A terahertz circularly polarized antenna array

Abstract

This invention provides a terahertz circularly polarized antenna array, comprising a waveguide feeding network and a microstrip array. The waveguide feeding network includes a feeding waveguide, a sequential rotating feeding network, and a subarray feeding network. The sequential rotating feeding network includes four branches arranged in a swastika shape and is equipped with a wedge structure for evenly distributing the energy transmitted from the feeding waveguide to the four branches and achieving impedance matching at the input ports. Each branch is connected to a subarray feeding network. The microstrip array includes a dielectric substrate with a first metal layer and a second metal layer disposed on opposite sides. Rotationally arranged slot combinations are disposed on the first metal layer corresponding to the positions of each branch. A microstrip patch antenna array is disposed on the second metal layer. This invention employs a hybrid feeding scheme, combining the waveguide feeding network and the microstrip array to achieve array feeding, and introducing sequential rotating feeding technology, which has the advantage of wide bandwidth.

Description

Technical Field

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

[0002] Terahertz technology has become a research area that has attracted widespread attention in recent years. Due to the strong penetrating power and low photon energy of electromagnetic waves in the terahertz band, it is frequently used in fields such as non-destructive testing, security imaging, and biomedicine. Furthermore, due to the high frequency and wide spectrum characteristics of terahertz waves, this technology is also applied to ultra-high-speed and ultra-wideband wireless communication systems. Antennas, as an indispensable component in terahertz systems, have therefore become a key focus of industry research. In terms of polarization, circular polarization avoids problems such as multipath distortion and polarization mismatch; therefore, researching circularly polarized terahertz antennas has significant practical application value.

[0003] Currently, there are many reports on terahertz circularly polarized antennas in publicly available literature, but these antennas generally suffer from problems such as high manufacturing difficulty, high cost, and limited performance.

[0004] First, regarding fabrication, because terahertz antennas operate at very high frequencies, their dimensions become extremely small, typically on the order of micrometers. At this size scale, traditional fabrication processes used for microwave and millimeter-wave antennas are difficult to apply. Currently, common terahertz antenna fabrication processes mainly include semiconductor processes. [1] Metal / ceramic diffusion welding process [2][3] These processes are generally quite expensive and have relatively complex workflows. In recent years, CNC machining and PCB manufacturing processes have also been adopted. [4] Terahertz antennas have been proposed, but these antennas are generally multi-layered structures. Too many layers and the interconnection between layers will 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 processing difficulty.

[0005] Secondly, regarding antenna performance, currently reported terahertz circularly polarized antennas generally suffer from narrow operating bandwidth, typically not exceeding 20%. This problem is mainly due to two reasons: firstly, the circularly polarized terahertz antenna elements in the reported literature themselves have only a limited axial ratio bandwidth. [5] On the other hand, the coupling between elements in the antenna array also affects the impedance bandwidth and axial ratio bandwidth. [2] At the same time, the more complex the antenna structure, 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 Thin Metallic Walls,"in IEEE Access,vol.8,pp.125223-125233,2020. Summary of the Invention

[0011] To at least solve 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, realizes array feeding by combining a waveguide feeding network and a microstrip array, and has the advantage of wide bandwidth by introducing a sequential rotation feeding technique into the array.

[0012] To achieve the object of the present invention, a terahertz circularly polarized antenna array provided by the present invention includes a waveguide feeding network and a microstrip array;

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

[0014] The microstrip array includes a dielectric plate, and a first metal layer and a second metal layer are respectively provided on the opposite two sides of the dielectric plate. Rotating slot combinations are provided on the first metal layer at positions corresponding to each branch, and a microstrip patch antenna array is provided on the second metal layer.

[0015] Further, 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] Further, the output signal amplitudes of the four branches are equal, and the relative phases are 0°, 90°, 180° and 270° respectively.

[0017] Further, each sub-array 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 by the branch into two paths and input them into the two H-plane T-junctions respectively.

[0018] Further, each sub-array feeding network also includes a second ridge structure, which is used to divide 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 subarray feed network also includes a third ridge structure, which is a structure used for impedance matching during the process of the waveguide feed network coupling energy to the microstrip array.

[0020] Furthermore, each gap assembly includes four gaps corresponding to the waveguide branches of the H-plane T-junction, with the center of the gaps being at the same distance from the end of the waveguide branch as the center of the third ridge structure.

[0021] Furthermore, the microstrip patch antenna array includes four sequentially rotating first-stage antenna subarrays, each of which includes four second-stage antenna subarrays, the second-stage antenna subarrays coinciding 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 elements connected to the microstrip lines respectively.

[0023] Furthermore, the microstrip four-way power divider has notches on the metal edges on both sides of the slot.

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

[0025] 1) This invention proposes a hybrid feeding scheme with a dual-layer topology structure, which adopts a simple circular polarization unit structure, thereby reducing the processing cost and difficulty of terahertz antennas to a certain extent.

[0026] 2) The circular polarization unit of the present invention has excellent performance and introduces sequential rotation feeding technology, resulting in superior performance of the circular polarization antenna array. Its operating bandwidth can reach 28%, which is better than the current technology and has the advantage of wide bandwidth.

[0027] 3) This invention avoids the introduction of metal through holes in its structure, and the processing technology can adopt low-cost PCB and CNC processes, which has the advantages of simple structure, low cost and low processing difficulty. Attached Figure Description

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

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

[0030] Figure 3 This is a top view of the waveguide feed network in an embodiment of the present invention.

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

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

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

[0034] Figure 7 This is a schematic diagram illustrating the working principle of the microstrip patch unit in an embodiment of the present invention.

[0035] Figure 8 A schematic diagram illustrating the working principle of the subarray with wires in this embodiment of the invention.

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

[0037] Figure 10 A schematic diagram of the reflection coefficient when power is supplied through port 1 and the amplitude of the transmission coefficients from port 2 to port 5 in the sequential rotating power supply network in this embodiment of the invention.

[0038] Figure 11 A schematic diagram of the relative phase of the transmission coefficients of ports 2 to 5 in an embodiment of the present invention.

[0039] Figure 12 The reflection coefficient and axial ratio curves of the antenna array in this embodiment of the invention.

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

[0041] Figure 14 , Figure 15 and Figure 16 The radiation patterns of the E-plane (xz plane) and H-plane (yz plane) at three frequency points within the operating frequency band, namely 121, 139, and 157 GHz, are shown respectively. Detailed Implementation

[0042] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0043] This invention provides a low-cost terahertz circularly polarized antenna array, with a full view and layered schematic diagram of the antenna structure shown in the figures below. Figure 1 and Figure 2As shown, the antenna comprises two parts: a waveguide feed network 11 and a microstrip array 12. The waveguide feed network 11 is manufactured using CNC machining 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, including a dielectric substrate 24. A first metal layer 23 and a second metal layer 25 are respectively disposed on both sides of the dielectric substrate 24. In one embodiment of the invention, the dielectric substrate 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 diagram shows a top view of the waveguide feed network 11, which includes a feed waveguide 21, a sequential rotating feed network 31, and a subarray feed network 32. The feed waveguide 21 supplies power to the entire antenna array. The sequential rotating feed 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 have the same dimensions, as do the second branch 34 and the fourth branch 36. 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, with relative phases of 0°, 90°, 180°, and 270°, respectively. Four wedge structures 37 are provided in the sequential rotating feed network 31 to evenly distribute the energy transmitted from the feed waveguide 21 to the four branches, while simultaneously achieving impedance matching at the input ports. Figure 4 The diagram shows a partially 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 divides the energy transmitted from the four branches into two paths, which are then input into the two H-plane T-junctions 41 respectively. The second ridge structure 43 divides the energy input into the H-plane T-junctions 41 into two paths, which are then transmitted to the ends of the two branch waveguides of the H-plane T-junctions 41. The third ridge structure 44 is located approximately one-quarter of the center frequency waveguide wavelength from the end of the waveguide branch and is used for impedance matching during the coupling of energy from the waveguide feed network 11 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, and it is located at the geometric center of the entire waveguide feed network 11 and forms a 45° angle with the x-axis.

[0046] Figure 5The diagram shows a top view of the relative positions of the first metal layer 23 and the waveguide feed network 11. Four rotatingly arranged slot combinations 51 are disposed on the first metal layer 23. The other three slot combinations 51 on the first metal layer 23 can be obtained by rotating one of the slot combinations 51 clockwise by 90°, 180°, and 270° sequentially around the z-axis. In one embodiment of the invention, each slot combination 51 includes four rectangular slots 52 of the same size, arranged in a 2×2 configuration. The center of each rectangular slot 52 is at the same distance from the center of the third ridge structure 44 to the end of the waveguide branch. The long side of each rectangular slot 52 is parallel to the transmission direction of the electromagnetic waves in the waveguide feed network 11.

[0047] Figure 6 The diagram 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 invention, the microstrip patch antenna array includes four sequentially rotating first-stage antenna subarrays 61. 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 quad power divider 63, four bent microstrip lines 64, and four circularly polarized patch elements 65 respectively 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 quad power divider 63 has two notches 66 on the metal edges on both sides of the slot 52. These 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 this invention operates as follows: the feed waveguide 21 feeds the antenna in a back-feed configuration. Four wedge structures 37 divide the electromagnetic waves transmitted from the feed waveguide 21 into four signals. These four signals pass through the first branch 33, the second branch 34, the third branch 35, and the fourth branch 36 of the sequentially rotating feed network 31, outputting four signals with relative phases of 0°, 90°, 180°, and 270°, respectively. The subarray feed network 32, connected to the ends of the four branches of the sequentially rotating feed network 31, further divides the input signal of each branch into four equal paths. After the electromagnetic waves reach the ends of each waveguide in the waveguide power divider network (waveguide feed network 11), they are coupled to the second metal layer 25 through four sets of slot combinations 51 arranged in a sequential rotation on the first metal layer 23. In the second metal layer 25, sixteen microstrip power dividers 63 are excited, and their end microstrip lines 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 excited by electromagnetic wave signals with relative phases of 0°, 90°, 180°, and 270°, respectively, and finally the antenna array radiates circularly polarized waves outward.

[0049] The working principle of the microstrip patch unit 64 is as follows: Figure 7 As shown, the microstrip line inputs excitation from the semi-elliptical patch in a direction parallel to the minor axis. The arc-shaped contour of the patch guides the direction of current flow on the patch surface. At times 0, T / 4, T / 2, and 3T / 4 (T represents a time period), the direction of the surface current forms angles of 0°, 90°, 180°, and 270° with the positive x-axis, respectively. This indicates that the current generated on the patch surface is a circularly polarized current, and therefore the patch unit can radiate circularly polarized electromagnetic waves outward. Figure 9 The diagram shows the reflection coefficient and axial ratio of the microstrip patch unit 64. It can be seen that the unit has good performance, with a reflection coefficient bandwidth and axial ratio bandwidth of 32% and 21%, respectively. Figure 8 The diagram illustrates the working principle of the microstrip subarray. In feeding the 2×2 microstrip subarray 62, this invention employs a slot-coupled feeding method without vias. This feeding method results in differential output signals from the microstrip power divider 63 (output signals on either side of the centerline have phases of 0° and 180°, respectively). Therefore, when arranging the patch cells on both sides of the centerline, the two patch cell structures on the same side need to be rotated 180° around the z-axis and placed on the other side of the slot. With this arrangement, the current polarization direction on the four patch cells is consistent.

[0050] The core of the sequential rotating feed technology lies in the design of the sequential rotating feed network 31. The wedge structure 37 splits the electromagnetic wave input from the feed waveguide 21 into four paths, two at 0° and two at 180°. To achieve rotating feed in a compact topology, each branch is bent at 90°. Simultaneously, to achieve sequential feed, one of the 0° and one of the 180° electromagnetic wave signals undergoes a 90° phase delay, ultimately obtaining four electromagnetic wave signals with relative phases of 0°, 90°, 180°, and 270°. By utilizing the waveguide dispersion characteristics and jointly adjusting the waveguide width and length, a stable 90° phase delay can be achieved across a wide frequency band. Figure 10 The figure shows the reflection coefficient when fed through port 1 and the amplitude of the transmission coefficients from port 2 to port 5 in the sequential rotating feed network 31. It can be seen that the reflection coefficient is below 10dB over a wide frequency band; at the same time, the amplitude of the signal transmission coefficients at the four ports is almost the same and remains around -6dB. Figure 11 The figure shows the relative phase of the transmission coefficients from port 2 to port 5. Within a wide frequency band, the phase difference between adjacent ports from port 2 to port 5 is almost stable at 90°, which meets the requirements of sequential power supply.

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

[0052] The 8×8 terahertz circularly polarized antenna array provided by the foregoing embodiments of the present invention features a simple structure, low manufacturing cost, and wide operating bandwidth. It employs a hybrid feeding scheme (microstrip / waveguide hybrid structure), achieving array feeding through a combination of waveguide power divider networks and microstrip power divider networks (waveguide feeding network and microstrip array). The entire antenna requires only two layers to achieve an 8×8 array. In terms of manufacturing, the antenna can be fabricated using traditional low-cost CNC and PCB technologies, and it does not involve complex structures such as metal vias. The wideband circularly polarized patch unit achieves an impedance bandwidth of 32% and an axial ratio bandwidth of 21%. By introducing sequential rotation feeding technology into the array, the overall operating bandwidth of the array reaches 28%, with a peak gain of 23.7 dBic, which is superior to current technological advancements.

[0053] The above description of the disclosed embodiments enables those skilled in the art to make or use the 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 invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A terahertz circularly polarized antenna array, characterized in that, It includes a waveguide feeding network and a microstrip array; The waveguide feeding network includes a feeding waveguide, a sequential rotation feeding network, and a sub-array feeding network. The feeding waveguide is used to feed the entire antenna array. The sequential rotation feeding network includes four branches arranged in a "卍" shape and is provided with a wedge-shaped structure for evenly distributing the energy transmitted by the feeding waveguide to the four branches and achieving impedance matching of the input port. Each branch is respectively connected to a sub-array feeding network; The microstrip array includes a dielectric plate, and a first metal layer and a second metal layer are respectively provided on the opposite two sides of the dielectric plate. A rotationally arranged slit combination is provided on the first metal layer at positions corresponding to each branch, and a microstrip patch antenna array is provided on the second metal layer.

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

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

4. A terahertz circularly polarized antenna array according to any one of claims 1-3, characterized in that, Each sub-array 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 evenly divide the energy transmitted by the branch into two paths and input them into the two H-plane T-junctions respectively.

5. A 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 evenly divide the energy input into the H-plane T-junction into two paths and transmit it to the ends of the two branch waveguides of the H-plane T-junction.

6. A terahertz circularly polarized antenna array according to claim 5, characterized in that, Each sub-array feeding network also includes a third ridge structure, which is a structure for impedance matching during the process of the waveguide feeding network coupling energy to the microstrip array.

7. A terahertz circularly polarized antenna array according to claim 6, characterized in that, Each slit combination includes 4 slits provided corresponding to the waveguide branches of the H-plane T-junction, and the center of the slit is at the same distance from the center of the third ridge structure to the end of the waveguide branch.

8. A terahertz circularly polarized antenna array according to claim 7, characterized in that, The microstrip patch antenna array includes four sequentially rotated first-level antenna sub-arrays, and each first-level antenna sub-array includes four second-level antenna sub-arrays, and the second-level antenna sub-arrays coincide with the geometric centers of the slits.

9. A terahertz circularly polarized antenna array according to claim 8, characterized in that, Each second-level antenna sub-array includes a microstrip four-way power divider, four bent microstrips, and four circularly polarized patch units respectively connected to the microstrips.

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

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