A miniaturized log-periodic antenna and its assembly and design methods

Abstract

This invention discloses a miniaturized log-periodic antenna and its assembly and design methods, belonging to the field of communication antenna technology. The antenna includes a dielectric substrate, a semi-steel cable, an adapter plate, and a copper layer; the copper layer is disposed on the front and back sides of the dielectric substrate; an adapter plate is disposed at one end of the dielectric substrate; the outer shell of the semi-steel cable is welded to the copper layer at the center line of the back side of the dielectric substrate, and the inner core of the semi-steel cable is bent upwards through the side of the dielectric substrate without the adapter plate and then welded to the copper layer on the front side of the dielectric substrate; the antenna operates in the frequency band of 150MHz–400MHz, with a VSWR ≤2, and uses linear polarization. This invention addresses the performance shortcomings of traditional antennas in this frequency band by optimizing the structure of the vibrator and improving the feeding method, enabling it to cover the target frequency band while meeting the lightweight and miniaturized usage requirements of different scenarios.

Description

Technical Field

[0001] This invention belongs to the field of communication antenna technology, and relates to a miniaturized log-periodic antenna and its assembly and design methods. Background Technology

[0002] Log-periodic antennas, as typical non-frequency-varying antennas, have become an indispensable core technology in the field of ultra-wideband antennas since engineer D. Isbell proposed the design concept based on non-frequency-varying antenna theory in 1957, thanks to their core advantage of maintaining stable impedance, gain, and radiation direction over a wide bandwidth. They are widely used in many key fields such as communication, detection, and measurement. With the rapid popularization and in-depth development of technologies such as the Internet of Things, emergency communication, and scientific research observation, communication scenarios are becoming increasingly diversified and deployment environments are becoming more complex. The performance requirements for log-periodic antennas are also evolving towards more precise and demanding directions. Their technical approach is gradually shifting from early general-purpose broadband design to customized and scenario-specific adaptation for specific frequency bands.

[0003] In the field of civilian dispatch communication, multi-band collaborative operation has become a key requirement for ensuring smooth communication in complex scenarios: The 150MHz band, due to its strong diffraction and penetration capabilities, is widely used in wireless intercom dispatching in scenarios with severe obstruction or large-area coverage, such as tunnels, large stadiums, and transportation. This scenario requires antennas to be stably deployed in confined spaces (such as tunnel equipment compartments and vehicle-mounted brackets) while meeting the signal transmission requirements in mobile states; The 350MHz band, as the core band of my country's public safety network (such as the PDT network), has become the "backup" communication band for key scenarios such as emergency command and public security duty due to its long propagation distance and strong anti-interference capabilities. It has extremely high requirements for antenna reliability, gain stability, and lightweight design to adapt to mobile deployment equipment such as portable terminals and emergency command vehicles. In the field of scientific observation, solar radio radiation detection in the 150-450MHz frequency band is an important means of studying space phenomena such as coronal mass ejections. These phenomena directly affect the safe and stable operation of Earth's communication systems and power grids. Therefore, antennas in this scenario need to maintain extremely high performance consistency within a specific wide frequency band, while also adapting to the miniaturization and integration requirements of scientific research equipment to avoid affecting the deployment flexibility of observation equipment due to excessively large antenna size.

[0004] However, existing commercially available dipole-type log-periodic antennas still have significant technical shortcomings, making it difficult to meet the customized needs of current niche scenarios. On the one hand, early commercial products were mostly designed for the 225-400MHz frequency band, which is not well-suited for the 150-350MHz band (including the low-band 150-225MHz and the mid-band 225-350MHz). In the low-band 150-225MHz, problems such as gain attenuation (usually less than 2dB) and high VSWR (often exceeding 3) are common, along with poor impedance matching stability, resulting in severe signal reflection and failing to guarantee communication quality in complex scenarios such as tunnels, utility tunnels, and emergency command centers. On the other hand, to ensure wide-band performance, traditional log-periodic antennas often adopt large-size dipole arrays and heavy structural designs, with overall dimensions typically exceeding 800mm×500mm and weight generally exceeding 3kg. This makes them unsuitable for installation in confined spaces or mobile deployment scenarios such as vehicle-mounted communication equipment, portable emergency terminals, and integrated scientific research and observation equipment. More importantly, as low profile, miniaturization, and lightweighting become the core development trends of log-periodic antennas, existing miniaturization solutions (such as fractal structure design, end loading of the vibrator, etc.) often have performance compromises: some solutions achieve miniaturization by shortening the vibrator length, but this leads to a significant reduction in bandwidth, making it impossible to cover the target frequency band of 150-350MHz; other solutions can retain some bandwidth, but this will cause a significant decrease in gain or unstable radiation direction, making it difficult to meet the dual requirements of wide-band coverage, high gain, and miniaturization.

[0005] In summary, the technical problems of traditional log-periodic antennas in the 150-350MHz target frequency band, such as "too large size and too heavy weight", "insufficient gain", "high VSWR and poor impedance matching", and "existing miniaturization solutions cannot achieve both wide bandwidth and high performance", have become the core bottlenecks restricting their in-depth application in key scenarios such as civilian dispatch communication, public safety emergency communication, and scientific research observation. Summary of the Invention

[0006] The purpose of this invention is to solve the technical problems of existing log-periodic antennas in the 150-350MHz target frequency band, namely "too large size and too heavy weight", "insufficient gain", "high VSWR and poor impedance matching", and to provide a miniaturized log-periodic antenna and its assembly and design methods.

[0007] To achieve the above objectives, the present invention employs the following technical solution: In a first aspect, embodiments of the present invention disclose a miniaturized log-periodic antenna, comprising a dielectric substrate, a semi-steel cable, an adapter plate, and a copper layer; the copper layer is disposed on the front and back sides of the dielectric substrate; an adapter plate is disposed at one end of the dielectric substrate; the outer shell of the semi-steel cable is welded to the copper layer at the center line position of the back side of the dielectric substrate, and the inner core of the semi-steel cable is bent upward through the side of the dielectric substrate without the adapter plate and then welded to the copper layer on the front side of the dielectric substrate; the antenna operates in the frequency band of 150MHz-400MHz, has a VSWR ≤2, and adopts linear polarization.

[0008] Further improvements are needed in the following areas: The copper layer includes a front copper layer and a back copper layer. Both the front copper layer and the back copper layer are provided with several pairs of oscillators. Several pairs of oscillators in the front copper layer and the back copper layer are provided with block-shaped notches for adjusting the resistance matching.

[0009] The several pairs of vibrators are arranged in parallel, with the length of the vibrators gradually increasing from the front end to the rear end of the antenna. The feed point of the antenna is located at one end of the short vibrator. Adjacent vibrators are fed in a cross-feed configuration.

[0010] The longest element of the antenna is half the wavelength corresponding to the lowest operating frequency, and the shortest element is less than half the wavelength corresponding to the highest operating frequency; the semi-steel cable is a 50Ω semi-steel cable.

[0011] Secondly, embodiments of the present invention disclose an assembly method for a miniaturized log-periodic antenna based on the above-described antenna, comprising: The dielectric substrate is subjected to copper stripping and surface treatment to form copper layers with a preset oscillator structure on the front and back sides of the dielectric substrate, and block-shaped notches are cut at the preset oscillator locations of the front and back copper layers. The outer shell of the semi-steel cable is welded to the copper layer at the center line position on the back of the dielectric substrate. The inner core of the semi-steel cable is bent upward from one side of the dielectric substrate and soldered to the end face of the copper layer on the front side of the dielectric substrate. Fix the adapter plate to the other side of the dielectric substrate to complete the antenna assembly.

[0012] Thirdly, embodiments of the present invention disclose a design method for a miniaturized log-periodic antenna based on the above-described antenna, comprising: Determine the target operating frequency band of the antenna, and clarify the minimum and maximum operating frequencies corresponding to the target operating frequency band; Determine the antenna's scaling factor τ, spacing factor σ, and antenna apex angle α; The longest element length of the antenna is calculated based on the lowest operating frequency, the shortest element length of the antenna is determined based on the highest operating frequency, and the structural bandwidth S and the number of elements N of the antenna are calculated. Based on the scaling factor τ, the length of the vibrator, and the antenna apex angle α, the spacing d between adjacent vibrators is calculated, and the gradual change law of the vibrator length is obtained. Based on the number of oscillators N, the gradual change law of oscillator length and the spacing d between adjacent oscillators, a parallel oscillator structure is designed, and a cross-feeding method is adopted to make the output voltage of adjacent oscillators 180° out of phase. By using a design that extends the dipole stub, the current path is extended, increasing the electrical length within the same physical size, thus achieving antenna miniaturization. The low-current region of the oscillator is identified, and part of the copper layer is removed in the low-current region to adjust the impedance matching, thus completing the design of a miniaturized log-periodic antenna.

[0013] The determination of the antenna's scaling factor τ, spacing factor σ, and antenna apex angle α specifically involves: The lengths of the longest and shortest elements of the antenna are expressed as follows: The endpoints of the vibrator are connected by lines, and the intersection of the extensions of the two lines forms a virtual vertex. The vertical distance from the virtual vertex to the antenna vibrator is determined by... The distance between adjacent elements of the antenna is expressed as... Representation; scaling factor Defined as the ratio of the length of the shorter element to the length of the longer element in an antenna's adjacent elements:

[0014] Among them, the oscillator spacing and the vertical distance from the virtual vertex to the oscillator The relationship between them is represented as follows:

[0015] The included angle between the connecting lines at the ends of the antenna element is called the apex angle. The expression is:

[0016] Oscillator Spacing It can be used through the scaling factor oscillator length and included angle Represented as:

[0017] To facilitate the description of log-periodic antennas, another parameter is introduced: the antenna spacing factor. Its definition is:

[0018] Antenna spacing factor , scaling factor and antenna apex The following relationship exists between them: .

[0019] The longest antenna element length is calculated based on the lowest operating frequency, and the shortest antenna element length is determined based on the highest operating frequency, specifically as follows: The length of the longest element in the antenna Represented as:

[0020] Length of the shortest element of the antenna Represented as: .

[0021] The specific calculation of the antenna's structural bandwidth S and the number of elements N is as follows: The formula for calculating the number of elements in a log-periodic antenna is:

[0022] in, For structure bandwidth; Antenna operating bandwidth Defined as the ratio between the antenna's highest operating frequency and its lowest operating frequency:

[0023] in, The structure bandwidth is expressed as:

[0024] The average bandwidth of the antenna's radiation region: .

[0025] The length of the miniaturized log-periodic antenna Calculated using the following formula: .

[0026] Compared with the prior art, the present invention has the following beneficial effects: This invention discloses a miniaturized log-periodic antenna. First, in terms of frequency band coverage and performance stability, this antenna can stably cover the target wide frequency band of 150MHz-400MHz with a VSWR ≤2, effectively solving the problems of gain attenuation and poor impedance matching in the low frequency band of 150-225MHz of traditional log-periodic antennas. This ensures the signal transmission quality in obstructed scenarios such as tunnels, large stadiums, etc. At the same time, it maintains stable high gain and anti-interference capability in the 350MHz public safety core frequency band, which can meet the "bottom-line" communication needs of key scenarios such as emergency command and public security duty. Secondly, regarding miniaturization and lightweight adaptability, the integrated structure design of the dielectric substrate and copper layer, combined with the optimization of the vibrator structure, significantly reduces the overall size and weight of the antenna. Compared to traditional commercial products (larger than 800mm×500mm in size and weighing ≥3kg), it is more suitable for installation in confined spaces or mobile deployment scenarios such as vehicle-mounted communication equipment and portable emergency terminals, improving the antenna's deployment flexibility in complex environments and efficiently matching the usage conditions of limited installation spaces such as tunnel equipment compartments and vehicle-mounted brackets. Finally, regarding power supply and structural reliability, the semi-steel cable adopts a power supply method of "welding the copper layer on the back of the substrate to the outer shell and bending and welding the copper layer on the front of the inner core," which not only ensures the stability of signal transmission but also simplifies the assembly process. Combined with the fixed design of the adapter plate, it further enhances the structural robustness of the antenna, making it adaptable to complex operating conditions such as vibration and bumps of mobile devices. At the same time, the adoption of linear polarization ensures the consistency of the antenna's radiation direction within the target frequency band, enabling stable adaptation to the signal transmission and reception needs of various scenarios such as civilian dispatching, public safety, and scientific research observation. In summary, this invention achieves a balance of high performance, miniaturization, and lightweight design within the target wideband through structural and feeding method optimization. It effectively fills the application gaps of traditional log-periodic antennas in specific scenarios and enhances their adaptability and practicality in multiple fields.

[0027] This invention discloses an assembly method for a miniaturized log-periodic antenna. Firstly, regarding process adaptability and performance assurance, the method employs a step-by-step design: "first forming a pre-defined copper layer for the vibrator structure on both sides of the dielectric substrate, then creating a block-shaped notch at the pre-defined vibrator location." This precisely achieves standardized forming of the vibrator structure and allows for targeted removal of the copper layer in low-current regions of the vibrator, effectively adjusting impedance matching and ensuring an antenna performance index of ≤2 VSWR in the 150MHz-400MHz frequency band. Simultaneously, it avoids interference from subsequent processing on the effective radiation area of ​​the vibrator, ensuring the stability of gain and radiation direction over a wide frequency band. Secondly, regarding assembly efficiency and connection reliability, the semi-steel cable adopts a step-by-step welding method: "welding the outer shell to the copper layer on the back center line of the substrate, and bending and welding the inner core to the copper layer end face on the front." This clear and precise operation process simplifies the assembly difficulty of the feed structure, strengthens the electrical connection stability between the cable and the copper layer, reduces reflection and loss during signal transmission, and adapts to the structural characteristics of the semi-steel cable, ensuring mechanical strength at the bend and adapting to the vibration conditions of mobile devices. Finally, regarding structural integration and scenario adaptability, the step of fixing the adapter board to the other side of the dielectric substrate further enhances the overall structural robustness of the antenna. This allows the assembled antenna to stably adapt to installation scenarios such as vehicle mounts and portable device interfaces. Furthermore, the entire assembly process requires no complex specialized equipment, exhibits strong process compatibility, and facilitates mass production, efficiently meeting the large-scale application needs of antennas in fields such as civilian dispatching and public safety. In summary, this assembly method, through rational planning of steps, not only ensures the antenna's electrical performance indicators but also improves assembly efficiency and structural reliability, effectively supporting the miniaturized and lightweight deployment requirements of antennas in multiple scenarios.

[0028] This invention discloses a design method for a miniaturized log-periodic antenna. First, regarding frequency band adaptation and performance accuracy, the method employs a process of "first determining the lowest and highest operating frequencies of the target operating frequency band, and then calculating the length, number, and spacing of the elements by combining parameters such as scaling factor and spacing factor." This achieves precise matching of the antenna structure with the 150MHz-400MHz target frequency band, ensuring the coverage capability of the longest element for the lower frequency band while avoiding performance degradation in the higher frequency band through the reasonable design of the shortest element. This effectively solves the problem of balancing wide bandwidth and performance stability in traditional designs, ensuring that the antenna maintains stable impedance and gain within the target frequency band. Secondly, regarding the balance between miniaturization and electrical performance, the design approach of "extending dipole stubs to increase electrical length" can meet the requirements for the electric length of the vibrator in the low-frequency band without increasing the physical size, directly supporting the goal of antenna miniaturization. Simultaneously, the step of "identifying low-current regions and removing part of the copper layer" adjusts impedance matching without affecting effective radiation, further ensuring a VSWR ≤2 performance index. This achieves a balance between miniaturization and wide-band high performance, adapting to the needs of deployment scenarios in confined spaces such as vehicle-mounted and portable applications. Finally, regarding structural rationality and radiation stability, the "parallel arrangement of vibrators + cross-feeding" design ensures that the phase difference of the output voltage of adjacent vibrators remains stable at 180°, guaranteeing the consistency of the antenna's polarization radiation direction and avoiding the radiation direction deviation problem under traditional feeding methods. This allows for stable adaptation to the signal transmission and reception needs of scenarios such as civilian dispatching and public safety. Furthermore, the quantitative calculation of the gradual change law of vibrator length and spacing makes the antenna structure design more standardized and replicable, facilitating rapid parameter adjustment according to different sub-band requirements and improving design flexibility and adaptability. In summary, this design method, through the combination of parameter quantification calculation and structural optimization, not only accurately achieves the performance coverage of the target frequency band, but also efficiently meets the miniaturization requirements, while ensuring the radiation stability and design flexibility of the antenna, effectively supporting its application value in multiple scenarios. Attached Figure Description

[0029] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 This is a schematic diagram of the overall structure of a miniaturized log-periodic antenna according to an embodiment of the present invention; Figure 2 This is a top view of a miniaturized log-periodic antenna according to an embodiment of the present invention; Figure 3This is a bottom view of a miniaturized log-periodic antenna according to an embodiment of the present invention; Figure 4 This is a side view of a miniaturized log-periodic antenna according to an embodiment of the present invention; Figure 5 This is a schematic diagram of the log-periodic antenna structure in an embodiment of the present invention; Figure 6 This is a diagram showing the relationship between the parameters and directivity of a log-periodic antenna in an embodiment of the present invention. Figure 7 This is a schematic diagram of the working region of the log-periodic antenna in an embodiment of the present invention; Figure 8 The passive voltage standing wave ratio (VSWR) in the simulation results of this embodiment of the invention; Figure 9 This is a two-dimensional orientation pattern from the simulation results of an embodiment of the present invention; Figure 10 This is a two-dimensional polarization pattern from the simulation results of an embodiment of the present invention.

[0031] Wherein: 1-Dielectric substrate; 2-Semi-steel cable; 3-Adapter board; 4-Copper layer; 201-Inner core; 202-Insulation layer; 203-Outer shell. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0033] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0034] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0035] In the description of the embodiments of the present invention, it should be noted that if terms such as "upper," "lower," "horizontal," or "inner" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of the invention is in use, they are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention. Furthermore, terms such as "first" and "second" are only used to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0036] Furthermore, the use of the term "horizontal" does not imply that the component must be absolutely horizontal, but rather that it can be slightly tilted. For example, "horizontal" simply 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.

[0037] In the description of the embodiments of the present invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in the present invention according to the specific circumstances.

[0038] The present invention will now be described in further detail with reference to the accompanying drawings: See Figure 1 , Figure 2 , Figure 3 and Figure 4This invention discloses a miniaturized log-periodic antenna, comprising a dielectric substrate 1, a semi-steel cable 2, an adapter plate 3, and a copper layer 4. The copper layer 4 is disposed on the front and back sides of the dielectric substrate 1. The adapter plate 3 is disposed at one end of the dielectric substrate 1. The outer shell of the semi-steel cable 2 is welded to the copper layer at the center line of the back side of the dielectric substrate 1, and the inner core of the semi-steel cable 2 is bent upwards through the side of the dielectric substrate 1 without the adapter plate 3 and then welded to the copper layer 4 on the front side of the dielectric substrate 1. The antenna operates in the frequency band of 150MHz-400MHz, has a VSWR ≤2, and uses linear polarization. At 250MHz and phi=90°, the maximum gain is ≥3.6dBi, and the antenna weight is <1.7kg. The dielectric substrate is a GNC3010 dielectric substrate with a dielectric constant of 10.2, a dielectric loss tangent of 0.0023, and a density of 2.7g / cm³. The dimensions of the dielectric substrate are 660mm×460mm×4mm. The copper layer 4 includes a front copper layer and a back copper layer. Both the front and back copper layers have several pairs of vibrators, and several pairs of vibrators in both layers have block-shaped notches for adjusting impedance matching. The pairs of vibrators are arranged in parallel, with the vibrator length gradually increasing from the front to the rear of the antenna. The antenna's feed point is located at one end of the shortest vibrator. Adjacent vibrators are cross-fed. The longest vibrator in the antenna is half the wavelength corresponding to the lowest operating frequency, and the shortest vibrator is less than half the wavelength corresponding to the highest operating frequency. The semi-steel cable 2 is a 50Ω semi-steel cable.

[0039] This invention discloses a miniaturized log-periodic antenna. First, in terms of frequency band coverage and performance stability, this antenna can stably cover the target wide frequency band of 150MHz-400MHz with a VSWR ≤2, effectively solving the problems of gain attenuation and poor impedance matching in the low frequency band of 150-225MHz of traditional log-periodic antennas. This ensures the signal transmission quality in obstructed scenarios such as tunnels, large stadiums, etc. At the same time, it maintains stable high gain and anti-interference capability in the 350MHz public safety core frequency band, which can meet the "bottom-line" communication needs of key scenarios such as emergency command and public security duty. Secondly, regarding miniaturization and lightweight adaptability, the integrated structure design of the dielectric substrate and copper layer, combined with the optimization of the vibrator structure, significantly reduces the overall size and weight of the antenna. Compared to traditional commercial products (larger than 800mm×500mm in size and weighing ≥3kg), it is more suitable for installation in confined spaces or mobile deployment scenarios such as vehicle-mounted communication equipment and portable emergency terminals, improving the antenna's deployment flexibility in complex environments and efficiently matching the usage conditions of limited installation spaces such as tunnel equipment compartments and vehicle-mounted brackets. Finally, regarding power supply and structural reliability, the semi-steel cable adopts a power supply method of "welding the copper layer on the back of the substrate to the outer shell and bending and welding the copper layer on the front of the inner core," which not only ensures the stability of signal transmission but also simplifies the assembly process. Combined with the fixed design of the adapter plate, it further enhances the structural robustness of the antenna, making it adaptable to complex operating conditions such as vibration and bumps of mobile devices. At the same time, the adoption of linear polarization ensures the consistency of the antenna's radiation direction within the target frequency band, enabling stable adaptation to the signal transmission and reception needs of various scenarios such as civilian dispatching, public safety, and scientific research observation. In summary, this invention achieves a balance of high performance, miniaturization, and lightweight design within the target wideband through structural and feeding method optimization. It effectively fills the application gaps of traditional log-periodic antennas in specific scenarios and enhances their adaptability and practicality in multiple fields.

[0040] This invention also discloses an assembly method for a miniaturized log-periodic antenna, comprising: The dielectric substrate 1 is subjected to copper stripping and surface treatment, and copper layers 4 with preset oscillator structures are formed on the front and back sides of the dielectric substrate 1. Block-shaped notches are cut at the preset oscillator locations of the front and back copper layers. The outer shell of the semi-steel cable 2 is welded onto the copper layer 4 located at the center line of the back side of the dielectric substrate 1. The inner core of the semi-steel cable 2 is bent upward from one side of the dielectric substrate 1 and soldered to the end face of the copper layer 4 on the front side of the dielectric substrate 1. Fix the adapter plate 3 to the other side of the dielectric substrate 1 to complete the antenna assembly.

[0041] This invention discloses an assembly method for a miniaturized log-periodic antenna. Firstly, regarding process adaptability and performance assurance, the method employs a step-by-step design: "first forming a pre-defined copper layer for the vibrator structure on both sides of the dielectric substrate, then creating a block-shaped notch at the pre-defined vibrator location." This precisely achieves standardized forming of the vibrator structure and allows for targeted removal of the copper layer in low-current regions of the vibrator, effectively adjusting impedance matching and ensuring an antenna performance index of ≤2 VSWR in the 150MHz-400MHz frequency band. Simultaneously, it avoids interference from subsequent processing on the effective radiation area of ​​the vibrator, ensuring the stability of gain and radiation direction over a wide frequency band. Secondly, regarding assembly efficiency and connection reliability, the semi-steel cable adopts a step-by-step welding method: "welding the outer shell to the copper layer on the back center line of the substrate, and bending and welding the inner core to the copper layer end face on the front." This clear and precise operation process simplifies the assembly difficulty of the feed structure, strengthens the electrical connection stability between the cable and the copper layer, reduces reflection and loss during signal transmission, and adapts to the structural characteristics of the semi-steel cable, ensuring mechanical strength at the bend and adapting to the vibration conditions of mobile devices. Finally, regarding structural integration and scenario adaptability, the step of fixing the adapter board to the other side of the dielectric substrate further enhances the overall structural robustness of the antenna. This allows the assembled antenna to stably adapt to installation scenarios such as vehicle mounts and portable device interfaces. Furthermore, the entire assembly process requires no complex specialized equipment, exhibits strong process compatibility, and facilitates mass production, efficiently meeting the large-scale application needs of antennas in fields such as civilian dispatching and public safety. In summary, this assembly method, through rational planning of steps, not only ensures the antenna's electrical performance indicators but also improves assembly efficiency and structural reliability, effectively supporting the miniaturized and lightweight deployment requirements of antennas in multiple scenarios.

[0042] This invention also discloses a design method for a miniaturized log-periodic antenna, comprising: Step 1: Determine the target operating frequency band of the antenna, and clarify the minimum and maximum operating frequencies corresponding to the target operating frequency band; Step 2: Determine the antenna's scaling factor τ, spacing factor σ, and antenna apex angle α; The lengths of the longest and shortest elements of the antenna are expressed as follows: The endpoints of the vibrator are connected by lines, and the intersection of the extensions of the two lines forms a virtual vertex. The vertical distance from the virtual vertex to the antenna vibrator is determined by... The distance between adjacent elements of the antenna is expressed as... Representation; scaling factor Defined as the ratio of the length of the shorter element to the length of the longer element in an antenna's adjacent elements:

[0043] Among them, the oscillator spacing and the vertical distance from the virtual vertex to the oscillator The relationship between them is represented as follows:

[0044] The included angle between the connecting lines at the ends of the antenna element is called the apex angle. The expression is:

[0045] Oscillator Spacing It can be used through the scaling factor oscillator length and included angle Represented as:

[0046] To facilitate the description of log-periodic antennas, another parameter is introduced: the antenna spacing factor. Its definition is:

[0047] Antenna spacing factor , scaling factor and antenna apex The following relationship exists between them: .

[0048] Step 3: Calculate the longest element length of the antenna based on the lowest operating frequency, determine the shortest element length of the antenna based on the highest operating frequency, and calculate the structural bandwidth S and the number of elements N of the antenna. The length of the longest element in the antenna Represented as:

[0049] Length of the shortest element of the antenna Represented as: .

[0050] The formula for calculating the number of elements in a log-periodic antenna is:

[0051] in, For structure bandwidth; Antenna operating bandwidth Defined as the ratio between the antenna's highest operating frequency and its lowest operating frequency:

[0052] in, The structure bandwidth is expressed as:

[0053] The average bandwidth of the antenna's radiation region: .

[0054] Step 4: According to the number of oscillators N, the gradual change law of oscillator length and the spacing d between adjacent oscillators, design a parallel oscillator structure and adopt a cross-feeding form to make the output voltage of adjacent oscillators 180° out of phase. Step 5: Extend the current path by using the design method of extending the dipole stub, thereby increasing the electrical length within the same physical size and realizing antenna miniaturization; Step six: Identify the low-current region of the oscillator, remove part of the copper layer in the low-current region to adjust impedance matching, and complete the design of the miniaturized log-periodic antenna.

[0055] The length of the miniaturized log-periodic antenna Calculated using the following formula: .

[0056] This invention discloses a design method for a miniaturized log-periodic antenna. First, regarding frequency band adaptation and performance accuracy, the method employs a process of "first determining the lowest and highest operating frequencies of the target operating frequency band, and then calculating the length, number, and spacing of the elements by combining parameters such as scaling factor and spacing factor." This achieves precise matching of the antenna structure with the 150MHz-400MHz target frequency band, ensuring the coverage capability of the longest element for the lower frequency band while avoiding performance degradation in the higher frequency band through the reasonable design of the shortest element. This effectively solves the problem of balancing wide bandwidth and performance stability in traditional designs, ensuring that the antenna maintains stable impedance and gain within the target frequency band. Secondly, regarding the balance between miniaturization and electrical performance, the design approach of "extending dipole stubs to increase electrical length" can meet the requirements for the electrical length of the vibrator in the low-frequency band without increasing the physical size, directly supporting the goal of antenna miniaturization. Simultaneously, the step of "identifying low-current regions and removing part of the copper layer" adjusts impedance matching without affecting effective radiation, further ensuring a VSWR ≤2 performance index. This achieves a balance between miniaturization and wide-band high performance, adapting to the needs of deployment scenarios in confined spaces such as vehicle-mounted and portable applications. Finally, regarding structural rationality and radiation stability, the "parallel arrangement of vibrators + cross-feeding" design ensures that the phase difference of the output voltage of adjacent vibrators remains stable at 180°, guaranteeing the consistency of the antenna's linear polarization radiation direction and avoiding the radiation direction deviation problem under traditional feeding methods. This allows for stable adaptation to the signal transmission and reception needs of scenarios such as civilian dispatching and public safety. Furthermore, the quantitative calculation of vibrator spacing makes the antenna structure design more standardized and replicable, facilitating rapid parameter adjustments according to different sub-band requirements, and improving design flexibility and adaptability. In summary, this design method, through the combination of parameter quantification calculation and structural optimization, not only accurately achieves the performance coverage of the target frequency band, but also efficiently meets the miniaturization requirements, while ensuring the radiation stability and design flexibility of the antenna, effectively supporting its application value in multiple scenarios.

[0057] The working principle of this invention is as follows: This invention proposes a novel miniaturized log-periodic antenna. The antenna is linearly polarized, with a normal gain greater than 3dB. It radiates electromagnetic waves directionally, exhibiting a standing wave ratio (SWR) ≤2 within the 150MHz–350MHz range, covering 80% of the relative bandwidth. The antenna weighs approximately 1.6kg. The antenna assembly process is as follows: First, the dielectric substrate 1 undergoes copper stripping and surface treatment, leaving a copper layer 4. Then, the outer shell of a 50Ω semi-steel cable 2 is soldered onto the copper layer 4 at the center line of the back side of the dielectric substrate 1. The inner core of the semi-steel cable 2 is bent upwards from the rightmost side of the dielectric substrate 1 and soldered to the right end face of the copper layer 4 on the front side of the dielectric substrate 1. Finally, the adapter plate 3 is fixed onto the dielectric substrate.

[0058] See Figure 5There are many types of log-periodic antennas, among which the most widely used is the log-periodic dipole antenna array composed of several pairs of dipoles. The antenna's feed point is located at one end of a short dipole, and the dipole lines are arranged in parallel. The lengths of the symmetrical dipole lines vary according to a certain ratio, with the dipole length gradually increasing from the front end to the rear end of the antenna. Dips of different lengths resonate at different frequencies, which means that the log-periodic antenna resonates at fixed discrete frequencies. By satisfying the self-similarity condition, the antenna exhibits non-frequency-varying characteristics, with its VSWR, impedance, gain, and other electrical properties remaining constant over a wide frequency band. The log-periodic antenna uses a cross-feed configuration between adjacent elements, with the transmission line swapping positions between nearby elements. This results in a 180° phase difference between the output voltages of adjacent elements, causing the output phase at the short element end to lag behind the phase at the long element end. This allows the power of the vertically polarized log-periodic antenna to be emitted from the short element end. In this case, the short element of the log-periodic antenna acts as a guide, while the long element acts as a reflector, thus improving the antenna gain. The port at the antenna end (the long element end) can be open-circuited or connected to a matching load or short-circuit line to reduce the reflection of the end current. Connecting a load or short-circuit line effectively introduces the antenna end current into the load and short-circuit stubs, resulting in better port matching performance at the antenna front end and reduced antenna reflection. The operating frequency range of a log-periodic antenna is determined by the lengths of its shortest and longest elements. The shortest element determines the highest frequency, and the longest element determines the lowest frequency. Generally, the length of the longest element is half the wavelength corresponding to the lowest operating frequency, while the length of the shortest element, considering the antenna's high-frequency radiation characteristics, is usually less than half the wavelength corresponding to the highest operating frequency.

[0059] The lengths of the longest and shortest elements of the antenna are expressed as follows: The ends of the antenna element are connected by lines, and the intersection of the extensions of the two lines forms a virtual vertex. The perpendicular distance from the virtual vertex to the antenna element is... The distance between adjacent elements of the antenna is expressed as... express.

[0060] Scale factor Defined as the ratio of the length of the shorter element to the length of the longer element in an antenna's adjacent elements:

[0061] The spacing between the oscillators and the vertical distance from the virtual vertex to the oscillator The relationship between them can be represented as:

[0062] The included angle between the connecting lines at the ends of the antenna element is called the apex angle. Its expression is:

[0063] The derivation shows that the oscillator spacing It can be used through the scaling factor oscillator length and included angle Represented as:

[0064] In engineering, another parameter is usually introduced to facilitate the description of log-periodic antennas: the antenna spacing factor. Its definition is:

[0065] The derivation shows that the antenna spacing factor , scaling factor and apex The following relationship exists between them:

[0066] From the above formula, we can see that the antenna spacing factor , scaling factor and apex The three parameters are interconnected; knowing just two of them is sufficient to obtain the antenna structure dimensions. Figure 6 As shown, the variation pattern of the logarithmic periodic antenna can be determined.

[0067] In actual simulations, the width of the dipole stub also affects the antenna's impedance matching, but its impact is relatively small and not considered a critical parameter. In the actual design of log-periodic antennas, since the scaling factor is known... Given a fixed number of antenna stubs, the ratio of the longest to the shortest stub can be determined, thus providing the antenna's relative bandwidth.

[0068] When the antenna scaling factor and interval factor Once determined, in order to determine the length of the dipole of the log-periodic antenna, it is first necessary to determine the lengths of the longest and shortest dipoles of the antenna.

[0069] The length of the longest element of the antenna Represented as:

[0070] The length of the shortest element of the antenna Represented as:

[0071] The formula for calculating the number of elements in a log-periodic antenna is:

[0072] in, This refers to the structure bandwidth.

[0073] Antenna operating bandwidth Defined as the ratio between the antenna's highest operating frequency and its lowest operating frequency:

[0074] in, The structure bandwidth is expressed as:

[0075] The average bandwidth of the antenna's radiation region:

[0076] Length of a log-periodic antenna The expression is:

[0077] Log-periodic antennas are typically miniaturized using fractal structures, end loading, and other methods. Limited by the radiation modes of the dipole, miniaturization is achieved by extending the dipole stub design, thus lengthening the current path within the same physical size, thereby obtaining a longer electrical length and ultimately realizing the antenna miniaturization goal.

[0078] The electrical performance of a log-periodic antenna remains constant over a wide operating frequency band, a characteristic primarily determined by the antenna's specific structure. After being fed from the feed point, electromagnetic energy propagates backward along the antenna's centerline. When this energy reaches a resonant length close to the current operating frequency, the antenna element resonates and radiates electromagnetic waves in free space. The other elements of the antenna play different roles. Based on these roles, a log-periodic antenna can be divided into three regions: the transmission region, the radiation region, and the unexcited region. Figure 7 As shown.

[0079] The essence of standing waves is the mismatch between the antenna input impedance and the feed line impedance, which causes the radio frequency signal to be unable to be fully radiated, and some of the signal is reflected back to the transmission line and superimposed. Figure 7 The current distribution is strong in the effective radiation region, while the current distribution in the unexcited region far from the feed point is extremely small. Although these low-current regions do not participate in effective radiation, they introduce additional impedance components as ineffective structures. Therefore, in Figure 5In the middle, a rectangular block of copper layer is removed from the fifth pair of oscillators on the front and back sides of copper layer 4. The current distribution in this area is extremely small. The removed part can reduce signal reflection without affecting antenna radiation, thereby reducing the standing wave ratio.

[0080] Simulation results are as follows Figures 8-10 As shown, Figure 8 It is the passive voltage standing wave ratio (VSWR). The horizontal axis is the frequency, and the vertical axis is the passive voltage VSWR. The VSWR is ≤2.0516 in the frequency range of 150MHz-350MHz, and <2 in the frequency bands of 236±3MHz, 281±3MHz, and 321±3MHz. The relative bandwidth of VSWR ≤2 is 94% (152.74MHz-424.98MHz). Figure 9 This is the gain pattern at 250MHz, with a maximum gain of 3.6dBi at phi=90°. Figure 10 It is the polarization gain pattern at 250MHz. The cross-polarization level is 42dB when phi=90°, indicating high polarization purity and obvious polarization.

[0081] The novel miniaturized log-periodic antenna of the present invention has the following beneficial effects: (1) The antenna has a simple structure and feeding method, excellent electrical performance, and features lightweight, miniaturization and low cost, with a weight of <1.7kg; (2) The antenna has a wide bandwidth, with a standing wave ratio (SWR) of ≤2.0516 in the frequency range of 150MHz-350MHz, and a SWR of <2 in the frequency bands of 236±3MHz, 281±3MHz and 321±3MHz. The relative bandwidth of SWR ≤2 is 94% (152.74MHz-424.98MHz); (3) The antenna polarization mode is linear polarization, and the polarization purity is high and the polarization is obvious.

[0082] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A miniaturized log-periodic antenna, characterized in that, The antenna includes a dielectric substrate (1), a semi-steel cable (2), an adapter plate (3), and a copper layer (4). The copper layer (4) is disposed on the front and back sides of the dielectric substrate (1). An adapter plate (3) is disposed at one end of the dielectric substrate (1). The outer shell of the semi-steel cable (2) is welded to the copper layer at the center line position on the back side of the dielectric substrate (1). The inner core of the semi-steel cable (2) is bent upward through the side of the dielectric substrate (1) without the adapter plate (3) and then welded to the copper layer (4) on the front side of the dielectric substrate (1). The antenna operates in the frequency band of 150MHz-400MHz, has a standing wave ratio ≤2, and adopts linear polarization.

2. The miniaturized log-periodic antenna according to claim 1, characterized in that, The copper layer (4) includes a front copper layer and a back copper layer. Both the front copper layer and the back copper layer are provided with several pairs of oscillators. Several pairs of oscillators in the front copper layer and the back copper layer are provided with block-shaped notches for adjusting resistance matching.

3. The miniaturized log-periodic antenna according to claim 2, characterized in that, The several pairs of vibrators are arranged in parallel, with the length of the vibrators gradually increasing from the front end to the rear end of the antenna. The feed point of the antenna is located at one end of the short vibrator. Adjacent vibrators are fed in a cross-feed configuration.

4. The miniaturized log-periodic antenna according to claim 3, characterized in that, The longest element of the antenna is half the wavelength corresponding to the lowest operating frequency, and the shortest element is less than half the wavelength corresponding to the highest operating frequency; the semi-steel cable (2) is a 50Ω semi-steel cable.

5. A method for assembling a miniaturized log-periodic antenna based on the antenna described in any one of claims 1-4, characterized in that, include: The dielectric substrate (1) is subjected to copper stripping and surface treatment, and a copper layer (4) with a preset oscillator structure is formed on the front and back sides of the dielectric substrate (1), and a block-shaped notch is cut at the preset oscillator of the front copper layer and the back copper layer. The outer shell of the semi-steel cable (2) is welded onto the copper layer (4) at the center line position on the back side of the dielectric substrate (1); The inner core of the semi-steel cable (2) is bent upward from one side of the dielectric substrate (1) and soldered to the end face of the copper layer (4) on the front side of the dielectric substrate (1). The adapter plate (3) is fixed on the other side of the dielectric substrate (1) to complete the antenna assembly.

6. A method for designing a miniaturized log-periodic antenna based on the antenna described in any one of claims 1-4, characterized in that, include: Determine the target operating frequency band of the antenna, and clarify the minimum and maximum operating frequencies corresponding to the target operating frequency band; Determine the antenna's scaling factor τ, spacing factor σ, and antenna apex angle α; The longest element length of the antenna is calculated based on the lowest operating frequency, the shortest element length of the antenna is determined based on the highest operating frequency, and the structural bandwidth S and the number of elements N of the antenna are calculated. Based on the scaling factor τ, the length of the vibrator, and the antenna apex angle α, the spacing d between adjacent vibrators is calculated, and the gradual change law of the vibrator length is obtained. Based on the number of oscillators N, the gradual change law of oscillator length and the spacing d between adjacent oscillators, a parallel oscillator structure is designed, and a cross-feeding method is adopted to make the output voltage of adjacent oscillators 180° out of phase. By using a design that extends the dipole stub, the current path is extended, increasing the electrical length within the same physical size, thus achieving antenna miniaturization. The low-current region of the oscillator is identified, and part of the copper layer is removed in the low-current region to adjust the impedance matching, thus completing the design of a miniaturized log-periodic antenna.

7. The design method for a miniaturized log-periodic antenna according to claim 6, characterized in that, The determination of the antenna's scaling factor τ, spacing factor σ, and antenna apex angle α specifically involves: The lengths of the longest and shortest elements of the antenna are expressed as follows: The endpoints of the vibrator are connected by lines, and the intersection of the extensions of the two lines forms a virtual vertex. The vertical distance from the virtual vertex to the antenna vibrator is determined by... The distance between adjacent elements of the antenna is expressed as... express; Scale factor Defined as the ratio of the length of the shorter element to the length of the longer element in an antenna's adjacent elements: Among them, the oscillator spacing and the vertical distance from the virtual vertex to the oscillator The relationship between them is represented as follows: The included angle between the connecting lines at the ends of the antenna element is called the apex angle. The expression is: Oscillator Spacing Through the scaling factor oscillator length and included angle Represented as: To facilitate the description of log-periodic antennas, another parameter is introduced: the antenna spacing factor. Its definition is: Antenna spacing factor , scaling factor and antenna apex The following relationship exists between them: 。 8. The design method for a miniaturized log-periodic antenna according to claim 7, characterized in that, The longest antenna element length is calculated based on the lowest operating frequency, and the shortest antenna element length is determined based on the highest operating frequency, specifically as follows: The length of the longest element in the antenna Represented as: Length of the shortest element of the antenna Represented as: 。 9. The design method for a miniaturized log-periodic antenna according to claim 8, characterized in that, The specific calculation of the antenna's structural bandwidth S and the number of elements N is as follows: The formula for calculating the number of elements in a log-periodic antenna is: in, For structure bandwidth; Antenna operating bandwidth Defined as the ratio between the antenna's highest operating frequency and its lowest operating frequency: in, The structure bandwidth is expressed as: The average bandwidth of the antenna's radiation region: 。 10. The design method for a miniaturized log-periodic antenna according to claim 9, characterized in that, The length of the miniaturized log-periodic antenna Calculated using the following formula: 。

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