A surface wave suppression structure suitable for use in a closely coupled phased array antenna

Abstract

The application discloses a surface wave suppression structure suitable for a tight coupling phased array antenna and belongs to the technical field of antenna engineering. The application is based on the tight coupling phased array antenna. In order to realize wideband scanning, the tight coupling phased array antenna usually needs to add an impedance matching layer, and the matching layer as a kind of periodic structure can guide surface waves at the same time. The appearance of the surface waves can cause serious pattern deterioration, gain reduction, standing wave lifting, isolation deterioration and the like. The application cuts part of a traditional tight coupling phased array antenna medium and adds a columnar metal structure, so that the propagation condition of the surface waves in the periodic environment is destroyed, the surface waves are obviously suppressed, the pattern shape is restored to normal, the gain is obviously improved, and the standing wave and the isolation are also greatly improved. The suppression structure is composed of metal, has the characteristics of lossless, obvious surface wave suppression effect, simple structure and being suitable for a millimeter wave frequency band and the like.

Description

Technical Field

[0001] This invention belongs to the field of antenna engineering technology and relates to a surface wave suppression structure suitable for use in tightly coupled phased array antennas. Tightly coupled phased array antennas are widely used in communications, radar, detection, and other fields. This surface wave suppression structure is lossless, has a significant suppression effect, and a simple structure. Background Art

[0002] With the continuous development of radar and mobile communication systems, antenna reuse to reduce equipment cost and complexity has become an inevitable result. The broadband characteristics and stable beam scanning capabilities of tightly coupled phased array antennas have made them widely used in many airborne, shipborne, satellite communications and other fields. However, in order to reduce system costs, methods of increasing the array unit aperture and thus reducing the number of units within a fixed aperture area are also being explored. When the unit aperture is increased, one of the urgent problems that need to be solved is the surface wave during beam scanning. The surface wave deteriorates the antenna standing wave ratio, reduces the gain, and splits the lobe, seriously reducing the scanning performance of the tightly coupled phased array antenna. In the paper "Fully-planar ultrawideband tightly-coupled array (FPU-TCA) with integrated feed for wide-scanning millimeter-wave applications", a tightly coupled phased array antenna was proposed, but due to the existence of surface waves, its unit spacing was severely reduced to only 0.425×0.425λ. h 2 (λ his the free-space wavelength corresponding to the highest frequency of the antenna), which will greatly increase the system cost; in the paper "Low-profile planar ultrawideband modular antenna array loaded with parasitic metal strips", a surface wave suppression method is proposed. By cutting off a part of the metasurface matching layer and the dielectric plate, the frequency of the TE mode surface wave during H-plane scanning is increased and moved outside the operating frequency band. However, this method involves large-area cutting of the antenna dielectric plate and is suitable for lower-frequency tightly coupled antenna arrays. As the antenna operating frequency increases to the millimeter wave band, this method will be limited by the PCB process and will be difficult to implement; in the paper "Planar, ultra-wideband and dual-polarized phased array antenna for millimeter-wave vehicular communication", a surface wave suppression method is proposed. By inserting a cross metal structure at a key position of the matching layer, a surface wave suppression method is proposed to suppress the TM mode surface wave during E-plane scanning without affecting the normal radiation pattern of the antenna, thereby moving the surface wave to a higher out-of-band frequency. However, this method is also limited in its effect on surface wave suppression. Summary of the Invention

[0003] Building on the background art, this paper proposes a surface wave suppression structure suitable for use in tightly coupled phased array antennas. Made of metal, this structure is lossless, exhibits significant surface wave suppression effectiveness, is simple in structure, and is suitable for millimeter wave frequencies. This structure effectively suppresses TM-mode surface waves during E-plane scanning, significantly optimizing the radiation pattern and increasing antenna gain.

[0004] The technical solution adopted in the present invention is as follows:

[0005] A surface wave suppression structure suitable for use in a tightly coupled phased array antenna. The surface wave suppression structure is a metal cylinder with a continuously changing axial diameter. It is arranged in the hollow part of each unit antenna in the tightly coupled phased array antenna; one end is fixed to the metal floor of the antenna, and the other end is higher than the upper surface of the tightly coupled phased array antenna.

[0006] Furthermore, the surface wave suppression structure includes N segments connected in sequence, N being greater than or equal to 3, and each segment includes two parts with different diameters, and the diameter of the lower part is less than half of the diameter of the upper part.

[0007] Furthermore, the surface wave suppression structure is formed by turning a metal cylinder with uniform thickness.

[0008] A tightly coupled phased array antenna with surface wave suppression structure, the antenna is composed of a plurality of unit antennas arranged in an array, each unit antenna comprises an antenna part and a surface wave suppression structure, the antenna part comprises, from bottom to top, a metal ground plate, a first dielectric substrate, a ground coupling patch, a first layer of prepreg, a second dielectric substrate, a dipole, a second layer of prepreg, a third dielectric substrate, a metamaterial metal patch, a third layer of prepreg, and a fourth dielectric substrate, the antenna part as a whole has a cross shape, the third dielectric substrate, the metamaterial metal patch, the third layer of prepreg, and the fourth dielectric substrate at the center of the cross-shaped antenna structure are provided with a cross-shaped cavity, each wall of the cavity is metal, the metal arms of the cavity are not in contact with the metamaterial metal patch, the metamaterial metal patch has a square patch structure and is arranged on the upper surface of the third dielectric substrate, and the ground coupling patch has a cross shape and is smaller than the projection size of the cross-shaped cavity, the ground coupling patch is connected to the metal ground plate through a ground column passing through the first dielectric substrate.

[0009] The surface wave suppression structure is arranged at the gap between adjacent antenna parts.

[0010] Further, the dipole comprises four metal patches in a diamond structure, the vertices of which point to the center of the cross-shaped antenna structure, and the opposite points of the vertices are connected points, wherein the connected points of adjacent two diamond structures are connected through a metal column, and the connected points of the other two diamond structures are connected through a metal column.

[0011] Further, each branch of the ground coupling patch is provided with a ground column.

[0012] The present application is based on a tightly coupled phased array antenna. In order to realize wideband scanning, the tightly coupled phased array antenna usually needs to add an impedance matching layer, and the matching layer as a kind of periodic structure will guide surface waves at the same time, the appearance of surface waves will cause serious pattern deterioration, gain reduction, standing wave lifting, isolation deterioration, etc. In the present application, a columnar metal structure is added by cutting part of the traditional tightly coupled phased array antenna medium, so that the propagation condition of surface waves in the periodic environment is destroyed, and then the surface waves are obviously suppressed, the pattern shape is restored to normal, the gain is significantly improved, and the standing wave and isolation are also greatly improved. BRIEF DESCRIPTION OF DRAWINGS

[0013] Figure 1 A tightly coupled phased array antenna unit to which a surface wave suppression structure is added according to the present application is shown in the 3D layered view.

[0014] Figure 2 A tightly coupled phased array antenna unit to which a surface wave suppression structure is added according to the present application is shown in the side view.

[0015] Figure 3A top view of the antenna layer of a tightly coupled phased array antenna unit with a surface wave suppression structure added to the present invention.

[0016] Figure 4 A top view of the matching layer of the tightly coupled phased array antenna unit with the addition of a surface wave suppression structure in the present invention.

[0017] Figure 5 An 8×8 phased array 3D view of the surface wave suppression structure was added for the present invention.

[0018] Figure 6 This is a graph showing how the voltage standing wave ratio of the antenna unit of the present invention changes with frequency when the E plane is scanned to 30° before and after the surface wave suppression structure is added.

[0019] Figure 7 This is a graph showing how the isolation of the antenna unit of the present invention changes with frequency when the E-plane is scanned to 30° before and after the surface wave suppression structure is added.

[0020] Figure 8 This is the directional pattern of the 8×8 antenna array of the present invention before and after adding the surface wave suppression structure when the E-plane is scanned to 30° at 30 GHz.

[0021] Figure 9 The figure shows the voltage standing wave ratio of the antenna unit of the present invention changing with frequency at various scanning angles.

[0022] Figure 10 Graph showing the variation of the orthogonal port isolation of the antenna unit of the present invention with frequency at various scanning angles.

[0023] Figure 11 The directional patterns of the 8×8 antenna array of the present invention at various scanning angles in the E-plane at 30 GHz.

[0024] Figure 12 The directional patterns of the 8×8 antenna array of the present invention at various scanning angles in the 30GHz H plane.

[0025] Figure 13 This is a 3D layered view of the surface wave suppression structure of the present invention in another tightly coupled phased array antenna unit.

[0026] Figure 14 This is the radiation pattern of another tightly coupled phased array antenna 12×13 array before and after adding the surface wave suppression structure when the E plane is scanned to 60° at 69GHz.

[0027] Figure 1 In the middle, structure 1 is the matching layer, structure 2 is the surface wave suppression structure, structure 3 is the antenna layer, and structure 4 is the floor; Figure 2The middle structure 5 is the first dielectric plate, the structure 6 is the second dielectric plate, the structure 7 is the third dielectric plate, the structure 8 is the fourth dielectric plate, the structure 9 is the first prepreg, the structure 10 is the second prepreg, and the structure 11 is the third prepreg. Figure 3 The middle structure 12 is a dipole arm, and the structure 13 is a ground coupling plate; Figure 4 The middle structure 14 is a metasurface metal patch, and the structure 15 is a cross metal structure. DETAILED DESCRIPTION

[0028] The surface wave suppression structure of the present invention is a metal cylinder with uneven diameter, which is composed of three groups of metal cylinders of different thicknesses connected together; from the ground upwards, there is a metal cylinder with a smaller diameter, and then upwards, there is a metal cylinder with a larger diameter, and the two are connected; further upwards, there are two other groups of metal cylinders with the same thickness and thinness as the above-mentioned metal cylinders, and the three groups of metal cylinders are connected to each other; this structure can be turned from a metal cylinder of uniform thickness.

[0029] This structure is suitable for tightly coupled phased array antennas. The tightly coupled phased array antenna in the present invention is composed of multiple antenna units, each of which is composed of a PCB board part and a metal floor part;

[0030] The tightly coupled phased array antenna unit PCB board is divided into two parts: an antenna multilayer board part and a matching layer multilayer board part;

[0031] The multilayer board portion of the antenna has a similar structure to a conventional tightly coupled phased array antenna unit, consisting of two sets of dipoles fed orthogonally, feeding and shorting posts, and a ground coupling plate located below the ends of the dipoles.

[0032] The matching layer multilayer board consists of two main parts: a cross-shaped metal structure located above the tail of the orthogonal dipole antenna; and a metamaterial metal patch matching layer. Each antenna unit originally contained four rows and four columns of square metamaterial metal patches. However, to make room for the cross-shaped metal structure, a portion of the metal patches was removed. Furthermore, the dielectric removal of the tightly coupled antenna unit also removed a portion of the metal patches, resulting in the final metamaterial matching layer shape.

[0033] A portion of the dielectric plate above the metamaterial metal patch was removed, leaving only the cross structure and some dielectric plates around it.

[0034] The PCB board has a total of four layers. The PCB board close to the metal floor is named the first layer, and the remaining layers are named the second, third, and fourth layers from bottom to top. The layers are bonded by prepreg. The dipole is located above the second dielectric board. The feed and short-circuit posts pass through the first and second dielectric boards. The ground coupling plate is located above the first dielectric board, and its grounding post passes through the first dielectric board. The cross metal structure passes through the third to fourth dielectric boards. The metamaterial metal patch is located above the third dielectric board.

[0035] The 3D layered view of the tightly coupled phased array antenna unit in this embodiment is as follows: Figure 1 The antenna operates in the 17-31 GHz frequency band. The spacing between adjacent elements in this phased array is 6 mm, or 0.62 times the high-frequency wavelength. The maximum scanning angle of this phased array is ±30°. Calculations show that the condition for a phased array to achieve a maximum scanning angle of ±30° without grating lobes requires that the element spacing be less than 0.66 times the high-frequency wavelength. Therefore, this design maximizes the element spacing while still meeting the grating lobe-free condition. This reduces the number of elements for the same aperture, significantly reducing costs. This phased array element consists of a matching layer 1, a surface wave suppression structure 2, an antenna layer 3, and a metal floor 4. The multilayer dielectric plates of the matching layer 1 and antenna layer 3 are partially cut. This cut portion is an octagonal prism, which, when viewed from above, resembles a square with four corners cut off. The square has a side length of 4.4 mm, and the cut corners are isosceles right triangles with right angles of 0.9 mm. The surface wave suppression structure 2 is machined from a uniformly thick metal column. The thicker portion has a diameter of 1 mm and a height of 0.3 mm; the thinner portion has a diameter of 0.2 mm and a height of 0.7 mm. The total height of the entire structure is 3 mm. It is located at the center of the cut portion of the dielectric plate. The surface wave suppression structure 2 is present in every phased array element. By altering the periodic environment required for surface wave propagation, it significantly suppresses surface waves, thereby optimizing the antenna pattern, reducing standing waves, improving isolation between orthogonal polarizations, and enhancing cross-polarization.

[0036] The layered view of the tightly coupled phased array antenna unit in this embodiment is as follows: Figure 2. The thickness of the first dielectric plate 5 is 1.016mm, the thickness of the second dielectric plate 6 is 0.127mm, the thickness of the third dielectric plate 7 is 0.508mm, and the thickness of the fourth dielectric plate 8 is 0.254mm. The relative dielectric constant of the first dielectric plate 5 is 3.5, and the relative dielectric constants of the remaining dielectric plates are 3. The thickness of the first, second, and third layers of semi-cured sheets 9, 10, and 11 are all 0.111mm, and the relative dielectric constant is 3. Among them, the first layer of dielectric plate 5 adopts a higher dielectric constant, and its purpose is to move the common mode resonance that enters the working band due to the large unit spacing back to outside the working frequency band together with the ground coupling sheet. The fourth layer of dielectric plate 8 and the third layer of semi-cured sheet 11 are further cut compared to other multilayer board parts. The cutting position is the part above the dipole feed and short-circuit column, and the length of the cut part is 3mm.

[0037] The top view of the antenna layer of the tightly coupled phased array antenna unit in this embodiment is as follows: Figure 3 . The dipole arm 12 is hollow. The ground coupling plate 13 has a total of 5 grounding posts, which are arranged in a cross shape. The center grounding post and the two thicker grounding posts on both sides have a diameter of 0.4mm, and the two thinner ones have a diameter of 0.2mm. The two thicker ones are 1mm away from the center, and the two thinner ones are 0.9mm away from the center. The antenna layer design of the tightly coupled antenna is relatively mature and is not the focus of this patent, so the remaining dimensions will not be repeated.

[0038] The matching layer diagram of the tightly coupled phased array antenna unit in this embodiment is as follows: Figure 4 Each antenna unit originally contained 4 rows and 4 columns of square metamaterial metal patches, with a side length of 1.4mm and a spacing of 0.1mm between adjacent patches. However, in order to leave space for the cross-shaped metal structure 15, a portion of the metal patch was removed. After removal, the distance between the metal patch and the cross metal structure 15 was 0.1mm. On the other hand, the dielectric removal of the tightly coupled antenna unit also removed a portion of the metal patch, thus obtaining the final shape of the metamaterial matching layer. The cross metal structure 15 is located above the end of the dipole. From a top view, its center is aligned with the center of the ground coupling plate 13. It consists of a metalized blind groove and solder pads on the upper and lower sides of the blind groove. The blind groove is in the shape of a cross from a top view. The cross is 2mm long and 0.7mm wide. The height is 0.92mm across the third and fourth dielectric plates 7, 8 and the third semi-cured sheet 11. The solder pads on the upper and lower sides of the blind groove are 0.2mm on each side.

[0039] The 3D view of the tightly coupled 8×8 phased array in this embodiment is as follows: Figure 5 The antenna array was expanded on all four sides to facilitate assembly, resulting in an overall array size of 60mm*60mm.

[0040] Figure 6A graph showing the voltage standing wave ratio of the antenna unit of the present invention before and after adding the surface wave suppression structure is given as a function of frequency when the E-plane is scanned to 30°. When the surface wave suppression structure is not added, the antenna unit has an obvious standing wave peak at 30 GHz, but after adding the surface wave suppression structure, the peak disappears, and the overall standing wave shows a downward trend.

[0041] Figure 7 A graph showing the frequency variation of the isolation of the antenna unit before and after adding the surface wave suppression structure is presented when scanning the E plane to 30°. When the surface wave suppression structure is not added, the antenna unit exhibits an obvious isolation deterioration peak at 30 GHz, while the peak disappears after adding the surface wave suppression structure. At the same time, the overall isolation shows a downward trend.

[0042] Figure 8 The directional patterns of the 8×8 antenna array of the present invention before and after adding the surface wave suppression structure when scanning the E-plane to 30° at 30 GHz are presented. Without the surface wave suppression structure, the directional pattern of the 8×8 antenna array is severely distorted when scanning the E-plane to 30°, with a zero depth near 30°. At the same time, the cross-polarization is severely deteriorated, with the amplitude equal to that of the main polarization. After adding the surface wave suppression structure, the directional pattern returns to normal, with the main lobe pointing in the direction of 30°. Ultimately, the gain in the 30° direction is improved by 16.14 dB, and the cross-polarization gain is improved by 36.4 dB.

[0043] Figure 9 A graph showing the voltage standing wave ratio of the antenna unit of the present invention varying with frequency at various scanning angles is given. The antenna can achieve a standing wave ratio of less than 2.2 in the range of 17 to 31 GHz (or even wider) at scanning angles of 0°, 30° on the E plane, and 30° on the H plane.

[0044] Figure 10 A graph showing the variation of the orthogonal port isolation of the antenna unit of the present invention with frequency at various scanning angles is given. The antenna can achieve an orthogonal port isolation of less than -22dB in the range of 17 to 31 GHz at scanning angles of 0°, 30° on the E plane, and 30° on the H plane.

[0045] Figure 11 The directional patterns of the 8×8 antenna array of the present invention at various scanning angles in the E-plane at 30 GHz, where the beams point to 0°, 30°, and -30°, respectively. It can be seen that the beam pointing of this antenna array is stable, with excellent cross-polarization at all scanning angles and no grating lobes. When scanning to the maximum angle, the gain decreases by less than 0.89 dB.

[0046] Figure 12The directional patterns of the 8×8 antenna array of the present invention at various scanning angles in the 30GHz H-plane, where the beams point to 0°, 30°, and -30°, respectively. It can be seen that the beam pointing of this antenna array is stable, the cross-polarization is excellent at various scanning angles, and no grating lobes appear. When scanning to the maximum angle, the gain reduction is less than 0.99dB.

[0047] Figure 13 This is a 3D layered view of the surface wave suppression structure in another tightly coupled phased array antenna unit. To demonstrate the universal applicability of this surface wave suppression structure in tightly coupled phased array antennas, it was applied to another tightly coupled hollow dipole phased array antenna for verification. This tightly coupled hollow dipole phased array antenna has a maximum operating frequency of 69 GHz and an antenna unit spacing of 2.1 mm. The surface wave suppression structure in this antenna unit adopts a five-segment structure with a total height of 2 mm.

[0048] Figure 14 The following are the radiation patterns of another tightly coupled phased array antenna (12×13) before and after adding a surface wave suppression structure, at 69 GHz, when the E-plane scanned to 60°. Without the SAW structure, the 12×13 antenna exhibited severe distortion when scanning the E-plane to 60°, with a zero depth near 60°. However, with the SAW structure added, the radiation pattern returned to normal, with the main lobe correctly pointing toward 60°. Ultimately, the gain at 60° increased by 12 dB, and the cross-polarization gain increased by 8.5 dB. This secondary verification demonstrates the universality and portability of the SAW structure's surface wave suppression capability during beam scanning in tightly coupled phased array antennas.

[0049] The surface wave suppression structure can achieve surface wave suppression during E-plane scanning of a tightly coupled phased array antenna. When the 8×8 antenna array of the present invention is scanned to 30° in the E-plane at 30 GHz, the gain in the 30° direction is increased by 16.14 dB, and the cross-polarization is increased by 36.4 dB. Ultimately, continuous beam scanning from -30° to 30° is achieved within the 17-31 GHz frequency band with a unit spacing of 0.63 times the high-frequency wavelength. The suppression structure is characterized in that the basic unit is a metal cylinder with uneven axial diameter, fixed to the metal base plate of the antenna. The metal cylinder structure is present in each phased array antenna unit, specifically at the center of the cutout portion of the dielectric of each antenna unit of the tightly coupled phased array antenna. The uneven diameter metal cylinders are formed by connecting three groups of metal cylinders of different thicknesses: a metal cylinder with a smaller diameter extending upward from the ground, a metal cylinder with a larger diameter extending upward from the ground, and two more groups of metal cylinders with the same diameter extending upward from the ground, with the three groups of metal cylinders connected to each other. The invention relates to a structure suitable for use in tightly coupled phased array antennas. The tightly coupled phased array antennas of the present invention are composed of multiple antenna units, each of which is composed of a PCB board portion and a metal floor portion. The tightly coupled phased array antenna unit PCB board is divided into two parts: an antenna multilayer board and a matching layer multilayer board. The impedance matching layer that is usually required to be added to a tightly coupled antenna is a periodic structure that supports surface wave propagation. The surface waves that appear during scanning will cause serious deterioration of the directivity pattern, reduced gain, increased standing waves, and deteriorated isolation. The present invention, by cutting off part of the dielectric of a traditional tightly coupled phased array antenna and adding a columnar metal structure, destroys the propagation conditions of the surface waves in a periodic environment. As a result, the surface waves are significantly suppressed, the directivity pattern shape returns to normal, the gain is significantly improved, and the standing waves and isolation are also greatly improved. This design maximizes the unit spacing while meeting the grating lobe-free condition, reduces the number of units under the same caliber, significantly reduces costs, and provides as much space as possible for the back-end chip and circuit design.

Claims

1. A tightly coupled phased array antenna using a surface wave suppression structure, the antenna comprising an array of multiple unit antennas, each unit antenna comprising an antenna portion and a surface wave suppression structure, the antenna portion comprising, from bottom to top: A metal floor, a first dielectric substrate, a ground coupling sheet, a first layer of prepreg, a second dielectric substrate, a dipole, a second layer of prepreg, a third dielectric substrate, a metamaterial metal patch, a third layer of prepreg, and a fourth dielectric substrate. The antenna portion has an overall cross-shaped structure. A cross-shaped cavity is provided in the center of the third dielectric substrate, the metamaterial metal patch, the third layer of prepreg, and the fourth dielectric substrate. The walls of the cross-shaped cavity are all made of metal, and the metal arms of the cross-shaped cavity do not contact the metamaterial metal patch. The metamaterial metal patch has a square sheet structure. The metamaterial metal patch array is arranged on the upper surface of the third dielectric substrate. The ground coupling sheet is cross-shaped and smaller than the projected size of the cross-shaped cavity. The ground coupling sheet passes through the first dielectric substrate via a grounding post and connects to the metal floor. The surface wave suppression structure is located in the gap between adjacent antenna parts; The surface wave suppression structure is a metal cylinder with a continuously changing axial diameter, which is arranged in the hollow of each unit antenna in the tightly coupled phased array antenna; one end is fixed to the metal floor of the antenna, and the other end is higher than the upper surface of the tightly coupled phased array antenna; The surface wave suppression structure includes N segments connected in sequence, N being greater than or equal to 3, each segment including two parts with different diameters, the diameter of the lower part being less than half the diameter of the upper part; The dipole includes four diamond-shaped metal pieces, with the vertices pointing to the center of the antenna's "cross" structure. The points opposite to the vertices are connection points, where the connection points of two adjacent diamond structures are grounded through metal pillars, and the connection points of the other two diamond structures are connected to the signal input end through metal pillars.

2. The tightly coupled phased array antenna using a surface wave suppression structure according to claim 1, wherein: The surface wave suppression structure is formed by turning a metal cylinder with uniform thickness.

3. The tightly coupled phased array antenna using a surface wave suppression structure according to claim 1, wherein: Each branch of the ground coupling plate is correspondingly provided with a grounding column.

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