Ku wave band low RCS monopulse array antenna

Abstract

The invention provides a Ku-band low-RCS monopulse array antenna. The Ku-band low-RCS monopulse array antenna comprises a reflection and radiation integrated AMC unit, an inverse matching AMC unit, a monopulse array antenna, a first dielectric plate, a metal grounding plate, a second dielectric plate and a sum-difference feed network, the reflection and radiation integrated AMC units and the inverse matching AMC units are alternately arranged on the upper surface of the first dielectric plate in a chessboard shape to form an AMC array; the lower layer of the first dielectric plate is the metal grounding plate; the lower layer of the metal grounding plate is a second dielectric plate; and the lower layer of the second dielectric plate is a sum-difference feed network. According to the invention, a second type of AMC unit having a 180-degree reflection phase difference with a first type of AMC unit in a broadband is designed as an anti-phase matching AMC unit, and broadband RCS reduction is realized based on a phase cancellation principle. The problems that a traditional RCS reduction antenna is complex in structure, multiple in layer and high in profile are solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of microwave and millimeter wave bands, and particularly relates to a Ku-band low RCS single pulse array antenna. Background Art

[0002] In modern military and aerospace fields, radar detection and stealth technologies for targets have long been a hot topic of research. Radar antennas detect a target's position, velocity, and shape by transmitting electromagnetic waves and receiving reflected waves. A target's ability to reflect radar waves is typically measured by its radar cross section (RCS). RCS is defined as the ratio of the power reflected by a target per unit solid angle to the incident power. Its magnitude depends not only on the geometry of the object being detected but also on factors such as its material properties, the frequency, and polarization of the radar wave. RCS directly affects a target's detectability by radar, leading to increasing interest in technologies that achieve radar stealth by reducing RCS. Artificial magnetic conductors (AMCs) are a widely used RCS reduction solution. By periodically arranging reflective elements, they create a 180-degree phase difference between reflected waves from adjacent elements. Based on the principle of interference, the reflected waves cancel each other out at the receiver, thereby reducing RCS.

[0003] Furthermore, due to the need for external communications, weapon platforms are often equipped with multi-functional antennas. Monopulse antennas are a specialized antenna system primarily used in electronic equipment such as radar. Monopulse antennas are capable of simultaneously providing multiple beams, using a single pulse echo to generate the sum and difference signals required for direction finding. They are primarily used for tracking and locating high-speed targets.

[0004] Antennas that haven't undergone low RCS design and are directly installed on stealth-capable equipment often severely impact the device's overall stealth performance. Furthermore, RCS-reduction surfaces installed on weapon platforms can also affect the antenna's radiation performance, leading to uneven patterns, polarization distortion, and a reduction in operating frequency band. Currently, most collaborative designs utilize two separate physical structures to achieve RCS reduction and antennas, with the RCS-reduction surface and array antenna stacked in a stacked arrangement. This not only increases volume but also processing and manufacturing costs. If the RCS-reduction surface and monopulse array antenna could be designed as a single structure, reusing both functions, this would be highly practical for achieving low-profile, low-cost RCS reduction and monopulse antenna technology. Summary of the Invention

[0005] Purpose of the invention: The technical problem to be solved by the present invention is to address the deficiencies in the existing technology and provide a Ku-band low RCS monopulse array antenna that has the characteristics of broadband RCS reduction, high gain and beam, highly symmetric E-face difference beam, highly symmetric H-face difference beam and low profile.

[0006] The antenna array of the present invention includes an integrated reflection and radiation AMC unit, an anti-matching AMC unit, a single pulse array antenna, a first dielectric plate, a metal ground plate, a second dielectric plate, and a sum and differential feed network; The reflection and radiation integrated AMC units and the anti-matching AMC units are alternately arranged in a checkerboard pattern on the upper surface of the first dielectric plate to form an AMC array; The center of the AMC array is a monopulse array antenna composed of integrated reflection and radiation AMC units; The lower layer of the first dielectric plate is a metal ground plate; The lower layer of the metal ground plate is a second dielectric plate; The lower layer of the second dielectric plate is a sum and difference feeding network.

[0007] The reflection and radiation integrated AMC unit and the anti-matching AMC unit are both composed of a dielectric plate and a metal square patch attached to the dielectric plate; In order to achieve RCS attenuation of electromagnetic waves incident in different polarization directions, the metal square patch is set to a square structure.

[0008] The integrated reflection and radiation AMC unit and the anti-matching AMC unit are arranged in a two-dimensional periodic arrangement. The two-dimensional period of the integrated reflection and radiation AMC unit and the anti-matching AMC unit is the same, but the patches have two sizes. The size of the metal square patch of the integrated reflection and radiation AMC unit is larger than the size of the metal square patch of the anti-matching AMC unit.

[0009] The AMC unit, which combines reflection and radiation, simultaneously reflects normally incident electromagnetic waves in phase and radiates them as a patch antenna. Its size is determined by the operating frequency of the array antenna unit, and its shape remains consistent with the array antenna unit. Sixteen AMC units are arranged in a 4x4 (4 rows by 4 columns) configuration to form a 1-bit array.

[0010] The anti-matching AMC unit is used to match the reflection-radiation integrated AMC unit, so that there is a 180-degree phase difference when the electromagnetic wave incident from the normal direction is reflected on the surfaces of the reflection-radiation integrated AMC unit and the anti-matching AMC unit, thereby realizing anti-phase cancellation of the far-field signals, thereby achieving the effect of RCS reduction.

[0011] In order to achieve anti-matching with the reflection-radiation integrated AMC unit within a wide frequency band, the anti-matching AMC unit does not serve as an antenna radiation unit but only as an AMC reflection unit.

[0012] The significant size difference between the anti-matched AMC unit and the integrated reflective-radiative AMC unit leads to different resonant frequencies, which reduces electric field coupling between the two units and mitigates far-field interference with the integrated reflective-radiative AMC unit. Sixteen anti-matched AMC units are arranged in a 4×4 array to form a 0-bit array.

[0013] The 1-bit array and the 0-bit array are arranged in a checkerboard pattern. Specifically, virtual lines arranged horizontally and vertically on the metal ground plane form a grid, and the 1-bit array and the 0-bit array are alternately arranged in each grid. Only one 1-bit array or one 0-bit array can be placed in a grid.

[0014] The 1-bit array and the 0-bit array are covered on the upper layer of the first dielectric plate, and the first dielectric plate is made of F4B material with a dielectric constant of 2.65.

[0015] The lower surface of the second dielectric plate is provided with a differential feeding network to feed the 1-bit array.

[0016] The monopulse array antenna consists of four adjacent 1-bit arrays, a metal ground plane, and a sum and difference feed network beneath the second dielectric layer. The 1-bit array elements are integrated reflective and radiative AMC units. By configuring the feed, these integrated reflective and radiative AMC units function as antenna elements in the monopulse array antenna. The operating principle is similar to that of a microstrip patch antenna.

[0017] Feeding is achieved by arranging a metal probe below the antenna unit, passing through the first dielectric plate, the metal ground plate, the second dielectric plate, and connecting to the sum and differential feeding network.

[0018] The present invention arranges four 1-bit arrays at the center of the upper surface of the first dielectric plate, sets a feed to realize a monopulse array antenna, and arranges four 1-bit arrays and eight 0-bit arrays around the monopulse array antenna to form a checkerboard structure to form an RCS reduction surface, thereby realizing multiplexing of the monopulse array antenna and the RCS reduction surface.

[0019] The sum and difference feeding network includes four orthogonal couplers and four four-level power dividers; the four orthogonal couplers are respectively a first orthogonal coupler, a second orthogonal coupler, a third orthogonal coupler and a fourth orthogonal coupler; The orthogonal coupler is composed of a symmetrical microstrip line network and has four ports: an input port, a through port, a coupled port, and an isolated port. The impedance matrix of the structure is reciprocal, and the four ports are interchangeable. When a signal is input from the input port, the power of the input port is divided into the same amplitude at the through port and the coupled port corresponding to the orthogonal coupler, and there is a 90° phase difference between the through port and the coupled port.

[0020] Connect the through-end of the first orthogonal coupler to the input end of the second orthogonal coupler; connect the coupling end of the first orthogonal coupler to the isolation end of the third orthogonal coupler; connect the through-end of the fourth orthogonal coupler to the input end of the third orthogonal coupler; and connect the coupling end of the fourth orthogonal coupler to the isolation end of the second orthogonal coupler. Introduce 90° phase shifters at the coupling end of the first orthogonal coupler, the coupling end of the second orthogonal coupler, the isolation end of the third orthogonal coupler, and the isolation end of the fourth orthogonal coupler. The first orthogonal coupler and the fourth orthogonal coupler are arranged horizontally symmetrically; the second orthogonal coupler and the third orthogonal coupler are arranged vertically symmetrically. After the above operations, a sum-difference network with 4 input ports and 4 output ports is finally obtained. The sum-difference network S matrix is: S= , D= (1), Where j represents the unit imaginary number; T represents the matrix transpose; and D represents the transfer function matrix.

[0021] The sum-difference network is introduced into a power divider to form a sum-difference feeding network; The four-stage power divider has a T-type power distribution structure at each stage, which can divide the input signal into two output signals with the same amplitude and phase. 0 +2 1 +2 2 +2 3 A total of 15 T-type power dividers can equally divide one input signal into 16 output signals with the same amplitude and phase.

[0022] The present invention designs two types of AMC reflective units, one of which serves as both a reflective unit for incident waves and a radiating unit for feeding signals (referred to as an integrated reflection-radiation AMC unit), and the other serves only as a reflective unit for incident waves (referred to as an anti-matching AMC unit). The reflected signal having a phase difference of 180 degrees from the first AMC unit is provided to achieve RCS reduction based on reflection cancellation. A single-pulse antenna is realized by designing and feeding the integrated reflection-radiation AMC unit with a differential feeding network.

[0023] Beneficial Effects: This invention provides a single-layer RCS reduction and array antenna reuse surface. Without adding additional physical structure, this design integrates reflection and radiation, utilizing one type of AMC element as an antenna radiating element to achieve beam-directional radiation. A second type of AMC element, with a 180-degree reflection phase difference across a wide bandwidth, is designed as an anti-matching AMC element, achieving broadband RCS reduction based on the principle of phase cancellation. This invention addresses the complex, multi-layered, and high-profile nature of conventional RCS reduction antennas. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic diagram of the overall structure of the present invention.

[0025] Figure 2 It is a structural schematic diagram of the reflection and radiation integrated AMC unit of the present invention.

[0026] Figure 3 Schematic diagram of the structure of the reverse matching AMC unit of the present invention.

[0027] Figure 4 Schematic diagram of the relationship between the phase difference of the reflected wave and the frequency when the two AMC units of the present invention receive the incident wave in phase.

[0028] Figure 5 Schematic diagram of the probe feeding structure of the present invention.

[0029] Figure 6 It is a schematic diagram of the sum and difference feeding network structure of the present invention.

[0030] Figure 7 It is a structural schematic diagram of a 4-level power divider of the present invention.

[0031] Figure 8 Schematic diagram of the structure of the orthogonal coupler and 90° phase shifter of the present invention.

[0032] Figure 9 This is a schematic diagram of the sum-difference network topology structure of the present invention.

[0033] Figure 10 This is a diagram showing the reduction effect of the single-station RCS of the present invention compared with the reference antenna.

[0034] Figure 11 This is a port reflection parameter diagram of the present invention.

[0035] Figure 12 This is the radiation pattern of the present invention and port input.

[0036] Figure 13 This is the radiation pattern of the E-face difference port input of the present invention.

[0037] Figure 14This is the radiation pattern of the H-face difference port input of the present invention.

[0038] Explanation of the reference numerals: 1: AMC array; 2: first dielectric plate; 3: metal ground plane; 4: second dielectric plate; 5: sum and differential feed network; 6: single pulse array antenna. DETAILED DESCRIPTION

[0039] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments, and the above and / or other advantages of the present invention will become more apparent.

[0040] like Figure 1 As shown, an embodiment of the present invention provides a Ku-band low RCS monopulse array antenna. The present invention has a five-layer structure, namely an AMC array 1 composed of an integrated reflection and radiation AMC unit and an anti-matching AMC unit, a first layer of dielectric plate 2, a metal ground plate 3, a second layer of dielectric plate 4, and a sum and differential feed network 5.

[0041] An AMC unit usually consists of a top surface patch, an intermediate dielectric layer, and a ground plane. Figure 2 It is an integrated AMC unit for reflected radiation; Figure 3 The top surface of the integrated radiation and reflection AMC unit is a square metal patch with a side length of W0 = 6.2mm; the top surface of the anti-matching AMC unit is a square metal patch with a side length of W1 = 3.4mm. The thickness of the intermediate dielectric layer of both AMC units is h1 = 2.4mm. The intermediate dielectric layers of all AMC units are arranged periodically to form the first dielectric plate. The periodic spacing between units is P = 14mm. Figure 1 The two types of AMC units are arranged in a manner, wherein the center of the AMC array is a 1-bit array composed of four integrated reflection and radiation AMC units in a 2×2 form to form a single pulse array antenna 6.

[0042] When irradiated by a plane wave of the same phase, the phase difference between the reflection phases of the two AMC units is one of the criteria for reflecting the RCS reduction performance of the AMC structure. When the reflection phase difference between the two units is 180°±37°, the RCS reduction performance of the AMC structure is considered to be good. Figure 6 As shown, the reflection phase difference between the two AMC units is 143° at 11.5 GHz and 16.4 GHz, reaching its extreme value of 211° at 14 GHz. Therefore, the phase difference requirement of 180°±37° is met from 11.5 GHz to 16.4 GHz, indicating good low RCS performance in this band.

[0043] The metal patch that constitutes the integrated reflective radiation AMC unit will also partially act as the radiating element of the antenna. Figure 5As shown, a feed probe is introduced at a distance of d = 1.6 mm from the center of the patch. The feed probe penetrates the first dielectric layer, the metal ground plane, and the second dielectric layer, transmitting the signal output by the summing and difference network to the antenna patch. The radius of the feed probe is R0 = 0.35 mm. When drilling the ground plane, care must be taken to prevent the probe from contacting the ground plane. Therefore, the ground plane drilling radius is R1 = 1.2 mm.

[0044] The first dielectric plate is made of F4B material with a dielectric constant of 2.65. Its top view is a square with a side length of Wd = 224 mm and a thickness of h1 = 2.4 mm. Below the first dielectric plate is a metal ground plane, and below this is the second dielectric plate, made of Rogers 5880 with a dielectric constant of 2.2 and a thickness of h2 = 0.2 mm. The sum and differential feed networks are located on the second dielectric plate.

[0045] The copper cladding thickness of the AMC unit patch, metal ground plate, and sum and differential feed networks mentioned above is T=0.127mm.

[0046] like Figure 6 As shown, the sum-difference feed network has four inputs and four outputs. The inputs are categorized by function as sum ports, E-difference ports, H-difference ports, and load matching ports. The sum port outputs signals for range detection; the E-difference port outputs signals for horizontal position detection; and the H-difference port outputs signals for elevation angle detection. The load matching port is not involved. The four output ports are connected to four 4-stage power dividers, which evenly distribute the power from each output port to the four 4×4 antenna arrays.

[0047] like Figure 6 As shown in the figure, the main components of the sum and differential feed network are 50Ω characteristic impedance microstrip lines with a width of W50 = 0.7mm. The lengths of the segments marked in the figure are L1 = 109.3mm, L2 = 4mm, L3 = 24.95mm, L4 = 25.65mm, L5 = 13.35mm, L6 = 13.3mm, L7 = 6.3mm, L8 = 6.3mm, and L9 = 3.3mm. The sum and differential feed network uses a conformal structure, so the structural parameters of the entire network are derived by referring to a single feed branch.

[0048] like Figure 7 As shown in the figure, the four-stage power divider consists of 15 T-shaped power dividers. To achieve impedance matching, a 35Ω characteristic impedance microstrip line with a length of L10 = 3.65mm and a width of W35 = 1.2mm is added to the first and second stage T-shaped power dividers. To improve energy transmission efficiency and optimize the performance of the T-shaped power divider, a 90° bend is performed at each location where the electromagnetic wave propagation direction changes. The bend angle can be adjusted to any desired value.

[0049] like Figure 8 As shown, multiple 90° phase shifters are arranged in the sum and differential feed network, which can cause the input signal to undergo a 90-degree phase shift. This can be achieved by raising a microstrip line with a length of L12 = 3.4 mm by L11 = 2.6 mm to form an arch structure.

[0050] like Figure 8 As shown in the figure, a 70Ω characteristic impedance microstrip line with a width of W70 = 0.3mm is built between two 50Ω characteristic impedance microstrip lines. Furthermore, a 120Ω characteristic impedance microstrip line with a width of W120 = 0.13mm is placed at each end of the 70Ω characteristic impedance at a position L13 = 4mm. This structure implements the function of an orthogonal coupler, not only isolating the two input ports using odd and even modes but also splitting the input signals into two signals with equal amplitudes and a 90° phase difference.

[0051] Reference for the combination of orthogonal coupler and 90° phase shifter Figure 9 , four orthogonal couplers and four 90° phase shifters constitute the sum-difference network structure of the present invention.

[0052] like Figure 10 As shown in Figure 2, the low RCS antenna of the present invention can achieve an RCS reduction of more than -10dB at 12GHz~15.7GHz compared to the antenna without low RCS design. Considering the influence of the feed structure on the RCS performance, this result is consistent with the Figure 4 The predicted results are basically consistent.

[0053] Figure 11 is the reflection coefficient of the four input ports. It can be seen that at 13 GHz, the reflection coefficient of each port is less than -10 dB. At this time, most of the energy is radiated by the antenna. This frequency is also the main operating frequency of the antenna.

[0054] Figure 12 、 Figure 13 、 Figure 14 The antenna radiation patterns for three input conditions are shown below. When inputted to the sum port, the pattern is a single beam with a maximum gain of 23dB. When inputted to the E-plane difference port, the pattern is a dual beam split in the E-plane with a maximum gain of 22dB and a normal gain of -1dB. When inputted to the H-plane difference port, the pattern is a dual beam split in the H-plane with a maximum gain of 22.5dB and a normal gain of 5dB. The matching ports are not used in actual operation and are therefore not demonstrated.

[0055] The present invention provides a Ku-band low-RCS monopulse array antenna. There are numerous methods and approaches for implementing this technical solution. The foregoing merely represents a preferred embodiment of the present invention. It should be noted that those skilled in the art may make various improvements and modifications without departing from the principles of the present invention, and such improvements and modifications are also within the scope of protection of the present invention. Components not specified in this embodiment may be implemented using existing technologies.

Claims

1. A Ku-band low RCS monopulse array antenna, characterized in that: It includes a reflection-radiation integrated AMC unit, an anti-matching AMC unit, a single pulse array antenna, a first dielectric plate, a metal ground plate, a second dielectric plate, and a sum and differential feeding network; The reflection and radiation integrated AMC units and the anti-matching AMC units are alternately arranged in a checkerboard pattern on the upper surface of the first dielectric plate to form an AMC array; The lower layer of the first dielectric plate is a metal ground plate; The lower layer of the metal ground plate is a second dielectric plate; The lower layer of the second dielectric plate is a sum and difference feeding network.

2. The Ku-band low RCS monopulse array antenna according to claim 1, characterized in that: The center of the AMC array is a single pulse array antenna composed of reflection and radiation integrated AMC units.

3. The Ku-band low RCS monopulse array antenna according to claim 2, characterized in that: The reflection-radiation integrated AMC unit and the anti-matching AMC unit are both composed of a dielectric plate and a metal square patch attached to the dielectric plate.

4. The Ku-band low RCS monopulse array antenna according to claim 3, characterized in that: The metal square patch is arranged in a square structure.

5. The Ku-band low RCS monopulse array antenna according to claim 4, characterized in that: The integrated reflection and radiation AMC unit and the anti-matching AMC unit are arranged in a two-dimensional periodic arrangement. The two-dimensional period of the integrated reflection and radiation AMC unit and the anti-matching AMC unit is the same. The size of the metal square patch of the integrated reflection and radiation AMC unit is larger than the size of the metal square patch of the anti-matching AMC unit.

6. The Ku-band low RCS monopulse array antenna according to claim 5, characterized in that: The integrated reflection and radiation AMC unit simultaneously realizes the in-phase reflection of normally incident electromagnetic waves and the patch antenna radiation function, and 16 integrated reflection and radiation AMC units are arranged in 4 rows and 4 columns to form a 1-bit array.

7. The Ku-band low RCS monopulse array antenna according to claim 6, characterized in that: The anti-matching AMC unit is used to match the reflection-radiation integrated AMC unit, so that there is a 180-degree phase difference when the electromagnetic wave incident from the normal direction is reflected on the surfaces of the reflection-radiation integrated AMC unit and the anti-matching AMC unit, thereby realizing anti-phase cancellation of the far-field signals, thereby achieving the effect of RCS reduction.

8. The Ku-band low RCS monopulse array antenna according to claim 7, characterized in that: The anti-matching AMC unit does not serve as an antenna radiation unit, but only as an AMC reflection unit.

9. The Ku-band low RCS monopulse array antenna according to claim 8, characterized in that: Inversely, 16 anti-matching AMC units are arranged in 4 rows and 4 columns to form a 0-bit array; The 1-bit array and the 0-bit array are arranged in a checkerboard pattern: virtual lines arranged horizontally and vertically on the metal ground plane are used to divide the grid, and the 1-bit array and the 0-bit array are alternately arranged in each grid; only one 1-bit array or one 0-bit array can be placed in a grid; The 1-bit array and the 0-bit array are covered on the upper layer of the first dielectric plate, and the first dielectric plate is made of F4B material with a dielectric constant of 2.65; The lower surface of the second dielectric plate is provided with a differential feeding network to feed the 1-bit array; The monopulse array antenna is composed of four adjacent 1-bit arrays, a metal ground plane, and a sum and difference feed network under the second dielectric plate; The 1-bit array element is a reflection-radiation integrated AMC unit, which is used as an antenna unit of a monopulse array antenna by setting the feed; A metal probe is arranged under the antenna unit, passing through the first dielectric plate, the metal ground plate, the second dielectric plate, and connected to the sum and differential feeding network to achieve feeding; Four 1-bit arrays are arranged in the center of the upper surface of the first dielectric plate, and a feed is set to realize a monopulse array antenna. Four 1-bit arrays and eight 0-bit arrays are arranged around the monopulse array antenna to form a checkerboard structure to form an RCS reduction surface, realizing the multiplexing of the monopulse array antenna and the RCS reduction surface.

10. The Ku-band low RCS monopulse array antenna according to claim 9, characterized in that: The sum and difference feeding network includes four orthogonal couplers and four four-level power dividers; the four orthogonal couplers are respectively a first orthogonal coupler, a second orthogonal coupler, a third orthogonal coupler and a fourth orthogonal coupler; The orthogonal coupler is composed of a symmetrical microstrip line network and has four ports: an input port, a through port, a coupled port, and an isolated port. The four ports are interchangeable. When a signal is input from the input port, the power of the input port is divided equally at the through port and the coupled port corresponding to the orthogonal coupler, and there is a 90° phase difference between the through port and the coupled port. The through-end of the first orthogonal coupler is connected to the input end of the second orthogonal coupler; the coupling end of the first orthogonal coupler is connected to the isolation end of the third orthogonal coupler; the through-end of the fourth orthogonal coupler is connected to the input end of the third orthogonal coupler; the coupling end of the fourth orthogonal coupler is connected to the isolation end of the second orthogonal coupler, and 90° phase shifters are introduced at the coupling end of the first orthogonal coupler, the coupling end of the second orthogonal coupler, the isolation end of the third orthogonal coupler, and the isolation end of the fourth orthogonal coupler; the first orthogonal coupler and the fourth orthogonal coupler are arranged horizontally symmetrically; the second orthogonal coupler and the third orthogonal coupler are arranged vertically symmetrically; finally, a sum-difference network with 4 input ports and 4 output ports is obtained, and the sum-difference network S matrix is: S= ,D= (1), Where j represents a unit imaginary number; T represents matrix transpose; D represents transfer function matrix; The sum-difference network is introduced into a power divider to form a sum-difference feeding network; The four-stage power divider is a T-type power distribution structure at each stage, which can divide the input signal into two output signals with the same amplitude and phase. 0 +2 1 +2 2 +2 3 A total of 15 T-type power dividers can equally divide one input signal into 16 output signals with the same amplitude and phase.

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