A low sidelobe array antenna structure and design method

Abstract

The present invention specifically discloses a method for designing a low sidelobe array antenna, that is, constructing a parallel array antenna with non-uniform antenna unit spacing. The design method adopts a differential optimization algorithm to obtain the antenna element spacing distribution and the optimal solution of each antenna element excitation amplitude that minimizes the sidelobe level, and sets the antenna unit at the optimal solution position of the antenna element spacing distribution. The slot length of the coupling slot of the antenna unit is established according to the optimal solution of the excitation amplitude, and the microstrip feeder length of the antenna unit feeding network is established according to the optimal solution of the antenna element spacing distribution. The present invention also discloses a low sidelobe array antenna structure. The beneficial effect obtained is that the side lobes of the array antenna are reduced by changing the antenna unit spacing, and the Poynting vector method is applied to the design of the coupling slot to further reduce the side lobes. When testing the antenna, the error existing in the actual processing of the antenna is compensated by designing an adjustable microstrip feeder, so as to improve the antenna performance.

Description

Technical Field

[0001] The invention belongs to the field of array antenna design, and in particular relates to a low sidelobe array antenna structure and a design method. Background Art

[0002] The radiation characteristics of an array antenna depend on five major factors, namely the radiation characteristics of the antenna unit, the spacing between antenna units, the number of antenna units, the arrangement and the excitation of the antenna units. When designing a low sidelobe antenna, due to size limitations, there is not much room for choice in factors such as the number and arrangement of antenna units. Analytical methods are usually used to focus on the quantitative change of the antenna unit excitation amplitude, thus ignoring the effect of the antenna unit spacing on the radiation pattern. Array antennas are generally divided into two categories: uniform spacing and non-uniform spacing array antennas. The uniform spacing antenna array structure is consistent, the theoretical analysis is simple, and it is easy to expand the antenna scale. However, both high gain and narrow beam width require an increase in the antenna aperture, and increasing the aperture means using more antenna units, which leads to complex antenna system design, increased power consumption, and increased costs, bringing a series of problems to the array antenna design, such as high antenna sidelobe level, limited effective output power, and low transmission information rate; for non-uniform spacing array antennas, due to the unequal spacing of antenna units, the antenna introduces new variables and increases the design freedom. Antenna units placed at a specific spacing can directly reduce the antenna sidelobe level without the need to perform amplitude weighting on the antenna unit excitation; if the antenna unit spacing and the excitation amplitude are combined, the antenna sidelobe level can be further reduced, reducing the interference of the transmitted signal to , while the transmission energy can be concentrated on the beam main lobe. Summary of the invention

[0003] In view of the above-mentioned problems, the present invention proposes a low sidelobe array antenna structure and a design method to overcome the deficiencies of the prior art.

[0004] The technical solution adopted by the present invention is:

[0005] A low sidelobe array antenna design method is to construct a parallel array antenna with non-uniform antenna unit spacing. The design method adopts a differential optimization algorithm to obtain the antenna array element spacing distribution and the optimal solution of each antenna array element excitation amplitude that minimizes the sidelobe level, and the antenna unit is set at the optimal solution position of the antenna array element spacing distribution. The slot length of the coupling slot of the antenna unit is determined according to the optimal solution of the excitation amplitude, and the microstrip feed line length of the antenna unit feeding network is determined according to the obtained optimal solution of the antenna array element spacing.

[0006] Furthermore, the optimal solution process of the antenna array element spacing distribution and the excitation amplitude is as follows:

[0007] Step 1: Determine the array antenna pattern function from the array factor (AF) function.

[0008]

[0009] Where: x n It is the distance from the nth array element distributed linearly to both sides along the center of the array antenna to the linear center of the array antenna. n is the normalized excitation amplitude of the nth array element, k = 2π / λ, λ is the spatial wavelength, and u = sinθθ is the azimuth angle;

[0010] Step 2: Calculate the peak sidelobe level PSLL (PeakSideLobeLevel), the formula is:

[0011]

[0012] Where: u s is the side lobe range excluding the main lobe peak, AF(u s ) is any sidelobe level, x=[x1,x2,···,x n ] is the array element position;

[0013] Step 3: D min ≥0.5,d max ≤1 and As the constraint condition, the minimum sidelobe level PSLL in formula (2) is taken as the optimization goal, and the differential optimization algorithm is adopted. The final objective function is:

[0014]

[0015] Where: d min is the normalized minimum spacing of array elements, d max is the normalized maximum spacing of array elements;

[0016] Solve the above objective function and find a set of optimal solutions x=[x1,x2,···,x n ],I=[I1,22,···,I n ] value, obtain the antenna array element spacing distribution and the excitation amplitude of each array element;

[0017] Antenna units are set at positions of the obtained antenna array element spacing distribution.

[0018] Furthermore, the antenna unit has a three-layer structure, which includes, from bottom to top, a bottom substrate, a middle layer, and a top substrate. A microstrip feed line is arranged on the bottom surface of the bottom substrate, a ground plate and a coupling slot are arranged on the top surface of the bottom substrate, the middle layer is an air layer, and a patch antenna array element is placed on the bottom surface of the top substrate.

[0019] Furthermore, the coupling slot determination process is as follows:

[0020] Step 1: The coupling slot is set to be an H-type coupling slot, and the Poynting vector S of the slotted portion of the H-type coupling slot points from the center to both sides, and the vector direction of S is approximately perpendicular to the plane where the H-type coupling slot is located;

[0021] Step 2: The relationship between energy W and Poynting vector S is,

[0022]

[0023] Where: A is the closed space of H slot;

[0024] The energy of the H-type coupling slot is calculated using formula (4).

[0025] Step 3: Under the condition that the size of the patch antenna array element is constant, set the minimum length of the middle slot of the H-type coupling slot and the increase value of the length of the middle slot of the H-type coupling slot. Through energy calculation using formula (4), obtain the proportional relationship between the length of different H-type coupling slots and the excitation amplitude. Select a set of parameters that match the length of the middle slot of the H-type coupling slot with the required optimal excitation amplitude to design the length of the H-type coupling slot.

[0026] Furthermore, the feeding network is formed by cascading T-type power dividers, and a microstrip feed line is arranged at the output end of each branch feed line of the T-type power divider, and the microstrip feed line extends to the bottom surface of the bottom substrate of the antenna unit. The lengths of the microstrip feed lines of each branch are different and adjustable, wherein the mathematical relationship of the lengths of the microstrip feed lines is determined based on the position of the array element.

[0027] A low sidelobe array antenna structure comprises N antenna units and a feeding network, wherein the N antenna units are centrally symmetrically distributed non-uniformly, the antenna unit is a three-layer structure, comprising a bottom substrate, an intermediate layer, and a top substrate, the bottom surface of the bottom substrate is a microstrip feeder, a ground plate and a coupling slot are arranged on the top surface of the bottom substrate, the intermediate layer is an air layer, a patch antenna array element is placed on the bottom surface of the top substrate, the patch antenna array element is arranged in a square shape, the center of the coupling slot is arranged in the center of the square, the microstrip feeder is fed from the center of the patch edge and is perpendicular to the coupling slot, the feeding network is a cascade of multiple T-type power dividers, and the microstrip feeder is arranged at the output ends of the multiple T-type power dividers.

[0028] Furthermore, the bottom substrate has a thickness of h1=0.254 mm and a dielectric constant ε r The top substrate is a Rogers RT5800 substrate with a thickness of h3=0.787 mm.

[0029] Furthermore, the antenna unit N is set to 8, the distance between the two centrally symmetrical antenna units is 0.7λ, the excitation amplitude is 1, and the distances between the antenna units distributed at both ends and the previous antenna unit are 0.72λ, 0.75λ, and 0.77λ, and the corresponding excitation amplitudes are 0.89, 0.64, and 0.4.

[0030] Furthermore, the coupling groove is H-shaped, and the lengths of the H-shaped groove are 4.5 mm, 4 mm, 3.8 mm and 3.2 mm.

[0031] Compared with the prior art, the present invention has the following beneficial effects: the side lobes of the array antenna are reduced by changing the antenna unit spacing, and the side lobes are further reduced by applying the Poynting vector method to the design of the coupling slot. In addition, during the antenna test, an adjustable microstrip feed line is designed to compensate for the errors existing in the actual processing of the antenna, thereby further improving the antenna performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0033] Figure 1 , the process of constructing non-uniformly spaced array antennas

[0034] Figure 2 , Schematic diagram of 2N array element non-uniform spacing array antenna

[0035] Figure 3 , Antenna unit stereogram (a) Antenna unit top and side view (b)

[0036] Figure 4 , H-type coupling slot antenna unit voltage standing wave ratio

[0037] Figure 5 , H-type coupling slot antenna unit pattern

[0038] Figure 6 , T-type power divider

[0039] Figure 7 , 8-element parallel feed network branch structure relationship

[0040] Figure 8 , 8-element antenna feed network cascade structure simulation diagram

[0041] Fig. 9 , 8-element antenna feed network port power allocation and phase value

[0042] Fig.10 , Poynting vector

[0043] Fig.11 , low sidelobe array antenna physical picture

[0044] Fig.12 , 8-element antenna voltage standing wave ratio simulation and measurement comparison

[0045] Fig.13 , observe the antenna's directional pattern characteristics simulation and measured results at three frequencies: 14, 14.25 and 14.5 GHz DETAILED DESCRIPTION

[0046] In order to make the purpose, 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 in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0047] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0048] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0049] In the description of the present invention, it should be noted that the terms "first", "second", "third", etc. are only used to distinguish descriptions and cannot be understood as indicating or implying relative importance. In addition, the terms "horizontal", "vertical", etc. do not mean that the components are required to be absolutely horizontal or suspended, but can be slightly tilted. For example, "horizontal" only means that its direction is more horizontal than "vertical", and does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0050] In the description of the present invention, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "set", "install", "connect", and "connect" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0051] Reference Figure 1 As shown, the present invention specifically discloses a low sidelobe array antenna design method, which constructs a non-uniform spacing array antenna, including the following steps:

[0052] Module 100 sets antenna requirement parameters according to engineering design requirements. Specific parameters include operating frequency band, center frequency, bandwidth, polarization mode, array form, radiation direction, antenna gain, etc.

[0053] Module 101 selects antenna substrate material, thickness, antenna unit shape and size, and selects the number of antenna units;

[0054] Module 102 uses a differential optimization algorithm to obtain an optimal solution of antenna element spacing distribution and excitation amplitude of each antenna element that minimizes the sidelobe level, and sets an antenna unit at the optimal solution position of the antenna element spacing distribution;

[0055] Module 103 determines the slot length of the coupling slot of the antenna unit according to the optimal solution of the excitation amplitude;

[0056] Module 104 establishes the length of the microstrip feed line of the antenna unit feeding network according to the obtained optimal solution of the antenna array element spacing distribution.

[0057] Specifically, the optimal solution process for the antenna array element spacing and the excitation amplitude in module 102 is as follows:

[0058] Step 1: Determine the array antenna pattern function from the array factor (AF) function.

[0059]

[0060] Among them, x n It is the distance from the nth array element distributed linearly to both sides along the center of the array antenna to the linear center of the array antenna. n is the normalized excitation amplitude of the nth array element, k = 2π / λ, λ is the spatial wavelength, and u = sinθθ is the azimuth angle;

[0061] Step 2: Calculate the peak sidelobe level PSLL (PeakSideLobeLevel), the formula is:

[0062]

[0063] Where: u s is the side lobe range excluding the main lobe peak, AF(u s ) is any sidelobe level, x=[x1,x2,···,x n ] is the array element position;

[0064] Step 3: D min ≥0.5,d max ≤1 and As the constraint condition, the minimum sidelobe level PSLL in formula (2) is taken as the optimization goal, and the differential optimization algorithm is adopted. The final objective function is:

[0065]

[0066] Where: d min is the normalized minimum spacing of array elements, d max is the normalized maximum spacing of array elements;

[0067] Solve the above objective function and find a set of optimal solutions x=[x1,x2,···,x n ],I=[I1,22,···,I n ] value, obtain the antenna array element spacing distribution and the excitation amplitude of each array element;

[0068] Antenna units are set at positions of the obtained antenna array element spacing distribution.

[0069] Specifically, the antenna unit has a three-layer structure, which includes a bottom substrate, a middle layer, and a top substrate from bottom to top. A microstrip feed line is arranged on the bottom surface of the bottom substrate, a ground plate and a coupling slot are arranged on the top surface of the bottom substrate, the middle layer is an air layer, and a patch antenna array element is placed on the bottom surface of the top substrate.

[0070] Specifically, the coupling slot length determination process in module 103 is as follows:

[0071] Step 1: The coupling slot is set to be an H-type coupling slot, and the Poynting vector S of the slotted portion of the H-type coupling slot points from the center to both sides, and the vector direction of S is approximately perpendicular to the plane where the H-type coupling slot is located;

[0072] Step 2: The relationship between energy W and Poynting vector S is,

[0073]

[0074] Where: A is the closed space of H slot;

[0075] The energy of the H-type coupling slot is calculated using formula (4).

[0076] Step 3: Under the condition that the size of the patch antenna array element is constant, set the minimum length of the middle slot of the H-type coupling slot and the increase value of the length of the middle slot of the H-type coupling slot. Through energy calculation using formula (4), obtain the proportional relationship between the length of different H-type coupling slots and the excitation amplitude. Select a set of parameters that match the length of the middle slot of the H-type coupling slot with the required optimal excitation amplitude to design the length of the H-type coupling slot.

[0077] Specifically, the feeding network in module 104 is formed by cascading T-type power dividers, and a microstrip feed line is set at the output end of each branch feed line of the T-type power divider. The microstrip feed line extends to the bottom surface of the bottom substrate of the antenna unit. The lengths of the microstrip feed lines of each branch are different and adjustable, wherein the mathematical relationship of the lengths of the microstrip feed lines is determined based on the array element position.

[0078] A low sidelobe array antenna structure comprises N antenna units and a feeding network, wherein the N antenna units are centrally symmetrically distributed non-uniformly, the antenna unit is a three-layer structure, comprising a bottom substrate, an intermediate layer, and a top substrate, the bottom surface of the bottom substrate is a microstrip feeder, a ground plate and a coupling slot are arranged on the top surface of the bottom substrate, the intermediate layer is an air layer, a patch antenna array element is placed on the bottom surface of the top substrate, the patch antenna array element is arranged in a square shape, the center of the coupling slot is arranged in the center of the square, the microstrip feeder is fed from the center of the patch edge and is perpendicular to the coupling slot, the feeding network is a cascade of multiple T-type power dividers, and the microstrip feeder is arranged at the output ends of the multiple T-type power dividers.

[0079] Example:

[0080] The engineering design requirement parameters are shown in Table 1:

[0081] Table 1 Engineering design requirement parameters

[0082]

[0083] 1) Calculation of antenna unit spacing and excitation amplitude. A low sidelobe array antenna structure adopts a centrally symmetrical non-uniform distribution of antenna units, such as Figure 2 As shown, for 2N array elements, Δx n represents the distance between the Nth antenna unit and the N-1th antenna unit. The number of antenna units is set to 8. In order to reduce the antenna mutual coupling effect, the minimum spacing between antenna units is set to 0.7λ, the maximum spacing is set to λ, and the normalized minimum excitation amplitude is set to 0.4. According to formulas (1)(2)(3), the spacing between antenna units and the excitation amplitude can be calculated, as shown in Table 2.

[0084] Table 2 Array element spacing and excitation amplitude of 8-element antenna

[0085]

[0086] 2) Antenna unit design, the antenna unit adopts a three-layer design, such as Figure 3 As shown. The bottom layer has a thickness of h1 = 0.254 mm and a dielectric constant of ε r The Rogers RT5800 substrate with a thickness of 2.2 and tanδ of 0.0009, the bottom of the substrate is an adjustable microstrip feeder, and the top is a ground plane with an H-shaped slot; the middle layer is an air layer with a thickness of h2; the top layer uses a Rogers RT5800 substrate with a thickness of h3=0787, and the patch unit is placed on the bottom, so that the top substrate can also serve as an antenna cover to protect the antenna. Compared with the rectangular slot, the H-shaped slot can obtain greater coupling under the same size, which brings convenience to impedance matching. Therefore, the antenna unit design adopts an H-shaped slot, where the parameter ll is the length of the microstrip feeder passing through the center of the H-shaped slot.

[0087] In order to reduce too many variable parameters and reduce the difficulty of optimization, first, the antenna unit uses a square patch instead of a rectangular patch, that is, Wp = Lp, and the initial size of the square patch is still obtained by the calculation formula of the rectangular patch. Secondly, the H-shaped slot is placed in the center of the patch, and the microstrip feed line can be adjusted to feed from the center of the edge of the patch and be perpendicular to the H-shaped slot.

[0088] The simulation results of antenna voltage standing wave ratio and radiation pattern are as follows: Figure 4 and Figure 5 As shown by Figure 4 It can be seen that the antenna standing wave ratio is less than 2 in the range of 12.81GHz to 14.85GHz, and the relative bandwidth is 14.4%, which greatly broadens the antenna bandwidth. Figure 5 It can be seen that the unit gain is only 10dBi and the sidelobe level is too high to be applied in engineering. Therefore, the antenna is constructed by antenna unit array, in which the antenna unit spacing is set according to the table.

[0089] 3) Feed network design

[0090] A T-type power divider cascade network is used, where Figure 6 As shown, the A port of the T-type power divider is the input port, and the B and C ports are the output ports. When the output power is consistent, that is, the distribution ratio is 1:1, it satisfies

[0091] Since the change of excitation amplitude is achieved by changing the slot length, it is only necessary to design a feeding network with equal radiation and phase. The excitation amplitude of the feeding network is determined by the power ratio of each T-type power divider. Keeping the width of the feed line at the output end of each T-type power divider consistent can ensure that the excitation amplitude of the array element is equal. The phase of the antenna unit is determined by the length of the feed line from the feed end to the antenna unit. To ensure phase consistency, the total length of the feed line of each branch must be equal. Based on the position of the antenna unit, each small section of each branch feed line is set as a variable to determine the mathematical relationship of each section. Since the feeding network is a symmetrical structure, only the feed line relationship on one side of the antenna needs to be constructed, such as Figure 7 As shown. In combination with the characteristics of coupled feeding, adding a section of the same microstrip line to each output port and adjusting its size can quickly achieve impedance matching of the antenna without affecting power distribution. According to the position of the antenna unit, a one-to-eight parallel feeding network is constructed. According to the simulation results, the length of the corresponding feed line is adjusted multiple times to make the simulation results meet the requirements. Figure 8 The simulation results are as follows: Fig. 9 , the power value of each output port S *1 They are all around -9dB, the extreme difference does not exceed 0.4dB, and the power distribution is basically consistent; at the same time, the phase curves basically coincide, and the feeding network achieves in-phase excitation in a wider frequency range.

[0092] Due to the slots in the ground plane and the mutual coupling of the multi-layer substrate stack, the feed network may be affected in the energy distribution of the antenna unit. This paper further explores the energy obtained by each array element through the Poynting vector S. The relationship between energy W and Poynting vector S is:

[0093]

[0094] Where: A is a closed surface.

[0095] The Poynting vector of the patch and H-type coupling slot is as follows: Fig.10 shown.

[0096] The corresponding relationship between slot length and energy is obtained through simulation. The energy ratio passing through the slot surface is not completely equal to the slot length ratio. The energy and slot length are nonlinear. Therefore, the excitation amplitude ratio cannot be simply replaced by the slot length ratio. Under the condition that the patch size is determined, the slot length is the key factor affecting the gain and impedance matching. The slot length is continuously adjusted through simulation until the excitation amplitude ratio is met. When the input power is 1W, the length and power of the H-type coupling slot corresponding to each patch are shown in Table 3.

[0097] Table 3 Slot length and power distribution

[0098]

[0099] Under the above-mentioned length setting of the H-type coupling slot, the energy passing through the H-type coupling slot is close to the theoretical value of the excitation amplitude. It is approximately considered that the energy received by the patch meets the design requirements. The antenna parameters are shown in Table 4.

[0100] Table 4 Parameters of H-type slot broadband antenna

[0101]

[0102] Physical Fig.11

[0103] After testing, the antenna voltage standing wave ratio results are as follows Fig.12 As shown, it can be seen that during simulation, the voltage standing wave ratio of the antenna is less than 1.5 in the range of 13.67 to 15.48 GHz. During actual measurement, the voltage standing wave ratio of the antenna is less than 1.5 in the range of 13.84 to 15.5 GHz. The bandwidth covers 14 to 14.5 GHz, which meets the bandwidth requirements of the transmitting antenna.

[0104] The antenna's directional characteristics are observed at three frequencies: 14, 14.25, and 14.5 GHz. The simulation and measured results are as follows: Fig.13 The performance comparison of gain, sidelobe level and mainlobe width is shown in Table 5.

[0105] Table 5 Performance comparison of H-type slot broadband antenna at different frequencies

[0106]

[0107] As the frequency increases, the gain of the antenna decreases slightly, and the main lobe width changes in the same trend as the gain. The higher the gain, the narrower the main lobe width. The side lobe levels at the three frequency points are all lower than -19.5dB, and the antenna array achieves low side lobes within the working bandwidth.

[0108] The above is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent change made to the above embodiment according to the technical essence of the invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. A low sidelobe array antenna design method, characterized in that: A parallel array antenna with non-uniform antenna element spacing is constructed. The design method adopts a differential optimization algorithm to obtain the optimal solution of the antenna element spacing distribution and the excitation amplitude of each antenna element that minimizes the sidelobe level. The antenna element is set at the optimal solution position of the antenna element spacing distribution. The slot length of the coupling slot of the antenna element is determined according to the optimal solution of the excitation amplitude. The microstrip feed line length of the antenna element feeding network is determined according to the optimal solution of the antenna element spacing distribution. The optimal solution process for the antenna array element spacing distribution and excitation amplitude is as follows: Step 1: Determine the array antenna pattern function from the array factor (AF) function. Among them, x n It is the distance from the nth array element distributed linearly to both sides along the center of the array antenna to the linear center of the array antenna. n is the normalized excitation amplitude of the nth array element, k = 2π / λ, λ is the spatial wavelength, u = sinθ, θ is the azimuth angle; Step 2: Calculate the peak side lobe level PSLL (Peak Side Lobe Level), the formula is: Where: u s is the side lobe range excluding the main lobe peak, AF(u s ) is any sidelobe level, x=[x1,x2,…,x n ] is the array element position; Step 3: D min ≥0.5,d max ≤1 and As the constraint condition, the optimization goal is to minimize the sidelobe level PSLL in formula (2), and the differential optimization algorithm is adopted. The final objective function is: Where: d min is the normalized minimum spacing of array elements, d max is the normalized maximum spacing of array elements; Solve the above objective function and find a set of optimal solutions x=[x1,x2,f,x n ],I=[I1,22,…,I n ] value, obtain the antenna array element spacing distribution and the excitation amplitude of each array element; Antenna units are set at positions of the obtained antenna array element spacing distribution.

2. A low sidelobe array antenna design method according to claim 1, characterized in that: The antenna unit is a three-layer structure, which includes a bottom substrate, a middle layer, and a top substrate from bottom to top. A microstrip feed line is arranged on the bottom surface of the bottom substrate, a ground plate and a coupling slot are arranged on the top surface of the bottom substrate, the middle layer is an air layer, and a patch antenna array element is placed on the bottom surface of the top substrate.

3. A low sidelobe array antenna design method according to claim 2, characterized in that: The coupling slot determination process is as follows: Step 1: The coupling slot is set to be an H-type coupling slot, and the Poynting vector S of the slotted portion of the H-type coupling slot points from the center to both sides, and the vector direction of S is approximately perpendicular to the plane where the H-type coupling slot is located; Step 2: The relationship between energy W and Poynting vector S is, W=-∮∫ A S·dA (4) Where: A is the closed space of H slot; The energy of the H-type coupling slot is calculated by formula (4); Step 3: Under the condition that the size of the patch antenna array element is constant, set the minimum length of the middle slot of the H-type coupling slot and the increase value of the length of the middle slot of the H-type coupling slot. Through energy calculation using formula (4), obtain the proportional relationship between the length of different H-type coupling slots and the excitation amplitude. Select a set of parameters that match the length of the middle slot of the H-type coupling slot with the required optimal excitation amplitude to design the length of the H-type coupling slot.

4. A low sidelobe array antenna design method according to claim 3, characterized in that: The feeding network is formed by cascading T-type power dividers, and a microstrip feed line is arranged at the output end of each branch feed line of the T-type power divider. The microstrip feed line extends to the bottom surface of the bottom substrate of the antenna unit. The lengths of the microstrip feed lines of each branch are different and adjustable, wherein the mathematical relationship of the lengths of the microstrip feed lines is determined based on the position of the array element.

5. A low sidelobe array antenna structure, characterized in that: The invention comprises N antenna units and a feeding network, wherein the N antenna units are centrally symmetrically and non-uniformly distributed, the antenna unit is a three-layer structure, comprising a bottom substrate, an intermediate layer, and a top substrate, the bottom surface of the bottom substrate is a microstrip feeder, the top surface of the bottom substrate is provided with a ground plate and a coupling slot, the intermediate layer is an air layer, a patch antenna array element is placed on the bottom surface of the top substrate, the patch antenna array element is arranged in a square shape, the center of the coupling slot is arranged in the center of the square, the microstrip feeder is fed from the center of the patch edge and is perpendicular to the coupling slot, the feeding network is a cascade of multiple T-type power dividers, and the microstrip feeder is arranged at the output end of the multiple T-type power dividers.

6. A low sidelobe array antenna structure according to claim 5, characterized in that: The bottom substrate has a thickness of h1=0.254 mm and a dielectric constant ε r The top substrate is a Rogers RT5800 substrate with a thickness of h3=0.787 mm.

7. The low sidelobe array antenna structure according to claim 6, characterized in that: The antenna unit N is set to 8, the distance between the two centrally symmetrical antenna units is 0.7λ, the excitation amplitude is 1, and the distances between the antenna units distributed at both ends and the previous antenna unit are 0.72λ, 0.75λ, and 0.77λ, and the corresponding excitation amplitudes are 0.89, 0.64, and 0.

4.

8. The low sidelobe array antenna structure according to claim 7, characterized in that: The coupling groove is H-shaped, and the lengths of the H-shaped groove are 4.5 mm, 4 mm, 3.8 mm and 3.2 mm.

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