A design method for low sidelobe waveguide slot antenna

Abstract

The present invention provides a method for designing a low-sidelobe waveguide slot antenna. First, the theoretical aperture field distribution of the antenna is obtained based on the number of antenna slots and the target sidelobe level. Next, the slot conductance function, i.e., the relationship between slot parameters and normalized conductance, is determined. Then, based on full consideration of the mutual coupling between different slot units in the array and array edge effects, the antenna aperture field distribution is made to approximate the theoretical aperture field distribution through several iterative designs, and the sidelobe level of the radiation pattern reaches the target, thereby achieving the design of a low-sidelobe waveguide slot array antenna. The antenna of the present invention can be a waveguide slot traveling wave array, a standing wave array, or the like, and the slot units can be either waveguide wide-side slot units or waveguide narrow-side slot units. The present invention is particularly suitable for the design of electrically large-sized waveguide slot array antennas, saving design time and improving design efficiency. The present invention can also be extended to the design of antenna arrays with arbitrary aperture field distributions.

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 radar anti-interference requirements increase, there is a growing demand for low or ultra-low sidelobe antennas. Waveguide slot array antennas have the advantage of easily controllable aperture distribution, making them easy to meet the low sidelobe requirements. Therefore, they are widely used in radar, communications and other fields.

[0003] The Taylor synthesis method is generally 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 sidelobe has a certain gap with the theoretical Taylor synthesis sidelobe value or a lower sidelobe level cannot be achieved.

[0004] In the paper "Design of an Ultra-Low Sidelobe Slot Waveguide Antenna," the theoretical Taylor composite sidelobe value was chosen to be -50dB, while the designed antenna sidelobe level was -42dB. In the paper "Design of a Millimeter-Wave Low Sidelobe Waveguide Narrow-Slot Traveling Wave Array," the theoretical Taylor composite sidelobe value was chosen to be -40dB, while the designed antenna sidelobe level was -35dB. Generally, a Taylor composite sidelobe value of -40dB results in a gain loss of 1.15dB, while a Taylor composite sidelobe value of -35dB results in a gain loss of 0.9dB. Therefore, this design result, which is inconsistent with the theoretical design, will result in additional aperture efficiency loss and reduced antenna gain.

[0005] In patent application CN110287539B, "A Method for Automatic Design and Optimization of Waveguide Slot Array Antennas," the optimization target is 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 achieved. The reason is that the optimization target is inappropriate, and the slot aperture amplitude and phase distribution is the direct cause of the sidelobe level of the radiation pattern, not the slot admittance. In addition, adjusting the slot spacing superficially changes the phase distribution at the slot aperture, but actually fails to fundamentally solve the problem of the slot deviating from resonance, and makes the mutual coupling environment of the slot more complex, making it impossible to achieve an ideal aperture distribution and a lower sidelobe level.

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

[0007] The present invention aims to address the problems of aperture efficiency loss, antenna gain reduction, and discrepancies between designed and actual sidelobe designs. It provides a method for designing low-sidelobe waveguide slot antennas. First, the theoretical aperture field distribution (i.e., the slot normalized conductance distribution) of the antenna is obtained based on the number of antenna slots and the target sidelobe level. Next, the slot conductance function (i.e., the relationship between slot parameters and normalized conductance) is determined. Then, by fully considering the mutual coupling between different slot units in the array and the array edge effects, the antenna aperture field distribution is approximated to the theoretical aperture field distribution through several iterative designs, thereby achieving the design of a low-sidelobe waveguide slot array antenna. The antenna can be in the form of a waveguide slot traveling wave array, a standing wave array, or the like, and the slot units can be either waveguide wide-side slot units or waveguide narrow-side slot units. This method is particularly suitable for the design of electrically large-sized waveguide slot array antennas, saving design time and improving design efficiency. This method can also be extended to the design of antenna arrays with arbitrary aperture field distributions.

[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 type, a 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, where the admittance parameter model includes at least two gaps with the same gap size, gap spacing, and adjacent gap inversion as in actual conditions. Determine whether the gap is resonant by determining 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. 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 slot parameters are the slot inclination angle and the slot depth, the relationship between the normalized equivalent conductance of the slot in the resonant state and the slot parameters is obtained as follows: the initial slot inclination angle is fixed, and the parameter analysis function of the HFSS software is used 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 the resonant slot depth and normalized equivalent conductance under the first slot inclination angle condition are obtained; the slot inclination angle is increased by a specified angle to obtain the resonant slot depth and normalized equivalent conductance under the second slot inclination angle condition; the slot inclination angle is further increased by the specified angle until the upper limit of the slot inclination angle is reached; the obtained slot inclination angle, resonant slot depth, and normalized equivalent conductance are fitted to obtain a slot 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 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 the resonant gap length and normalized equivalent conductance under the first gap offset condition are obtained; 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 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 aperture amplitude and phase distribution is extracted, and the slot aperture amplitude and phase distribution is compared with the theoretical aperture 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. 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 directional pattern sidelobe level reach the target, a low sidelobe waveguide slot antenna design method is completed.

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

[0016] In the method for designing a low sidelobe waveguide slot antenna described in the present invention, as a preferred embodiment, 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 slot on the wide side of the waveguide, 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 is, as a preferred embodiment, to obtain a slot conductance function curve by fitting a nonlinear curve fitting function using 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) based on 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). Then, on the basis of fully considering the mutual coupling between different slot units in the array and the array edge effect, through several iterative designs, the antenna aperture field distribution is made to approach the theoretical aperture field distribution, thereby realizing the design of a 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-sized 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 and process the slot size and aperture field data. It 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 a 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 using 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 A comparison chart of the simulated and theoretical radiation patterns of the antenna array designed using a low-sidelobe waveguide slot array design method. DETAILED DESCRIPTION

[0032] 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 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 and the target sidelobe level of the waveguide slot array antenna to obtain normalized slot excitation, thereby inferring 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, thereby inferring the relationship between the normalized equivalent conductance of the slot in the resonant state and the slot parameters. The slot parameters and the equivalent conductance are interpolated to obtain the slot conductance function curve. Then, based on 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. Based on 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 directional pattern sidelobe level 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 angle, 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 uses a traveling wave array of waveguide slots as an example. The process is as follows: a slot array of 20 units is established, with the slots having exactly the same size, the spacing between each slot being the same as the actual spacing, and adjacent slots also alternating inverted directions; the slot inclination angle is fixed, and the parameter analysis function of the HFSS software is used to compare the equivalent susceptance at different cut depths. The cut depth h0 corresponding to zero equivalent susceptance is the resonant slot depth, and the resonant slot depth and normalized equivalent conductance at this time are recorded; the above process is repeated at a certain angle interval; finally, the nonlinear curve fitting function (lsqcurvefit function) of the Matlab software is used to fit the obtained slot inclination angle, slot depth, and normalized equivalent conductance to 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, based on 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. Based on the simulation results, the slot aperture amplitude and phase distribution is extracted and compared with the theoretical aperture 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 aperture amplitude and phase distribution is close to the theoretical aperture amplitude and phase distribution, and the directional pattern sidelobe level and other indicators meet the index requirements.

[0042] like Figure 2 The antenna array designed using a low-sidelobe waveguide slot array design method is shown in the figure: a narrow-side waveguide slot traveling wave array antenna. Alternating tilted slots are provided on the narrow side of the waveguide, and a matching load is connected to the end of the waveguide to absorb unradiated energy. The number of slots, N, is 146. The theoretical aperture amplitude distribution is selected to have a Taylor integrated sidelobe value of -35dB.

[0043] like Figure 3 As shown in the figure, the comparison between the simulated aperture amplitude distribution and the theoretical aperture amplitude distribution of the antenna array designed by the low sidelobe waveguide slot array design method of the present invention is shown in the figure, where the blue curve is the theoretical value and the red curve is the simulated value. Figure 4Figure 2 shows a comparison of the simulated aperture phase distribution and the theoretical aperture phase distribution of an antenna array designed using a low-sidelobe waveguide slot array design method according to the present invention. The green curve represents the theoretical value, and the red curve represents the simulated value. As can be seen from the figure, the simulated aperture amplitude distribution is essentially consistent with the theoretical aperture amplitude and phase distribution.

[0044] like Figure 5 Figure 2 shows a comparison of the simulated and theoretical radiation patterns of an antenna array designed using a low-sidelobe waveguide slot array design method. The theoretical sidelobe level is -35dB, while the simulated sidelobe level is -33dB, which is basically consistent with the theoretical design.

[0045] The principles of the present invention are as follows:

[0046] This paper proposes a low-sidelobe waveguide slot array design method. Matlab software is used to fit the slot conductance function and analyze 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 and phase. By combining these two software programs, the low-sidelobe waveguide slot array antenna design can be achieved by precisely controlling the aperture amplitude and phase distribution.

[0047] This paper proposes a new method for designing low-sidelobe waveguide slot arrays. The antennas designed can be traveling-wave arrays, standing-wave arrays, and other waveguide slot arrays. This method is particularly suitable for designing electrically large waveguide slot array antennas, saving design time and improving efficiency. The method can also be extended to design antenna arrays with arbitrary aperture distributions.

[0048] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A method for designing a low sidelobe waveguide slot antenna, characterized by: The following steps are involved: S1. According to the number of slots in the waveguide slot array antenna N , target sidelobe level and Taylor discrete aperture synthesis method category to obtain normalized slot excitation and deduce the ideal conductance value of each slot and the ideal conductance distribution of the waveguide slot array antenna; S2. Establish an admittance parameter extraction model, wherein the admittance parameters include at least two gap sizes, gap spacing, and adjacent gap inversion directions that are the same as the actual gap, determine 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; The gap parameters are the gap inclination and gap depth or the gap offset and gap length; When the gap parameters are the gap inclination angle and the gap depth, a specific method for obtaining the relationship between the normalized equivalent conductance of the gap in a resonant state and the gap parameters is as follows: fixing the initial gap inclination angle, using the parameter analysis function of the HFSS software to compare the equivalent susceptance at different gap depths, the gap depth h0 corresponding to zero equivalent susceptance is the resonant gap depth, and obtaining the resonant gap depth and normalized equivalent conductance under the first gap inclination angle condition; increasing the gap inclination angle by a specified angle to obtain the resonant gap depth and normalized equivalent conductance under the second gap inclination angle condition; continuing to increase the gap inclination angle by the specified angle until the upper limit of the gap inclination angle is reached; fitting the obtained gap inclination angle, resonant gap depth, and normalized equivalent conductance to obtain the gap 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: fixing the initial gap offset, using 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 obtaining the resonant gap length and normalized equivalent conductance under the first gap offset condition; increasing the gap offset by a specified value to obtain the resonant gap length and normalized equivalent conductance under the second gap offset condition; continuing to increase the gap offset by a specified angle until the gap offset upper limit is reached; and fitting the obtained gap offset, resonant gap length, and normalized equivalent conductance to obtain the gap conductance function curve; S3, obtaining the ideal conductivity distribution and the gap conductivity function curve N The initial parameters of the gap are established in the simulation software HFSS. N A waveguide slot array model with multiple slots is simulated, and the slot aperture amplitude and phase distribution is extracted according to the simulation results. The slot aperture amplitude and phase distribution is compared with the theoretical aperture 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. 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 directional pattern sidelobe level reach the target, a low sidelobe waveguide slot antenna design method is completed.

2. The method for designing a low sidelobe waveguide slot antenna according to claim 1, wherein: 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, wherein: 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. The method for designing a low sidelobe waveguide slot antenna according to claim 3, wherein: 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, wherein: 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. The method for designing a low sidelobe waveguide slot antenna according to claim 1, wherein: The gap conductance function curve is obtained by fitting the nonlinear curve fitting function of Matlab software.

7. The method for designing a low sidelobe waveguide slot antenna according to any one of claims 1 to 6, wherein: 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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