the phased array antenna of the present invention and a full array antenna of the same aperture.

[0040]

[0041] In summary, this invention discloses a large-pitch sparse phased array antenna design based on a low-profile Maxwell fisheye lens. This invention uses a low-profile Maxwell fisheye lens antenna as the array element and a simple microstrip patch antenna as the radiation feed for the lens, reducing the antenna design complexity and ensuring stability during operation. The microstrip patch antenna uses a planar arrangement, avoiding the drawback of the curved arrangement of the feed antenna in current lens phased array antennas, making it more suitable for engineering applications. The spacing between antenna elements is 134.8 mm, approximately 1.82λ, which is significantly higher than various large-pitch sparse antennas currently proposed, achieving a sparsity of 72.4%. The proposed antenna array can achieve ±43° scanning with a sidelobe level less than -7.4 dB. Compared to a full-array antenna with half-wavelength arrangement of the same aperture, it reduces the number of T / R components by 72.4%, significantly reducing the cost of the phased array system. Furthermore, the gain loss is less than 2 dB, and the zero-degree gain is higher than that of a full-array antenna, reducing system cost while ensuring the radiation characteristics of the array antenna.

Claims

1. A large-pitch sparse phased array antenna based on a low-profile Maxwell fisheye lens, the phased array antenna being composed of M×N periodically arranged lens antenna elements, characterized in that, The center distance between the lens antenna elements is greater than the free space wavelength corresponding to the working center frequency. The lens antenna unit includes a low-profile Maxwell fisheye lens, a metal cavity, and five microstrip patch antennas. The low-profile Maxwell fisheye lens has a cylindrical structure, consisting of K concentric nested circular lenses with gradually increasing radii from top to bottom. The topmost lens is a circular sheet, while the other lenses are circular sheets with a circular groove in the center. The dielectric constant of each lens layer decreases sequentially from top to bottom. The five microstrip patch antennas are arranged in one dimension, with the microstrip patch antennas on both sides serving as dummy elements and the three microstrip patch antennas in the middle serving as radiating elements. The working mode of the radiating elements is controlled to achieve pattern reconstruction. The metal cavity is composed of a square metal fence and a floor; the low-profile Maxwell fisheye lens is located inside the metal cavity, and the microstrip patch antenna is nested on the floor of the metal cavity.

2. The large-pitch sparse phased array antenna based on a low-profile Maxwell fisheye lens as described in claim 1, characterized in that, K is a positive integer greater than 5.

3. A large-pitch sparse phased array antenna based on a low-profile Maxwell fisheye lens as described in claim 1 or 2, characterized in that, M and N are any positive integers.

4. A large-pitch sparse phased array antenna based on a low-profile Maxwell fisheye lens as described in claim 3, characterized in that, The outer side of the lowest layer lens in the low-profile Maxwell fisheye lens has four arc-shaped sections cut off, and the four cut surfaces are parallel to the four faces of the square metal fence.

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