Optimization method of butterfly-shaped UHF antenna

Abstract

The invention discloses an optimization method of a butterfly-shaped UHF antenna, and the method comprises the following steps: determining a preset angle range of a semi-apex angle based on the matching relation between the characteristic impedance of the butterfly-shaped antenna and the working frequency band width, so as to achieve the stable change of the input impedance and the broadening of the frequency band; according to the wavelength of the low-frequency end of the working frequency band, a preset proportional relation between the arm length and the wavelength is established to determine the value of the arm length, so that the requirement of the antenna impedance bandwidth on low-frequency-band signal receiving is met; a butterfly antenna is arranged in a metal back cavity to form a back cavity type antenna, the height of the back cavity is determined according to the wavelength corresponding to the strongest frequency of a signal so as to suppress back radiation and enhance forward radiation gain, and systematic improvement of electromagnetic wave signal receiving performance is realized through collaborative optimization of structural parameters of the butterfly antenna and the back cavity.

Description

Technical Field

[0001] The present invention relates to the technical field of butterfly-shaped UHF antennas, and in particular to an optimization method for butterfly-shaped UHF antennas. Background Art

[0002] The detection mechanism of external ultra-high frequency (UHF, 300MHz-3GHz) sensors is based on the electromagnetic radiation effect of partial discharge in electrical equipment. When a partial discharge, such as dielectric breakdown, occurs within the equipment, the transient migration of charge generates a nanosecond pulse current. According to Maxwell's electromagnetic theory, this pulse current stimulates electromagnetic radiation through displacement current, generating UHF electromagnetic waves with broadband characteristics. When propagating in the SF6 insulating medium, these electromagnetic waves have an attenuation constant of less than 0.1dB / m and a propagation velocity of approximately 0.3c (where c is the speed of light). At dielectric interfaces, they follow the Fresnel reflection law, with the reflection coefficient determined by the difference in dielectric constant. These propagation characteristics provide the physical basis for the effective detection of UHF signals.

[0003] Existing detection devices primarily utilize two sensing architectures: capacitive coupling and antenna reception. Antenna sensors achieve signal pickup by sensing electromagnetic field components. Typical types include: While helical antennas offer an impedance bandwidth exceeding 3:1, their circular polarization leads to a mismatch between their electric field vector and the linear polarization of the localized electromagnetic waves at the pouring hole, reducing reception efficiency. Under ideal conditions, a dipole antenna has a gain of only 2dBi. Miniaturization shortens the current path, reducing its equivalent height, often less than 3mm in the 300MHz-1.5GHz frequency band. The omnidirectional radiation characteristic of biconical antennas transforms into unidirectional radiation after metal back-cavity encapsulation. However, the cavity resonance effect causes a standing wave ratio greater than 10 in the frequency band below 700MHz. Furthermore, the axial length of the three-dimensional structure exceeds 150mm, which cannot meet the installation space constraint of the pouring hole of GIS equipment, which is less than 80mm in diameter. Even with miniaturization achieved through loading technology, the standing wave ratio remains above 5 at low frequencies, failing to meet engineering application requirements.

[0004] Current external UHF sensors face two major technical bottlenecks: First, the open antenna structure causes coupling interference between spatial electromagnetic interference and the sidelobes of the antenna's radiation pattern, reducing the signal-to-noise ratio to below 10dB. Second, the half-apex angle parameters of traditional butterfly antennas are not synergistically optimized with the back cavity structure, resulting in a voltage standing wave ratio greater than 8 in the frequency band below 700MHz and a reduction of more than 30dB in low-frequency signal reception efficiency. These shortcomings lead to existing sensors failing to detect weak signals and exhibiting strong directional dependence in actual partial discharge detection. Summary of the Invention

[0005] In view of the above-mentioned prior art, the present invention provides an optimization method for a butterfly-shaped UHF antenna, which mainly solves the technical problems existing in the above-mentioned background technology.

[0006] To achieve the above-mentioned purpose, the technical solution of the embodiment of the present invention is implemented as follows: A method for optimizing a butterfly-shaped UHF antenna comprises the following steps: Based on the matching relationship between the characteristic impedance of the butterfly antenna and the operating bandwidth, the preset angle range of the half-apex angle is determined to achieve a smooth change in input impedance and widen the frequency band; According to the wavelength at the low-frequency end of the operating frequency band, a preset proportional relationship between the arm length and the wavelength is established to determine the value of the arm length, thereby meeting the antenna impedance bandwidth requirements for low-frequency signal reception; The butterfly antenna is placed in a metal back cavity to form a back cavity antenna. The back cavity height is determined according to the wavelength corresponding to the strongest signal frequency to suppress back radiation and enhance forward radiation gain.

[0007] Optionally, based on a matching relationship between the characteristic impedance of the butterfly antenna and the operating bandwidth, a preset angle range of the half apex angle is determined, specifically including: Setting limits based on frequency band requirements; Establishing characteristic impedance Angle to half apex angle The corresponding relationship:

[0008] Calculation difference Corresponding characteristic impedance, analyze the stability of input impedance in the target frequency band, and determine the half-apex angle in combination with miniaturization constraint optimization conditions. preset angles.

[0009] Optionally, the limited range is 40°~80°.

[0010] Optionally, the half-apex angle is determined The preset angle range is 63°±1°.

[0011] Optionally, the preset proportional relationship between the arm length and the wavelength is established as follows:

[0012] in, is the wavelength at the low frequency end of the working band; Substituting the characteristic impedance and the wavelength at the low-frequency end of the operating band into the above formula, the value of the arm length is obtained.

[0013] Optionally, the back cavity height is determined based on the wavelength corresponding to the strongest signal frequency, specifically including: Based on the frequency domain response test results of the target UHF band, determine the frequency point where the energy is most concentrated ,calculate Corresponding wavelength ; Based on the principle of array antenna mirror effect, the formula for maximizing the radiation field strength is solved to obtain the height of the back cavity. The best reception effect is achieved when

[0014] Optional, back cavity height Optimal reception is achieved at 75mm.

[0015] Optionally, the width and height of the back cavity are dynamically adapted according to the electromagnetic environment requirements of the target application scenario.

[0016] Optionally, the side wall of the back cavity is in contact with the butterfly antenna.

[0017] The beneficial effects of the present invention are: through the coordinated optimization of the butterfly antenna structural parameters and the back cavity, a systematic improvement in the electromagnetic wave signal receiving performance is achieved; by establishing a matching model between the characteristic impedance and the operating frequency band, the half-apex angle and arm length parameters are optimized, the antenna impedance bandwidth is effectively widened, the voltage standing wave ratio in the target frequency band is significantly reduced, and the impedance mismatch problem in the low-frequency band is solved; the back cavity height is designed based on the array antenna mirror principle, and the antenna radiation mode is converted from omnidirectional to unidirectional directional radiation, which greatly enhances the forward gain and suppresses the back interference, thereby improving the directionality and anti-interference ability of signal detection; combining the printed circuit board process with the metal back cavity integrated design, while meeting the miniaturized installation requirements, it is verified through experiments that the discharge signal detection sensitivity, integrity and conversion rate are comprehensively improved, which is more suitable for the efficient and accurate detection of partial discharge of electrical equipment than the existing technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a flow chart of the method in the embodiment of the present application; Figure 2 This is a schematic diagram of the original butterfly antenna in the embodiment of this application; Figure 3 Schematic diagram of the simulation model of the original butterfly antenna in the embodiment of the present application; Figure 4 Schematic diagram of the voltage standing wave ratio parameter curve of the original butterfly antenna in the embodiment of the present application; Figure 5 Schematic diagram of the radiation direction of the original butterfly antenna in the embodiment of the present application; Figure 6 Schematic diagram of a simulation model of an optimized butterfly antenna in an embodiment of the present application; Figure 7 Schematic diagram of the VWSR curve of the improved front and rear butterfly antenna in the embodiment of the present application; Figure 8 This is a theoretical schematic diagram of back cavity reflection in an embodiment of the present application; Figure 9Schematic diagram of voltage standing wave ratio parameter curves of three types of butterfly antennas after adding a back cavity in the embodiment of the present application; Figure 10 The radiation pattern of the optimized butterfly antenna in the embodiment of the present application; Figure 11 The radiation pattern of the semi-elliptical antenna in the embodiment of the present application; Figure 12 : is the radiation pattern of the semicircular antenna in the embodiment of the present application. DETAILED DESCRIPTION

[0019] The technical solution of the present invention is further elaborated in detail below in conjunction with the drawings and specific embodiments of the specification. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which the present invention belongs. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention. In the following description, reference is made to "some embodiments", which describes a subset of all possible embodiments, but it should be understood that "some embodiments" can be the same subset or different subsets of all possible embodiments, and can be combined with each other without conflict.

[0020] In the following description, numerous specific details are provided to provide a more thorough understanding of the present invention. However, it will be apparent to those skilled in the art that the present invention may be practiced without one or more of these details. In other instances, certain technical features well known in the art are not described to avoid confusion with the present invention.

[0021] It should be understood that the present invention can be implemented in different forms and should not be interpreted as being limited to the embodiments proposed herein. On the contrary, providing these embodiments will make the disclosure thorough and complete, and will fully convey the scope of the present invention to those skilled in the art. And the purpose of the terms used herein is only to describe specific embodiments and is not intended to limit the present invention. When used herein, the singular forms "one", "an" and "said / the" are also intended to include plural forms, unless the context clearly indicates another way. It should also be understood that the terms "comprising" and / or "comprising" when used in this specification determine the presence of the features, integers, steps, operations, elements and / or parts, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, parts and / or groups. When used herein, the term "and / or" includes any and all combinations of the relevant listed items.

[0022] It should also be noted that when an element is referred to as being "fixed to" another element, it may be directly on the other element or there may be an intermediate element. When an element is referred to as being "connected to" another element, it may be directly connected to the other element or there may be an intermediate element. The terms "vertical," "horizontal," "inner," "outer," "left," "right," and similar expressions used herein are for illustrative purposes only and do not represent the only implementation methods.

[0023] In order to fully understand the present invention, a detailed structure will be provided in the following description to illustrate the technical solution proposed by the present invention. Optional embodiments of the present invention are described in detail below. However, in addition to these detailed descriptions, the present invention may also have other implementations.

[0024] Please refer to the attached Figure 1 , the present application provides a method for optimizing a butterfly-shaped UHF antenna, comprising the following steps: S1. Based on the matching relationship between the characteristic impedance of the butterfly antenna and the operating bandwidth, the preset angle range of the half-apex angle is determined to achieve a smooth change in input impedance and widen the frequency band; S2. Establishing a preset proportional relationship between the arm length and the wavelength based on the low-frequency end wavelength of the operating frequency band to determine the value of the arm length so as to meet the antenna impedance bandwidth requirements for low-frequency signal reception; S3. Place the butterfly antenna in a metal back cavity to form a back cavity antenna. Determine the back cavity height based on the wavelength corresponding to the strongest signal frequency to suppress back radiation and enhance forward radiation gain.

[0025] In some embodiments, the preset angle range of the half apex angle is determined based on the matching relationship between the characteristic impedance of the butterfly antenna and the operating bandwidth, specifically including: Based on the frequency band requirements, the range is initially limited to 40°~80°; Establishing characteristic impedance Angle to half apex angle The corresponding relationship:

[0026] Calculation difference Corresponding characteristic impedance, analyze the stability of input impedance in the target frequency band, and determine the half-apex angle in combination with miniaturization constraint optimization conditions. The preset angle range is 63°±1°.

[0027] Specifically, a UHF sensor is a receiver for GIS partial discharge electromagnetic wave signals and is essentially a receiving antenna. According to antenna theory, basic antenna parameters include lobe pattern, directivity, gain, standing wave ratio, and radiation pattern. However, for engineering applications, improving some of these parameters presents difficulties. In practical applications, the proximity of UHF sensors to numerous metal conductors, including the GIS metal casing, can severely interfere with and attenuate the antenna's far-field characteristics. In practical engineering applications, the sensor's frequency response and sensitivity to partial discharge RF signals are two of its most important performance indicators. Improving these two parameters will significantly enhance sensor effectiveness.

[0028] The operating frequency and gain of an antenna are closely related to the length of its current path. Theoretically, the smaller the antenna, the narrower its operating bandwidth. Therefore, in the actual antenna development process, it is necessary to comprehensively consider the size and operating frequency band requirements to select the antenna with the optimal dimensions. Currently, typical broadband antennas used in the UHF band include biconical antennas and their variations (such as discone antennas and butterfly antennas), horn antennas and their variations (ridged horn antennas and TEM horn antennas), dipole antennas, helical antennas (Archimedean spiral antennas and equiangular spiral antennas), and log-periodic antennas and their variations (log-periodic dipole array antennas, trapezoidal linear tooth structure log-periodic antennas, and trapezoidal tooth log-periodic antennas).

[0029] A bowtie antenna, also known as a bowtie or bowtie antenna, is a variation of the conical antenna. Its two oscillators are typically symmetrical isosceles triangles or other shapes. The oscillator arms are made of metal and are mounted on a dielectric substrate. The maximum gain of a bowtie antenna is in the direction normal to the bowtie plane.

[0030] Based on characteristic impedance Angle to half apex angle The corresponding relationship:

[0031] It can be seen that the characteristic impedance of the butterfly antenna is only determined by The decision has nothing to do with the distance from different points on the vibrator arm to the feeding point. As the value increases, the characteristic impedance decreases, the change of input impedance becomes more stable, and the working frequency band of the antenna becomes wider. If the angle is too large, the base of the triangle will be too long, and the miniaturization of the antenna will not be easy to achieve. In this application, the range is initially limited to 40°~80° based on the frequency band requirements. Corresponding characteristic impedance, analyze the stability of input impedance in the target frequency band, and determine the half-apex angle in combination with miniaturization constraint optimization conditions. The preset angle range is 63°±1°.

[0032] In some embodiments, the preset proportional relationship between the arm length and the wavelength is established as follows:

[0033] in, is the wavelength at the low frequency end of the working band; Substituting the characteristic impedance and the wavelength at the low-frequency end of the operating band into the above formula, the value of the arm length is obtained.

[0034] Specifically, the arm length of the butterfly antenna The low-end frequency largely determines the antenna's impedance bandwidth. The larger the value, the lower the low-end frequency of the antenna operating band. If the characteristic impedance remains unchanged, Proportional to the low-end frequency.

[0035] In some embodiments, the normal direction of the butterfly plane in the direction of maximum gain of the butterfly antenna radiates in two directions, that is, the antenna detects the signal on the front side while also detecting the signal on the back side. This not only reduces the receiving efficiency of the antenna in the main detection direction, but also the clutter in the surrounding environment will be received by the antenna, resulting in signal distortion and reduced signal-to-noise ratio.

[0036] After simulation and computer engineering tests, placing the antenna within a metal back cavity resulted in a cavity-backed antenna. This design not only enhances signal reception but also improves the system's signal-to-noise ratio. The metal back cavity shields and isolates the antenna, significantly reducing the directional pattern on the back of the antenna and increasing the front-to-back ratio, transforming the bow-shaped antenna into a unidirectional, directional antenna.

[0037] However, the back cavity itself is a strong reflection source, and the size of the back cavity has a significant impact on the reflection of electromagnetic waves. Figure 8 As shown in the figure, in order to effectively suppress back radiation while enhancing forward radiation, the most important factor affecting the radiation capability of the cavity-backed antenna is the mirror effect of the large cavity bottom surface on the antenna. Given that any cavity of a certain size is a narrowband system relative to the ultra-wideband pulse signal, and the height of the cavity directly determines the effect of the mirror effect, the choice of the cavity height parameter should be based on the strongest frequency point of the pulse signal. Therefore, the cavity height is determined according to the wavelength corresponding to the strongest signal frequency, including: Based on the frequency domain response test results of the target UHF band, determine the frequency point where the energy is most concentrated ,calculate Corresponding wavelength ; Based on the principle of mirror effect of array antenna, the formula for maximizing the radiation field strength is solved:

[0038] in is the electric field strength radiated by the antenna itself in space, k is the wave number, and in order to radiate the maximum signal energy upward, the height of the back cavity should be calculated. When the antenna is added with the back cavity, the radiation field strength E is the strongest, and the total field is the largest. , the best reception effect is achieved at this time.

[0039] Furthermore, when the signal frequency is at its strongest point of 1 GHz, the height of the back cavity is Optimal reception is achieved at 75mm.

[0040] Furthermore, the width and height of the back cavity are dynamically adapted according to the electromagnetic environment requirements of the target application scenario, and the side wall of the back cavity is in contact with the butterfly antenna.

[0041] Specifically, the structural characteristics of a cavity-backed antenna indicate that its four sidewalls do not mirror the antenna. However, the induced currents on the cavity sidewalls will undergo cross-polarization, creating mutual coupling between the induced currents and the antenna, which can affect the antenna's standing wave performance to a certain extent, but has little impact on the antenna's radiation performance. Therefore, the cavity width and length can be determined based on the antenna's application requirements. To minimize the antenna's size, the sidewalls should be designed close to the antenna, depending on the antenna's size.

[0042] In order to verify the effect of the present invention, the original butterfly antenna model was established using existing simulation software, such as Figure 2-3 As shown, the voltage standing wave ratio parameters of the antenna are as follows Figure 4 , the radiation direction of the antenna is as follows Figure 5 ,Depend on Figure 4 As can be seen from the data, the voltage standing wave ratio (VSWR) of the bowtie antenna is significantly higher than 10 in the frequency band below 700 MHz. After 700 MHz, the VSWR decreases stepwise, falling below 5 at 800 MHz. From 800 MHz to 2.4 GHz, the VSWR remains between 2 and 6. These data indicate that the antenna's impedance matching characteristics do not meet design requirements, and the VSWR performance deteriorates significantly at low frequencies.

[0043] In addition, from Figure 5 Further analysis shows that the main reason for the degradation of antenna performance is physical size constraints: the short antenna arm length results in insufficient electrical length in the low-frequency band, causing the impedance bandwidth to fail to cover the target starting frequency band. The maximum gain of the E-plane (the electric field vector plane, the red solid line in the figure) occurs at 0° and 180°, that is, perpendicular to the normal of the antenna plane; while the gain of the H-plane (the magnetic field vector plane, the blue dotted line in the figure) decreases with The change is not significant, and it is similar to an omnidirectional antenna, which does not meet the directivity requirements. Therefore, some improvements and optimizations are needed for the butterfly antenna.

[0044] According to antenna theory, a series of improvements, simulations and optimizations were attempted on the original butterfly antenna, and finally an improved butterfly antenna was obtained. The model of the improved butterfly antenna built in the simulation software is as follows: Figure 6 As shown in the figure, the VSWR curves of the improved and unimproved butterfly antennas are compared. Figure 7 shown.

[0045] Depend on Figure 7 It can be seen that the voltage standing wave ratio parameters of the improved butterfly antenna are significantly better than those of the butterfly antenna before the improvement within the required frequency band. Except that the standing wave ratio of the butterfly slot antenna in the low frequency band is slightly higher than the design requirements, the standing wave ratios of the other two butterfly antennas in the required frequency band are basically within 2, meeting the design requirements. The comparison results of signal strength and standing wave ratio are as follows: Figure 8-12 As shown. Figure 7 and Figure 9 It can be seen that after adding the back cavity, the standing wave of the butterfly antenna increases slightly compared to before adding the back cavity, but the change is not significant, and the impedance bandwidth of the antenna is basically within the design requirements. Figure 10-12 The directional diagram of the middle antenna (the red solid line is the E-plane diagram, and the blue dotted line is the H-plane diagram) shows that after adding the back cavity, the radiation direction of the butterfly antenna becomes unidirectional, and the gain on the back of the antenna is greatly reduced. Figure 7 and 9 , it can be seen that the maximum gain of the three butterfly antennas increases to varying degrees after adding the back cavity compared to before. The above simulation results show that by adding a metal back cavity to the antenna, the requirements of effectively suppressing backward radiation and increasing forward radiation gain are basically achieved.

[0046] Depend on Figure 7 It can be seen that the voltage standing wave ratio parameters of the improved butterfly antenna are significantly better than those of the butterfly antenna before the improvement within the required frequency band. Except for the butterfly slot antenna, whose standing wave ratio in the low frequency band is slightly higher than the design requirements, the standing wave ratios of the other two butterfly antennas within the required frequency band are basically within 2. The signal reception angle margin and the signal amplification strength after reception are greatly superior to the butterfly antennas under other parameters.

[0047] The angle, length, and back cavity height of the butterfly antenna designed by the present invention are combined to achieve the best effect, and the structural parameters of the butterfly antenna are obtained. The antenna designed using these parameters can improve the measurement accuracy and efficiency of receiving UHF signals.

[0048] The above are merely specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. The scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A method for optimizing a butterfly-shaped UHF antenna, characterized in that: The following steps are involved: Based on the matching relationship between the characteristic impedance of the butterfly antenna and the operating bandwidth, the preset angle range of the half-apex angle is determined to achieve a smooth change in input impedance and widen the frequency band; According to the wavelength at the low-frequency end of the operating frequency band, a preset proportional relationship between the arm length and the wavelength is established to determine the value of the arm length, thereby meeting the antenna impedance bandwidth requirements for low-frequency signal reception; The butterfly antenna is placed in a metal back cavity to form a back cavity antenna. The back cavity height is determined according to the wavelength corresponding to the strongest signal frequency to suppress back radiation and enhance forward radiation gain.

2. The method for optimizing a butterfly-shaped UHF antenna according to claim 1, wherein: Based on the matching relationship between the characteristic impedance of the butterfly antenna and the operating bandwidth, the preset angle range of the half-apex angle is determined, specifically including: Setting limits based on frequency band requirements; Establishing characteristic impedance Angle to half apex angle The corresponding relationship: Calculation difference Corresponding characteristic impedance, analyze the stability of input impedance in the target frequency band, and determine the half-apex angle in combination with miniaturization constraint optimization conditions. preset angles.

3. The method for optimizing a butterfly-shaped UHF antenna according to claim 2, wherein: The limited range is 40°~80°.

4. The method for optimizing a butterfly-shaped UHF antenna according to claim 3, wherein: Determined half apex angle The preset angle range is 63°±1°.

5. The method for optimizing a butterfly-shaped UHF antenna according to claim 4, wherein: The established preset proportional relationship between the arm length and the wavelength is: in, is the wavelength at the low frequency end of the working band; Substituting the characteristic impedance and the wavelength at the low-frequency end of the operating band into the above formula, the value of the arm length is obtained.

6. The method for optimizing a butterfly-shaped UHF antenna according to claim 1, wherein: The back cavity height is determined based on the wavelength corresponding to the strongest signal frequency, specifically including: Based on the frequency domain response test results of the target UHF band, determine the frequency point where the energy is most concentrated ,calculate Corresponding wavelength ; Based on the principle of array antenna mirror effect, the formula for maximizing the radiation field strength is solved to obtain the height of the back cavity. The best reception effect is achieved when 7. The method for optimizing a butterfly-shaped UHF antenna according to claim 6, wherein: Height of back cavity Optimal reception is achieved at 75mm.

8. The method for optimizing a butterfly-shaped UHF antenna according to claim 7, wherein: The width and height of the back cavity are dynamically adapted according to the electromagnetic environment requirements of the target application scenario.

9. The method for optimizing a butterfly-shaped UHF antenna according to claim 8, wherein: The side wall of the back cavity is in contact with the butterfly antenna.

Images