A broadband low-scattering array antenna based on a feed network design

Abstract

A kind of broadband low scattering array antenna based on feed network design, including N×N identical structure periodic arrangement antenna unit, antenna unit includes first dielectric layer, second dielectric layer, third dielectric layer, fourth dielectric layer placed in turn from top to bottom superimposed;First upper layer metal patch is equipped with on the upper surface of first dielectric layer, second lower layer metal patch is equipped with on the upper surface of second dielectric layer, third L-shaped feed structure is equipped with on the upper surface of third dielectric layer;Every four identical structure periodic arrangement antenna unit forms a subarray, and the bottom of each subarray is equipped with a broadband feed network structure;Third L-shaped feed structure is connected with broadband feed network structure by passing through metallized via;The present application is through the broadband design of antenna unit and the broadband design of various passive microwave devices used, both can guarantee the radiation performance of broadband, and can realize the scattering reduction effect of broadband, can be applied to radar cross section reduction and electrically controlled adjustable control broadband field.

Description

Technical Field

[0001] This invention belongs to the field of artificial electromagnetic surface technology, specifically relating to a broadband low-scatter array antenna based on a feed network design. Background Technology

[0002] As a new technology, electromagnetic metamaterials have attracted widespread attention since their inception due to their unique electromagnetic properties, and have rapidly developed into a cutting-edge interdisciplinary field involving physics, chemistry, materials science, and information science. Compared to early electromagnetic metasurfaces that could only achieve a single function, multifunctional metasurfaces can achieve multi-dimensional control of electromagnetic waves, and their application scenarios are also more extensive. Various countries and institutions are constantly promoting the industrial application of multidimensional metamaterials.

[0003] RCS reduction technology for antennas is currently a research hotspot in the antenna field. In recent years, many experts and scholars at home and abroad have published numerous research results in this area, which can be broadly divided into two categories: loading metamaterials and integrated radiation and scattering design. The method of loading metamaterials to reduce antenna RCS can be further divided into three categories, corresponding to the manipulation of the amplitude, phase, and polarization of the electromagnetic waves scattered by the antenna. Integrated radiation and scattering design can also be divided into three categories: changing the antenna shape, randomly rotating elements, and changing the antenna feed structure.

[0004] In recent years, domestic experts and scholars have conducted extensive research on antenna RCS reduction technology. Some methods reduce antenna RCS by loading metamaterials above the antenna or around its radiating aperture. Examples include loading radar-absorbing materials (RAM), frequency-selective surfaces (FSS), artificial magnetic conductors (AMC), phase-gradient metasurfaces (PGM), and polarization-conventional metasurfaces (PCM). While these methods have achieved good RCS reduction performance, they can negatively impact the antenna's radiation performance. Specifically, loading metamaterials can increase the antenna's profile or introduce additional area outside the radiating aperture, thus reducing the antenna's aperture efficiency.

[0005] To address the problems introduced by loading metamaterials, some researchers have recently achieved a balance between good RCS reduction and unaffected radiation characteristics by integrating radiation and scattering in antenna design. This involves the three methods mentioned above: changing the antenna shape, randomly rotating elements, and altering the antenna feed structure.

[0006] Antennas, as special scatterers, possess unique scattering mechanisms compared to ordinary scatterers, making RCS reduction significantly more challenging. Current techniques for reducing antenna RCS all have drawbacks, hindering their large-scale array deployment. For stealth aircraft, large-scale phased array antennas on the nose are indispensable for ensuring communication; however, such large-scale arrays lead to an order-of-magnitude increase in the RCS of specific angular regions.

[0007] Patent application CN107579346A discloses a microstrip antenna based on a polarization conversion surface, comprising a dielectric layer, a metal ground plane, a polarization conversion surface, radiating elements, and a coaxial connector. The metal ground plane is printed on the lower surface of the dielectric layer, and the polarization conversion surface is printed on the upper surface of the dielectric layer. A rectangular cavity is disposed at the center of the upper side of the dielectric layer, and a radiating element fixed to the output end of the coaxial connector is disposed above the cavity. The polarization conversion surface consists of four polarization conversion element groups, each containing several decreasing fractal elements, with the decreasing fractal elements in adjacent polarization conversion element groups arranged in directions differing by 90°. However, this invention exhibits a peak gain of only 7.13 dBi at 14 GHz, indicating poor antenna gain.

[0008] Patent application CN111900547B discloses a broadband low-scatter microstrip array antenna based on a coded metasurface. It comprises a square upper dielectric substrate, a middle dielectric substrate, and a lower dielectric substrate arranged vertically and not in contact with each other. The upper dielectric substrate has M×M periodically arranged rectangular microstrip radiating patches printed at its center. The middle dielectric substrate has a coded metasurface printed on its upper surface. The lower dielectric substrate has a single-input M-to-2 output microstrip feed network printed on its upper surface and a metal ground plane printed on its lower surface. The microstrip feed network is connected to the rectangular microstrip radiating patches via metal probes penetrating the middle and upper dielectric substrates. However, this invention cannot achieve the low in-band RCS characteristic of arbitrary linearly polarized electromagnetic wave incidence. Summary of the Invention

[0009] To overcome the shortcomings of the prior art, the present invention aims to provide a broadband low-scatter array antenna based on a feed network design. By designing the antenna elements and various passive microwave devices, the entire feed network is designed to be broadband, which can ensure both broadband radiation performance and broadband scattering reduction effect. It can be applied to the fields of radar cross-section reduction and electronically controllable broadband.

[0010] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0011] A broadband low-scatter array antenna based on a feed network design includes N×N antenna elements 10 arranged periodically with the same structure, where N≥2 and N is a positive integer. Each antenna element 10 includes a first dielectric layer 2, a second dielectric layer 4, a third dielectric layer 6, and a fourth dielectric layer 7 stacked sequentially from top to bottom. A first upper metal patch 1 is disposed on the upper surface of the first dielectric layer 2, a second lower metal patch 3 is disposed on the upper surface of the second dielectric layer 4, and a third L-shaped feed structure 5 is disposed on the upper surface of the third dielectric layer 6.

[0012] Four antenna elements 10 arranged periodically with the same structure form a subarray, and a broadband feed network structure 8 is provided at the bottom of each subarray; the third L-shaped feed structure 5 is connected to the broadband feed network structure 8 through a metallized via.

[0013] The broadband power supply network structure 8 includes a broadband crossover bridge 8.2 located in the middle. The broadband crossover bridge 8.2 includes a first port 8.2.1, a second port 8.2.2, a third port 8.2.3, and a fourth port 8.2.4. Four broadband three-branch couplers 8.1 are arranged around the broadband crossover bridge 8.2. The four broadband three-branch couplers 8.1 include: a first broadband three-branch coupler 8.11 and a third broadband three-branch coupler 8.13 arranged diagonally; and a second broadband three-branch coupler 8.12 and a fourth broadband three-branch coupler 8.14 arranged diagonally. Branch line coupler 8.1 includes an input port 8.1.1, an isolation port 8.1.2, a through port 8.1.3, and a coupling port 8.1.4. The isolation ports 8.1.2 of the first broadband three-branch branch line coupler 8.11 and the third broadband three-branch branch line coupler 8.13, located diagonally, are connected to the first port 8.2.1 and the third port 8.2.3 of the broadband cross bridge 8.2, respectively. The isolation ports 8.1.2 of the second broadband three-branch branch line coupler 8.12 and the fourth broadband three-branch branch line coupler 8.14, located diagonally, are connected to the second port 8.2.2 and the fourth port 8.2.4 of the broadband cross bridge 8.2, respectively.

[0014] The input port 8.1.1 of the first broadband three-branch line coupler 8.11 and the second broadband three-branch line coupler 8.12 are respectively connected to the first output port 8.4.2 and the second output port 8.4.3 of the first Wilkinson power divider 8.41; the input port 8.1.1 of the third broadband three-branch line coupler 8.13 and the fourth broadband three-branch line coupler 8.14 are respectively connected to the first output port 8.4.2 and the second output port 8.4.3 of the second Wilkinson power divider 8.42.

[0015] The input port 8.4.1 of the first Wilkinson power divider 8.41 is connected to the first output port 8.4.2 of the third Wilkinson power divider 8.43 through the open stub 8.3.2 of the 180° broadband stub-loaded phase shifter 8.3; the input port 8.4.1 of the second Wilkinson power divider 8.42 is connected to the second output port 8.4.3 of the third Wilkinson power divider 8.43 through the λ / 8 short circuit 8.3.1 of the 180° broadband stub-loaded phase shifter 8.3; the input port 8.4.1 of the third Wilkinson power divider 8.43 is connected to an external power supply to power the entire power supply structure.

[0016] When the first port 8.2.1 and the third port 8.2.3 of the broadband cross bridge 8.2 on the broadband feed network structure 8 are connected, feed network A is formed; when the second port 8.2.2 and the fourth port 8.2.4 are connected, feed network B is formed. There is a broadband feed network structure 8 at the bottom of every subarray composed of four antenna elements 10. Every antenna array composed of four subarrays contains two feed networks A and two feed networks B distributed in a checkerboard pattern.

[0017] Each of the subarrays includes four third L-shaped feed structures 5, each third L-shaped feed structure 5 including a first L-shaped feed structure port 5.1 and a second L-shaped feed structure port 5.2;

[0018] Each first L-shaped power supply structure port 5.1 is connected to the through port 8.1.3 of the first broadband three-branch line coupler 8.11, the second broadband three-branch line coupler 8.12, the third broadband three-branch line coupler 8.13, and the fourth broadband three-branch line coupler 8.14 respectively through the first metallized via 9.1 penetrating the fourth dielectric layer 7;

[0019] Each second L-shaped power supply structure port 5.2 is connected to the coupling ports 8.1.4 of the first broadband three-branch coupler 8.11, the second broadband three-branch coupler 8.12, the third broadband three-branch coupler 8.13, and the fourth broadband three-branch coupler 8.14 respectively through the second metallized via 9.2 penetrating the fourth dielectric layer 7.

[0020] The first dielectric layer 2, the second dielectric layer 4, and the third dielectric layer 6 are all made of F4BM with a dielectric constant of 2.2 and a loss tangent of 0.002. The fourth dielectric layer 7 is made of Rogers RT / duroid6010 / 6010LM(tm) with a dielectric constant of 10.2 and a loss tangent of 0.0023.

[0021] The side length of the first upper metal patch 1 is L1, L1 = 13mm~15mm. The first upper metal patch 1 passes through the metallized vias located between the first dielectric layer 2 and the second dielectric layer 4 and is connected to the fourth dielectric layer 7 and the broadband power supply network structure 8.

[0022] The first upper metal patch 1, the second lower metal patch 3, and the broadband power supply network structure 8 are all made of copper, and their thicknesses are all 0.01mm to 0.02mm.

[0023] The second lower metal patch 3 has a side length of L2, L2 = 15mm to 17mm. The second lower metal patch 3 passes through the metallized via located in the second dielectric layer 4 and is connected to the fourth dielectric layer 7 and the broadband power supply network structure 8.

[0024] The thickness of the first dielectric layer 2 is H1, where H1 = 5 mm to 7 mm; the thickness of the second dielectric layer 4 is H2, where H2 = 1 mm to 2 mm; the thickness of the third dielectric layer 6 is H3, where H3 = 3 mm to 5 mm; and the side lengths of the first dielectric layer 2, the second dielectric layer 4, and the third dielectric layer 6 are all P, where P = 33 mm to 37 mm.

[0025] The third L-shaped feed structure 5 is the metal strip portion of the L-shaped feed probe. The two ends of the third L-shaped feed structure 5 pass through the first metallized via 9.1 and the second metallized via 9.2 of the fourth dielectric layer 7, respectively.

[0026] The fourth dielectric layer 7 is the upper floor of the broadband power supply network structure 8, and the thickness of the fourth dielectric layer 7 is H4, where H4 = 0.6 mm to 0.7 mm.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0028] 1. The broadband power supply network structure 8 of the present invention consists of a broadband three-branch line coupler 8.1, a broadband cross bridge 8.2, a 180° broadband stub-loaded phase shifter 8.3, and three Wilkinson power dividers 8.4. The operating bandwidth of these devices can meet the bandwidth requirements of broadband design. The isolation of the broadband power supply network structure 8 designed with the above devices can meet the bandwidth requirements of broadband design.

[0029] 2. The present invention can achieve in-band RCS reduction of the antenna through the structural design of the broadband feed network structure 8. Since there is a 180° reflection phase difference between the subarrays of different feed networks loaded on the antenna array, the surface current of the antenna is designed to have a reverse effect about the center regardless of the polarization of the incident electromagnetic wave.

[0030] 3. This invention achieves an array antenna with low in-band RCS characteristics through the design of a broadband feed network structure 8 for the array antenna, which has the prospect of large-scale array application. It avoids the defects of existing antenna RCS reduction methods and proposes a new technical method for in-band RCS reduction of antennas. It has the characteristics of wide frequency band coverage, flexible control, diverse functions and strong practicality. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the unit structure of the present invention; wherein, Figure 1 (a) is a schematic diagram of the structure of the antenna element 10 of the present invention. Figure 1 (b) is a schematic diagram of the structure of a subarray formed by four periodically arranged antenna elements 10 with the same structure according to the present invention.

[0032] Figure 2 This is a schematic diagram of the antenna structure of the present invention, which consists of N×N identical antennas arranged periodically.

[0033] Figure 3 These are schematic diagrams of two 2x2 subarray X-type broadband feeder network structures according to the present invention. Figure 3 (a) is diagram A of the broadband feeder network. Figure 3 (b) is a diagram of broadband feeder network B; the broadband feeder network B can be seen as a result of broadband feeder network A rotating 90° around the center of the subarray.

[0034] Figure 4 This is a schematic diagram of the broadband power supply network structure 8 of the present invention; wherein, Figure 4 (a) is a schematic diagram of the structure of the broadband three-branch line coupler 8.1 of the present invention. Figure 4 (b) is a schematic diagram of the structure of the broadband cross-bridge 8.2 of the present invention. Figure 4 (c) is a schematic diagram of the 180° broadband stub-loaded phase shifter 8.3 of the present invention. Figure 4 (d) is a schematic diagram of the Wilkinson power divider 8.4 of the present invention.

[0035] Figure 5 This is a comparison chart of the radiation performance of the present invention and a reference antenna; wherein, Figure 5 (a) S11, which compares the designed antenna with the reference antenna. Figure 5 (b) shows the axial ratio and gain diagram of the maximum radiation direction.

[0036] Figure 6 The simulation results of the normalized radiation pattern of the present invention and the reference antenna are shown; wherein, Figure 6 (a), 6(b), and 6(c) are the designed antennas. Figure 6 (d), 6(e), and 6(f) are reference antenna 1. Figure 6(g), 6(h), and 6(i) are reference antenna 2.

[0037] Figure 7 The following are simulation results of the surface current of the reference antenna patch under X-polarized and Y-polarized incident waves according to the present invention; wherein, Figure 7 (a) is the incident X-polarized wave. Figure 7 (b) is the incident Y-polarized wave.

[0038] Figure 8 The following are simulation results of the scattering patterns of the X-polarized and Y-polarized incident waves with the reference antenna according to the present invention; wherein, Figure 8 (a) Simulation results of the scattering patterns of the designed antenna and the reference antenna under X-polarized incident wave. Figure 8 (b) is a simulation result of the scattering pattern of the designed antenna and the reference antenna under Y-polarized incident wave.

[0039] Figure 9 To compare the monostatic RCS of this invention with that of a reference antenna, wherein, Figure 9 (a) Design antenna and reference antenna 1 under X-polarized wave incidence. Figure 9 (b) Design of the antenna and reference antenna 1 under Y-polarized wave incidence. Figure 9 (c) Design of antenna and reference antenna 2 under X-polarized wave incidence. Figure 9 (d) shows the design antenna and reference antenna 2 under Y-polarized wave incidence.

[0040] The structure comprises: 1. First upper metal patch; 2. First dielectric layer; 3. Second lower metal patch; 4. Second dielectric layer; 5. Third L-shaped feed structure; 5.1. First L-shaped feed structure port; 5.2. Second L-shaped feed structure port; 6. Third dielectric layer; 7. Fourth dielectric layer; 8. Broadband feed network structure; 8.1. Broadband three-branch coupler; 8.11. Broadband three-branch coupler; 8.12. Second broadband three-branch coupler; 8.13. Third broadband three-branch coupler; 8.14. Fourth broadband three-branch coupler; 8.1.1. Input port; 8.1.2. Isolation port; 8.1.3. Straight-through port; 8.1.4. Coupling port; 8.2 Broadband crossover bridge; 8.2.1 First port; 8.2.2 Second port; 8.2.3 Third port; 8.2.4 Fourth port; 8.3 180° broadband stub-loaded phase shifter; 8.3.1 λ / 8 short circuit; 8.3.2 Open stub; 8.4 Wilkinson power divider; 8.4.1 First Wilkinson power divider; 8.4.2 Second Wilkinson power divider; 8.4.3 Third Wilkinson power divider; 8.4.1 Input port; 8.4.2 First output port; 8.4.3 Second output port; 9.1 First metallized via 1; 9.2 Second metallized via 2; 10 Antenna element. Detailed Implementation

[0041] The present invention will now be described in further detail with reference to the accompanying drawings.

[0042] like Figure 1 , Figure 2 As shown, a reflective broadband low-scatter array antenna based on a feed network design includes N×N antenna elements 10 arranged periodically with the same structure, where N≥2 and N is a positive integer. Each antenna element 10 is a metal structure. The antenna element 10 includes a first dielectric layer 2, a second dielectric layer 4, a third dielectric layer 6, and a fourth dielectric layer 7 stacked sequentially from top to bottom. A first upper metal patch 1 is disposed on the upper surface of the first dielectric layer 2, a second lower metal patch 3 is disposed on the upper surface of the second dielectric layer 4, and a third L-shaped feed structure 5 is disposed on the upper surface of the third dielectric layer 6.

[0043] Four antenna elements 10 arranged periodically with the same structure form a subarray, and a broadband feed network structure 8 is provided at the bottom of each subarray; the third L-shaped feed structure 5 is connected to the broadband feed network structure 8 through a metallized via.

[0044] like Figure 3 , Figure 4As shown, the broadband power supply network structure 8 includes a broadband crossover bridge 8.2 located in the middle. The broadband crossover bridge 8.2 includes a first port 8.2.1, a second port 8.2.2, a third port 8.2.3, and a fourth port 8.2.4. Four broadband three-branch line couplers 8.1 are arranged around the broadband crossover bridge 8.2. The four broadband three-branch line couplers 8.1 include: a first broadband three-branch line coupler 8.11 and a third broadband three-branch line coupler 8.13 arranged diagonally; and a second broadband three-branch line coupler 8.12 and a fourth broadband three-branch line coupler 8.14 arranged diagonally. The branch line coupler 8.1 includes an input port 8.1.1, an isolation port 8.1.2, a through port 8.1.3, and a coupling port 8.1.4. The isolation ports 8.1.2 of the first broadband three-branch branch line coupler 8.11 and the third broadband three-branch branch line coupler 8.13, located diagonally, are connected to the first port 8.2.1 and the third port 8.2.3 of the broadband cross bridge 8.2, respectively. The isolation ports 8.1.2 of the second broadband three-branch branch line coupler 8.12 and the fourth broadband three-branch branch line coupler 8.14, located diagonally, are connected to the second port 8.2.2 and the fourth port 8.2.4 of the broadband cross bridge 8.2, respectively.

[0045] The input port 8.1.1 of the first broadband three-branch line coupler 8.11 and the second broadband three-branch line coupler 8.12 are respectively connected to the first output port 8.4.2 and the second output port 8.4.3 of the first Wilkinson power divider 8.41; the input port 8.1.1 of the third broadband three-branch line coupler 8.13 and the fourth broadband three-branch line coupler 8.14 are respectively connected to the first output port 8.4.2 and the second output port 8.4.3 of the second Wilkinson power divider 8.42.

[0046] The input port 8.4.1 of the first Wilkinson power divider 8.41 is connected to the first output port 8.4.2 of the third Wilkinson power divider 8.43 through the open stub 8.3.2 of the 180° broadband stub-loaded phase shifter 8.3; the input port 8.4.1 of the second Wilkinson power divider 8.42 is connected to the second output port 8.4.3 of the third Wilkinson power divider 8.43 through the λ / 8 short circuit 8.3.1 of the 180° broadband stub-loaded phase shifter 8.3; the input port 8.4.1 of the third Wilkinson power divider 8.43 is connected to an external power supply to power the entire power supply structure.

[0047] When the first port 8.2.1 and the third port 8.2.3 of the broadband cross bridge 8.2 on the broadband feed network structure 8 are connected, a feed network A is formed. When the second port 8.2.2 and the fourth port 8.2.4 are connected, a feed network B is formed. There is a broadband feed network structure 8 (either feed network A or feed network B) at the bottom of every subarray composed of four antenna elements 10. Every antenna array composed of four subarrays contains two feed networks A and two feed networks B distributed in a checkerboard pattern.

[0048] Each of the subarrays includes four third L-shaped feed structures 5, each third L-shaped feed structure 5 including a first L-shaped feed structure port 5.1 and a second L-shaped feed structure port 5.2;

[0049] Each first L-shaped power supply structure port 5.1 is connected to the through port 8.1.3 of the first broadband three-branch line coupler 8.11, the second broadband three-branch line coupler 8.12, the third broadband three-branch line coupler 8.13, and the fourth broadband three-branch line coupler 8.14 respectively through the first metallized via 9.1 penetrating the fourth dielectric layer 7;

[0050] Each second L-shaped feed structure port 5.2 is connected to the coupling ports 8.1.4 of the first broadband three-branch coupler 8.11, the second broadband three-branch coupler 8.12, the third broadband three-branch coupler 8.13, and the fourth broadband three-branch coupler 8.14 respectively through a second metallized via 9.2 penetrating the fourth dielectric layer 7. That is, the four through ports 8.1.3 and four coupling ports 8.1.4 of a broadband feed network structure 8 are connected to the four third L-shaped feed structures 5 through eight metallized vias respectively.

[0051] Considering high temperature resistance, low dielectric constant, low dielectric loss, and good flame retardant and mechanical properties, the first dielectric layer 2, the second dielectric layer 4, and the third dielectric layer 6 are all made of F4BM with a dielectric constant of 2.2 and a loss tangent of 0.002. The fourth dielectric layer 7 is made of Rogers RT / duroid 6010 / 6010LM(tm) with a dielectric constant of 10.2 and a loss tangent of 0.0023. The first dielectric layer 2, the second dielectric layer 4, the third dielectric layer 6, and the fourth dielectric layer 7 are spaced apart by insulating resin gaskets to achieve the desired height.

[0052] The first upper metal patch 1, the second lower metal patch 3, and the broadband power supply network structure 8 are all made of copper. Copper is used as the material because it requires excellent conductivity, good processing performance, and relatively low cost. The thickness of each material is 0.01mm to 0.02mm.

[0053] The first upper metal patch 1 has a side length of L1, where L1 = 13mm to 15mm. The first upper metal patch 1 passes through the metallized vias located between the first dielectric layer 2 and the second dielectric layer 4, and is connected to the fourth dielectric layer 7 and the broadband power supply network structure 8.

[0054] The second lower metal patch 3 has a side length of L2, L2 = 15mm to 17mm. The second lower metal patch 3 passes through the metallized via located in the second dielectric layer 4 and is connected to the fourth dielectric layer 7 and the broadband power supply network structure 8.

[0055] The thickness of the first dielectric layer 2 is H1, where H1 = 5 mm to 7 mm; the thickness of the second dielectric layer 4 is H2, where H2 = 1 mm to 2 mm; the thickness of the third dielectric layer 6 is H3, where H3 = 3 mm to 5 mm; and the side lengths of the first dielectric layer 2, the second dielectric layer 4, and the third dielectric layer 6 are all P, where P = 33 mm to 37 mm.

[0056] The radius of the metallized via is R1, where R1 = 0.1 mm to 0.2 mm.

[0057] The third L-shaped feed structure 5 is the metal strip portion of the L-shaped feed probe. The two ends of the third L-shaped feed structure 5 pass through the first metallized via 9.1 and the second metallized via 9.2 of the fourth dielectric layer 7, respectively. The first metallized via 9.1 and the second metallized via 9.2 serve as the probe portion of the L-shaped feed probe.

[0058] The fourth dielectric layer 7 is the upper floor of the broadband power supply network structure 8, and the thickness of the fourth dielectric layer 7 is H4, where H4 = 0.6 mm to 0.7 mm.

[0059] The broadband three-branch coupler 8.1 includes four ports, referred to as input port 8.1.1, isolation port 8.1.2, pass-through port 8.1.3, and coupling port 8.1.4. Its -10dB operating bandwidth is 3.5–6 GHz, with an in-band coupling of approximately 3dB. The phase difference between pass-through port 8.1.3 and coupling port 8.1.4 remains stable at 90° ± 5° within the operating bandwidth, and the isolation between input port 8.1.1 and isolation port 8.1.2 is above 17dB. When input port 8.1.1 is connected, the output energy amplitudes of pass-through port 8.1.3 and coupling port 8.1.4 are equal, but with a 90° phase difference. When isolation port 8.1.2 is connected, the output energy amplitudes of pass-through port 8.1.3 and coupling port 8.1.4 are equal, but with a 90° phase difference.

[0060] The first length Lp1, second length Lp2, third length Lp3, first width Wp1, second width Wp2, and third width Wp3 of the broadband three-branch line coupler 8.1 are as follows: first length Lp1 = 12mm~14mm, second length Lp2 = 5.5mm~5.7mm, third length Lp3 = 4.3mm~4.5mm, first width Wp1 = 0.5mm~0.7mm, second width Wp2 = 0.8mm~1mm, and third width Wp3 = 0.1mm~0.2mm.

[0061] The broadband crossover bridge 8.2 includes four ports: port 8.2.1, port 8.2.2, port 8.2.3, and port 8.2.4. Due to its structure having double symmetry about X and Y, the designed broadband crossover bridge 8.2 has a -10dB operating bandwidth of 3.6 to 6.5 GHz, good transmission characteristics between crossover ports, and an isolation of more than 15dB between adjacent ports within the operating frequency band.

[0062] The fourth length Lp4, fifth length Lp5, sixth length Lp6, seventh length Lp7, eighth length Lp8, ninth length Lp9, tenth length Lp10, eleventh length Lp11, fourth width Wp4, fifth width Wp5, and sixth width Wp6 of the broadband cross-bridge 8.2 device are respectively: fourth length Lp4 = 3.2mm~3.4mm, fifth length Lp5 = 0.4mm~0.5mm, and sixth length Lp6 = 2.6mm~2.7mm. mm, seventh length Lp7 = 2.2mm~2.3mm, eighth length Lp8 = 1.7mm~1.9mm, ninth length Lp9 = 1.4mm~1.5mm, tenth length Lp10 = 0.8mm~0.9mm, eleventh length Lp11 = 2mm~2.1mm, fourth width Wp4 = 0.05mm~0.15mm, fifth width Wp5 = 0.7mm~0.8mm, sixth width Wp6 = 0.2mm~0.3mm.

[0063] The 180° broadband stub-loaded phase shifter 8.3 is a transmission line segment. The phase-stabilizing part of the broadband stub-loaded phase shifter 8.3 is achieved by connecting a λ / 8 short-circuit 8.3.1 and an open-circuit stub 8.3.2 in parallel on the transmission line, while the phase-shifting part is achieved by varying the length of the transmission line. Its operating bandwidth meets the requirements of 3.3 to 6.6 GHz, and the phase difference between the main line and the reference line within the operating band meets the requirements of 180° ± 5°, which satisfies our design requirements. The operating bandwidth of this broadband stub-loaded phase shifter 8.3 covers 3 to 7 GHz, and the phase difference between the main line and the reference line within the operating band meets the requirements of 90°.

[0064] The twelfth length Lp12, thirteenth length Lp13, fourteenth length Lp14, seventh width Wp7, and eighth width Wp8 of the 180° broadband stub-loaded phase shifter 8.3 device are respectively: twelfth length Lp12 = 2.7mm~2.8mm, thirteenth length Lp13 = 11.2mm~11.3mm, fourteenth length Lp14 = 6.1mm~6.3mm, seventh width Wp7 = 0.05mm~0.15mm, and eighth width Wp8 = 1.9mm~2.1mm.

[0065] The Wilkinson power divider 8.4 is a lossy power divider with three ports: an input port 8.4.1, a first output port 8.2.2, and a second output port 8.2.3. It ensures that all ports are matched, and due to resistor losses, there is no coupling energy between the first output port 8.2.2 and the second output port 8.2.3, thus providing excellent isolation. Its operating bandwidth covers 3–7 GHz, and the isolation between the output ports reaches over 15 dB within the operating frequency band.

[0066] The eighteenth length Lp18, eleventh width Wp11, and twelfth width Wp12 of the Wilkinson power divider 8.4 device are respectively: eighteenth length Lp18 = 3.1mm~3.3mm, eleventh width Wp11 = 0.15mm~0.2mm, and twelfth width Wp12 = 0.3mm~0.5mm.

[0067] The broadband feed network structure 8 is a microwave transmission line in stripline form; it consists of a broadband three-branch line coupler 8.1, a broadband cross bridge 8.2, a 180° broadband stub-loaded phase shifter 8.3, and three Wilkinson power dividers 8.4. The isolation ports 8.1.2 of the broadband three-branch line coupler 8.1 in each antenna element 10 are interconnected by striplines. The connection is such that two antenna elements 10 located diagonally opposite each other in the subarray are interconnected. Therefore, a 2×2 subarray will generate two connecting lines, and these two connecting lines will intersect. To solve the problem of stripline intersection, the broadband cross bridge 8.2 designed in this invention is used. To control the transmission phase of the connecting striplines and to address the issue of split lobes in the antenna subarray scattering pattern caused by sequential rotation, this invention introduces a 180° broadband stub-loaded phase shifter 8.3 on one of the two connecting striplines, thus forming the designed feed network A. To ensure normal circular polarization radiation performance and to feed the 2×2 subarray, a three Wilkinson power divider 8.4 was designed, and the phase requirements for sequential rotation feeding were met by adjusting the microstrip line length. The broadband cross-bridge 8.2 is a four-port passive microwave device, where ports 1 and 3 are through, and ports 2 and 4 are isolated. The isolation ports 8.1.2 of the broadband three-branch coupler 8.1 are interconnected via microstrip lines, with the connection being the interconnection of two antenna elements 10 located diagonally across the subarray. A 180° broadband stub-loaded phase shifter 8.3 is introduced on both connecting microstrip lines.

[0068] The broadband power supply network structure 8 uses a broadband cross bridge 8.2, which can solve the problem of transmission line crossing when connecting 2×2 subarrays.

[0069] Furthermore, the broadband feed network structure 8 is a microwave transmission line in the form of a stripline, which plays a key role in separating radiation scattering. It consists of four sequentially rotating broadband three-branch line couplers 8.1, a broadband cross bridge 8.2, a 180° broadband stub-loaded phase shifter 8.3, and three Wilkinson power dividers 8.4. Among them, the broadband three-branch line coupler 8.1 plays the role of radiating circularly polarized electromagnetic waves and separating radiation scattering performance; the 180° broadband stub-loaded phase shifter 8.3 can make its transmission line lead the transmission phase by 180°; the broadband cross bridge 8.2 can solve the problem of stripline crossing during wiring. The entire array antenna is composed of feed networks of two feed networks A and two feed networks B. The transmission lines of the 180° broadband stub-loaded phase shifter 8.3 in the two adjacent feed networks (broadband feed network A and broadband feed network B) are exactly different, thus achieving a 180° phase difference in reflection between adjacent subarrays.

[0070] The broadband low-scatter array antenna elements are sequentially rotated and fed to form a 2×2 subarray, and broadband passive microwave devices are applied to form broadband feed networks A and B. The performance of the subarrays loaded with broadband feed networks A and B is analyzed. They have similar radiation characteristics and exhibit a 180° scattering phase difference under arbitrary linearly polarized incident waves.

[0071] When the antenna receives electromagnetic wave illumination, the first upper metal patch 1 and the second lower metal patch 3 form a partial reflective surface. The second lower metal patch 3, because the size of each unit is different from that of the first upper metal patch 1, can reflect electromagnetic waves in different directions, reducing the electromagnetic waves reflected in one direction. This results in a large number of electromagnetic waves being reflected in non-threatening directions, greatly reducing the radar cross-section within the antenna's operating frequency band.

[0072] In this invention, the first upper metal patch 1 is a microstrip square patch.

[0073] like Figure 5 , Figure 6 As shown, the radiation performance of the designed antenna array was simulated and compared with two newly designed reference antenna arrays. The two reference antennas are an antenna array using feed network A alone and an antenna array using feed network B alone, respectively. Reference Antenna Figure 5 (a) shows the designed antenna and two reference antennas S 11 The simulation results show that the -10dB impedance bandwidth of the designed antenna array is 3.9 to 6 GHz, with a relative bandwidth of 42.4%. The -10dB impedance bandwidth of reference antenna array 1 is 3.9 to 6 GHz, with a relative bandwidth of 42.4%. The -10dB impedance bandwidth of reference antenna array 2 is 4 to 6 GHz, with a relative bandwidth of 40%. Figure 5 (b) shows a comparison of the simulation results of the gain and axial ratio of the maximum radiation direction of the designed antenna array and the two reference antenna arrays as a function of frequency. It can be seen that the 3dB axial ratio bandwidth of the designed antenna is 3.7 to 5.8 GHz, and the relative bandwidth is 44.2%. The 3dB axial ratio bandwidth of reference antenna 1 is 3.9 to 6 GHz, and the relative bandwidth is 42.4%. The 3dB axial ratio bandwidth of reference antenna 2 covers 3 to 6 GHz. The in-band gain of both the designed antenna array and the reference antenna array is good, and the gain is greater than 12dBic in the operating frequency band.

[0074] like Figure 6 A comparison of the normalized radiation patterns of the designed antenna and the reference antenna at the high, low, and mid frequencies shows that both antennas exhibit good radiation directivity and normal cross-polarization performance, with cross-polarization ratios exceeding 15 dB at all three frequencies. These simulation results demonstrate the excellent radiation performance of the broadband low-scatter array antenna designed in this invention.

[0075] like Figure 7 As shown, a simulation comparison of the scattering performance of the designed antenna array and two reference antenna arrays was performed. Figure 7 (a) and Figure 7 (b) shows the simulation results of the surface current distribution of the designed antenna array and the reference antenna array patch at three frequency points (high, medium and low) under two polarized incident waves. It can be seen that due to the 180° reflection phase difference between the subarrays with different feed networks, the surface current of the designed antenna shows a reverse effect about the center regardless of the polarized incident electromagnetic wave. However, since the two reference antennas do not have the function of phase cancellation, their surface currents are in the same direction.

[0076] like Figure 8 As shown, the designed antenna array and two reference antenna arrays were tested in the far field. Figure 8 (a) and Figure 8 (b) shows the simulation results of the scattering patterns at the high, medium and low frequencies. It can be seen that under the incident electromagnetic wave of arbitrary polarization, the scattering pattern of the designed antenna is canceled out, presenting four lobes split about the center of the array, while the scattering pattern of the reference antenna is not canceled out at all, and the entire scattering pattern presents a large main lobe.

[0077] like Figure 9 As shown, the single-station RCS reduction of the designed antenna array and two reference antenna arrays were compared. It can be seen that under X-polarized electromagnetic wave incidence, the designed antenna's single-station RCS reduction band compared to reference antenna 1 is 3.9–5.6 GHz, with a relative bandwidth of 35.8%, and the maximum reduction reaches 15.78 dB at 4.6 GHz. The designed antenna's single-station RCS reduction band compared to reference antenna 2 is 3–5.4 GHz, with a relative bandwidth of 57%, and the maximum reduction reaches 19.22 dB at 4.6 GHz. Under Y-polarized electromagnetic wave incidence, the designed antenna's single-station RCS reduction band compared to reference antenna 1 is 3.4–5.1 GHz, with a relative bandwidth of 40%, and the maximum reduction reaches 16.79 dB at 4.6 GHz. The designed antenna's single-station RCS reduction band compared to reference antenna 2 is 3–5.4 GHz, with a relative bandwidth of 57%, and the maximum reduction reaches 22.18 dB at 3.8 GHz.

[0078] The simulation results above demonstrate that the reduction in RCS of the designed antenna compared to the reference antenna at a single station proves the feasibility of our method of reducing the RCS of the array antenna through feed network design, and also demonstrates the success of the broadband design presented in this chapter. Compared with existing technologies, the antenna of this invention simultaneously achieves both broadband and low-scatter radar cross-section functions through the first upper metal patch 1 and the second lower metal patch 3, simplifying the antenna structure, increasing the reduction in in-band radar cross-section, improving antenna gain, and addressing the shortcomings of existing technologies.

[0079] Broadband feed network structure 8: By combining several passive microwave devices, including a broadband three-branch coupler 8.1, a broadband cross bridge 8.2, a 180° broadband stub-loaded phase shifter 8.3, and a Wilkinson power divider 8.4, the function of independently controlling the radiation and scattering performance of the same antenna was successfully achieved. Furthermore, by using different loading methods for the 180° broadband stub-loaded phase shifter 8.3, phase cancellation of the scattered field between different subarrays was successfully achieved, thus realizing low monostation RCS performance of the antenna array. To solve the problem of microstrip line intersection, the broadband miniaturized broadband cross bridge 8.2 designed in this invention can be used. To control the transmission phase of the connecting microstrip lines and to solve the problem of split lobes in the scattering pattern of the antenna subarray caused by sequential rotation, the 180° broadband stub-loaded phase shifter 8.3 designed in this invention is introduced into two connecting microstrip lines, one of which is the main line with a phase stabilizer section, and the other is the slave line that performs the phase shifting function. To achieve normal circular polarization radiation performance of the antenna, this invention also designed a 1-to-4 sequential rotating power divider. The two-stage Wilkinson power divider 8.4 designed in this invention is cascaded to form a 1-to-4 power distribution effect. The phase requirement of sequential rotating feed is achieved by using 90° and 180° broadband stub-loaded phase shifters 8.3.

[0080] Dual-circular polarized antenna element structure: First, a broadband dual-polarized antenna element needs to be designed. There are many methods to broaden the bandwidth of a microstrip antenna; this invention chooses the simplest and most practical method: adding a first upper metal patch 1. Adding the first upper metal patch 1 is equivalent to introducing a new resonant point on the basis of the original single-resonant microstrip antenna, thereby broadening the antenna's operating bandwidth. High isolation between the ports of the dual-circular polarized antenna requires good port matching characteristics. Therefore, to better optimize the port matching of the dual-polarized antenna and ensure structural symmetry, the dual-polarized antenna element designed in this invention uses a third L-shaped feeding structure 5. The capacitance formed between the third L-shaped feeding structure 5 and the fourth dielectric layer 7 can cancel out the inductive part of the antenna input impedance, thus enabling the antenna to achieve good impedance matching characteristics.

[0081] Application prospects of this invention:

[0082] Antennas, as special scatterers, possess unique scattering mechanisms compared to ordinary scatterers, making RCS reduction more challenging. Current techniques for reducing antenna RCS all have drawbacks, hindering large-scale array deployment. For stealth aircraft, large-scale phased array antennas on the nose are indispensable for ensuring communication; however, large-scale arrays lead to orders-of-magnitude increases in RCS within specific angular regions. Therefore, this invention, based on the design of the array antenna feed network, realizes an array antenna with low in-band RCS characteristics. Through broadband design of antenna elements and various passive microwave devices, the entire feed network is ultimately broadbanded, ensuring both broadband radiation performance and broadband scattering reduction. This approach shows promise for large-scale array applications. It avoids the shortcomings of previous antenna RCS reduction methods and proposes a new technical approach for in-band RCS reduction.

[0083] The above description and embodiments are merely preferred examples of the present invention and do not constitute any limitation on the present invention. Obviously, those skilled in the art, after understanding the content and design principles of the present invention, may make various modifications and changes in form and detail based on the principles and structure of the present invention. However, these modifications and changes based on the ideas of the present invention are still within the protection scope of the claims of the present invention.

Claims

1. A broadband low-scatter array antenna based on a feed network design, comprising N×N antenna elements (10) arranged periodically with the same structure, where N≥2 and N is a positive integer, characterized in that: The antenna unit (10) includes a first dielectric layer (2), a second dielectric layer (4), a third dielectric layer (6), and a fourth dielectric layer (7) stacked from top to bottom; a first upper metal patch (1) is provided on the upper surface of the first dielectric layer (2), a second lower metal patch (3) is provided on the upper surface of the second dielectric layer (4), and a third L-shaped feeding structure (5) is provided on the upper surface of the third dielectric layer (6). Four antenna elements (10) arranged periodically with the same structure form a subarray, and a broadband feed network structure (8) is provided at the bottom of each subarray; the third L-shaped feed structure (5) is connected to the broadband feed network structure (8) through a metallized via. The broadband power supply network structure (8) includes a broadband crossover bridge (8.2) located in the middle. The broadband crossover bridge (8.2) includes a first port (8.2.1), a second port (8.2.2), a third port (8.2.3), and a fourth port (8.2.4). Four broadband three-branch line couplers (8.1) are arranged around the broadband crossover bridge (8.2). The four broadband three-branch line couplers (8.1) include: a first broadband three-branch line coupler (8.11) and a third broadband three-branch line coupler (8.13) arranged diagonally, and a second broadband three-branch line coupler (8.12) and a fourth broadband three-branch line coupler (8.14) arranged diagonally. The coupler (8.1) includes an input port (8.1.1), an isolation port (8.1.2), a pass-through port (8.1.3), and a coupling port (8.1.4). The isolation port (8.1.2) of the first broadband three-branch line coupler (8.11) and the third broadband three-branch line coupler (8.13) located on the diagonal is connected to the first port (8.2.1) and the third port (8.2.3) of the broadband cross bridge (8.2), respectively. The isolation port (8.1.2) of the second broadband three-branch line coupler (8.12) and the fourth broadband three-branch line coupler (8.14) located on the diagonal is connected to the second port (8.2.2) and the fourth port (8.2.4) of the broadband cross bridge (8.2), respectively. The input ports (8.1.1) of the first broadband three-branch line coupler (8.11) and the second broadband three-branch line coupler (8.12) are connected to the first output port (8.4.2) and the second output port (8.4.3) of the first Wilkinson power divider (8.41), respectively; the input ports (8.1.1) of the third broadband three-branch line coupler (8.13) and the fourth broadband three-branch line coupler (8.14) are connected to the first output port (8.4.2) and the second output port (8.4.3) of the second Wilkinson power divider (8.42), respectively. The input port (8.4.1) of the first Wilkinson power divider (8.41) is connected to the first output port (8.4.2) of the third Wilkinson power divider (8.43) via an open stub (8.3.2) of a 180° broadband stub-loaded phase shifter (8.3); the input port (8.4.1) of the second Wilkinson power divider (8.42) is connected to the first output port (8.4.2) of the third Wilkinson power divider (8.43) via an open stub (8.3.2) of a 180° broadband stub-loaded phase shifter (8.3). The short circuit (8.3.1) is connected to the second output port (8.4.3) of the third Wilkinson power divider (8.43); the input port (8.4.1) of the third Wilkinson power divider (8.43) is connected to an external power supply to power the entire power supply structure.

2. The broadband low-scatter array antenna based on a feed network design according to claim 1, characterized in that: When the first port (8.2.1) and the third port (8.2.3) of the broadband cross bridge (8.2) on the broadband feed network structure (8) are connected, feed network A is formed. When the second port (8.2.2) and the fourth port (8.2.4) are connected, feed network B is formed. There is a broadband feed network structure (8) at the bottom of every subarray composed of four antenna elements (10). Every antenna array composed of four subarrays contains two feed networks A and two feed networks B distributed in a checkerboard pattern.

3. A broadband low-scatter array antenna based on a feed network design according to claim 1, characterized in that: Each of the subarrays includes four third L-shaped feed structures (5), each third L-shaped feed structure (5) including a first L-shaped feed structure port (5.1) and a second L-shaped feed structure port (5.2). Each first L-shaped feed structure port (5.1) is connected to the through port (8.1.3) of the first broadband three-branch line coupler (8.11), the second broadband three-branch line coupler (8.12), the third broadband three-branch line coupler (8.13), and the fourth broadband three-branch line coupler (8.14) respectively through the first metallized via (9.1) penetrating the fourth dielectric layer (7); Each second L-shaped feed structure port (5.2) is connected to the coupling ports (8.1.4) of the first broadband three-branch line coupler (8.11), the second broadband three-branch line coupler (8.12), the third broadband three-branch line coupler (8.13), and the fourth broadband three-branch line coupler (8.14) through a second metallized via (9.2) penetrating the fourth dielectric layer (7).

4. A broadband low-scatter array antenna based on a feed network design according to claim 1, characterized in that: The first dielectric layer (2), the second dielectric layer (4) and the third dielectric layer (6) are all made of F4BM with a dielectric constant of 2.2 and a loss tangent of 0.

002. The fourth dielectric layer (7) is made of Rogers RT / duroid 6010 / 6010LM (tm) with a dielectric constant of 10.2 and a loss tangent of 0.0023.

5. A broadband low-scatter array antenna based on a feed network design according to claim 1, characterized in that: The side length of the first upper metal patch (1) is L1, L1=13mm~15mm. The first upper metal patch (1) passes through the metallized vias located between the first dielectric layer (2) and the second dielectric layer (4) and is connected to the fourth dielectric layer (7) and the broadband power supply network structure (8). The first upper metal patch (1), the second lower metal patch (3), and the broadband power supply network structure (8) are all made of copper, and their thicknesses are all 0.01mm~0.02mm.

6. A broadband low-scatter array antenna based on a feed network design according to claim 1, characterized in that: The side length of the second lower metal patch (3) is L2, L2=15mm~17mm. The second lower metal patch (3) passes through the metallized via located in the second dielectric layer (4) and is connected to the fourth dielectric layer (7) and the broadband power supply network structure (8).

7. A broadband low-scatter array antenna based on a feed network design according to claim 1, characterized in that: The thickness of the first dielectric layer (2) is H1, H1=5mm~7mm, the thickness of the second dielectric layer (4) is H2, H2=1mm~2mm, the thickness of the third dielectric layer (6) is H3, H3=3mm~5mm, and the side length of the first dielectric layer (2), the second dielectric layer (4) and the third dielectric layer (6) is P, P=33mm~37mm.

8. A broadband low-scatter array antenna based on a feed network design according to claim 1, characterized in that: The third L-shaped feed structure (5) is the metal strip portion of the L-shaped feed probe. The two ends of the third L-shaped feed structure (5) pass through the first metallized via 9.1 and the second metallized via 9.2 of the fourth dielectric layer (7), respectively.

9. A broadband low-scatter array antenna based on a feed network design according to claim 1, characterized in that: The fourth dielectric layer (7) is the upper floor of the broadband power supply network structure (8), and the thickness of the fourth dielectric layer (7) is H4, where H4 = 0.6 mm to 0.7 mm.

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