Strongly Coupled Dual-Polarized Ultra-Wideband Phased Array Antenna Based on Fishbone Slot Loading

Abstract

This invention discloses a strongly coupled dual-polarized ultra-wideband phased array antenna based on fishbone-shaped slot loading and its fabrication method. By proposing a series of fishbone-shaped slots of varying sizes and spacing on the dipole, the traditional cross-shaped dipole is improved, thus extending the antenna's operating bandwidth. The resistive loading of traditional ultra-wideband arrays is not used, improving radiation efficiency. A power divider plus dual balun feeding structure achieves better matching and reduces the antenna's profile height. The entire antenna array uses a thin dielectric substrate, eliminating the need for a thick, wide-angle impedance matching layer, resulting in lighter weight. This invention achieves ±45-degree scanning in the 0.25-1.85 GHz frequency band, and the overall antenna height is 0.054 times the low-frequency wavelength.

Description

Technical Field

[0001] This invention belongs to the field of antenna engineering technology, specifically relating to a strongly coupled dual-polarized ultrawideband phased array antenna based on fishbone-shaped slot loading. Background Technology

[0002] Compared to traditional mechanically scanned antennas, phased array antennas offer advantages such as ease of beamforming, arbitrary beam pointing, and easy multi-beam formation. Ultra-wideband (UWB) phased arrays have garnered significant attention in multifunctional applications, utilizing multiple beams, polarizations, and frequency bands to achieve diverse functions. Traditional UWB antenna elements typically possess large lateral or longitudinal dimensions, hindering the achievement of low-profile, conformal, and lightweight designs. Addressing these drawbacks, a novel type of strongly coupled antenna has emerged in recent years. Unlike traditional broadband phased arrays, strongly coupled antennas utilize coupling between elements to extend the antenna's bandwidth. This type of phased array antenna combines the advantages of wide bandwidth, small size, low profile, and easy conformal design.

[0003] In 2018, the paper "Broadband Antenna Array Aperture Made of Tightly Coupled Printed Dipoles" proposed an ultra-wideband phased array based on tight coupling technology. This antenna uses printed dipoles as radiators in an "egg-box" layout, with coupling capacitors applied at the boundaries of adjacent elements. The feeding structure employs a double-Y balun integrating a balun and an impedance transformer, achieving a VSWR of less than 3 at 60° scanning within a 1.2-6 GHz (5:1) bandwidth. However, this design utilizes vertically placed dipoles and a thick dielectric matching layer, increasing the antenna's profile height and mass, which is detrimental to extending to lower frequencies.

[0004] In patent CN110085975A, the inventors proposed an airborne low-scattering ultra-wideband phased array based on tight coupling technology, achieving a bandwidth of 0.5-2 GHz (4:1). This design uses magnetic dipoles as the basic radiating unit, which is beneficial for conformal design. By loading resistive electromagnetic absorbing metamaterials designed in a conformal environment, the out-of-band RCS of the antenna itself is further reduced over a wide frequency range. However, it is difficult to achieve dual polarization, and the antenna profile is relatively high.

[0005] In patent CN112038753A, the inventors addressed this problem by using cross-placed electric dipoles to achieve dual polarization and replacing the traditional dielectric matching layer with an artificial metamaterial impedance matching layer. This overcomes the shortcomings of the traditional dielectric matching layer, such as its high profile and bulkiness, and offers advantages in conformal processing. However, the operating bandwidth of this array antenna still needs to be further expanded, making it difficult to meet the requirements for wider bandwidth.

[0006] To address the aforementioned problems, this invention discloses a strongly coupled dual-polarized ultrawideband phased array antenna based on fishbone-shaped slot loading, aiming to achieve breakthroughs in expanding bandwidth and reducing profile. Summary of the Invention

[0007] The purpose of this invention is to address the problems of insufficient bandwidth, especially in the low-frequency band, and high profile of traditional strongly coupled ultra-wideband antennas. By adding a series of fishbone-shaped slots of varying sizes and spacing to the structure of the antenna radiator and using a power divider plus a dual balun feeding structure, a profile height of 0.054 low-frequency wavelengths and a bandwidth of 0.25-1.85 GHz (7.4:1) are achieved. The antenna operates in a dual-polarization mode and can achieve ±45-degree scanning.

[0008] To achieve the aforementioned objectives, the technical solution adopted in this invention is as follows: a strongly coupled dual-polarized ultra-wideband phased array antenna based on a herringbone-shaped slot loading. The antenna array includes a double-layered, thin antenna dielectric substrate (100), a cross-shaped dipole element (101) with herringbone-shaped slots printed on the upper surface of the upper layer of the antenna dielectric substrate, triangular parasitic patches (102) and square parasitic patches (103) printed on the lower surface of the upper layer of the antenna dielectric substrate, a Marchand balun (201) without short-circuit posts, a Marchand balun (202) with short-circuit posts, a microstrip power divider (300) placed on a metal floor, and a metal floor (400).

[0009] The dipole layer employs a thin, dual-layer dielectric substrate. The upper surface of the first substrate is printed with modified triangular cross-shaped dipoles, filling in the gaps at non-crossing dipole locations with identical shapes rotated 90°. A series of herringbone-shaped slots of varying sizes and spacing are formed within the dipole structure; this structure improves the antenna's low-frequency characteristics without resistive loading. The lower surface is printed with similarly shaped triangular parasitic patches. Correspondingly, the lower surface of the second substrate has three square coupling parasitic patches printed. The dipoles and parasitic patches are tightly connected, and the gaps between the metal patches and between the upper and lower metal patches generate sufficient capacitive coupling to counteract the inductance caused by ground short circuits at low frequencies, thereby extending the low-frequency bandwidth.

[0010] Furthermore, two dipoles are placed in each polarization direction of the antenna element, arranged in a cross shape. Each dipole is fed by a Marchand balun and connected to a power divider placed on a metal ground plane. The power divider is fed by a 50Ω coaxial connector. This dual balun feeding method enables impedance transformation from the 50Ω coaxial connector to the dipoles.

[0011] Furthermore, in each polarized element, a metal strip is loaded on the right side of the two elements relative to the power divider. This strip is printed on the back of the Marchand balun and is electrically connected to the dipole and the ground at its top and bottom ends, respectively, serving as a short-circuit post to suppress the common-mode resonance effect of the array.

[0012] Furthermore, the metal floor is provided with a series of through holes and threaded holes for mounting connectors, fixing power dividers, and fixing the upper dielectric substrate. The floor and the upper dielectric substrate are supported and fixed together by nylon pillars.

[0013] In summary, this antenna design has the following innovations: (1) It improves upon the traditional approach of achieving ultra-wideband characteristics based on resistive loading, achieving ultra-wideband operation without resistive loading and improving radiation efficiency. (2) It fills the gaps in the dipoles with the same shape, making the three parts of the radiator structure identical in shape and increasing the coupling capacitance. (3) It opens a series of fishbone-shaped slots of varying sizes and spacing on the dipoles, improving low-frequency performance. (4) In the dual baluns of each polarization direction of the antenna array element, the right balun, with the power divider position as a reference, is loaded with a printed metal strip as a short-circuit post, while the left balun remains unchanged, improving the common-mode resonance problem of the antenna array. (5) It reduces the profile height, achieves a working frequency band of 7.4 octaves, and has a profile height of only 0.054 low-frequency wavelengths, eliminating the traditional thick wide-angle impedance matching layer, making the entire antenna lighter. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of a strongly coupled dual-polarized ultrawideband phased array antenna element based on a herringbone-shaped slot loading. In this diagram, 100 is a double-layered, thin antenna dielectric substrate; 101 is a cross-shaped dipole element with herringbone-shaped slots printed on the upper surface of the upper layer of the antenna dielectric substrate; 201 and 202 are Marchand baluns with and without short-circuit posts, respectively; 300 is a microstrip power divider; and 400 is a metal ground plane.

[0015] Figure 2 and Figure 3 This is a schematic diagram of the entire two-dimensional planar array antenna at different angles. The antenna is arranged according to... Figure 1 The units are arranged in a 10×4 array to excite the central 8×2 unit.

[0016] Figure 4 This describes the structure of the coupling parasitic patches in the antenna radiator. 102 is a triangular metal patch, similar in shape to a dipole, printed on the back side of the first dielectric substrate, aligned with the center of the dipole. 103 is a square metal patch, printed on the back side of the second dielectric substrate. The gaps between the parasitic patches and between the upper and lower patches can generate sufficient capacitive coupling, thereby improving the low-frequency bandwidth.

[0017] Figure 5 The power divider is fed by a dual balun. 201 and 202 are the Marchand balun with and without a shorting post, respectively. Square holes are opened at the top and bottom ground of the balun to optimize impedance matching. 203 is the shorting post loaded on the right balun. 204 is the vertical connection between the balun and the dipole. 205 is the vertical connection between the balun and the power divider. 300 is the microstrip power divider. 301 is the isolation resistor of the power divider. 302 is the vertical connection between the power divider and the balun. 400 is the metal ground plane.

[0018] Figure 6 and Figure 7 The simulation results show the active standing waves at 0-45 degrees scanning on typical ports when the array antenna scans in the E-plane and H-plane, respectively.

[0019] Figure 8 The simulation results show the radiation efficiency of the entire antenna during the 0-45 degree scan when the array antenna is scanned in the E-plane.

[0020] Figure 9 , 10 Figures 1 and 11 show the simulation results of the scanning patterns of the array antenna at low frequency (0.4 GHz), mid frequency (0.9 GHz), and high frequency (1.8 GHz) when scanning the E-plane, respectively.

[0021] Figure 12 , 13 Figures 1 and 14 show the simulation results of the scanning patterns of the array antenna at low frequency (0.4 GHz), mid frequency (0.9 GHz), and high frequency (1.8 GHz) when scanning the H-plane, respectively. Detailed Implementation

[0022] like Figure 1 As shown, this embodiment is based on a tightly coupled ultra-wideband low-profile conformal phased array antenna with resistor ring loading. It consists of a double-layer thin antenna dielectric substrate 100, a cross-shaped dipole element 101 with fishbone-shaped slots printed on the upper surface of the upper layer of the antenna dielectric substrate, a Marchand balun 201 without short-circuit posts, a Marchand balun 202 with short-circuit posts, a microstrip power divider 300, and a metal ground plane 400.

[0023] All antenna dielectric substrates are made of Rogers RO4350 dielectric substrate. The radiating patch layer 100 is composed of two dielectric substrates laminated together. The feed balun is a stripline structure, composed of two dielectric substrates laminated together. The ground plane is made of aluminum plate. The back of the microstrip power divider and the metal ground plane need to be bonded together with conductive adhesive, and holes are made in the power divider dielectric substrate and the ground plane for fixation. The vertical connection between the balun and the power divider, and the electrical connection between the balun and the dipole are ensured by welding. The through holes in the antenna layer and the ground plane are fixed by nylon posts.

[0024] Figure 5 The power divider and balun substrate shown both use Rogers RO4350 dielectric substrates. The balun has a stripline structure, with its top and bottom grounds connected via metallized vias, and its ends soldered to a metal ground plane to ensure grounding. The power divider is soldered to the ground plane, and its 1-to-2 splitting configuration allows for a 50Ω to 100Ω conversion of the coaxial connector. The stripline structure of the balun can handle the input impedance variation from 100Ω to the antenna layer, achieving excellent impedance matching without increasing the balun length.

[0025] The overall profile height of the antenna is 0.054 times the low-frequency wavelength, excluding the thickness of the metal ground plane, and the spacing between adjacent elements is 75mm.

[0026] Figure 6 The simulation results show the active standing waves of the array antenna when scanning the E-plane at 0°, 30°, and 45°. It can be seen that good matching performance is achieved in the 0.25-1.85 GHz frequency band.

[0027] Figure 7 The simulation results show the active standing wave (VSWR) of the array antenna when scanning the H-plane at 0°, 30°, and 45°. It can be seen that good matching performance is achieved in the 0.25-1.85 GHz frequency band.

[0028] Figure 8 The simulation results show the radiation efficiency of the array antenna when scanning the E-plane at 0°, 30°, and 45°. It can be seen that the radiation efficiency is relatively high in the 0.25-1.85GHz frequency band, except for a few frequency points.

[0029] Figure 9 The simulation results show the scanning pattern of the array antenna at a low frequency of 0.4 GHz when scanning in the E-plane. The beam directivity of the pattern is good, and the polarization isolation is above 34 dB.

[0030] Figure 10 The simulation results show the scanning pattern of the array antenna at an intermediate frequency of 0.9 GHz when scanning in the E-plane. The beam directivity of the pattern is good, and the polarization isolation is above 28 dB.

[0031] Figure 11 The simulation results show the scanning pattern of the array antenna at a high frequency of 1.8 GHz when scanning in the E plane. The beam directivity of the pattern is good, the cross polarization is slightly increased, but the isolation is still above 14 dB.

[0032] Figure 12 The simulation results show the scanning pattern of the array antenna at a low frequency of 0.4 GHz when scanning in the H-plane. The beam directivity of the pattern is good, and the polarization isolation is above 37 dB.

[0033] Figure 13The simulation results show the scanning pattern of the array antenna at an intermediate frequency of 0.9 GHz when scanning in the H-plane. The beam directivity of the pattern is good, and the polarization isolation is above 35 dB.

[0034] Figure 14 The simulation results show the scanning pattern of the array antenna at a high frequency of 1.8 GHz when scanning in the H-plane. The beam directivity of the pattern is good, the cross polarization is slightly increased, but the isolation is still above 13 dB.

[0035] The embodiments described above are merely illustrative of specific implementations of the present invention. Their descriptions are quite specific and detailed, and should be understood as being presented only as examples and not as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention.

Claims

1. A strongly coupled dual-polarized ultra-wideband phased array antenna based on fishbone-shaped slot loading, characterized in that, It includes a double-layer thin antenna dielectric substrate (100), a cross-shaped dipole unit (101) with fishbone-shaped slots printed on the upper surface of the upper layer of the antenna dielectric substrate, a triangular parasitic patch (102) printed on the lower surface of the first layer of the antenna dielectric substrate, a square parasitic patch (103) printed on the lower surface of the second layer of the antenna dielectric substrate, a Marchand balun without shorting posts (201), a Marchand balun with shorting posts (202), a microstrip power divider (300) placed on a metal floor, and a metal floor (400). The microstrip power divider and the Marchand balun are both printed on a thin dielectric substrate. The dielectric substrate of the microstrip power divider is placed parallel to the dielectric substrate of the antenna, and the balun is placed perpendicular to the dielectric substrate of the antenna. The overlapping part is fixed by opening a rectangular slot. A combination of triangular and square parasitic patches is used to be tightly connected to the dipole antenna structure to enhance the coupling between antenna elements. A series of fishbone-shaped slots of different sizes and spacings are opened on the dipole. The resistive loading of traditional ultra-wideband array antennas is not used, which effectively expands the operating bandwidth of the low frequency band and improves the radiation efficiency.

2. The strongly coupled dual-polarized ultra-wideband phased array antenna based on fishbone-shaped slot loading according to claim 1, characterized in that... A power divider plus dual balun feeding structure is applied. In the antenna element, there are two dipoles in the same polarization direction, each fed by a Marchand balun and connected to a 1-to-2 power divider. This can effectively achieve impedance matching from the characteristic impedance of the coaxial connector to the dipole. The balun performs less impedance transformation function, which can realize the miniaturization of the balun and reduce the overall profile height of the antenna.

3. The strongly coupled dual-polarized ultra-wideband phased array antenna based on fishbone-shaped slot loading according to claim 1, characterized in that... The dielectric substrates are all made of thin, flexible dielectric material, eliminating the traditional thick, wide-angle impedance matching layer and making them lighter. The array antenna uses a metal ground plane to enhance mechanical strength, and the metal ground plane is bonded to the lower surface of the power divider with conductive adhesive to ensure good electrical connection between the metal ground plane and other structures that need to share a ground.

Images