A differential antenna array based on high-order modes of substrate integrated waveguide

Abstract

A differential antenna array based on high-order modes of substrate integrated waveguide disclosed by the present invention includes a first dielectric plate, a second dielectric plate, a third dielectric plate and a fourth dielectric plate. A first metal layer and a second metal layer are respectively disposed on the lower and upper surfaces of the first dielectric plate. A third metal layer is disposed on the upper surface of the second dielectric plate, and a fourth metal layer is disposed on the upper surface of the third dielectric plate. A microstrip power divider is disposed on the first metal layer, and a first coupling slot is disposed at a position near the end of each path of the microstrip power divider on the second metal layer. A plurality of sub-arrays are disposed on the second dielectric plate, and a second coupling slot is disposed on the third metal layer. A metal patch is disposed on the fourth metal layer at a position corresponding to each second coupling slot. Every two adjacent and oppositely placed metal patches form a pair of differential microstrip lines. It is a differential antenna array with broadband, low profile, low cross polarization, stable in-band performance and operating in the Ka band.

Description

Technical Field

[0001] The present invention relates to the technical field of antennas, and particularly relates to a differential antenna array based on a high-order mode of a substrate integrated waveguide. Background Art

[0002] Differential antennas are a common type of antenna. They are usually fed with two signals of equal amplitude and opposite phase, and have advantages such as low cross-polarization, symmetric radiation pattern, and high common-mode signal rejection ratio. To achieve differential feeding, common methods include: First, using an equal-amplitude splitting one-to-two power divider, and then adjusting the lengths of the two transmission lines at the output to achieve a 180-degree phase difference, such as the microstrip line differential circuit shown in (W.Yang, K.Ma, K.S.Yeo and W.M.Lim, "A compact high-performance patch antenna array for 60-GHz applications," IEEE Antennas Wireless Propag. Lett., vol.15, pp.313-316, 2016); Second, using a 180-degree coupler, such as the microstrip ring hybrid shown in (X.S.Fang, K.W.Leung, E.H.Lim and R.S.Chen, "Compact differential rectangular dielectric resonator antenna," IEEE Antennas Wireless Propag. Lett., vol.9, pp.662-665, 2010) and the magic-T hybrid shown in (J.M.Rebollar, J.Esteban and J.E.Page, "Full wave analysis of three and four-port rectangular waveguide junctions," IEEE Trans. Microw. Theory Tech., vol.42, no.2, pp.256-263, Feb. 1994); Third, using an E-plane waveguide power divider, which has natural differential characteristics at the two output ports, as shown in (X.Ruan, K.B.Ng and C.H.Chan, "A differentially fed transmission-line-excited magnetoelectric dipole antenna array for 5G applications," IEEE Trans. Antennas Propag., vol.66, no.10, pp.5224-5230, Oct. 2018); Fourth, by opening slits that cut the current lines on a metal plate or waveguide structure, the currents on both sides of the slit are often regarded as differential signals, such as (H.-T.Hu and C.H.Chan,"Substrate-integrated-waveguide-fed wideband filtering antenna for millimeter-wave applications,"IEEE Trans.AntennasPropag.,vol.69,no.12,pp.8125-8135,Dec.2021); 5. Using a dual-conductor transmission line, the signals on the two conductors in the transmission line can also be regarded as differential signals, as shown in (RAAlhalabi and GMRebeiz,"High-gain yagi-uda antennas for millimeter-wave switched-beam systems,"IEEETrans.AntennasPropag.,vol.57,no.11,pp.3672-3676,Nov.2009.). The above are all relatively common differential circuit solutions, but they all have some problems to varying degrees. For example, the ring hybrids in Solutions 1 and 2 usually have a narrow impedance bandwidth, and the differential phase varies significantly with frequency, making it difficult to maintain a constant 180-degree phase difference within a broadband range. The magic T hybrids in Solutions 3 and 2, due to their special E-plane waveguide T-junction structure, can achieve an ideal 180-degree phase difference within the impedance bandwidth, but the device structure is too complex, often a three-dimensional structure, and difficult to integrate on a PCB board. For Solutions 4 and 5, strictly speaking, the signals they generate are not ideal differential signals, because it is difficult to ensure that the currents on both sides of the gap or on the two conductors in a two-conductor transmission line are completely equal in amplitude and opposite in phase, and the differential signals they generate may be mixed with common-mode interference. On the other hand, when differential feeding circuits are applied to antenna arrays, issues such as array layout, size, and feeder routing must also be considered. The above solutions are difficult to address all of these issues. Therefore, it is of practical significance to propose a differential circuit with wide impedance bandwidth, completely equal amplitude and opposite phase of output signals, which can be integrated on PCB boards and is suitable for antenna array feeding.

[0003] In recent years, people have conducted in-depth research on high-order modes in waveguide structures. It is found that high-order modes in rectangular waveguides have the characteristic of half-wavelength phase inversion, that is, for TE n0(n≥2) traveling wave mode, there is a natural phase difference of 180 degrees between the electric fields of two adjacent half-wavelengths in the transverse direction (the direction of subscript n). Therefore, as long as the waveguide of the higher-order mode can meet the impedance matching condition at the input end, the phase difference at the output end can be constantly differentiated within the entire impedance bandwidth range. Currently, the reported research on higher-order mode antennas usually focuses on using the waveguide of the higher-order mode to simplify the feed network of the antenna array, and most of such antennas operate in the higher-order cavity resonance mode, usually with a narrow bandwidth. For example, as shown in (W.Han, F.Yang, J.Ouyang and P.Yang, "Low-cost wideband and high-gain slotted cavity antenna using high-order modes for millimeter-wave application," IEEE Trans. Antennas Propag., vol.63, no.11, pp.4624-4631, Nov.2015), it cannot meet the usage requirements of people. Summary of the Invention

[0004] In order to solve the problems that the traditional differential feeding circuit is difficult to achieve: wideband, constant differential phase, integrated on the PCB board, suitable for feeding the antenna array, etc., the present invention provides a differential antenna array based on the higher-order mode of substrate integrated waveguide, which is a differential antenna array with wideband, low profile, low cross-polarization, stable in-band performance, and operating in the Ka band.

[0005] To achieve the object of the present invention, a differential antenna array based on the higher-order mode of substrate integrated waveguide provided by the present invention is successively provided with a first dielectric plate, a second dielectric plate, a third dielectric plate, and a fourth dielectric plate from bottom to top. A first metal layer and a second metal layer are respectively provided on the lower surface and the upper surface of the first dielectric plate, a third metal layer is provided on the upper surface of the second dielectric plate, and a fourth metal layer is provided on the upper surface of the third dielectric plate, wherein,

[0006] A microstrip power divider is provided on the first metal layer, and a first coupling slot is provided on the second metal layer at a position near the end of each path corresponding to the microstrip power divider. A plurality of sub-arrays are provided on the second dielectric plate, and a second coupling slot is provided on the third metal layer at a position corresponding to each sub-array. A metal patch orthogonal to it is provided on the fourth metal layer at a position corresponding to each second coupling slot. Each two adjacent and oppositely placed metal patches form a pair of differential microstrip lines.

[0007] With this solution, electromagnetic energy is equally and in-phase distributed to each path through a microstrip power divider. The first coupling slot is used to couple the electromagnetic energy from the microstrip line into the upper sub-array. High-order TE 40 modes propagate in the sub-array waveguide, and the differential field excites the microstrip line through the second coupling slot, and finally radiates into the atmosphere through the fourth dielectric plate.

[0008] The second coupling slot is used to excite the differential microstrip line.

[0009] Further preferably, the materials of the first dielectric plate, the second dielectric plate, the third dielectric plate, and the fourth dielectric plate are all Rogers 5880.

[0010] Further preferably, the fourth dielectric plate is a pure dielectric plate without metal patterns on its upper and lower surfaces.

[0011] Further preferably, the microstrip power divider is a five-stage microstrip power divider with one input and thirty-two outputs.

[0012] Further preferably, traveling waves of TE 40 mode are excited in each sub-array, including four differential radiation units arranged in a 2×2 form.

[0013] Further preferably, the differential field in the waveguide excites the differential microstrip line through the second coupling slot.

[0014] Further preferably, each sub-array is excited by the microstrip-line-slot coupling method.

[0015] Further preferably, dielectric blocks are provided at positions on the fourth dielectric plate corresponding to each pair of differential microstrip lines.

[0016] Further preferably, the cross-section of the dielectric block is rectangular.

[0017] Further preferably, a connection structure is provided on the fourth dielectric plate.

[0018] Further preferably, the connection structure includes four dielectric strips.

[0019] Compared with the prior art, the present invention can at least achieve the following beneficial effects:

[0020] The present invention utilizes the half-wavelength inversion characteristic of the high-order mode of a rectangular waveguide to propose a method for realizing differential feeding. This method has the advantages of broadband, constant differential phase, low profile, integratable, and can be used for large-scale array design. Based on this method, a differential antenna array operating in the Ka band is proposed, which has the advantages of bandwidth, high gain, low cross-polarization, low profile, and stable radiation performance within the operating frequency band. Brief Description of the Drawings

[0021] To more clearly illustrate the technical solutions in the embodiments of the invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings, where:

[0022] Figure 1 is a schematic structural diagram of a differential antenna array based on the high-order mode of a substrate integrated waveguide provided by an embodiment of the present invention.

[0023] Figure 2 is an exploded view of the structure of a differential antenna array based on the high-order mode of a substrate integrated waveguide provided by an embodiment of the present invention.

[0024] Figure 3 is a top view of the first dielectric plate and the metal layers on its upper and lower surfaces in an embodiment of the present invention.

[0025] Figure 4 is a top view of the second dielectric plate and the metal layers on its upper and lower surfaces in an embodiment of the present invention.

[0026] Figure 5 is a top view of the third dielectric plate and the metal layers on its upper and lower surfaces in an embodiment of the present invention.

[0027] Figure 6 is a top view of the fourth dielectric plate and the fourth metal layer in an embodiment of the present invention.

[0028] Figure 7 is a schematic diagram of the working principle of a sub-array in an embodiment of the present invention.

[0029] Figure 8 is a schematic diagram of the impedance bandwidth of the antenna array in an embodiment of the present invention.

[0030] Figure 9 is the radiation pattern of the antenna array at the center frequency of 32 GHz in an embodiment of the present invention. (a) is the E-plane, and (b) is the H-plane.

[0031] Figure 10 is a schematic diagram of the gain characteristic of the antenna array in an embodiment of the present invention. Detailed implementation manners

[0032] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts are within the scope of protection of the present invention.

[0033] In the present invention, descriptions such as "first" and "second" are for descriptive purposes only, and do not particularly refer to the meaning of order or sequence, nor are they used to limit the present invention. They are merely used to distinguish components or operations described with the same technical terms, and cannot be understood as indicating or implying their relative importance or implicitly indicating the quantity of the indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include at least one such feature. In addition, terms such as "comprising" and "including" are used in a similar sense, intending to cover a non-exclusive scope. For example, a process, method, system, product or device that includes a series of steps or modules does not have to be limited to the details listed, but may include inherent content related to these steps or modules that are not listed. Additionally, the technical solutions between various embodiments can be combined with each other, but it must be based on the ability of those of ordinary skill in the art to implement. When the combination of technical solutions results in contradictions or cannot be implemented, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0034] A differential antenna array based on high-order modes of substrate integrated waveguides provided by the present invention, as Figure 1 and Figure 2 shown, the array includes four layers of PCB boards. The coordinate system is established as follows: the x-axis and y-axis of the rectangular coordinate system are respectively parallel to two rectangular sides of the PCB board, the maximum radiation direction of the array points to the z-axis, the feeding point 29 is located on the y-axis, and it is stipulated that the -z and +z directions are respectively downward and upward. Then, the four layers of PCB boards are defined as the first dielectric board 21, the second dielectric board 22, the third dielectric board 23, and the fourth dielectric board 24 from bottom to top. The metal layers are defined as the first metal layer 25, the second metal layer 26, the third metal layer 27, and the fourth metal layer 28 from bottom to top. Among them, the first metal layer 25 and the second metal layer 26 are respectively located on the lower surface and the upper surface of the first dielectric board 21; the third metal layer 27 is located on the upper surface of the second dielectric board 22; the fourth metal layer 28 is located on the upper surface of the third dielectric board 23; the fourth dielectric board 24 is a pure dielectric board, and there are no metal patterns on both the upper and lower surfaces.

[0035] In some embodiments of the present invention, all the PCB boards are Rogers 5880, with a dielectric constant of 2.2, a loss tangent angle of 0.0009, and a size of 75mm * 72mm.

[0036] In some embodiments of the present invention, the plate thicknesses of the first dielectric plate 21, the second dielectric plate 22, the third dielectric plate 23, and the fourth dielectric plate 24 are 0.127mm, 0.508mm, 0.787mm, and 0.787mm respectively. In other embodiments, other values can be adopted.

[0037] In some embodiments of the present invention, the microstrip power divider 31 is a five - stage microstrip power divider with a one - to - thirty - two way division, and the first coupling slots 32 are arranged in an 8×4 form. In other embodiments, other numbers of power division stages and divided paths can also be adopted.

[0038] Figure 3 The circuit design on the first dielectric plate 21 is shown. A microstrip power divider 31 is provided on the first metal layer 25 on the lower surface of the first dielectric plate 21. On the second metal layer 26 on the upper surface of the first dielectric plate 21, first coupling slots 32 are provided at positions near the end of each path of the microstrip power divider 31, and are arranged in an 8×4 form. Figure 4 The circuit design on the second dielectric plate 22 is shown, including 16 sub - arrays 41 arranged in a 4×4 form, and each sub - array 41 is surrounded by metallized vias arranged in a rectangular form. On the upper surface of each sub - array 41, that is, on the third metal layer 27, 8 second coupling slots 42 are provided and arranged in a 4×2 form. Figure 5 The circuit design on the third dielectric plate 23 is shown. On the upper surface of the third dielectric plate 23, that is, on the fourth metal layer 28, a metal patch orthogonal to each second coupling slot 42 is provided, and every two adjacent and oppositely placed metal patches form a pair of differential microstrip lines 51. Figure 6 The structural diagram of the fourth dielectric plate 24 is shown. A rectangular dielectric block 61 is provided on the fourth dielectric plate 24 corresponding to each pair of differential microstrip lines 51 on the fourth metal layer 28. Among them, in some embodiments of the present invention, the rectangular dielectric block 61 is obtained by digging a hole in a whole pure dielectric plate, and its connection with the surrounding structure is connected through a connection structure 62. Among them, the connection structure 62 is four dielectric strips, which are respectively located around the rectangular dielectric block 61 and are used to connect the dielectric block 61 with the surrounding dielectric plate structure.

[0039] In the entire array, the first coupling slot 31 is used to couple electromagnetic energy from the microstrip line into the upper sub-array 41. The second coupling slot 42 is used to excite the differential microstrip line 51. The rectangular dielectric block 61 serves to improve the impedance matching of the antenna.

[0040] In terms of the working principle, the entire array is excited by the feeding point 29 through a coaxial connector, and then the electromagnetic energy is equally divided and in-phase distributed to each path through the microstrip power divider 31. The working principle of the sub-array 41 is as Figure 7 shown. Each sub-array 41 is excited by two of the first coupling slots 32, and the higher-order TE 40 mode propagates in the waveguide, with the propagation directions being +x and -x respectively. The electric field forms 4 half-wavelength standing waves along the y direction. Each sub-array 41 includes 4 pairs of differential radiation units, which are respectively defined as unit 71, unit 72, unit 73, and unit 74, and the element spacing is 0.74 free-space wavelengths. The differential field in the waveguide excites the differential microstrip line 51 through the second coupling slot 42, and finally radiates into the atmosphere through the rectangular dielectric block 61. In some embodiments of the present invention, the sub-array 41 is a 2×2 differential array composed based on the substrate integrated waveguide TE 40 mode. In other designs, the order n of the higher-order mode can be flexibly adjusted on this basis to achieve designs based on TE 20 , TE 40 , TE 60 etc. For forming differential radiation, the order n needs to be an even number.

[0041] In terms of the antenna performance, Figure 8 is the impedance bandwidth of the antenna. This antenna can achieve impedance matching below -10 dB in the frequency band from 26.7 GHz to 37.7 GHz, and the impedance bandwidth is 34.2%, which is better than the current technical level of 8×8 differential arrays in the same frequency band and has broadband characteristics. Figure 9 is the radiation pattern at the center frequency of 32 GHz. The side lobes of the antenna are below -15 dB and the cross polarization is below -50 dB, indicating that the antenna has the characteristics of low side lobes and low cross polarization. This cross polarization performance is far better than the technical level of non-differential 8×8 arrays in the same frequency band. Figure 10 is the gain characteristic of the antenna. In the working frequency band (26.7 GHz - 37.7 GHz), the maximum gain is 25.3 dBi and the gain within the band is stable.

[0042] In summary, the differential antenna array based on the higher-order mode of the substrate integrated waveguide provided by the embodiments of the present invention has the advantages of broadband, high gain, low cross polarization, and stable radiation performance within the working frequency band.

[0043] The foregoing description of the disclosed embodiments enables those skilled in the art to practice 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. Thus, the present invention is not intended 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 differential antenna array based on high-order modes of substrate integrated waveguide, characterized in that A first dielectric plate (21), a second dielectric plate (22), a third dielectric plate (23) and a fourth dielectric plate (24) are sequentially arranged from bottom to top. A first metal layer (25) and a second metal layer (26) are respectively arranged on the lower surface and the upper surface of the first dielectric plate (21). A third metal layer (27) is arranged on the upper surface of the second dielectric plate (22). A fourth metal layer (28) is arranged on the upper surface of the third dielectric plate (23). Among them, a microstrip power divider (31) is arranged on the first metal layer (25). A first coupling slot (32) is arranged on the second metal layer (26) at a position near the end of each path corresponding to the microstrip power divider (31). A plurality of sub-arrays (41) are arranged on the second dielectric plate (22). A second coupling slot (42) is arranged on the third metal layer (27) at a position corresponding to each sub-array (41). A metal patch orthogonal to each second coupling slot (42) is arranged on the fourth metal layer (28). Every two adjacent and oppositely placed metal patches form a pair of differential microstrip lines (51).

2. The differential antenna array based on the high-order mode of the substrate integrated waveguide according to claim 1, characterized in that The fourth dielectric plate (24) is a pure dielectric plate, and there is no metal pattern on its upper and lower surfaces.

3. A differential antenna array based on a high-order mode of a substrate integrated waveguide according to claim 1, characterized in that, The microstrip power divider (31) is a five-stage microstrip power divider with one input and thirty-two outputs.

4. The differential antenna array based on the high-order mode of substrate integrated waveguide according to claim 1, wherein Excite a TE 40 mode traveling wave within each sub-array (41), including four differential radiation units arranged in a 2×2 form.

5. The differential antenna array based on the high-order mode of the substrate integrated waveguide according to claim 4, wherein The differential field in the waveguide excites the differential microstrip lines (51) through the second coupling slots (42).

6. The differential antenna array based on the high-order mode of the substrate integrated waveguide according to claim 4, wherein Each sub-array (41) is excited by the microstrip-line slot coupling method.

7. The differential antenna array based on the high-order mode of substrate integrated waveguide according to claim 1, characterized in that Dielectric blocks (61) are arranged on the fourth dielectric plate (24) at positions corresponding to each pair of differential microstrip lines (51).

8. The differential antenna array based on high-order modes of substrate integrated waveguide according to claim 1, wherein The cross-section of the dielectric block (61) is rectangular.

9. A differential antenna array based on a high-order mode of a substrate integrated waveguide according to any one of claims 1-8, characterized in that, A connection structure (62) is arranged on the fourth dielectric plate (24).

10. A differential antenna array based on a high-order mode of a substrate integrated waveguide according to claim 9, characterized in that, The connection structure (62) includes four dielectric strips.

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