Design method of low-sidelobe waveguide slot antenna

Abstract

The invention provides a low-sidelobe waveguide slot antenna design method, which comprises the following steps of: firstly, obtaining antenna theoretical aperture field distribution according to the number of antenna slots and target sidelobe level, and secondly, determining a slot conductance function, namely a relationship between slot parameters and normalized conductance; and on the basis of fully considering mutual coupling between different slot units of the array and an array edge effect, through multiple times of iterative design, antenna aperture field distribution approaches theoretical aperture field distribution, and a directional diagram sidelobe level reaches a target, so that the design of the low-sidelobe waveguide slot array antenna is realized. The antenna can be in the form of a waveguide slot traveling wave array, a standing wave array and the like, and the slotted unit can be a waveguide wide-edge slotted unit or a waveguide narrow-edge slotted unit; the method is especially suitable for the design of an electrically large waveguide slot array antenna, the design time can be saved, and the design efficiency can be improved; the method can also be expanded to antenna array design with any aperture field distribution.

Description

Technical Field

[0001] The present invention relates to the field of antenna technology, and in particular to a design method for a low sidelobe waveguide slot antenna. Background Art

[0002] As the requirements for radar anti-interference increase, low or ultra-low sidelobe antennas are increasingly needed. Waveguide slot array antennas have the advantage of easy control of the aperture distribution, so they are easy to meet the requirements of low sidelobe antennas. Therefore, they are widely used in radar, communication and other fields.

[0003] Generally, the Taylor synthesis method is used to design the parameters of each slot. However, due to defects in the design method, the mutual coupling between slots is not fully considered, and the designed side lobe has a certain gap with the theoretical Taylor synthesis side lobe value or a lower side lobe level cannot be achieved.

[0004] In the paper "Design of an Ultra-Low Sidelobe Slot Waveguide Antenna", the theoretical Taylor comprehensive sidelobe value was selected as -50dB, and the designed antenna sidelobe level was -42dB. In the paper "Design of Millimeter-Wave Low Sidelobe Waveguide Narrow Edge Slot Traveling Wave Array", the theoretical Taylor comprehensive sidelobe value was selected as -40dB, and the designed antenna sidelobe level was -35dB. Generally, when the Taylor comprehensive sidelobe value is -40dB, the gain loss is 1.15dB; when the Taylor comprehensive sidelobe value is -35dB, the gain loss is 0.9dB. Therefore, this design result that is inconsistent with the theoretical design will cause additional aperture efficiency loss and antenna gain reduction.

[0005] In patent application CN110287539B "A method for automatic design and optimization of waveguide slot array antennas", the optimization target is the ideal slot admittance, and the slot spacing is adjusted to assist in phase compensation. The designed sidelobe level of the radiation pattern is only -29dB, and a lower sidelobe level cannot be obtained. The reason is that the optimization target is not appropriate, and the slot mouth amplitude and phase distribution is the direct cause of the sidelobe level of the radiation pattern rather than the slot admittance. In addition, adjusting the slot spacing superficially changes the phase distribution at the slot mouth, but actually fails to fundamentally solve the problem of the slot deviating from resonance, and makes the mutual coupling environment of the slot more complicated, making it impossible to achieve an ideal mouth distribution and a lower sidelobe level.

[0006] Therefore, a waveguide slot antenna design method is needed in which the theoretical Taylor synthesis sidelobe is consistent with the actual antenna sidelobe level. Summary of the invention

[0007] The present invention is to solve the problems of aperture efficiency loss, antenna gain reduction and difference between sidelobe design and actual, and provides a method for designing low sidelobe waveguide slot antenna. First, the theoretical aperture field distribution of the antenna (i.e., the normalized conductance distribution of the slot) is obtained according to the number of antenna slots and the target sidelobe level. Secondly, the slot conductance function (i.e., the relationship between the slot parameter and the normalized conductance) is determined. Then, on the basis of fully considering the mutual coupling between different slot units in the array and the edge effect of the array, the antenna aperture field distribution is made close to the theoretical aperture field distribution through several iterative designs, thereby realizing the design of low sidelobe waveguide slot array antenna. The antenna form can be a waveguide slot traveling wave array, a standing wave array, etc., and the slot unit can be a waveguide wide side slot unit or a waveguide narrow side slot unit. This method is particularly suitable for the design of electrically large size waveguide slot array antennas, which can save design time and improve design efficiency. This method can also be extended to the design of antenna arrays with arbitrary aperture field distribution.

[0008] The present invention provides a method for designing a low sidelobe waveguide slot antenna, comprising the following steps:

[0009] S1. According to the number of slots N of the waveguide slot array antenna, the target sidelobe level and the Taylor discrete aperture synthesis method category, the normalized slot excitation is obtained and the ideal conductance value of each slot and the ideal conductance distribution of the waveguide slot array antenna are calculated;

[0010] S2. Establish an admittance parameter extraction model, wherein the admittance parameter model includes at least two gaps whose gap sizes, gap spacing, and adjacent gap inversion directions are the same as the actual gaps, and judge whether the gap is resonant by whether the susceptance is zero, and obtain the relationship between the normalized equivalent conductance of the gap in the resonant state and the gap parameters, and interpolate the gap parameters and the normalized equivalent conductance to obtain a gap conductance function curve;

[0011] The gap parameters are the gap inclination and gap depth or the gap offset and gap length;

[0012] When the gap parameters are the gap inclination angle and the gap depth, the relationship between the normalized equivalent conductance of the gap in the resonant state and the gap parameters is obtained in the following specific method: fix the initial gap inclination angle, use the parameter analysis function of the HFSS software to compare the equivalent susceptance at different gap depths, the gap depth h0 corresponding to the equivalent susceptance being zero is the resonant gap depth, and the resonant gap depth and normalized equivalent conductance under the first gap inclination angle condition are obtained; increase the gap inclination angle by a specified angle, and obtain the resonant gap depth and normalized equivalent conductance under the second gap inclination angle condition; continue to increase the gap inclination angle by a specified angle until the upper limit of the gap inclination angle is reached; fit the obtained gap inclination angle, resonant gap depth and normalized equivalent conductance to obtain the gap conductance function curve;

[0013] When the gap parameters are the gap offset and the gap length, the relationship between the normalized equivalent conductance of the gap in the resonant state and the gap parameters is obtained in the following specific method: fix the initial gap offset, use the parameter analysis function of the HFSS software to compare the equivalent susceptance at different gap lengths, the gap length corresponding to zero equivalent susceptance is the resonant gap length, and the resonant gap length and normalized equivalent conductance under the first gap offset condition are obtained; increase the gap offset by a specified value, and obtain the resonant gap length and normalized equivalent conductance under the second gap offset condition; continue to increase the gap offset by a specified angle until the upper limit of the gap offset is reached; fit the obtained gap offset, resonant gap length and normalized equivalent conductance to obtain the gap conductance function curve;

[0014] S3. According to the ideal conductance distribution and the slot conductance function curve, the initial parameters of N slots are obtained, and a waveguide slot array model containing N slots is established in the simulation software HFSS for simulation. According to the simulation results, the slot mouth amplitude and phase distribution is extracted, and the slot mouth amplitude and phase distribution is compared with the theoretical mouth amplitude and phase distribution to obtain the amplitude distribution difference between the simulated amplitude and phase distribution and the theoretical amplitude and phase distribution. The relationship between the amplitude distribution difference and the slot inclination angle or the slot offset, and the relationship between the phase difference and the slot depth or slot length are constructed, and the slot parameters are adjusted according to the difference and then simulation is performed; through several iterative designs, until the amplitude distribution difference and the sidelobe level of the radiation pattern reach the target, a low sidelobe waveguide slot antenna design method is completed.

[0015] The low sidelobe waveguide slot antenna design method described in the present invention is, as a preferred embodiment, that the antenna form of the waveguide slot array antenna is a waveguide slot traveling wave array or a standing wave array.

[0016] The low sidelobe waveguide slot antenna design method described in the present invention is, as a preferred embodiment, that the antenna unit of the waveguide slot array antenna is a waveguide narrow side slot or a waveguide wide side slot.

[0017] The low sidelobe waveguide slot antenna design method described in the present invention is, as a preferred embodiment, in step S2, when the antenna unit of the waveguide slot array antenna is a waveguide narrow side slot, the slot parameters are the slot inclination angle and the slot depth, and the slot conductance function curve is a relationship curve between the slot inclination angle, the slot depth and the slot equivalent conductance.

[0018] The low sidelobe waveguide slot antenna design method described in the present invention is, as a preferred embodiment, in step S2, when the antenna unit of the waveguide slot array antenna is a waveguide wide side slot, the slot parameters are the slot offset and the slot length, and the slot conductance function curve is a relationship curve between the slot offset, the slot length and the slot equivalent conductance.

[0019] The low sidelobe waveguide slot antenna design method described in the present invention, as a preferred embodiment, obtains the slot conductance function curve by fitting through the nonlinear curve fitting function of Matlab software.

[0020] The low sidelobe waveguide slot antenna design method described in the present invention is, as a preferred embodiment, applicable to any of the following aperture field distributions: Taylor distribution, Chebyshev distribution and cosecant square distribution.

[0021] The present invention first obtains the theoretical aperture field distribution of the antenna (i.e., the normalized conductance distribution of the slot) according to the number of antenna slots and the target sidelobe level, and then determines the slot conductance function (i.e., the relationship between the slot parameters and the normalized conductance), and then makes the antenna aperture field distribution approach the theoretical aperture field distribution through several iterative designs on the basis of fully considering the mutual coupling between different slot units in the array and the edge effect of the array, thereby realizing the design of low sidelobe waveguide slot array antenna. The antenna form can be a waveguide slot traveling wave array, a standing wave array, etc., and the slot unit can be a waveguide wide side slot unit or a waveguide narrow side slot unit. This method is particularly suitable for the design of electrically large size waveguide slot array antennas, which can save design time and improve design efficiency. This method can also be extended to the design of antenna arrays with arbitrary aperture field distributions.

[0022] The present invention has the following advantages:

[0023] (1) The present invention proposes a universal method for waveguide slot array design, which uses Matlab software to fit the slot conductance function and analyze the slot size and aperture field data, and uses Ansys HFSS simulation software to perform electromagnetic simulation of the antenna model and extract the aperture amplitude and phase. Combining Matlab software and Ansys HFSS simulation software, through several iterative designs, the antenna aperture distribution is made close to the theoretical aperture distribution, thereby realizing the design of low sidelobe waveguide slot array antenna.

[0024] (2) The antenna form applicable to the present invention may be a waveguide slot traveling wave array, a standing wave array, etc. The slot unit may be a waveguide wide side slot unit or a waveguide narrow side slot unit.

[0025] (3) The present invention is particularly suitable for the design of electrically large-sized waveguide slot array antennas, saving design time and improving design efficiency.

[0026] (4) The aperture field distribution adopted by the present invention generally refers to Taylor distribution, which can obtain higher aperture efficiency; it can also be extended to the antenna array design of any aperture field distribution such as Chebyshev, cosecant square, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 A flow chart of a design method for a low sidelobe waveguide slot antenna;

[0028] Figure 2 Schematic diagram of the antenna array designed for a low sidelobe waveguide slot array design method;

[0029] Figure 3 A comparison chart of the simulated aperture amplitude distribution and the theoretical aperture amplitude distribution of the antenna array designed by a low sidelobe waveguide slot array design method;

[0030] Figure 4 Comparison diagram of simulated aperture phase distribution and theoretical aperture phase distribution of antenna array designed by a low sidelobe waveguide slot array design method;

[0031] Figure 5 Comparison diagram between the simulated radiation pattern and the theoretical radiation pattern of the antenna array designed by a low sidelobe waveguide slot array design method. DETAILED DESCRIPTION

[0032] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0033] Example 1

[0034] like Figure 1 As shown, a low sidelobe waveguide slot antenna design method first selects the Taylor discrete aperture synthesis method according to the slot number N of the waveguide slot array antenna and the target sidelobe level to obtain the normalized slot excitation, thereby calculating the ideal conductance value of each slot.

[0035] Secondly, an admittance parameter extraction model is established. The model contains multiple identical slots. Whether the slot is resonant is determined by whether the admittance is zero, so as to deduce the relationship between the normalized equivalent conductance of the slot in the resonant state and the slot parameters. The slot parameters and equivalent conductance are interpolated to obtain the slot conductance function curve. Then, according to the ideal conductance distribution and the slot conductance function curve, the initial parameters of N slots are obtained, and a waveguide slot array model containing N slots is established in the simulation software for simulation. According to the simulation results, the slot aperture amplitude-phase distribution is extracted and compared with the theoretical aperture amplitude-phase distribution. The slot parameters are adjusted according to the difference and then simulated. Through several iterative designs, the slot aperture amplitude-phase distribution is close to the theoretical aperture amplitude-phase distribution, and the sidelobe level of the directional pattern meets the index requirements.

[0036] The slot conductance function curve, for the slot on the narrow side of the waveguide, refers to the relationship curve between the slot inclination, slot depth and the slot equivalent conductance; for the slot on the wide side of the waveguide, refers to the relationship curve between the slot offset, slot length and the slot equivalent conductance.

[0037] The antenna may be in the form of a waveguide slot traveling wave array, a standing wave array, etc. The slot unit may be a waveguide wide side slot unit or a waveguide narrow side slot unit.

[0038] The aperture field distribution generally refers to Taylor distribution, which can obtain higher aperture efficiency; it can also be any aperture field distribution such as Chebyshev, cosecant square, etc.

[0039] The number of slots N is determined according to the required array aperture and operating frequency and can be any value.

[0040] This embodiment takes a waveguide slot traveling wave array as an example, and the process is as follows: establish a slot array of 20 units with completely identical slot sizes, the same slot spacing as the actual spacing, and adjacent slots also alternately inverted; fix the slot inclination angle, use the parameter analysis function of the HFSS software to compare the equivalent susceptance at different cut depths, the cut depth h0 corresponding to zero equivalent susceptance is the resonant slot depth, and record the resonant slot depth and normalized equivalent conductance at this time; repeat the above process at a certain angle interval; finally, use the nonlinear curve fitting function (lsqcurvefit function) of the Matlab software to fit the obtained slot inclination angle, slot depth and normalized equivalent conductance, and obtain the functional relationship between the slot inclination angle and the normalized equivalent conductance, and the functional relationship between the slot inclination angle and the slot depth.

[0041] Then, according to the ideal conductance distribution and the slot conductance function curve, the initial parameters of N slots (slot inclination and slot depth) are obtained, and a waveguide slot array model containing N slots is established in the simulation software for simulation. According to the simulation results, the slot mouth amplitude and phase distribution is extracted and compared with the theoretical mouth amplitude and phase distribution to obtain the difference between the simulated amplitude and phase distribution and the theoretical amplitude and phase distribution. By constructing the relationship between the amplitude distribution difference and the slot inclination or offset, and the relationship between the phase difference and the slot depth or slot length, the slot parameters are adjusted according to the difference and then simulated. Through multiple iterative designs, the slot mouth amplitude and phase distribution is close to the theoretical mouth amplitude and phase distribution, and the directional pattern side lobe level and other indicators meet the requirements.

[0042] like Figure 2 As shown, the antenna array designed by the low sidelobe waveguide slot array design method of the present invention is a narrow side waveguide slot traveling wave array antenna. Alternating inclined slots are opened on the narrow side of the waveguide, and a matching load is connected to the end of the waveguide to absorb the unradiated energy. The number of slots N is 146. The theoretical aperture amplitude distribution is selected as the Taylor comprehensive sidelobe value -35dB.

[0043] like Figure 3 As shown in FIG. 1 , a comparison diagram of the simulated aperture amplitude distribution and the theoretical aperture amplitude distribution of the antenna array designed by a low sidelobe waveguide slot array design method of the present invention is shown, where the blue curve is the theoretical value and the red curve is the simulated value. Figure 4As shown in the figure, the simulated aperture phase distribution and the theoretical aperture phase distribution of the antenna array designed by the low sidelobe waveguide slot array design method of the present invention are compared, where the green curve is the theoretical value and the red curve is the simulated value. It can be seen from the figure that the aperture amplitude distribution obtained by simulation is basically consistent with the theoretical aperture amplitude distribution.

[0044] like Figure 5 As shown in the figure, the simulated directional pattern and the theoretical directional pattern distribution comparison diagram of the antenna array designed by the low sidelobe waveguide slot array design method of the present invention are shown in the figure. The theoretical directional pattern sidelobe level is -35dB, while the simulated sidelobe level is -33dB, which is basically consistent with the theoretical design.

[0045] The principle of the present invention is as follows:

[0046] The present invention proposes a low sidelobe waveguide slot array design method, which uses Matlab software to fit the slot conductance function and analyze the slot size and aperture field data. Ansys HFSS simulation software is used to perform electromagnetic simulation of the antenna model and extract the aperture amplitude phase. The two softwares are combined to accurately control the aperture amplitude phase distribution of the waveguide slot array antenna, thereby realizing the design of a low sidelobe waveguide slot array antenna.

[0047] The present invention designs a low sidelobe waveguide slot array design method, and proposes a new method for low sidelobe waveguide slot array design method. The designed antenna form can be a waveguide slot traveling wave array, a standing wave array, etc. The method is particularly suitable for the design of electrically large-sized waveguide slot array antennas, saving design time and improving design efficiency. The method can also be extended to the design of antenna arrays with arbitrary aperture distribution.

[0048] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for designing a low sidelobe waveguide slot antenna, characterized in that: The following steps are involved: S1. According to the number of slots N of the waveguide slot array antenna, the target sidelobe level and the Taylor discrete aperture synthesis method category, the normalized slot excitation is obtained and the ideal conductance value of each slot and the ideal conductance distribution of the waveguide slot array antenna are calculated; S2, establishing an admittance parameter extraction model, wherein the admittance parameter model includes at least two gaps whose gap sizes, gap spacings, and adjacent gap inversion directions are the same as the actual gaps, judging whether the gap is resonant by whether the susceptance is zero, and obtaining the relationship between the normalized equivalent conductance of the gap in the resonant state and the gap parameters, and interpolating the gap parameters and the normalized equivalent conductance to obtain a gap conductance function curve; The gap parameters are the gap inclination angle and the gap depth or the gap offset and the gap length; When the slot parameters are the slot inclination angle and the slot depth, the specific method for obtaining the relationship between the normalized equivalent conductance of the slot in a resonant state and the slot parameters is as follows: fix the initial slot inclination angle, use the parameter analysis function of the HFSS software to compare the equivalent susceptance at different slot depths, the slot depth h0 corresponding to the equivalent susceptance being zero is the resonant slot depth, and obtain the resonant slot depth and normalized equivalent conductance under the first slot inclination angle condition; increase the slot inclination angle by a specified angle, and obtain the resonant slot depth and normalized equivalent conductance under the second slot inclination angle condition; continue to increase the slot inclination angle by a specified angle until the slot inclination upper limit is reached; fit the obtained slot inclination angle, resonant slot depth and normalized equivalent conductance to obtain the slot conductance function curve; When the gap parameters are the gap offset and the gap length, the specific method for obtaining the relationship between the normalized equivalent conductance of the gap in the resonant state and the gap parameters is as follows: fix the initial gap offset, use the parameter analysis function of the HFSS software to compare the equivalent susceptance at different gap lengths, the gap length corresponding to zero equivalent susceptance is the resonant gap length, and obtain the resonant gap length and normalized equivalent conductance under the first gap offset condition; increase the gap offset by a specified value to obtain the resonant gap length and normalized equivalent conductance under the second gap offset condition; continue to increase the gap offset by a specified angle until the gap offset upper limit is reached; fit the obtained gap offset, resonant gap length and normalized equivalent conductance to obtain the gap conductance function curve; S3. According to the ideal conductance distribution and the slot conductance function curve, the initial parameters of N slots are obtained, and a waveguide slot array model containing N slots is established in the simulation software HFSS for simulation. According to the simulation results, the slot mouth amplitude and phase distribution is extracted, and the slot mouth amplitude and phase distribution is compared with the theoretical mouth amplitude and phase distribution to obtain the amplitude distribution difference between the simulated amplitude and phase distribution and the theoretical amplitude and phase distribution. The relationship between the amplitude distribution difference and the slot inclination angle or the slot offset, and the relationship between the phase difference and the slot depth or the slot length are constructed, and the slot parameters are adjusted according to the difference and then simulation is performed; through several iterative designs, until the amplitude distribution difference and the sidelobe level of the radiation pattern reach the target, a low sidelobe waveguide slot antenna design method is completed.

2. A low sidelobe waveguide slot antenna design method according to claim 1, characterized in that: The antenna form of the waveguide slot array antenna is a waveguide slot traveling wave array or a standing wave array.

3. The method for designing a low sidelobe waveguide slot antenna according to claim 1, characterized in that: The antenna unit of the waveguide slot array antenna is a slot on a narrow side of the waveguide or a slot on a wide side of the waveguide.

4. A method for designing a low sidelobe waveguide slot antenna according to claim 3, characterized in that: In step S2, when the antenna unit of the waveguide slot array antenna is a waveguide narrow side slot, the slot parameters are the slot inclination angle and the slot depth, and the slot conductance function curve is a relationship curve between the slot inclination angle, the slot depth and the slot equivalent conductance.

5. The method for designing a low sidelobe waveguide slot antenna according to claim 3, characterized in that: In step S2, when the antenna unit of the waveguide slot array antenna is a waveguide wide side slot, the slot parameters are the slot offset and the slot length, and the slot conductance function curve is a relationship curve between the slot offset, the slot length and the slot equivalent conductance.

6. A method for designing a low sidelobe waveguide slot antenna according to claim 1, characterized in that: The gap conductance function curve is obtained by fitting through the nonlinear curve fitting function of Matlab software.

7. A method for designing a low sidelobe waveguide slot antenna according to any one of claims 1 to 6, characterized in that: The low sidelobe waveguide slot antenna design method is applicable to any of the following aperture field distributions: Taylor distribution, Chebyshev distribution and cosecant square distribution.

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