Dual-frequency low radar cross-section reflectarray antenna based on three-dimensional frequency selective structure

Abstract

The present invention discloses a dual-frequency, low radar cross-section reflector array antenna based on a three-dimensional frequency selective structure. The reflector unit employed is composed of a cascade of an absorption slot with an absorption function and a phase-modulation slot with a phase-shifting function, which separately regulate electromagnetic waves of different polarization directions. When electromagnetic waves of two frequencies are emitted from a feed antenna in different polarization directions, the phases are compensated by adjusting the lengths of the phase-modulation slots in the corresponding polarization directions. This allows the two electromagnetic waves of different frequencies to be converted from spherical waves to plane waves after passing through the reflector array, achieving high-gain radiation at dual frequencies. By loading lossy components, electromagnetic waves outside the radiation center frequency are absorbed, thereby achieving the function of reducing the radar cross-section. While ensuring the high gain of the reflector array antenna, the present invention achieves dual-frequency operation and low radar cross-section functions, and has the advantages of a simple structure and ease of processing, making it suitable for advanced communication and radar antenna systems.

Description

Technical Field

[0001] The present invention relates to the field of radar technology, and in particular to a dual-frequency low radar cross-section reflectarray antenna based on a three-dimensional frequency selective structure. Background Art

[0002] With the advancement of the electronics industry and radar technology, a variety of new, high-precision, intelligent radars and advanced detectors have emerged. The essence of radar stealth is to prevent radar from accurately detecting a target's return signal. Developing stealth technology, thereby improving the survivability and defensive capabilities of weapon systems, is a pressing need in modern warfare. When electromagnetic waves emitted by a radar encounter a target, they scatter. The backscattered power, or radar echo power, returns to the radar and is received by the radar antenna, allowing the radar to determine the target's presence and location. Radar cross section (RCS) is a physical quantity that measures the strength of a target's electromagnetic scattering properties. Reducing a target's RCS reduces the probability of detection by enemy radar, significantly enhancing the defensive capabilities of its own weapons and equipment.

[0003] High-gain, highly directional antennas are widely used in modern weaponry and radar detection systems. Reflectarray antennas are one such high-gain antenna. Reflectarray antennas consist of a feed antenna and a reflector array. The reflector array modulates the phase of the incident electromagnetic wave, transforming the spherical wave emitted by the feed into a uniform plane wave, achieving high-gain radiation performance. However, while achieving high gain, the reflector array has a large electrical size, making it susceptible to radar detection and potentially revealing targets in military applications. Therefore, the development of low-radar-cross-section reflectarray antennas is of great significance. With the continuous advancement of technology, wireless communication systems are becoming increasingly complex, placing increasing demands on antennas, driving their development towards miniaturization and multi-band design. Compared to single-frequency antennas, multi-frequency antennas can reduce the number of antennas required in a system, thereby saving space and reducing costs. Therefore, the research and design of multi-frequency reflectarray antennas is of great significance.

[0004] Three-dimensional frequency selective structures (FSSs) are a newly emerging type of FSS. They are typically composed of a periodic arrangement of three-dimensional cavity / transmission line-like structural units of a defined thickness. The increased spatial dimension of the periodic unit structure provides a richer range of control options and greater degrees of freedom for electromagnetic wave manipulation, significantly improving the performance of electromagnetic wave manipulation. Three-dimensional FSSs based on planar slot lines offer a simple structure, ease of fabrication, and integration, making them particularly well-suited for applications such as reflectarray antennas and antenna radar cross-section reduction. Summary of the Invention

[0005] The purpose of the present invention is to provide a dual-frequency low radar cross-section reflectarray antenna based on a three-dimensional frequency selective structure, which can achieve high gain at different frequencies, reduce the number of antennas required in the system, reduce space costs, and at the same time have the characteristics of low radar cross-section, which can be used in the military field.

[0006] To achieve the above functions, the present invention designs a dual-frequency low radar cross-section reflectarray antenna based on a three-dimensional frequency selective structure. A three-dimensional coordinate system is established based on the horizontal plane, wherein the xoz plane determined by the x-axis and the z-axis is the horizontal plane, and the axis perpendicular to the horizontal plane is the y-axis. The reflectarray antenna is composed of a horn feed antenna and a reflector array. The horn feed antenna is used to transmit and receive electromagnetic waves, and its bottom surface is located on the xoy plane.

[0007] The reflective array consists of a periodic arrangement of several reflective units of the same size, shape, and material. Each reflective unit includes a horizontal structure and a vertical structure. The horizontal structure and the vertical structure are respectively composed of metal layers covered on a rectangular dielectric substrate of the same thickness. The horizontal structure is parallel to the xoz plane, and the vertical structure is parallel to the yoz plane. Both the horizontal and vertical structures are perpendicular to the xoy plane.

[0008] The horizontal structure and the vertical structure are used to regulate the incident electromagnetic waves in the horizontal polarization and vertical polarization directions, respectively. A first card slot and a first metallized through-hole array are etched along the z-axis direction in the horizontal structure, wherein the upper and lower bottom edges of the first card slot are parallel to each other, and the first metallized through-hole array is composed of a preset number of circular through-holes arranged in a straight line along the z-axis direction, and the straight line connecting the centers of the circular through-holes is collinear with the lower bottom edge of the first card slot; a second card slot and a second metallized through-hole array are etched along the z-axis direction in the vertical structure, wherein the second metallized through-hole array is composed of a preset number of circular through-holes arranged in a straight line along the z-axis direction, and the straight line connecting the centers of the circular through-holes is collinear with the upper bottom edge of the second card slot, the number of circular through-holes in the second metallized through-hole array is the same as the number of the first metallized through-hole array and the positions correspond to each other, the first card slot and the second card slot are the same size and the positions correspond to each other, the horizontal structure and the vertical structure are plugged together through the first card slot and the second card slot, and when the horizontal structure and the vertical structure are plugged together, the first metallized through-hole array and the second metallized through-hole array are connected to each other;

[0009] The horizontal structure includes a horizontal absorption groove with an absorption function and a horizontal phase-modulating groove with a phase-shifting function etched on the metal layer; the vertical structure includes a vertical absorption groove with an absorption function and a vertical phase-modulating groove with a phase-shifting function etched on the metal layer; the dielectric substrates of the horizontal structure in each adjacent reflection unit are connected to each other, and the dielectric substrates of the vertical structure are connected to each other to form a centrally symmetrical reflection array.

[0010] As a preferred technical solution of the present invention, the horizontal absorption slot and the horizontal phase modulation slot on the horizontal structure are respectively located on both sides of the first card slot, and one end of the horizontal phase modulation slot coincides with the short side of the dielectric substrate of the horizontal structure. The horizontal absorption slot is composed of two sections of unequal widths, a first slot line, a second slot line, a first pad at the slot line connection, and a first lossy element. One end of the first slot line coincides with the short side of the dielectric substrate of the horizontal structure. From the positive direction of the z-axis to the negative direction of the z-axis, there are the first slot line, the first pad, and the second slot line. The center lines of the first and second slot lines are collinear and parallel to the long side of the dielectric substrate of the horizontal structure. The first and second slot lines are connected by the first pad. The first lossy element is located on the first pad, and the first lossy element is connected to the first and second slot lines on both sides.

[0011] The vertical absorption groove and the vertical phase modulation groove on the vertical structure are respectively located on both sides of the second metallized through-hole array. One end of the vertical phase modulation groove coincides with the short side of the dielectric substrate of the vertical structure. The vertical absorption groove is composed of three sections of unequal widths, namely the third groove line, the fourth groove line, and the fifth groove line, as well as the second pad at the connection between the third groove line and the fourth groove line, the third pad at the connection between the fourth groove line and the fifth groove line, and the second lossy element and the third lossy element. One end of the third groove line coincides with the short side of the dielectric substrate of the vertical structure, and extends from the positive direction of the z-axis to the negative direction of the z-axis. The order is the third slot line, the second pad, the fourth slot line, the third pad, and the fifth slot line; the center lines of the third slot line, the fourth slot line, and the fifth slot line are collinear and parallel to the long side of the dielectric substrate of the vertical structure; the third slot line and the fourth slot line are connected through the second pad, the second lossy element is located on the second pad, and the second lossy element is connected to the third slot line and the fourth slot line on both sides; the fourth slot line and the fifth slot line are connected through the third pad, the third lossy element is located on the third pad, and the third lossy element is connected to the fourth slot line and the fifth slot line on both sides.

[0012] As a preferred technical solution of the present invention: the reflective array has different response frequencies to incident electromagnetic waves with different polarization directions. Specifically, electromagnetic waves with an electric field direction parallel to the x-axis are defined as horizontally polarized electromagnetic waves, and electromagnetic waves with an electric field direction parallel to the y-axis are defined as vertically polarized electromagnetic waves. When the incident electromagnetic wave is a horizontally polarized electromagnetic wave, the horizontal structure in the reflective unit works, and the reflective array antenna operates in the low frequency band. When the incident electromagnetic wave is a vertically polarized electromagnetic wave, the vertical structure in the reflective unit works, and the reflective array antenna operates in the high frequency band. By selecting a phase-modulation slot at an appropriate position, the phase of the incident electromagnetic wave is controlled.

[0013] As a preferred technical solution of the present invention, the lengths of the first and second card slots along the z-axis direction are half the lengths of the long sides of the horizontal and vertical structures, respectively; the widths of the first and second card slots are greater than and uniformly greater than the thicknesses of the dielectric substrates of the horizontal and vertical structures; the intersection of the first card slot and the horizontal structure dielectric substrate is connected using a first metallized through-hole array arranged equidistantly along the z-axis direction, and the intersection of the second card slot and the vertical structure dielectric substrate is connected using a second metallized through-hole array arranged equidistantly along the z-axis direction.

[0014] As a preferred technical solution of the present invention: the horn feed antenna is placed on the central axis of the reflective array. At different operating frequencies, the distance between the horn feed antenna and the reflective array is different. The horizontal phase-modulation slot and the vertical phase-modulation slot are respectively a slot line with uniform width, and their length is determined by the distance between the reflective unit in which they are located and the horn feed antenna.

[0015] Beneficial effects: Compared with the prior art, the advantages of the present invention include:

[0016] (1) The reflector unit can perform separate phase control on the linearly polarized electromagnetic waves in the two polarization directions, which ensures that the reflector array antenna can operate at two frequencies (5 GHz and 9 GHz) simultaneously, while ensuring high gain, increasing space utilization and reducing costs.

[0017] (2) The dual-polarization out-of-band absorption characteristics of the reflector are inherited by the reflector array. When the incident electromagnetic wave is horizontally polarized, the reflector array can achieve a -9dB radar cross section reduction in the 1.25GHz-8.8GHz range, with a relative bandwidth of 150.2%. When the vertically polarized electromagnetic wave irradiates the reflector array, the reflector array can achieve a -7dB radar cross section reduction in the 1.7GHz-14.2GHz range, with a relative bandwidth of 157.2%. This achieves ultra-wideband radar cross section reduction. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is a three-dimensional structural diagram of a dual-frequency low radar cross-section reflectarray antenna provided according to an embodiment of the present invention;

[0019] Figure 1 Middle: 1. Horn-fed antenna; 2. Reflector array; 3. Reflector unit;

[0020] Figure 2 is a three-dimensional structural diagram of a reflective unit of a dual-frequency low radar cross-section reflectarray antenna provided according to an embodiment of the present invention;

[0021] Figure 2 Middle: 3, reflector unit; 4, horizontal structure; 5, vertical structure; 6, horizontal absorption trough; 7, horizontal phase-modulation trough; 8, vertical absorption trough; 9, vertical phase-modulation trough;

[0022] Figure 3 is a schematic diagram of a metal surface of a horizontal structure in a reflective unit provided by an embodiment of the present invention;

[0023] Figure 3 Middle: 4, horizontal structure; 6, horizontal absorption slot; 6-1, first slot line; 6-2, second slot line; 7, horizontal phase modulation slot; 14, first pad; 15, first lossy element; 16, first card slot; 17, first metallized through-hole array;

[0024] Figure 4 is a schematic diagram of a metal surface of a vertical structure in a reflective unit provided according to an embodiment of the present invention;

[0025] Figure 4 Middle: 5, vertical structure; 8, vertical absorption slot; 8-1, third slot line; 8-2, fourth slot line; 8-3, fifth slot line; 9, vertical phase adjustment slot; 10, second pad; 11, third pad; 12, second lossy element; 13, third lossy element; 18, second card slot; 19, second plated through hole array;

[0026] Figure 5 is a schematic diagram of a dielectric layered structure of a reflection unit provided in an embodiment of the present invention;

[0027] Figure 5 Middle: 20, horizontal structure dielectric substrate; 21, vertical structure dielectric substrate;

[0028] Figure 6 3. This is a diagram showing the relationship between the length of the horizontal phase-modulation slot and its reflection phase at the antenna radiation center frequency of 5 GHz provided by the reflection unit according to an embodiment of the present invention;

[0029] Figure 7 3. This is a diagram showing the relationship between the length of the vertical phase-modulation slot and its reflection phase at the antenna radiation center frequency of 9 GHz provided by the reflection unit according to an embodiment of the present invention;

[0030] Figure 8 This is a graph showing how antenna gain varies with frequency at the antenna radiation center frequency of 5 GHz, provided in an embodiment of the present invention;

[0031] Figure 9 This is a graph showing how antenna gain varies with frequency at the antenna radiation center frequency of 9 GHz, provided in accordance with an embodiment of the present invention;

[0032] Figure 10 is a far-field pattern at the antenna radiation center frequency of 5 GHz provided by an embodiment of the present invention;

[0033] Figure 11is a far-field pattern at the antenna radiation center frequency of 9 GHz provided by an embodiment of the present invention;

[0034] Figure 12 This is a comparison chart of radar cross-section results of a reflectarray antenna and a metal plate of equal size under irradiation of horizontally polarized electromagnetic waves in the frequency band of 1 GHz to 10 GHz, provided in accordance with an embodiment of the present invention;

[0035] Figure 13 This is a comparison diagram of radar cross-section results of a reflectarray antenna and a metal plate of equal size under irradiation of vertically polarized electromagnetic waves in the frequency band range of 1 GHz to 18 GHz, provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0036] The present invention will be further described below in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention.

[0037] The dual-frequency low radar cross-section reflectarray antenna based on a three-dimensional frequency selective structure provided by an embodiment of the present invention establishes a three-dimensional coordinate system based on a horizontal plane, wherein the xoz plane determined by the x-axis and the z-axis is the horizontal plane, and the axis perpendicular to the horizontal plane is the y-axis. The reflectarray antenna is composed of a horn feed antenna and a reflectarray. The horn feed antenna is used to transmit and receive electromagnetic waves, and its bottom surface is located on the xoy plane.

[0038] The reflective array consists of a periodic arrangement of several reflective units of the same size, shape, and material. Each reflective unit includes a horizontal structure and a vertical structure. The horizontal structure and the vertical structure have the characteristics of reflecting electromagnetic waves at different frequencies. The horizontal structure and the vertical structure are respectively composed of metal layers covered on a rectangular dielectric substrate of the same thickness. The horizontal structure is parallel to the xoz plane, and the vertical structure is parallel to the yoz plane. Both the horizontal structure and the vertical structure are perpendicular to the xoy plane.

[0039] The horizontal structure and the vertical structure are used to regulate the incident electromagnetic waves in the horizontal polarization and vertical polarization directions, respectively. A first card slot and a first metallized through-hole array are etched along the z-axis direction in the horizontal structure, wherein the upper and lower bottom edges of the first card slot are parallel to each other, and the first metallized through-hole array is composed of a preset number of circular through-holes arranged in a straight line along the z-axis direction, and the straight line connecting the centers of the circular through-holes is collinear with the lower bottom edge of the first card slot; a second card slot and a second metallized through-hole array are etched along the z-axis direction in the vertical structure, wherein the second metallized through-hole array is composed of a preset number of circular through-holes arranged in a straight line along the z-axis direction, and the straight line connecting the centers of the circular through-holes is collinear with the upper bottom edge of the second card slot, the number of circular through-holes in the second metallized through-hole array is the same as the number of the first metallized through-hole array and the positions correspond to each other, the first card slot and the second card slot are the same size and the positions correspond to each other, the horizontal structure and the vertical structure are plugged together through the first card slot and the second card slot, and when the horizontal structure and the vertical structure are plugged together, the first metallized through-hole array and the second metallized through-hole array are connected to each other;

[0040] The horizontal structure includes a horizontal absorption groove with an absorption function and a horizontal phase-modulating groove with a phase-shifting function etched on the metal layer; the vertical structure includes a vertical absorption groove with an absorption function and a vertical phase-modulating groove with a phase-shifting function etched on the metal layer; the dielectric substrates of the horizontal structure in each adjacent reflection unit are connected to each other, and the dielectric substrates of the vertical structure are connected to each other to form a centrally symmetrical reflection array.

[0041] Reference Figure 1 The reflectarray of the dual-band low radar cross-section reflectarray antenna designed in this invention is 384 mm long in the x-axis and 380 mm wide in the y-axis, consisting of 48 x 38 reflective elements. When the reflectarray antenna operates at 5 GHz, the horn feed antenna emits horizontally polarized electromagnetic waves 285 mm above the center of the reflector array. When the reflectarray antenna operates at 9 GHz, the incident electromagnetic wave is vertically polarized and is located 513 mm above the center of the reflector array.

[0042] The horizontal absorption slot and horizontal phase modulation slot on the horizontal structure are located on either side of the first card slot, respectively. One end of the horizontal phase modulation slot coincides with the short side of the dielectric substrate of the horizontal structure. The horizontal absorption slot consists of two sections of unequal widths: a first slot line, a second slot line, a first pad at the slot line connection, and a first lossy element. One end of the first slot line coincides with the short side of the dielectric substrate of the horizontal structure. From the positive direction of the z-axis to the negative direction of the z-axis, there are the first slot line, the first pad, and the second slot line. The centerlines of the first and second slot lines are collinear and parallel to the long side of the dielectric substrate of the horizontal structure. The first and second slot lines are connected by the first pad. The first lossy element is located on the first pad, and the first lossy element is connected to the first and second slot lines on both sides. The horizontal absorption slot not only absorbs electromagnetic waves but also reflects electromagnetic waves. The frequency of the reflected electromagnetic waves is determined by the length of the second slot line.

[0043] The vertical absorption groove and the vertical phase modulation groove on the vertical structure are respectively located on both sides of the second metallized through-hole array. One end of the vertical phase modulation groove coincides with the short side of the dielectric substrate of the vertical structure. The vertical absorption groove is composed of three sections of the third groove line, the fourth groove line, and the fifth groove line with different widths, as well as the second solder pad at the connection of the third groove line and the fourth groove line, the third solder pad at the connection of the fourth groove line and the fifth groove line, and the second lossy element and the third lossy element. One end of the third groove line coincides with the short side of the dielectric substrate of the vertical structure. From the positive direction of the z-axis to the negative direction of the z-axis, the third groove line, the second solder pad, and the third lossy element are arranged in sequence. The vertical absorption slot comprises a first slot line, a second slot line, a third slot line, and a fourth slot line. The center lines of the third slot line, the fourth slot line, and the fifth slot line are collinear and parallel to the long side of the dielectric substrate of the vertical structure. The third slot line and the fourth slot line are connected by a second slot line. The second lossy element is located on the second slot line, and the second lossy element is connected to the third slot line and the fourth slot line on both sides respectively. The fourth slot line and the fifth slot line are connected by a third slot line. The third lossy element is located on the third slot line, and the third lossy element is connected to the fourth slot line and the fifth slot line on both sides respectively. The length of the fifth slot line determines the frequency of the electromagnetic wave reflected by the vertical absorption slot.

[0044] The reflectarray has different response frequencies to incident electromagnetic waves with different polarization directions. Specifically, electromagnetic waves with an electric field parallel to the x-axis are defined as horizontally polarized electromagnetic waves, and electromagnetic waves with an electric field parallel to the y-axis are defined as vertically polarized electromagnetic waves. Under the illumination of electromagnetic waves with different polarizations, the reflectarray can operate in different bands. When the incident electromagnetic wave is horizontally polarized, the horizontal structure of the reflector unit operates, and the reflectarray antenna operates in the low-frequency band. When the incident electromagnetic wave is vertically polarized, the vertical structure of the reflector unit operates, and the reflectarray antenna operates in the high-frequency band. Selecting the phase-modulation slots in appropriate positions minimizes the coupling between the horizontal and vertical structures, thereby enabling the phase of the incident electromagnetic waves of the two frequencies to be controlled separately. Varying the length of the horizontal and vertical phase-modulation slots only controls the phase at their corresponding center frequencies, and the control range meets the phase shift requirements (greater than 300 degrees), while ensuring that the phase at the other operating center frequency remains almost unchanged.

[0045] When irradiated by horizontally polarized electromagnetic waves and vertically polarized electromagnetic waves, the reflective array inherits the out-of-band absorption characteristics of the unit and has the performance of reducing the radar cross section of dual polarization.

[0046] The lengths of the first card slot and the second card slot along the z-axis direction are half the lengths of the long sides of the horizontal structure and the vertical structure, respectively. The widths of the first card slot and the second card slot are greater than and uniformly greater than the thicknesses of the dielectric substrates of the horizontal structure and the vertical structure. The intersection of the first card slot and the dielectric substrate of the horizontal structure is connected by a first metallized through-hole array arranged equidistantly in the z-axis direction, and the intersection of the second card slot and the dielectric substrate of the vertical structure is connected by a second metallized through-hole array arranged equidistantly in the z-axis direction. This ensures the stability of the connection while maintaining the out-of-band electromagnetic wave absorption function of the absorption slot and the phase shifting function of the phase modulation slot.

[0047] Reference Figure 2-Figure 5The horizontal and vertical structures use Rogers 4003C dielectric substrates with a relative dielectric constant of 3.55, a loss tangent of 0.0027, and a thickness of d = 0.508mm. The metal layer uses a copper clad layer with a thickness of 0.0175mm. The horizontal and vertical structures in the reflector unit can respond to electromagnetic waves of different polarizations. The horizontal absorption slot in the horizontal structure consists of two slot lines of unequal widths, a first pad at the slot line connection, and a first lossy element. From the positive z-axis to the negative z-axis, the first and second slot lines are arranged in order. While providing electromagnetic wave absorption, they also reflect electromagnetic waves. The first lossy element is a thin-film chip resistor in a 0402 package, with a length of 1mm, a width of 0.5mm, and a resistance of 120 ohms. The vertical absorption slot in the vertical structure is composed of three slot lines of unequal lengths, with the second pad, the third pad, the second lossy element and the third lossy element loaded in the middle. From the positive direction to the negative direction of the z-axis, there are the third slot line, the fourth slot line and the fifth slot line respectively. The second lossy element and the third lossy element are both thin-film chip resistors in 0402 package, with a length of 1mm, a width of 0.5mm, and resistance values ​​of 600 ohms and 90 ohms respectively. The horizontal structure and the vertical structure in the reflection unit can regulate electromagnetic waves of different polarization directions, and are connected through the first card slot, the second card slot, the first metallized through-hole array and the second metallized through-hole array. Both the horizontal structure and the vertical structure are composed of a number of planar slot line structures etched on one side of the dielectric substrate, and the etching direction is parallel to the z-axis. The physical parameters in this embodiment are: s c1 =3.825mm,s c2 =4.825mm, h=0.0175mm, d=0.508mm, w r =0.6mm, l r =0.6mm, w c =0.5255mm, l c =26mm, d1=1.5mm, d2=5.5mm, D=0.6mm, s1=0.8mm, w1=1.6mm, l1=24.4mm, w2=1.2mm, l2=23.7mm, s2=1.5 mm, w3=1mm, s3=0.7mm, w4=3mm, l4=15.5mm, w5=1mm, l5=12mm, w6=0.2mm, l6=12.5mm, s4=1.5mm, w7=1mm.

[0048] The horn feed antenna is placed on the central axis of the reflectarray. To achieve high aperture efficiency and operate at different operating frequencies, the distance between the horn feed antenna and the reflectarray varies. Both the horizontal and vertical phase-shifting slots are uniform slot lines, their lengths determined by the distance between the reflector unit and the horn feed antenna. Each reflector unit has two phase-shifting slots, each for phase-modulating electromagnetic waves of different frequencies. By periodically arranging reflectors with varying phase shift values, the spherical waves emitted by the horn feed antenna are transformed into uniform plane waves by the reflection array.

[0049] The relationship between the length of the horizontal phase-modulation slot and the vertical phase-modulation slot and the phase shift value at different working center frequencies is shown in the figure. Figure 6 and Figure 7 Each reflector unit has two phase-modulated slots that respond to electromagnetic waves of different polarization directions. Their physical lengths can be adjusted according to Figure 6 and Figure 7 The curve corresponds to its phase, and the reflection phase of each reflection unit can be determined by the following formula:

[0050]

[0051] in, It represents the reflection phase of the i-th reflection unit when the incident electromagnetic wave is a horizontally polarized electromagnetic wave, and the value of i ranges from 1 to 48×38; k is the propagation constant in free space, R ix It represents the distance from the horn feed antenna (horizontally polarized electromagnetic wave) to the i-th reflector unit when the center frequency of the reflector array antenna is 5 GHz. is the position vector of the i-th reflection unit, is the direction in which the antenna radiates the main beam. Indicates the reflection phase of the i-th reflection unit when the incident electromagnetic wave is a vertically polarized electromagnetic wave, and the value of i ranges from 1 to 48×38. iy It represents the distance from the horn feed antenna (vertically polarized electromagnetic wave) to the i-th reflector unit when the center frequency of the reflectarray antenna is 9 GHz. and Both represent phase constants, indicating that the phase shift value required by the reflect array is a relative phase value rather than an absolute phase value.

[0052] Figure 8This figure shows the gain versus frequency curve for a dual-band, low radar cross-section reflectarray antenna with a center frequency of 5 GHz. The horizontal axis represents frequency in GHz, and the vertical axis represents gain in dBi. The reflectarray antenna achieves a high gain of 24.8 dBi at the 5 GHz center frequency. The -3 dB gain range is 4.47 GHz to 5.77 GHz, with a relative bandwidth of approximately 25.4%. This demonstrates excellent high-gain radiation performance.

[0053] Figure 9 The reflectarray antenna gain versus frequency curve for a dual-band low radar cross-section reflectarray antenna with a center frequency of 9 GHz is shown. The horizontal axis of the figure represents frequency in GHz, and the vertical axis represents gain in dBi. The reflectarray antenna achieves a high gain of 29.8 dBi at the 9 GHz center frequency, with a -3 dB gain range of 7.8 GHz to 9.75 GHz and a relative bandwidth of approximately 22.2%. This demonstrates excellent high-gain radiation performance.

[0054] Figure 10 The E-plane and H-plane far-field patterns of a dual-band low radar cross-section reflectarray antenna operating at a center frequency of 5 GHz are shown. The horizontal axis represents the angle in degrees (deg), and the vertical axis represents the gain in dBi (dBi). The figures show that the reflectarray antenna has a narrow beamwidth and good directivity at 5 GHz, with a first sidelobe level less than -15 dB and an aperture efficiency greater than 56%.

[0055] Figure 11 The E-plane and H-plane far-field patterns of a dual-band low radar cross-section reflectarray antenna operating at a center frequency of 9 GHz are shown. The horizontal axis represents the angle in degrees (deg), and the vertical axis represents the gain in dBi (dBi). The figures show that the reflectarray antenna exhibits a narrow beamwidth and good directivity at 9 GHz, with a first sidelobe level less than -17 dB and an aperture efficiency greater than 57%.

[0056] When the incident wave is a horizontally polarized electromagnetic wave, the radar cross section of the reflection front is compared with the radar cross section of the same-sized PEC, such as Figure 12 As shown in FIG, the reflective front can achieve a -9 dB reduction in radar cross section in the range of 1.25 GHz to 8.8 GHz, and the relative bandwidth is 150.2%.

[0057] When the incident wave is a vertically polarized electromagnetic wave, the radar cross section of the reflection front is compared with the radar cross section of the same-sized PEC, such as Figure 13As shown in FIG, the reflective front can achieve a -7 dB reduction in radar cross section in the range of 1.7 GHz to 14.2 GHz, and the relative bandwidth is 157.2%.

[0058] The embodiments of the present invention are described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments. Various changes can be made within the scope of knowledge possessed by ordinary technicians in this field without departing from the spirit of the present invention.

Claims

1. A dual-frequency low radar cross-section reflectarray antenna based on a three-dimensional frequency selective structure, characterized in that: A three-dimensional coordinate system is established based on a horizontal plane, wherein the xoz plane determined by the x-axis and the z-axis is the horizontal plane, and the axis perpendicular to the horizontal plane is the y-axis. The reflectarray antenna is composed of a horn feed antenna and a reflectarray. The horn feed antenna is used to transmit and receive electromagnetic waves, and its bottom surface is located on the xoy plane. The reflective array consists of a periodic arrangement of several reflective units of the same size, shape, and material. Each reflective unit includes a horizontal structure and a vertical structure. The horizontal structure and the vertical structure are respectively composed of metal layers covered on a rectangular dielectric substrate of the same thickness. The horizontal structure is parallel to the xoz plane, and the vertical structure is parallel to the yoz plane. Both the horizontal and vertical structures are perpendicular to the xoy plane. The horizontal structure and the vertical structure are used to regulate the incident electromagnetic waves in the horizontal polarization and vertical polarization directions, respectively. A first card slot and a first metallized through-hole array are etched along the z-axis direction in the horizontal structure, wherein the upper and lower bottom edges of the first card slot are parallel to each other, and the first metallized through-hole array is composed of a preset number of circular through-holes arranged in a straight line along the z-axis direction, and the straight line connecting the centers of the circular through-holes is collinear with the lower bottom edge of the first card slot; a second card slot and a second metallized through-hole array are etched along the z-axis direction in the vertical structure, wherein the second metallized through-hole array is composed of a preset number of circular through-holes arranged in a straight line along the z-axis direction, and the straight line connecting the centers of the circular through-holes is collinear with the upper bottom edge of the second card slot, the number of circular through-holes in the second metallized through-hole array is the same as the number of the first metallized through-hole array and the positions correspond to each other, the first card slot and the second card slot are the same size and the positions correspond to each other, the horizontal structure and the vertical structure are plugged together through the first card slot and the second card slot, and when the horizontal structure and the vertical structure are plugged together, the first metallized through-hole array and the second metallized through-hole array are connected to each other; The horizontal structure includes a horizontal absorption groove with an absorption function and a horizontal phase-modulating groove with a phase-shifting function etched on the metal layer; the vertical structure includes a vertical absorption groove with an absorption function and a vertical phase-modulating groove with a phase-shifting function etched on the metal layer; the dielectric substrates of the horizontal structure in each adjacent reflection unit are connected to each other, and the dielectric substrates of the vertical structure are connected to each other to form a centrally symmetrical reflection array.

2. The dual-frequency low radar cross-section reflectarray antenna based on a three-dimensional frequency selective structure according to claim 1, characterized in that: The horizontal absorption slot and the horizontal phase modulation slot on the horizontal structure are respectively located on both sides of the first card slot, and one end of the horizontal phase modulation slot coincides with the short side of the dielectric substrate of the horizontal structure. The horizontal absorption slot is composed of two first slot lines of unequal widths, a second slot line, a first pad at the slot line connection, and a first lossy element. One end of the first slot line coincides with the short side of the dielectric substrate of the horizontal structure. From the positive direction of the z-axis to the negative direction of the z-axis, there are the first slot line, the first pad, and the second slot line. The center lines of the first and second slot lines are collinear and parallel to the long side of the dielectric substrate of the horizontal structure. The first and second slot lines are connected by the first pad. The first lossy element is located on the first pad, and the first lossy element is connected to the first and second slot lines on both sides. The vertical absorption groove and the vertical phase modulation groove on the vertical structure are respectively located on both sides of the second metallized through-hole array. One end of the vertical phase modulation groove coincides with the short side of the dielectric substrate of the vertical structure. The vertical absorption groove is composed of three sections of unequal widths, namely the third groove line, the fourth groove line, and the fifth groove line, as well as the second pad at the connection between the third groove line and the fourth groove line, the third pad at the connection between the fourth groove line and the fifth groove line, and the second lossy element and the third lossy element. One end of the third groove line coincides with the short side of the dielectric substrate of the vertical structure, and extends from the positive direction of the z-axis to the negative direction of the z-axis. The order is the third slot line, the second pad, the fourth slot line, the third pad, and the fifth slot line; the center lines of the third slot line, the fourth slot line, and the fifth slot line are collinear and parallel to the long side of the dielectric substrate of the vertical structure; the third slot line and the fourth slot line are connected through the second pad, the second lossy element is located on the second pad, and the second lossy element is connected to the third slot line and the fourth slot line on both sides; the fourth slot line and the fifth slot line are connected through the third pad, the third lossy element is located on the third pad, and the third lossy element is connected to the fourth slot line and the fifth slot line on both sides.

3. The dual-frequency low radar cross-section reflectarray antenna based on a three-dimensional frequency selective structure according to claim 1, characterized in that: The reflective array has different response frequencies to incident electromagnetic waves with different polarization directions. Specifically, electromagnetic waves with an electric field direction parallel to the x-axis are defined as horizontally polarized electromagnetic waves, and electromagnetic waves with an electric field direction parallel to the y-axis are defined as vertically polarized electromagnetic waves. When the incident electromagnetic wave is a horizontally polarized electromagnetic wave, the horizontal structure in the reflective unit works, and the reflective array antenna works in the low frequency band. When the incident electromagnetic wave is a vertically polarized electromagnetic wave, the vertical structure in the reflective unit works, and the reflective array antenna works in the high frequency band. The phase of the incident electromagnetic wave is controlled by selecting the phase adjustment slot in the appropriate position.

4. The dual-frequency low radar cross-section reflectarray antenna based on a three-dimensional frequency selective structure according to claim 1, characterized in that: The lengths of the first card slot and the second card slot along the z-axis direction are half the lengths of the long sides of the horizontal structure and the vertical structure, respectively. The widths of the first card slot and the second card slot are greater than and uniformly greater than the thicknesses of the dielectric substrates of the horizontal structure and the vertical structure. The first card slot is connected to the dielectric substrate of the horizontal structure at an intersection thereof by a first metallized through-hole array arranged equidistantly in the z-axis direction, and the second card slot is connected to the dielectric substrate of the vertical structure at an intersection thereof by a second metallized through-hole array arranged equidistantly in the z-axis direction.

5. The dual-frequency low radar cross-section reflectarray antenna based on a three-dimensional frequency selective structure according to claim 1, characterized in that: The horn feed antenna is placed on the central axis of the reflective array. At different operating frequencies, the distance between the horn feed antenna and the reflective array is different. The horizontal phase-modulation slot and the vertical phase-modulation slot are respectively a section of slot line with uniform width, and their length is determined by the distance between the reflective unit where they are located and the horn feed antenna.

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