Folding spiral arm loaded back cavity type four-arm spiral antenna and preparation method thereof

Abstract

The invention relates to a cavity-backed four-arm helical antenna loaded by a folding helical arm and a preparation method of the cavity-backed four-arm helical antenna. The cavity-backed four-arm helical antenna comprises a radiation unit, a parasitic radiation unit, a coaxial slotted balun structure, an SMA connector, an outer metal cavity and a top waterproof cover, the radiation unit comprises four spiral arm units which are arranged at the top end and the bottom end of the coaxial slotted balun in a circumferential array manner; the parasitic radiation unit is composed of a flexible PCB and a hollow cylindrical supporting piece. A parasitic folding spiral arm is etched on the surface of the flexible PCB. The inner wall of the hollow cylindrical supporting piece is bonded with the non-metal surface of the flexible PCB to serve as a support; the coaxial slotted balun structure is used as a feeding and supporting structure to be connected with the SMA connector and the central spiral arm; the outer metal cavity is connected with the antenna metal ground; the top layer waterproof cover is connected with the outer side metal wall in an embedded mode. The antenna provided by the invention is high in radiation efficiency and good in impedance bandwidth characteristic in buried and underground pipeline application, and has good circular polarization characteristic and omnidirectional characteristic in a frequency band range.

Description

Technical Field

[0001] The present application relates to the field of Internet of Things and wireless communication technology, and in particular to a cavity-backed four-arm helical antenna loaded with folded helical arms and a preparation method thereof. Background Art

[0002] The helical antenna was first proposed in the 1940s and has been gradually improved with the advancement of theory and scientific research tools. The four-arm helical antenna is developed from the axial mode single helical antenna. The radiator of the four-arm helical antenna is four rotating spiral arms, and the length of the spiral arm is an integer multiple of one quarter wavelength, that is, N×λ / 4: when the antenna terminal is short-circuited, N is an odd number; when the antenna terminal is open-circuited, N is an even number. For the feeding of the spiral arm, the self-phase shift feeding of the four arms is realized by the antenna itself. By making the length of one pair of arms slightly larger than the resonant length, the phase lags, and the length of the other pair of arms is smaller than the resonant length, the phase leads. When the length is selected appropriately, the phase difference can be exactly 90°, realizing circular polarization performance. By changing the sequential mode of the phase difference, the required left-handed or right-handed circular polarization can be achieved. In recent years, the four-arm spiral antenna has been widely used in the field of satellite communication technology due to its small size, compact structure, good circular polarization characteristics, and good front-to-back ratio.

[0003] In the past few decades, with the development of related software and hardware technologies and the continuous growth of various demands, the wide applicability and access convenience unique to mobile wireless communications have enabled it to gradually expand from communication between people to the interconnection of "everything" between people and things, and things and things. The era of the Internet of Everything is coming. In the current 5G era, with the popularization of "smart cities", narrowband Internet of Things frequency bands are widely used. In order to realize the remote collection of sensor data, it is necessary to transmit the data to the base station through the antenna for processing. However, the environment in which the sensor is located is often complex and changeable (such as underground pipelines, soil, human body wear, etc.), which puts higher requirements on the performance of the antenna.

[0004] In the application of narrowband IoT frequency band for underground pipeline management and soil detection, the environment has a very large attenuation on the antenna. When the antenna is placed under the manhole cover or buried in the soil, the attenuation of the antenna signal reaches more than 15dB, and almost most of the electromagnetic wave energy is reflected and absorbed by the manhole cover and soil. The sensor data in the well and soil cannot be transmitted smoothly, which greatly increases the management and maintenance difficulty of manhole cover maintenance and soil detection.

[0005] In order to cope with the above-mentioned complex environment, the transmitting antenna usually adopts a circularly polarized cavity-backed antenna. Compared with linearly polarized signals, the use of circularly polarized signals in complex electromagnetic environments can effectively reduce the interference caused by multipath signals and has little effect on the transmission quality of the signal. At the same time, the existence of the metal cavity minimizes the impact of the environment on the antenna matching. At present, conventional circularly polarized cavity-backed antennas include cross-diopter antennas, microstrip antennas, horn antennas and other antennas. The cross-diopter cavity-backed antenna has a simple structure, but the feeding network is complex and the size is large in the low frequency band. The circularly polarized microstrip cavity-backed antenna has a flexible design, but it has the disadvantages of narrow antenna bandwidth and complex feeding network; the circularly polarized horn antenna has good broadband characteristics and is less affected by the environment, but due to the use of a waveguide transmission structure, the antenna has the disadvantages of being large in size and too high in profile height.

[0006] Although the four-arm helical antenna is small in size and compact in structure, it can achieve a hemispherical radiation beam and good wide-angle axial ratio characteristics. Its radiation performance is less affected by the carrier and has many advantages. However, the antenna bandwidth is narrow and due to the lack of a back cavity structure, it is greatly affected by the environment and is not suitable for installation in a soil environment. Summary of the invention

[0007] The purpose of the present invention is to overcome the deficiencies in the background technology and to provide a cavity-backed quadrifilar helical antenna loaded with folded helical arms and a method for preparing the same.

[0008] In order to solve the above technical problems, the present invention provides a cavity-backed quadrifilar helical antenna loaded with folded helical arms, comprising a radiating unit, a parasitic radiating unit, a coaxial slotted balun structure, an SMA connector, an outer metal cavity and a top waterproof cover;

[0009] The radiation unit includes four spiral arm units, which constitute two pairs of central spiral arm units; the spiral arm units are arranged in a circular array at the top and bottom of the coaxial slotted balun structure;

[0010] The parasitic radiation unit comprises a flexible PCB board and a hollow cylindrical support, the parasitic folded spiral arm is etched on the surface of the PCB board; the inner wall of the hollow cylindrical support is bonded to the non-metallic surface of the flexible PCB board;

[0011] The bottom end of the coaxial slotted balun structure passes through the central circular hole of the metal bottom plate and is connected to the inner conductor of the connector, and the outer conductor of the coaxial slotted balun and the outer conductor of the connector are both connected to the metal bottom plate. The SMA connector passes through the central circular hole of the metal bottom plate and is connected to the coaxial slotted balun structure; the outer metal cavity is connected to the antenna ground; and the top waterproof cover is connected to the outer metal cavity in an inlaid manner.

[0012] In a preferred embodiment, there are four parasitic folded spiral arms, which are rotationally symmetrically distributed and have arbitrary angles relative to the central spiral arm unit.

[0013] In a preferred embodiment, the parasitic folded spiral arm is 0.5 turns, and the number of bends is adjusted according to the required resonance length.

[0014] In a preferred embodiment: the outer metal cavity has a diameter consistent with that of the antenna, and a height consistent with that of the coaxial slotted balun structure.

[0015] In a preferred embodiment: when the radiation unit is excited, the parasitic folded spiral arm is parasitic.

[0016] In a preferred embodiment, the parasitic folded spiral arm and the antenna ground are in an open circuit structure or a short circuit structure.

[0017] The present invention also provides a method for preparing a cavity-backed quadrifilar helical antenna loaded with folded helical arms, comprising the following steps:

[0018] Step 1, four antennas are respectively wound 0.5 turns to form two pairs of central spiral arm units, each pair of central spiral arm units is symmetrical about the origin, and are arranged in a circular array at the top and bottom of the coaxial slotted balun structure;

[0019] The circumference of the central spiral arm unit is determined according to the formula l=c / f, where l represents the circumference of one spiral turn, c represents the speed of light, and f represents the operating frequency;

[0020] The circumferences of the two pairs of central spiral arm units are set as follows: the circumference of one pair of central spiral arm units is greater than l, and the circumference of the other pair of central spiral arm units is less than l;

[0021] Step 2, two pairs of central spiral arm units are fed using a coaxial slotted balun structure, and the slot depth and width are determined according to the size of the central spiral arm unit and in combination with the parasitic folded spiral arm and the metal cavity;

[0022] Step 3, by etching two pairs of folded spiral arm units on the flexible PCB board, the sizes of the two pairs of folded spiral arm units are determined according to the operating frequency of the spiral antenna, one pair of folded spiral arm units is larger than half the wavelength of the operating frequency, and the other pair of folded spiral arm units is smaller than half the wavelength of the operating frequency; the flexible PCB board is bonded to the parasitic unit support;

[0023] The flexible PCB board is an FPC soft board, and the parasitic unit support is a PVC board;

[0024] Step 4, the central spiral arm unit, the coaxial slotted balun structure and the SMA connector are welded and integrated, and integrated with the parasitic unit, the metal cavity and the top waterproof cover to obtain a cavity-backed four-arm spiral antenna loaded with a folded spiral arm;

[0025] Step 5: Use a vector network and a microwave darkroom to test the above antenna.

[0026] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0027] 1. The present invention discloses a cavity-backed quadrifilar helical antenna loaded with folded helical arms, which has a gain greater than 5dBi within the working bandwidth, good omnidirectionality, and a half-power beam width coverage range of more than 100°.

[0028] 2. The present invention introduces new resonance by designing the size of the folded spiral arm of the metal cavity and the size of the metal cavity, thereby broadening the antenna bandwidth. The antenna has a compact structure and good mechanical properties, and the final volume of the antenna is φ0.5λ×0.31λ.

[0029] 3. The present invention prevents the energy of the antenna from being lost by the soil by adding a metal cavity outside the four-arm helical antenna, thereby greatly improving the radiation efficiency of the four-arm helical antenna in underground applications.

[0030] 4. The antenna of the present invention has high radiation efficiency, good impedance bandwidth characteristics, and good circular polarization characteristics within a wide bandwidth, and can be widely used in various buried, underground, and underground circular polarization communication systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a schematic diagram of the overall decomposition structure of the antenna of the present invention;

[0032] Figure 2 is a three-dimensional view of the waterproof cover on the top of the antenna of the present invention;

[0033] Figure 3 It is a three-dimensional view of the antenna unit, parasitic unit and feeding structure of the present invention;

[0034] Figure 4 is a three-dimensional schematic diagram of a single arm of the parasitic folded spiral arm of the present invention;

[0035] Figure 5 A cross-sectional view of the overall structure of the antenna of the present invention;

[0036] Figure 6 is a reflection loss diagram of the antenna of the present invention;

[0037] Figure 7 is a gain diagram within the frequency band of the antenna of the present invention;

[0038] Figure 8 is a diagram of the half-power beamwidth within the frequency band of the antenna of the present invention;

[0039] Fig. 9 is the E-plane and H-plane directional pattern within the frequency band of the antenna of the present invention; DETAILED DESCRIPTION

[0040] In order to make the technical solutions and features of the present invention clearer, the present invention is further described in detail below in conjunction with the accompanying drawings and specific examples. It should be understood that these examples are only used to illustrate the present invention and are not used to limit the scope of the present invention. After reading the present invention, various equivalent forms of modifications to the present invention by those skilled in the art all fall within the scope defined by the claims attached to this application.

[0041] This embodiment is a cavity-backed quadrifilar helical antenna loaded with folded helical arms. Figures 1 to 5 , which includes a radiation unit, a parasitic radiation unit, a coaxial slotted balun structure, an SMA connector, an outer metal wall and a top waterproof cover.

[0042] The radiation unit includes four spiral arm units, which constitute two pairs of central spiral arm units; the spiral arm units are arranged in a circular array at the top and bottom of the coaxial slotted balun structure. The number of winding turns of the spiral arm unit is 0.5 turns. Among the four spiral arm units, spiral arms 13 and 15 are a pair of central spiral arm units, with a total length slightly greater than 1 / 4λ and a phase lag, and spiral arms 14 and 16 are a pair of central spiral arm units, with a total length slightly less than 1 / 4λ and a phase advance, so that the phase difference is 90° to achieve circular polarization.

[0043] On the outside of the central spiral arm unit, a folded spiral arm is loaded as a parasitic radiation unit to introduce a new resonance point and expand the bandwidth. Figure 3 9 and 11 are a pair of folded spiral arms, and 10 and 12 are a pair of folded spiral arms. The total length of the two pairs is adjusted to achieve phase matching and adapt circular polarization. The antenna is fed by a coaxial slotted balun structure and SMA, which mainly realizes the unbalanced-balanced conversion of the feeding structure and completes the 50 ohm impedance transformation of the four-arm spiral structure. The outer metal cavity 2 is used to block the soil from absorbing the electromagnetic wave energy of the antenna, so as to achieve high radiation efficiency of the antenna in the soil, and is applicable in the field of buried narrowband Internet of Things and underground pipelines.

[0044] Specifically, the spiral arm units are arranged in a circular array at the top and bottom ends of the coaxial slotted balun structure;

[0045] The parasitic radiation unit includes a flexible PCB board and a hollow cylindrical support, the surface of the PCB board is etched with a parasitic folded spiral arm; the inner wall of the hollow cylindrical support is bonded to the non-metallic surface of the flexible PCB board; the bottom end of the coaxial slotted balun structure passes through the central circular hole of the metal bottom plate and is connected to the inner conductor of the connector, and the outer conductor of the coaxial slotted balun and the outer conductor of the connector are both connected to the metal bottom plate. The SMA connector passes through the central circular hole of the metal bottom plate and is connected to the coaxial slotted balun structure; the outer metal cavity is connected to the antenna ground; the top waterproof cover is connected to the outer metal cavity in an interlocking manner.

[0046] In order to achieve the above structure and radiation performance, the present invention adopts the following technical solutions.

[0047] 1) Preparation: The central spiral arm unit is wound by copper wire-copper wire with a diameter of 2mm. The spiral arm unit is etched on the FPC soft board, and the inner wall of the hollow cylindrical support is bonded to the non-metallic surface of the flexible PCB board to ensure the structural strength. The outer metal cavity and the coaxial slotted balun structure are customized for metal processing. The coaxial slotted balun structure is welded to the SMA and the central spiral arm, and the outer metal cavity is fixed to the antenna ground with metal screws. The folded spiral arm and the support are embedded with the top waterproof cover and the antenna to obtain the final folded spiral arm loaded back cavity type four-arm spiral antenna.

[0048] 2) Design: The design method of the present invention comprises the following steps:

[0049] Step 1: Use four half-turn spiral wires to form two pairs of central spiral arm units, corresponding to Figure 3 13 and 15, 14 and 16. Spiral arms 13 and 15 are a pair of spiral arms, with a total length slightly greater than 1 / 4λ and a phase lag, and spiral arms 14 and 16 are a pair of spiral arms, with a total length slightly less than 1 / 4λ and a phase advance, so that the phase difference is 90° to achieve circular polarization.

[0050] Step 2: On the outside of the central spiral arm unit, load a folded spiral arm etched on the FPC soft board with a support as a parasitic radiation unit to introduce a new resonance point and expand the bandwidth. Figure 3 Among them, 9 and 11 are a pair of folded spiral arms, and 10 and 12 are a pair of folded spiral arms. The total lengths of the two pairs are adjusted and optimized to achieve phase matching.

[0051] Step 3: Use the coaxial slotted balun structure to achieve unbalanced-balanced conversion of the feed current and complete the 50 ohm impedance transformation of the four-arm helical structure.

[0052] Step 4: Integrate the central spiral arm unit, the folded spiral arm, the outer metal cavity, and the SMA connector to obtain a cavity-backed quadrifilar spiral antenna loaded with a folded spiral arm.

[0053] Step 5: Use a vector network and a microwave darkroom to test the antenna, wherein the HFSS simulation software is used to design and simulate the antenna.

[0054] Specifically, the present invention provides a novel folded spiral arm loaded back cavity type four-arm spiral antenna, the center frequency is 0.92GHz, the radiation unit is composed of four central spiral arms, the parasitic unit is a folded spiral arm, etched on the PFC soft board, the feeding structure is a coaxial slotted balun structure, and finally the central spiral arm unit, the folded spiral arm, the outer metal cavity, and the SMA connector are integrated to obtain the final antenna. The specific design parameters and structure are as follows:

[0055] See also Figure 1 , Figure 1 The schematic diagram of the exploded structure of the cavity-backed quadrifilar helical antenna loaded with folded spiral arms is as follows: the top waterproof cover 1 is a waterproof structure; the outer metal cavity 2 has a diameter of 150 mm and a thickness of 7 mm, which is used to block the soil from absorbing the electromagnetic wave energy of the antenna and achieve high radiation efficiency of the antenna in the soil; the support 3 is used to support the folded spiral arms 9, 10, 11, and 12 etched on the FPC soft board 4; the antenna ground 5 and the fixing part 6 are used to support and fix the antenna structure.

[0056] See also Figure 2 , Figure 2 It is a three-dimensional view of the top waterproof cover, whose a structure is used to be embedded in the antenna and fix the support 3.

[0057] See also Figure 3 , 5, Figure 3 Provides a three-dimensional view of the antenna unit, parasitic unit, and feeding structure. Figure 5 It is a cross-sectional view of the overall structure of the antenna. At the operating frequency of 0.92GHz, the diameter of the central spiral arm unit is 2mm; the circumference of one spiral turn of spiral arms 13 and 15 is set to 342mm, and the pitch is set to 177mm; the circumference of one spiral turn of spiral arms 14 and 16 is set to 360mm, and the pitch is set to 180mm; the circumference affects the operating frequency, and the pitch affects the gain, axial ratio and front-to-back ratio. The coaxial slotted balun structure has a supporting function, with a height of 100mm, realizes the impedance transformation of the antenna and is welded to the SMA connector 18 for feeding. The circular groove 19 is used to fix the support member 3, and its size is consistent with the outer diameter of the fixing member 6.

[0058] See also Figure 4 , Figure 4 The 3D schematic diagram of the folded spiral arm is obtained by etching the FPC soft board, with a width of 6mm, a pitch of 190mm, and a height of 95mm. The total length 21 is adjusted to adjust the frequency of the newly introduced resonance point, which also affects the antenna radiation performance. The four parasitic spiral arms are on the same side relative to the central spiral line, and have the same size in this embodiment.

[0059] Antenna bandwidth and radiation characteristics please refer to Figure 6-Figure 9

[0060] Figure 6 The reflection and loss diagram of the antenna is shown in Figure 1. The impedance bandwidth of the antenna below -10dB is 0.86–0.97GHz (12%).

[0061] Figure 7 It is the gain and tail lobe gain diagram within the frequency band. The maximum gain of the antenna reaches 5.2dBi. The average gain of the antenna within 0.86-0.97GHz is 5dBi, and the average front-to-back ratio is 13dB.

[0062] Figure 8 The half-power beamwidth diagram of the antenna shows that the average beamwidth of the antenna on the E plane is 110°, and the average beamwidth of the antenna on the H plane is 112°, with a wide coverage range.

[0063] Fig. 9 It is the E-plane and H-plane radiation pattern within the antenna frequency band. (a), (b), and (c) are the E-plane and H-plane radiation patterns at 0.86 GHz, 0.920 GHz, and 0.970 GHz, respectively. The radiation patterns are omnidirectional and the shape of the radiation patterns is stable within the frequency band.

[0064] The above is only a specific implementation of the present invention, but the design concept of the present invention is not limited to this. Any non-substantial changes to the present invention using this concept shall be deemed as an infringement of the protection scope of the present invention.

Claims

1. A cavity-backed quadrifilar helical antenna loaded with folded helical arms, characterized in that: It includes a radiation unit, a parasitic radiation unit, a coaxial slotted balun structure, an SMA connector, an outer metal cavity and a top waterproof cover; The radiation unit includes four spiral arm units, which constitute two pairs of central spiral arm units; the spiral arm units are arranged in a circular array at the top and bottom of the coaxial slotted balun structure; The parasitic radiation unit comprises a flexible PCB board and a hollow cylindrical support, the parasitic folded spiral arm is etched on the surface of the PCB board; the inner wall of the hollow cylindrical support is bonded to the non-metallic surface of the flexible PCB board; The bottom end of the coaxial slotted balun structure passes through the central circular hole of the metal bottom plate and is connected to the inner conductor of the connector, and the outer conductor of the coaxial slotted balun and the outer conductor of the connector are both connected to the metal bottom plate. The SMA connector passes through the central circular hole of the metal bottom plate and is connected to the coaxial slotted balun structure; the outer metal cavity is connected to the antenna ground; and the top waterproof cover is connected to the outer metal cavity in an inlaid manner.

2. The cavity-backed quadrifilar helical antenna loaded with folded helical arms according to claim 1, characterized in that: There are four parasitic folded spiral arms, which are rotationally symmetrically distributed and have arbitrary angles relative to the central spiral arm unit.

3. The cavity-backed quadrifilar helical antenna loaded with folded helical arms according to claim 2, characterized in that: The parasitic folded spiral arm has 0.5 turns, and the number of bends is adjusted according to the required resonance length.

4. The cavity-backed quadrifilar helical antenna loaded with folded helical arms according to claim 1, characterized in that: The outer metal cavity has a diameter consistent with that of the antenna, and a height consistent with that of the coaxial slotted balun structure.

5. A cavity-backed quadrifilar helical antenna loaded with folded helical arms according to any one of claims 1 to 4, characterized in that: When the radiation unit is excited, the parasitic folded spiral arm becomes parasitic.

6. The cavity-backed quadrifilar helical antenna loaded with folded helical arms according to claim 3, characterized in that: The parasitic folded spiral arm and the antenna ground are in an open circuit structure or a short circuit structure.

7. A method for preparing a cavity-backed quadrifilar helical antenna loaded with folded helical arms, characterized in that The steps include: Step 1, four antennas are respectively wound 0.5 turns to form two pairs of central spiral arm units, each pair of central spiral arm units is symmetrical about the origin, and are arranged in a circular array at the top and bottom of the coaxial slotted balun structure; The circumference of the central spiral arm unit is determined according to the formula l=c / f, where l represents the circumference of one spiral turn, c represents the speed of light, and f represents the operating frequency; The circumferences of the two pairs of central spiral arm units are set as follows: the circumference of one pair of central spiral arm units is greater than l, and the circumference of the other pair of central spiral arm units is less than l; Step 2, two pairs of central spiral arm units are fed using a coaxial slotted balun structure, and the slot depth and width are determined according to the size of the central spiral arm unit and in combination with the parasitic folded spiral arm and the metal cavity; Step 3, by etching two pairs of folded spiral arm units on the flexible PCB board, the sizes of the two pairs of folded spiral arm units are determined according to the operating frequency of the spiral antenna, one pair of folded spiral arm units is larger than half the wavelength of the operating frequency, and the other pair of folded spiral arm units is smaller than half the wavelength of the operating frequency; the flexible PCB board is bonded to the parasitic unit support; The flexible PCB board is an FPC soft board, and the parasitic unit support is a PVC board; Step 4, the central spiral arm unit, the coaxial slotted balun structure and the SMA connector are welded and integrated, and integrated with the parasitic unit, the metal cavity and the top waterproof cover to obtain a cavity-backed quadrifilar spiral antenna loaded with folded spiral arms; Step 5: Use a vector network and a microwave darkroom to test the above antenna.

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