Terahertz circularly polarized antenna array

Abstract

The invention provides a terahertz circularly polarized antenna array. The terahertz circularly polarized antenna array comprises a waveguide feed network and a microstrip array, the waveguide feed network comprises a feed waveguide, a sequential rotation feed network and a sub-array feed network, and the sequential rotation feed network comprises four branches arranged in a swastika shape and is provided with a wedge-shaped structure used for evenly distributing energy transmitted by the feed waveguide to the four branches and achieving impedance matching of an input port. Each branch is connected with one sub-array feed network; the microstrip array comprises a dielectric plate, a first metal layer and a second metal layer are arranged on the two opposite faces of the dielectric plate respectively, rotationally-arranged gap combinations are arranged at the positions, corresponding to the branches, of the first metal layer, and a microstrip patch antenna array is arranged on the second metal layer. According to the invention, a mixed feed scheme is adopted, array feed is realized through combination of the waveguide feed network and the microstrip array, a sequential rotation feed technology is introduced, and the antenna has the advantage of wide bandwidth.

Description

Technical Field

[0001] The present invention relates to the field of antenna technology, and in particular to a terahertz circularly polarized antenna array. Background Art

[0002] Terahertz technology has attracted widespread attention in recent years. Due to the strong penetrating properties and low-energy photon emission of electromagnetic waves in the terahertz frequency band, it is often used in fields such as nondestructive testing, security imaging, and biomedicine. Furthermore, due to the high frequency and wide spectrum characteristics of terahertz waves, this technology is also being applied to ultra-high-speed and ultra-wideband wireless communication systems. Antennas, as an essential component in terahertz systems, have therefore become a focus of industry research. Regarding polarization, circular polarization can avoid issues such as multipath distortion and polarization mismatch, so research on circularly polarized terahertz antennas has considerable practical application value.

[0003] At present, there have been many reports on terahertz circularly polarized antennas in public literature, but these antennas generally have problems such as difficulty in processing, high cost and limited performance.

[0004] First, regarding the processing problem, since the operating frequency band of terahertz antennas is very high, the size of the antenna becomes very small, generally in the micron range. At this size level, the processing technology traditionally used for microwave and millimeter wave antennas is difficult to apply. Currently, the common terahertz antenna processes mainly include semiconductor processes. [1] , Metal / Ceramic Diffusion Welding Process [2][3] These processes are generally expensive and the process is relatively complicated. In recent years, CNC and PCB processes have also been adopted. [4] However, these antennas are generally multi-layer structures. Too many layers and the interconnection between layers will also lead to increased process complexity and cost. In addition, the processing of fine structures such as metal through holes in the antenna structure will also increase the difficulty of processing.

[0005] Secondly, in terms of antenna performance, the terahertz circularly polarized antennas reported so far generally have a narrow operating bandwidth problem, which is generally difficult to exceed 20%. This problem is mainly caused by two reasons: First, the circularly polarized terahertz antenna units reported in the literature themselves have only limited axial ratio bandwidth. [5] On the other hand, the coupling between elements in the antenna array will also affect the impedance bandwidth and axial ratio bandwidth. [2] At the same time, the more complex the antenna structure is, the greater the negative impact on antenna performance.

[0006] [1]S.Kong,K.Man Shum and C.H.Chan,"425Ghz Highly Compact On-ChipSequential-Phased CP Antenna With19% Overlapped Impedance-AR Bandwidth,"inIEEE Transactions on Antennas and Propagation,vol.72,no.6,pp.4773-4784,June2024

[0007] [2]M.M.Zhou and Y.J.Cheng,"D-Band High-Gain Circular-Polarized PlateArray Antenna,"in IEEE Transactions on Antennas and Propagation,vol.66,no.3,pp.1280-1287,March 2018

[0008] [3]He X,Yang W,Liao S,et al.140-GHz high-efficiency low-profilereflectarray antenna using heterogeneous design strategy[J].IEEE Transactionson Antennas and Propagation,2023,72(1):932-937.

[0009] [4]Wang Y,Du B,Cao Z,et al.A substrate-integrated cavity-backed slotantenna array in y-band[J].IEEE Antennas and Wireless Propagation Letters,2023,22(12):2998-3002.

[0010] [5]D.Warmowska,K.A.Abdalmalak,L.E.G. and Z.Raida, "High-Gain, Circularly-Polarized THz Antenna With Proper Modeling of Structures With ThinMetallic Walls," in IEEE Access, vol.8, pp.125223-125233, 2020. Summary of the Invention

[0011] In order to solve at least one of the problems existing in the prior art, the present invention provides a low-cost terahertz circularly polarized antenna array, which adopts a hybrid feeding scheme and realizes array feeding through the combination of a waveguide feeding network and a microstrip array. By introducing sequential rotation feeding technology in the array, it has the advantage of wide bandwidth.

[0012] In order to achieve the purpose of the present invention, the present invention provides a terahertz circularly polarized antenna array, including a waveguide feeding network and a microstrip array;

[0013] The waveguide feeding network includes a feeding waveguide, a sequential rotation feeding network, and a subarray feeding network. The feeding waveguide is used to feed the entire antenna array. The sequential rotation feeding network includes four branches arranged in a swastika shape and is provided with a wedge-shaped structure for evenly distributing the energy transmitted from the feeding waveguide to the four branches and achieving impedance matching of the input port. Each branch is connected to a subarray feeding network.

[0014] The microstrip array includes a dielectric plate, on which a first metal layer and a second metal layer are respectively arranged on opposite sides. A rotationally arranged slot combination is arranged on the first metal layer at a position corresponding to each branch, and a microstrip patch antenna array is arranged on the second metal layer.

[0015] Furthermore, the feeding waveguide is located at the geometric center of the entire waveguide feeding network 11 and forms an angle of 45° with the x-axis.

[0016] Furthermore, the output signals of the four branches have equal amplitudes, and relative phases are 0°, 90°, 180°, and 270°, respectively.

[0017] Furthermore, each subarray feeding network includes a first ridge structure and two H-plane T-junctions. The first ridge structure is located between the two H-plane T-junctions and is used to divide the energy transmitted from the branch into two paths and input them into the two H-plane T-junctions respectively.

[0018] Furthermore, each subarray feeding network also includes a second ridge structure, which is used to split the energy input into the H-plane T-junction into two paths and transmit them to the ends of the two branch waveguides of the H-plane T-junction.

[0019] Furthermore, each sub-array feeding network also includes a third ridge structure, which is a structure used for impedance matching when the waveguide feeding network couples energy to the microstrip array.

[0020] Furthermore, each slot combination includes four slots arranged corresponding to the waveguide branches of the H-plane T-junction, and the distances between the centers of the slots and the centers of the third ridge structure and the ends of the waveguide branches are consistent.

[0021] Furthermore, the microstrip patch antenna array includes four first-stage antenna subarrays that rotate sequentially, each first-stage antenna subarray includes four second-stage antenna subarrays, and the second-stage antenna subarrays coincide with the geometric center of the slot.

[0022] Furthermore, each second-stage antenna subarray includes a microstrip line four-way power divider, four bent microstrip lines, and four circularly polarized patch units respectively connected to the microstrip lines.

[0023] Furthermore, notches are provided on the metal edges of the microstrip line four-way power divider on both sides of the gap.

[0024] Compared with the prior art, the present invention has the following two advantages:

[0025] 1) The present invention proposes a hybrid feeding scheme with a double-layer topology structure, which adopts a simple circularly polarized unit structure, thereby reducing the processing cost and difficulty of the terahertz antenna to a certain extent.

[0026] 2) The circularly polarized unit of the present invention has excellent performance, and the sequential rotation feeding technology is introduced. The circularly polarized antenna array has superior performance and its operating bandwidth can reach 28%. This performance index is better than the current technical status and has the advantage of wide bandwidth.

[0027] 3) The present invention avoids the introduction of metal through holes in the structure, and the processing technology can adopt low-cost PCB and CNC technology, which has the advantages of simple structure, low cost and low processing difficulty. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a schematic structural diagram of a terahertz circularly polarized antenna array provided by an embodiment of the present invention.

[0029] Figure 2 This is a layered schematic diagram of a terahertz circularly polarized antenna array provided by an embodiment of the present invention.

[0030] Figure 3 FIG. 4 is a top view of a waveguide feeding network in an embodiment of the present invention.

[0031] Figure 4 It is a partially enlarged view of the subarray feeding network in an embodiment of the present invention.

[0032] Figure 5 3 is a top view of the relative positions of the first metal layer and the waveguide feeding network in an embodiment of the present invention.

[0033] Figure 6 4 is a top view of the second metal layer in an embodiment of the present invention.

[0034] Figure 7 Schematic diagram of the working principle of the microstrip patch unit in an embodiment of the present invention.

[0035] Figure 8 Schematic diagram of the working principle of the stripline sub-array in an embodiment of the present invention.

[0036] Figure 9 Schematic diagram of the reflection coefficient and axial ratio of the patch unit in an embodiment of the present invention.

[0037] Figure 10 Schematic diagram of the amplitude of the reflection coefficient when feeding through port 1 and the transmission coefficient from port 2 to port 5 in the sequential rotation feeding network in an embodiment of the present invention.

[0038] Figure 11 Schematic diagram of the relative phase of the transmission coefficients from port 2 to port 5 in an embodiment of the present invention.

[0039] Figure 12 Reflection coefficient and axial ratio curves of the antenna array in an embodiment of the present invention.

[0040] Figure 13 Schematic diagram of the gain curve of the antenna in an embodiment of the present invention.

[0041] Figure 14 、 Figure 15 and Figure 16 The E-plane (xz-plane) and H-plane (yz-plane) radiation patterns of three frequency points in the working band, 121, 139, and 157 GHz, are displayed respectively. DETAILED DESCRIPTION

[0042] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0043] The embodiment of the present invention provides a low-cost terahertz circularly polarized antenna array, the full view and layered schematic diagram of the antenna structure are shown in FIG. Figure 1 and Figure 2As shown, the antenna comprises a waveguide feed network 11 and a microstrip array 12. The waveguide feed network 11 is machined using CNC technology and is an air-filled metal waveguide structure. The microstrip array 12 is manufactured using standard PCB technology and is a single-layer PCB board. The board includes a dielectric plate 24, with a first metal layer 23 and a second metal layer 25 disposed on either side. In one embodiment of the present invention, the dielectric plate 24 is made of Rogers 5880, has a thickness of 0.254 mm, and has a dielectric constant and loss tangent of 2.2 and 0.0009, respectively.

[0044] Figure 3 The figure shows a top view of the waveguide feeding network 11, which includes a feeding waveguide 21, a sequential rotation feeding network 31, and a subarray feeding network 32. The feeding waveguide 21 is used to feed the entire antenna array. The sequential rotation feeding network 31 includes a first branch 33, a second branch 34, a third branch 35, and a fourth branch 36. The first branch 33 and the third branch 35 are of the same size, and the second branch 34 and the fourth branch 36 are of the same size. The four branches are arranged in a "swastika" shape. The output signal amplitudes of the first branch 33, the second branch 34, the third branch 35, and the fourth branch 36 are equal, and the relative phases are 0°, 90°, 180°, and 270°, respectively. Four wedge-shaped structures 37 are provided in the sequential rotation feeding network 31 to evenly distribute the energy transmitted from the feeding waveguide 21 to the four branches and achieve impedance matching of the input port. Figure 4 The figure shows a partial enlarged view of the subarray feed network 32, which includes two H-plane T-junctions 41. The subarray feed network 32 also includes a first ridge structure 42, a second ridge structure 43, and a third ridge structure 44. The first ridge structure 42 is used to evenly split the energy transmitted from the four branches into two paths, respectively inputting them into the two H-plane T-junctions 41. The second ridge structure 43 is used to evenly split the energy input into the H-plane T-junction 41 into two paths, transmitting them to the ends of the two branch waveguides of the H-plane T-junction 41. The third ridge structure 44 is located approximately one-quarter of the center frequency waveguide wavelength away from the end of the waveguide branch and is the structure used for impedance matching when the waveguide feed network 11 couples energy to the microstrip array 12.

[0045] In one embodiment of the present invention, the inner diameter of the feed waveguide 21 is the same as that of the WR-07 standard waveguide, is located at the geometric center of the entire waveguide feed network 11 and forms an angle of 45° with the x-axis.

[0046] Figure 5The figure shows a top view of the relative positions of the first metal layer 23 and the waveguide feeding network 11. Four rotated slot combinations 51 are provided on the first metal layer 23. The other three slot combinations 51 on the first metal layer 23 can be obtained by rotating one slot combination 51 clockwise around the z-axis by 90°, 180°, and 270°, respectively. In one embodiment of the present invention, each slot combination 51 includes four rectangular slots 52 of uniform size. The four rectangular slots 52 are arranged in a 2×2 formation. The centers of the rectangular slots 52 and the third ridge structure 44 are at the same distance from the end of the waveguide branch. The long sides of the rectangular slots 52 are parallel to the propagation direction of the electromagnetic waves in the waveguide feeding network 11.

[0047] Figure 6 The figure shows a top view of the second metal layer 25, on which an 8×8 microstrip patch antenna array is etched. In one embodiment of the present invention, the microstrip patch antenna array includes four first-stage antenna subarrays 61 that rotate sequentially. Each first-stage antenna subarray 61 includes four second-stage antenna subarrays 62. The second-stage antenna subarrays 62 coincide with the geometric center of the slot 52. Each second-stage antenna subarray 62 includes a microstrip line four-way power divider 63, four curved microstrip lines 64, and four circularly polarized patch elements 65 connected to the microstrip lines 64. With the geometric center of the slot 52 as the origin, the circularly polarized patch elements 65 located on both sides of the slot 52 are symmetrical about the origin in the xy plane. The microstrip line four-way power divider 63 is provided with two notches 66 on the metal edges on both sides of the slot 52. The notches 66 are structures used for impedance matching when the second-stage antenna subarrays 62 are coupled to the slot 52.

[0048] The antenna array of the embodiment of the present invention operates as follows: the feed waveguide 21 feeds the antenna in a back-feed manner, and the four wedge-shaped structures 37 divide the electromagnetic waves transmitted from the feed waveguide 21 into four signals. The four equally divided signals pass through the first branch 33, second branch 34, third branch 35, and fourth branch 36 of the sequentially rotated feed network 31, outputting four signals with relative phases of 0°, 90°, 180°, and 270°, respectively. The subarray feed network 32 connected to the four branch ends of the sequentially rotated feed network 31 further divides the input signal of each branch into four equal paths. After the electromagnetic wave reaches the respective waveguide ends of the waveguide power splitter network (waveguide feed network 11), it is coupled to the second metal layer 25 through the four groups of slot combinations 51 sequentially rotated and arranged on the first metal layer 23. In the second metal layer 25, sixteen microstrip power dividers 63 are excited, and the microstrip lines at their ends output four equally divided signals. These four signals respectively excite four circularly polarized radiating patches 64 connected to the power dividers, generating circularly polarized currents on the patch surfaces. Overall, when the waveguide feed network 11 feeds the 8×8 microstrip patch antenna, the four sequentially rotated second-stage antenna subarrays 55 are sequentially excited by electromagnetic wave signals with relative phases of 0°, 90°, 180°, and 270°, respectively. Ultimately, the antenna array radiates circularly polarized waves.

[0049] The working principle of the microstrip patch unit 64 is as follows Figure 7 As shown in the figure, the microstrip line inputs excitation from the semi-elliptical patch in a direction parallel to the short axis. The arc profile of the patch guides the flow direction of the current on the surface of the patch. At times 0, T / 4, T / 2, and 3T / 4 (T represents a time period), the direction of the surface current is 0°, 90°, 180°, and 270° to the positive direction of the x-axis, respectively. This indicates that the current generated on the surface of the patch is circularly polarized, so the patch unit can radiate circularly polarized electromagnetic waves outward. Figure 9 Graphs 64 show the reflection coefficient and axial ratio of the microstrip patch unit. It can be seen that the unit has good performance, with a reflection coefficient bandwidth and an axial ratio bandwidth of 32% and 21% respectively. Figure 8 The figure shows the operating principle of the stripline subarray. When feeding the 2×2 microstrip line subarray 62, the present invention uses a slot-coupled feeding method that does not require a through-hole. This feeding method results in differential output signals from the microstrip line power divider 63 (the output signal phases on either side of the midline are 0° and 180°, respectively). Therefore, when arranging the patch units on both sides of the midline, the two patch unit structures on the same side need to be rotated 180° along the z-axis and then placed on the other side of the slot. With this arrangement, the current polarization direction of the four unit patches is consistent.

[0050] The core of the sequential rotary feeding technology lies in the design of the sequential rotary feeding network 31. The wedge structure 37 divides the electromagnetic waves input by the feeding waveguide 21 into four paths, two of which are 0° and two are 180°. In order to realize rotary feeding in a compact topology, each branch is bent 90°. At the same time, in order to realize sequential feeding, a 90° phase delay is performed on one 0° signal and one 180° signal of the four electromagnetic wave signals, and finally four electromagnetic wave signals with relative phases of 0°, 90°, 180°, and 270° are obtained. By utilizing the waveguide dispersion characteristics and jointly adjusting the width and length of the waveguide, the signal can have a stable 90° phase delay in a wider frequency band. Figure 10 The figure shows the reflection coefficient when feeding through port 1 and the amplitude of the transmission coefficient from port 2 to port 5 in the sequentially rotated feeding network 31. It can be seen that the reflection coefficient is less than 10dB across a wide frequency band, and the amplitude of the signal transmission coefficient at the four ports is almost the same and remains near -6dB. Figure 11 The figure shows the relative phase of the transmission coefficients from port 2 to port 5. The phase difference between adjacent ports from port 2 to port 5 is almost stable at 90° within a wide frequency band, meeting the requirement of sequential feeding.

[0051] In terms of antenna performance, the antenna designed by the present invention works around 140 GHz. Figure 12 The reflection coefficient and axial ratio curves of the antenna array are shown in Figure 1. The -10dB impedance bandwidth is approximately 29.8% (119.4-161.2GHz), and the 3dB axial ratio bandwidth is approximately 28.9% (118.3-158.2GHz). The gain curve of the antenna is shown in Figure 1. Figure 13 As shown in the figure, the 3dB gain bandwidth is about 28.7% (119.6-159.3GHz), with a peak gain of 23.7dBic at 139.5GHz. The -10dB impedance bandwidth of the antenna almost completely overlaps with the 3dB axial ratio bandwidth and the 3dB gain bandwidth, which indicates that the antenna has a wide operating frequency band, and within the operating frequency band, the circular polarization purity is high and the gain is stable. Figure 14 、 Figure 15 and Figure 16 The E-plane (xz-plane) and H-plane (yz-plane) radiation patterns of three frequency points (121, 139, and 157 GHz) within the operating frequency band are displayed respectively. It can be seen that at the selected frequency points, the antenna's radiation pattern has low side lobes, indicating that the antenna has good radiation characteristics.

[0052] The 8×8 terahertz circularly polarized antenna array provided by the aforementioned embodiment of the present invention has a simple structure, low manufacturing cost, and wide operating bandwidth. It adopts a hybrid feeding scheme (microstrip / waveguide hybrid structure) and realizes array feeding through the combination of waveguide power division network and microstrip power division network (waveguide feeding network and microstrip array). The entire antenna only requires a two-layer structure to realize an 8×8 array. In terms of process, the antenna can be processed by traditional low-cost CNC technology and PCB technology, and no structures with high processing difficulty such as metal through holes are involved in the antenna. The broadband circularly polarized patch unit adopted can achieve an impedance bandwidth of 32%, and the axial ratio bandwidth can reach 21%. By introducing sequential rotation feeding technology in the array, the operating bandwidth of the entire array can reach 28%, and the peak gain is 23.7dBic, which is better than the current technical status.

[0053] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A terahertz circularly polarized antenna array, characterized in that: including waveguide feed networks and microstrip arrays; The waveguide feed network includes a feed waveguide, a sequential rotation feed network, and a subarray feed network. The feed waveguide is used to feed the entire antenna array. The sequential rotation feed network includes four branches arranged in a swastika shape and is provided with a wedge-shaped structure for evenly distributing the energy transmitted from the feed waveguide to the four branches and achieving impedance matching at the input port. Each branch is connected to a subarray feed network. The microstrip array includes a dielectric plate, on which a first metal layer and a second metal layer are respectively arranged on opposite sides. A rotationally arranged slot combination is arranged on the first metal layer at a position corresponding to each branch, and a microstrip patch antenna array is arranged on the second metal layer.

2. The terahertz circularly polarized antenna array according to claim 1, wherein: The feeding waveguide is located at the geometric center of the entire waveguide feeding network 11 and forms an angle of 45° with the x-axis.

3. The terahertz circularly polarized antenna array according to claim 1, characterized in that: The output signals of the four branches have equal amplitudes, and their relative phases are 0°, 90°, 180°, and 270°, respectively.

4. A terahertz circularly polarized antenna array according to any one of claims 1 to 3, characterized in that: Each subarray feeding network includes a first ridge structure and two H-plane T-junctions. The first ridge structure is located between the two H-plane T-junctions and is used to divide the energy transmitted from the branch into two paths and input them into the two H-plane T-junctions respectively.

5. The terahertz circularly polarized antenna array according to claim 4, characterized in that: Each sub-array feeding network also includes a second ridge structure, which is used to split the energy input into the H-plane T-junction into two paths and transmit them to the ends of the two branch waveguides of the H-plane T-junction.

6. The terahertz circularly polarized antenna array according to claim 5, characterized in that: Each sub-array feeding network further includes a third ridge structure, which is a structure used for impedance matching when the waveguide feeding network couples energy to the microstrip array.

7. The terahertz circularly polarized antenna array according to claim 6, characterized in that: Each slot combination includes four slots arranged corresponding to the waveguide branches of the H-plane T-junction, and the distances between the centers of the slots and the centers of the third ridge structure and the ends of the waveguide branches are consistent.

8. The terahertz circularly polarized antenna array according to claim 7, characterized in that: The microstrip patch antenna array includes four first-stage antenna subarrays that rotate sequentially. Each first-stage antenna subarray includes four second-stage antenna subarrays. The second-stage antenna subarrays coincide with the geometric center of the slot.

9. The terahertz circularly polarized antenna array according to claim 8, characterized in that: Each second-stage antenna subarray includes a microstrip line four-way power divider, four bent microstrip lines and four circularly polarized patch units respectively connected to the microstrip lines.

10. The terahertz circularly polarized antenna array according to claim 8, characterized in that: The microstrip line four-way power divider is provided with notches on the metal edges on both sides of the gap.

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