Dual-polarization flexible transparent array antenna with high-isolation low-sidelobe performance

Abstract

The invention discloses a dual-polarization flexible transparent array antenna with high isolation and low side lobe performance. The dual-polarization flexible transparent array antenna comprises a dielectric substrate, a grounding layer and a radiation patch array. The dielectric substrate is made of polydimethylsiloxane (PDMS) with the thickness of 0.5 mm; according to the array antenna, 50-ohm microstrip line side feed power supply is adopted, an orthogonal series microstrip patch array is presented, a hollowed-out cross structure is adopted at the joint to excite a high-order mode, reverse current generated by the high-order mode is restrained at the same time, side lobes are effectively reduced, and the isolation degree of antenna gain and a dual-polarization port is improved; meanwhile, in order to further reduce side lobes, the gradually-changed patch width is adopted. The antenna is small in overall size, has the characteristics of low profile, high gain, high isolation and dual polarization, has good bending performance and transparency, and can be used as a beautified antenna for a millimeter wave wireless communication system.

Description

Technical Field

[0001] The present invention belongs to the field of millimeter wave array antennas, and in particular relates to a dual-polarization flexible transparent array antenna with high isolation and low sidelobe performance. Background Art

[0002] With recent advances in wireless communication technology, millimeter-wave flexible antennas with dual polarization, high isolation, and low sidelobe characteristics have demonstrated unique advantages in 5G / 6G communication systems. Flexible antennas, with their excellent bendability, portability, and scalability, have shown tremendous potential for application in scenarios such as urban micro-base stations, smart buildings, drone platforms, and high-density indoor and automotive window communications. Microstrip antenna arrays with microstrip feed structures, characterized by their compact size, light weight, low profile, conformability, and ease of integration, have become a hot topic in flexible antenna research in recent years.

[0003] Flexible antennas currently have many shortcomings that need to be addressed. First, due to the high loss tangent of flexible materials, the gain and radiation efficiency of flexible antennas are low, and this gain deficiency is often compensated by antenna arrays. However, due to their high sidelobes, traditional linear arrays suffer from low mainlobe power, poor anti-interference capabilities, and low overall signal quality in communication applications. These problems are exacerbated by the severe signal attenuation in the 5G millimeter wave band, severely limiting the development prospects of flexible antennas. Second, most current flexible antennas only support a single polarization mode, wasting increasingly scarce spectrum resources. Implementing dual-polarization antennas on flexible substrates still faces numerous technical bottlenecks and challenges. Therefore, designing a flexible dual-polarization millimeter wave array antenna that exhibits excellent antenna performance and achieves good dual-polarization port isolation through its own structure, thereby expanding channel capacity and improving spectrum utilization, while also possessing good light transmittance and concealment, is an important research direction in the current wireless communication field. Summary of the Invention

[0004] The purpose of the present invention is to provide a dual-polarization flexible transparent array antenna with high isolation and low sidelobe performance, which has the characteristics of low profile and easy conformality with curved surfaces, and also has the advantages of high gain, high isolation, low sidelobe, etc. It has good application prospects in millimeter wave communications and solves the technical problems mentioned in the background technology.

[0005] In order to solve the above technical problems, the specific technical solutions of the present invention are as follows:

[0006] A dual-polarization flexible transparent array antenna with high isolation and low sidelobe performance comprises a flexible antenna substrate, a ground layer located on the back of the antenna substrate, and an antenna array located on the upper surface of the antenna substrate; the antenna substrate is made of transparent material, and the antenna array is composed of a group of two identical serial patch antenna arrays arranged orthogonally along the x-axis and y-axis directions, wherein a single serial antenna array includes six patch-shaped radiating elements, the centers of each radiating element are located on the same straight line, and adjacent radiating elements are fed in series via a series of 100-ohm microstrip lines. The two serial patch antenna arrays are fed separately at two ports via the microstrip lines, which can achieve good dual-polarization performance. Finally, one side of the serial array is connected to a 50-ohm microstrip line via a quarter-wavelength impedance transformer, achieving good impedance matching; a cross-shaped hollow structure is used at the intersection of the two orthogonal serial patch antenna arrays; the antenna array and the ground layer are made of transparent material, so the antenna as a whole has good transparency.

[0007] Furthermore, the antenna substrate is made of transparent PDMS material with a dielectric constant of 2.8 and a thickness of 0.5 mm.

[0008] Furthermore, the antenna array and the ground layer use a transparent metal mesh as a conductive layer.

[0009] Furthermore, the antenna array is formed on the upper surface of the antenna substrate by adhesive bonding; and the ground layer is formed on the back surface of the antenna substrate by adhesive bonding.

[0010] Furthermore, in the single serial antenna array, the width of the radiation unit decreases gradually from the middle to the two ends according to the Chebyshev distribution law.

[0011] Furthermore, at the intersection of two orthogonal series arrays, the four radiating units with the largest width are connected by a group of two orthogonal metal strips. The group of two orthogonal metal strips serves as a microstrip line structure connecting the series arrays and also forms a cross hollow structure, guiding the current to flow in the vertical direction of the other polarization direction, thereby increasing the isolation between the two ports; the cross hollow structure and the radiating units on both sides are regarded as a whole as a two-three-wavelength patch antenna with a hollow middle, which plays a role in enhancing the gain of the antenna array.

[0012] Furthermore, the spacing between adjacent radiation units is set to half the medium wavelength, and the medium wavelength is given by the formula Determine, where C is the speed of light in vacuum, f is the operating frequency of the antenna, and ε is the effective dielectric constant of the medium.

[0013] Furthermore, in a single series antenna array, the width of the radiating elements gradually decreases from the middle to the ends according to the Chebyshev distribution law. Taking into account the parasitic effects caused by the hollow structure, the width of the patch element should be corrected, so that the excitation current of the six radiating elements of the series antenna array roughly conforms to the six-element Chebyshev distribution (I1:I2:I3:I4:I5:I6 = 0.296:0.684:1:1:0.684:0.296), thereby reducing the sidelobes of the antenna array. The six-element Chebyshev distribution ratio can be obtained by calculating the coefficients of the Chebyshev expansion by comparing the equation or using the chebwin function in MATLAB.

[0014] Furthermore, the two series-connected microstrip patch antenna arrays in the antenna array are connected at the intersection using a cross hollow structure. The cross hollow structure and the radiation units with a length of half a wavelength on both sides of the x-axis or y-axis are integrated as a whole. Its current distribution is similar to the TM03 mode of the traditional rectangular microstrip patch antenna, which improves the gain of the antenna array; by removing the central part of the patch to eliminate the reverse current, the side lobes generated by the reverse current in the high-order mode are reduced.

[0015] The present invention provides a dual-polarization flexible transparent array antenna with high isolation and low sidelobe performance, which has the following advantages: the antenna substrate is made of flexible material, which, combined with the low-profile characteristics of the microstrip antenna, makes it easy to conform to the curved surface; a group of two serially connected microstrip patch antenna arrays are orthogonally arranged to achieve dual polarization with a phase difference of 90°; a cross hollow structure is adopted at the connection to achieve high gain, high isolation, and low sidelobe antenna performance; the width of the serially connected array radiation unit gradually decreases from the middle to the two ends, which conforms to the Chebyshev distribution and further reduces the sidelobes; a transparent metal mesh is used, which is patterned and then pasted on the surface of the antenna substrate to form an array and a ground plane, and the manufacturing process is simple; the selected PDMS substrate and transparent metal mesh both have good light transmittance and can be used as a beautifying antenna in scenarios such as urban micro base stations, intelligent buildings, unmanned platforms, high-density indoor communications, and car windows. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 A top cross-sectional view of the present invention;

[0017] Figure 2 This is the E-plane radiation pattern of the present invention at a frequency of 25 GHz when placed horizontally;

[0018] Figure 3 This is the H-plane radiation pattern of the present invention at a frequency of 25 GHz when placed horizontally;

[0019] Figure 4 This is an S parameter diagram of the present invention when placed horizontally;

[0020] Figure 5A schematic diagram of the structure of the present invention for conformal bending;

[0021] Figure 6 : This is the E-plane directional diagram of the excitation port 1 when bending to different degrees in the embodiment of the present invention;

[0022] Figure 7 1 is the H-plane directional diagram of the excitation port 1 when bending to different degrees in the embodiment of the present invention;

[0023] Figure 8 : This is the E-plane directional diagram of the excitation port 2 when bending to different degrees in the embodiment of the present invention;

[0024] Figure 9 : H-plane directional diagram of the excitation port 2 when bending to different degrees in the embodiment of the present invention;

[0025] Figure 10 is the reflection coefficient of port 1 when bending to different degrees in the embodiment of the present invention;

[0026] Figure 11 is the reflection coefficient of port 2 when bending to different degrees in the embodiment of the present invention;

[0027] Figure 12 The isolation between port 1 and port 2 when bending to different degrees is performed in the embodiment of the present invention;

[0028] Explanation of the marks in the figure: 1. Antenna substrate; 2. Radiating element; 3. 50-ohm microstrip line; 41. 100-ohm microstrip line; 42. Cross hollow structure; 5. Quarter-wavelength impedance transformer. DETAILED DESCRIPTION

[0029] In order to better understand the purpose, structure and function of the present invention, the following is a further detailed description of a dual-polarization flexible transparent array antenna with high isolation and low sidelobe performance of the present invention in conjunction with the accompanying drawings.

[0030] The antenna substrate 1 in this embodiment is a flexible PDMS film with a dielectric constant of 2.8, a loss tangent of 0.02, and a thickness of 0.5 mm.

[0031] The antenna array as a whole is Figure 1 As shown, a single-layer patch antenna structure is used to achieve a low profile and flexibility. It is placed on one side of the antenna substrate 1, and the ground plane is placed on the other side. The antenna structure and ground plane are both made of copper foil, and the copper foil is fixed to the surface of the PDMS film using the adhesive backing.

[0032] This embodiment uses a six-element serial linear array structure to achieve unidirectional polarization. Six patch radiating elements 2 are connected in series via a 100-ohm microstrip line 41 with a width of 0.45 mm. The radiating elements 2 are 3.60 mm long, and the center-to-center spacing is set to 7.50 mm, approximately one wavelength in the medium. The linear array composed of radiating elements 2 is matched to a 50-ohm microstrip line 3 with a width of 1.38 mm on one side via a quarter-wavelength impedance transformer 5 with a width of 1.20 mm to achieve efficient feeding. During the design process, a non-uniform Chebyshev distribution was used to optimize the excitation of each radiating element 2 to reduce the sidelobe level. According to MATLAB calculation and simulation results, the normalized current excitation of each radiating element 2 in the six-element linear array is I1:I2:I3:I4:I5:I6 = 0.296:0.684:1:1:0.684:0.296. Based on the excitation amplitude, the width of the radiating element 2 is set so that it gradually decreases from the center to the ends. It's important to note that the cross-shaped hollow structure 42 between the two central radiating elements 2 will disrupt the impedance characteristics, so the ratio of the width of the four patches on either side to the width of the two central patches needs to be adjusted accordingly. After optimization and adjustment, the width of the radiating element 2 from the center to the ends is 4.10mm, 2.80mm, and 1.21mm, respectively.

[0033] To achieve dual-polarization functionality, this embodiment uses two orthogonal series arrays, which are placed orthogonally at a 90° angle. The two orthogonal arrays are connected at the intersection to form a cross-shaped hollow structure 42. The branch width of the cross-shaped hollow structure 42 is optimized to be 0.45 mm, which can achieve good dual-polarization impedance matching. Simulation results show that the cross-shaped hollow structure 42 and the radiating units 2 with a length of half a wavelength on both sides can act as a whole to jointly excite the TM30 mode, significantly improving the gain of the antenna array. In addition, the effect of the hollow part on the TM30 mode current distribution can effectively suppress the reverse current at the center of the mode, thereby further reducing the side lobes and improving the gain and isolation.

[0034] At a frequency of 25 GHz, if the antenna array is excited at port 1, the simulation results of the E-plane and H-plane radiation patterns are as follows: Figure 2 、 Figure 3 As shown in Figure 2, the gain can reach 10.7dB, while the sidelobe level is as low as about -20.87dB. The S parameter simulation results are shown in Figure 2. Figure 4 As shown, it includes the reflection coefficient S11 of port 1, the reflection coefficient S22 of port 2 and the isolation S21 between the two ports, wherein the port isolation reaches -37dB, verifying the excellent performance of the antenna array of this embodiment with high gain, low side lobe and high isolation.

[0035] In order to verify the bending and conformal capabilities of the antenna array in this embodiment, a bending test was conducted. Using Ansys HFSS software, a cylindrical model was constructed with the Y axis as the axis, and a cylindrical conformal simulation was performed on the antenna array. The Wrap Sheet function was used to fit the antenna array to the cylinder, as shown in the following figure. Figure 5 By setting three different bending radii (200mm, 300mm and 400mm respectively), the S11, S22 and S21 parameters are tested and the changes in the directional pattern are examined. The S parameter simulation results are shown in Figure 10 、 Figure 11 、 Figure 12 As shown in the figure, under three different bending radii, at the center frequency of 25 GHz, the reflection coefficient of port 1 and port 2 is always kept below -10 dB, and the isolation is always kept below -30 dB, which shows that the antenna array can still maintain stable working characteristics and high isolation performance under a certain bending radius. In the test of the directional pattern, when port 1 is stimulated, as shown in the figure, Figure 6 、 Figure 7 As shown in Figure 2, the antenna array can maintain a gain of 10.4 dB and an E-plane sidelobe of -15 dB under different degrees of bending. When port 2 is excited, as shown in Figure 2, Figure 8 、 Figure 9 As shown in Figure 1, due to the large bending angle of the array, the gain is reduced to 6.38dB, but communication is still possible.

[0036] The above simulation tests on this embodiment have demonstrated its good bending conformal capability, thus expanding its application scenarios. In addition, due to the symmetry of the array, similar results can be obtained by performing cylindrical conformal bending tests with the X-axis as the axis.

[0037] By using flexible PDMS material, this paper successfully designed a dual-polarized flexible transparent array antenna suitable for the millimeter-wave communication frequency band (25GHz). This antenna array combines a central hollow cross-shaped connection structure with gradient patch units, and uses the excitation of high-order modes to change the current distribution, thereby achieving high isolation, high gain, and low sidelobe performance. Furthermore, the antenna array exhibits excellent bending conformality and transparency, and can be used as a decorative antenna for signal transmission and reception in application scenarios such as urban micro base stations, intelligent buildings, unmanned platforms, high-density indoor communications, and automotive window glass.

[0038] It will be understood that the present invention is described by way of some embodiments, and it will be appreciated by those skilled in the art that various changes or equivalent substitutions may be made to these features and embodiments without departing from the spirit and scope of the present invention. In addition, under the teachings of the present invention, these features and embodiments may be modified to adapt to specific circumstances and materials without departing from the spirit and scope of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application are intended to be protected by the present invention.

Claims

1. A dual-polarization flexible transparent array antenna with high isolation and low sidelobe performance, characterized in that: The invention comprises a flexible antenna substrate (1), a grounding layer located on the back of the antenna substrate (1), and an antenna array located on the upper surface of the antenna substrate (1); the antenna substrate (1) is made of transparent material, the antenna array is composed of a group of two identical serial patch antenna arrays arranged orthogonally along the x-axis and y-axis directions, wherein a single serial antenna array comprises six patch-shaped radiation units (2), the centers of each radiation unit (2) are located on the same straight line, adjacent radiation units (2) are fed in series through a series 100 ohm microstrip line (41), and finally connected to a 50 ohm microstrip line (3) on one side of the serial array through a quarter-wavelength impedance transformer (5), thereby achieving impedance matching; a cross-shaped hollow structure (42) is used for connection at the intersection of a group of two orthogonal serial patch antenna arrays; the antenna array and the grounding layer are made of transparent material.

2. The dual-polarization flexible transparent array antenna with high isolation and low sidelobe performance according to claim 1, characterized in that: The antenna substrate (1) is made of transparent PDMS material with a dielectric constant of 2.8 and a thickness of 0.5 mm.

3. The dual-polarization flexible transparent array antenna with high isolation and low sidelobe performance according to claim 1, characterized in that: The antenna array and the ground layer use transparent metal mesh as the conductive layer.

4. The dual-polarization flexible transparent array antenna with high isolation and low sidelobe performance according to claim 1, characterized in that: The antenna array is formed on the upper surface of the antenna substrate (1) by adhesive bonding; and the grounding layer is formed on the back surface of the antenna substrate (1) by adhesive bonding.

5. The dual-polarization flexible transparent array antenna with high isolation and low sidelobe performance according to claim 1, characterized in that: In the single serial antenna array, the width of the radiation unit (2) decreases gradually from the middle to the two ends according to the Chebyshev distribution law.

6. The dual-polarization flexible transparent array antenna with high isolation and low sidelobe performance according to claim 1, characterized in that: The spacing between adjacent radiation units (2) is set according to half the medium wavelength, and the medium wavelength is given by the formula Determine, where C is the speed of light in vacuum, f is the operating frequency of the antenna, and ε is the effective dielectric constant of the medium.

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