Hemispherical helical antenna

Abstract

The invention relates to a hemispherical helical antenna, and belongs to the technical field of antennas. The antenna comprises an antenna body, the antenna body comprises a hemispherical shell, a metal guide rod and a metal wire, the metal wire is spirally wound on the peripheral wall of the hemispherical shell from the top of the hemispherical shell to an opening part, and the distance between every two adjacent turns of a spiral line formed by winding is gradually reduced from the winding starting point; the metal guide rod is located in the hemispherical shell, a hole for the metal guide rod to penetrate through is formed in the top of the hemispherical shell, one end of the metal guide rod is connected with the end, located on the top of the hemispherical shell, of the metal wire through the hole, the other end of the metal guide rod serves as a signal input end, and the other end of the metal wire is suspended. According to the antenna, the working bandwidth of the helical antenna is greatly improved, and the radiation and receiving performance of the antenna is improved, so that the antenna can keep the stability of a communication link in a complex working environment.

Description

Technical Field

[0001] The invention belongs to the technical field of antennas, and in particular relates to a hemispherical helical antenna. Background Art

[0002] The antenna is an important component in the wireless communication link, responsible for converting the guided waves on the transmission line into electromagnetic waves for communication in free space, or vice versa. The existing antennas have various structures, including wire antennas, planar antennas, array antennas, helical antennas, etc. Among them, helical antennas are widely used in the communication field due to their advantages such as wide bandwidth, circular polarization, high gain and compact structure. However, the existing helical antenna has a complex structure, and increasing the bandwidth is often achieved by increasing the size of the antenna. In the case of limited space in the application environment, the narrow bandwidth cannot meet the requirements of the broadband system. Summary of the invention

[0003] The object of the present invention is to provide a hemispherical helical antenna to solve the problem that the existing helical antenna has a narrow frequency band and cannot meet the requirements of a broadband system.

[0004] The present invention provides a hemispherical spiral antenna to solve the above technical problems. The antenna comprises an antenna body, which comprises a hemispherical shell, a metal guide rod and a metal wire. The metal wire is wound on the outer peripheral wall of the hemispherical shell in a spiral form from the top of the hemispherical shell to the opening, and the spacing between each two adjacent turns of the wound spiral line decreases from the winding starting point; the metal guide rod is located inside the hemispherical shell, and a hole is opened at the top of the hemispherical shell for the metal guide rod to pass through. One end of the metal guide rod is connected to one end of the metal wire located at the top of the hemispherical shell through the hole, and the other end of the metal guide rod is used as a signal input end, and the other end of the metal wire is suspended.

[0005] Furthermore, a spiral groove matched with the spiral line is opened on the outer peripheral wall of the hemispherical shell, and the metal wire is located in the spiral groove.

[0006] Furthermore, the spiral form of the spiral line is determined by the following formula:

[0007]

[0008]

[0009] t∈(SR,2*n*π)

[0010] Among them, x, y, z are the coordinates of each point of the helix, d is the radius of the hemispherical shell, n is the total number of turns of the helix, t is the helix angle, SR is the starting helix angle of the helix, and 2*n*π is the ending helix angle of the helix.

[0011] Furthermore, the antenna also includes an environment adaptive matching unit, which includes a bidirectional coupler, an adjustable matching network module, an environment detection module and a controller; the bidirectional coupler is respectively connected to the environment detection module and the adjustable matching network module, and is used to couple the incident signal to the environment detection module and the adjustable matching network module, and couple the echo signal reflected from the antenna to the environment detection module, and the environment detection module is used to detect whether the antenna working environment has changed according to the received incident signal and echo signal; the controller controls the connection between the environment detection module and the adjustable matching network module, and is used to feedback adjust the adjustable matching network module when the antenna impedance is mismatched, so as to achieve antenna impedance matching.

[0012] Furthermore, the adjustable matching network module includes an input terminal, a first series branch consisting of a first inductor and a second inductor, a second series branch consisting of a first capacitor and a variable capacitor, a third inductor and an output terminal, the two ends of the first series branch are respectively connected to the input terminal and the output terminal, one end of the second series branch close to the first capacitor is connected to the series point of the first inductor and the second inductor, the other end of the second series branch is grounded, one end of the third inductor is connected to the series point of the first capacitor and the variable capacitor, the other end of the third inductor is used as an adjustment voltage input terminal, the input terminal is used to access the radio frequency signal, and the output terminal is connected to the antenna body.

[0013] Furthermore, the antenna also includes an adjustable voltage module, the controller controls the connection of the adjustable voltage module, and the output end of the adjustable voltage module is connected to the adjustment voltage input end of the adjustable matching network module; the controller is used to control the output voltage of the adjustable voltage module according to the incident signal and the echo signal when the antenna impedance is mismatched.

[0014] The beneficial effects of the present invention are as follows: the helical antenna of the present invention is composed of a metal wire, a hemispherical shell and a metal wire, and is a linearly polarized antenna with a single radiator. The antenna has a simple structure; and the pitch of the wound helical wire decreases from the starting point of winding, thereby greatly improving the working bandwidth of the helical antenna, improving the radiation and receiving performance of the antenna, and meeting the broadband system's requirements for the wide bandwidth of the antenna. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 is a schematic structural diagram of a hemispherical helical antenna according to an embodiment of the present invention;

[0016] Figure 2 is a schematic structural diagram of a helical line in a hemispherical helical antenna according to an embodiment of the present invention;

[0017] Figure 3 is a schematic diagram of the structure of a hemispherical shell in a hemispherical helical antenna according to an embodiment of the present invention;

[0018] Figure 4 is a schematic diagram of test results of a hemispherical helical antenna according to an embodiment of the present invention;

[0019] Figure 5 is a structural block diagram of an environment adaptive matching unit according to an embodiment of the present invention;

[0020] Figure 6 is a circuit schematic diagram of an adjustable matching network module according to an embodiment of the present invention;

[0021] Figure 7 It is a flow chart of the environment adaptive impedance matching method of the hemispherical helical antenna system according to an embodiment of the present invention. DETAILED DESCRIPTION

[0022] The specific implementation of the present invention will be further described below in conjunction with the accompanying drawings.

[0023] The basic idea of ​​the present invention is to set the helical antenna structure to simplify the antenna structure on the one hand and to increase the bandwidth of the helical antenna on the other hand to meet the requirements of a broadband system.

[0024] Based on the above basic ideas, Figure 1 , 2 As shown, the hemispherical helical antenna of the present invention includes an antenna body, which includes a hemispherical shell, a metal guide rod and a metal wire. The metal wire is wound on the outer peripheral wall of the hemispherical shell in a spiral form from the top of the hemispherical shell to the opening, and the spacing between each two adjacent turns of the wound spiral line decreases from the winding starting point; the metal guide rod is located inside the hemispherical shell, and a hole is opened at the top of the hemispherical shell for the metal guide rod to pass through. One end of the metal guide rod is connected to one end of the metal wire located at the top of the hemispherical shell through the hole, and the other end of the metal guide rod is used as a signal input end, and the other end of the metal wire is suspended.

[0025] Different application scenarios of the antenna have different requirements for the working frequency, bandwidth and volume of the antenna. When setting the antenna structure according to the application scenario, the length of the metal wire of the antenna is related to the working frequency of the antenna, and the change in length affects the size of the working frequency; the diameter of the hemisphere is related to the volume of the antenna, and the diameter of the hemisphere can be set according to the space size of the antenna application scenario. Under normal circumstances, on the basis of meeting the space conditions, the larger the diameter of the hemisphere, the better the performance of the antenna. The pitch of the helix (that is, the spacing between two adjacent turns of metal wire) is related to the working bandwidth of the antenna. The working bandwidth of the antenna can be changed by setting the pitch change. In order to increase the bandwidth of the helical antenna to meet the requirements of the broadband system, the pitch of each spiral line decreases from the top of the hemisphere shell, that is, the pitch decreases successively, and the amount of reduction can be fixed or variable, which is set according to actual needs.

[0026] Specifically, for example, if a small electrical antenna is to be set up for use in coal mines, the present invention sets the diameter of the hemispherical shell according to the space size of the antenna application environment when setting the hemispherical spiral antenna, and then determines the length of the helix according to the requirements for the antenna operating frequency in the environment, and determines the change trend of each pitch of the helix according to the requirements for the antenna working bandwidth in the environment. After determining the size of the hemispherical shell diameter, the length of the metal wire and the change trend of the pitch, the spiral form of the metal wire winding can be determined, and then the hemispherical spiral antenna of the present invention is designed and installed.

[0027] To facilitate installation, Figure 3 As shown, a spiral groove matching the spiral line is provided on the outer peripheral wall of the hemispherical shell, and the metal wire is embedded in the spiral groove. When the hemispherical shell is automatically grooved, the spiral line is set in the following spiral form:

[0028]

[0029] t∈(SR,2*n*π)

[0030] Among them, x, y, z are the coordinates of each point of the helix, d is the radius of the hemispherical shell, n is the total number of turns of the helix, t is the helix angle, SR is the starting helix angle of the helix, and 2*n*π is the ending helix angle of the helix.

[0031] The advantages of the helical antenna of the present invention are illustrated by taking the small electric antenna used in a mine as an example. The traditional small electric antenna used in a mine cannot be set too large due to the limitation of the space position, which also leads to the limitation of its bandwidth, which is usually below 500Hz. The radiation and reception performance of this antenna is not good. The helical antenna of the present invention is set on the hemispherical shell. Although the volume is still limited by the space and does not increase, the pitch of the helix is ​​set so that the pitch of the helix is ​​not fixed, but changes, such as Figure 1 As shown in FIG. 1 , the spacings L1 to L5 between two adjacent turns of metal wire are different and decrease from L5 to L1. This change in pitch can increase the working bandwidth of the antenna, so that the bandwidth of the helical antenna of the present invention can reach more than 5 MHz. Figure 4As shown, the horizontal axis is frequency, and the vertical axis is reflection coefficient (the reflection coefficient of the antenna is a parameter that describes the relationship between the reflected wave and the incident wave at the antenna input end. It is mainly used to measure the impedance matching degree between the antenna and the transmission line. It can be calculated by the input impedance Zin of the antenna and the characteristic impedance Z0 of the transmission line. The S parameter is used to describe the relationship between the incident wave and the reflected wave of each port of the multi-port network. For a single-port network such as the antenna in the present invention, S11 and the reflection coefficient are the same for the antenna, and S11 is used to represent its reflection characteristics). In the case of antenna impedance matching, in the three propagation media of air, water, and soil, the operating frequency with a reflection coefficient below 10dB is between 170MHz and 180MHz. Among them, for the soil medium, the antenna's operating bandwidth is the narrowest, but it can also reach about 6MHz. Therefore, the helical antenna of the present invention greatly increases the operating bandwidth of the traditional small electric antenna used in mines, and improves the antenna radiation and receiving performance.

[0032] The antenna is in close contact with the external environment, and changes in the environment will cause changes in the antenna impedance. For example, in mine environment monitoring communications, the environment of these special application scenarios is complex, and the antenna will be affected by various media such as water, soil, and air. In particular, mine collapse often occurs, causing the antenna to be buried. In this special application scenario, the design of the traditional antenna plus matching network is difficult to resist interference from the outside world because the parameters are fixed after the design is completed, which in turn causes the antenna's operating frequency to shift, the impedance to change, and the impedance mismatch between the antenna and the RF signal source, affecting the stability of the communication link, reducing power transmission efficiency, and generating additional noise and signal distortion. In order to solve the problem of enabling the antenna to adapt to the new environment when the environment changes, the present invention improves the peripheral circuit in the hemispherical helical antenna, and adds an environmental adaptive matching unit that adaptively adjusts the antenna impedance according to the environment. The unit includes a bidirectional coupler, an environmental detection module, a controller, and an adjustable matching network module.

[0033] like Figure 5 As shown, the bidirectional coupler is connected to the environment detection module and the adjustable matching network module respectively. The input end of the bidirectional coupler is used to input the RF signal, and the input RF signal is divided into two outputs, one of which is transmitted to the antenna through the adjustable matching network module, and the other is output to the environment detection module. The bidirectional coupler also couples the echo signal reflected from the antenna to the environment detection module. Preferably, the bidirectional coupler block is composed of a bidirectional coupler ADCB-20-82+, which is mainly used for coupling the input signal power and the reflected signal power. Its coupling coefficient is 20dB, which can couple a small part of the energy to the environment detector for detection.

[0034] The environment detection module receives the incident RF signal output by the bidirectional coupler and the echo signal reflected from the antenna, and detects whether the antenna working environment has changed based on the received incident signal and echo signal. Preferably, the environment detection module uses a power detection chip LT5581, which is mainly used to detect the power of the coupled signal input thereto. Preferably, the environment detection module can determine whether the environment has changed based on the power difference between the incident signal and the echo signal, and whether the impedance of the antenna needs to be adjusted to adapt to the new environment. Of course, as another implementation method, it can also be judged based on the voltage ratio of the incident signal to the echo signal.

[0035] The controller controls the connection between the environment detection module and the adjustable matching network module; the controller is used to perform feedback adjustment on the adjustable matching network module when the antenna impedance is mismatched to achieve antenna impedance matching. Preferably, the controller can use a microprocessor of model STM32F103RCT6, which is mainly used to output a DC voltage with adjustable accuracy of 0-3.3V, compare the voltage output by the environment detection module, and output a signal to control the adjustable voltage module.

[0036] like Figure 6 As shown, the adjustable matching network module of the present invention preferably adopts a T-type matching network, including an input terminal RF-in, a first series branch composed of a first inductor L1 and a second inductor L2, a second series branch composed of a first capacitor C1 and a variable capacitor C2, a third inductor L3 and an output terminal Antenna, the two ends of the first series branch are respectively connected to the input terminal and the output terminal, one end of the second series branch close to the first capacitor C1 is connected to the series point of the first inductor L1 and the second inductor L2, the other end of the second series branch is grounded, one end of the third inductor L3 is connected to the series point of the first capacitor C1 and the variable capacitor C2, the other end of the third inductor L3 is used as an adjustment voltage input terminal, the input terminal is used to access the radio frequency signal, and the output terminal is used to connect to the antenna body.

[0037] The values ​​of the first inductor L1, the second inductor L2, the third inductor L3, the first capacitor C1 and the variable capacitor C2 are determined by the input impedance of the hemispherical helical antenna in this embodiment. When the incident signal reaches the hemispherical helical antenna via the T-type matching network composed of the high-Q inductors L1, L2 and the variable capacitor C2, the DC voltage applied to both ends of the variable capacitor C2 is changed, thereby changing the impedance of the entire antenna to meet the matching requirements. The first capacitor C1 is a DC blocking capacitor, which blocks the influence of the DC voltage of the variable capacitor on the RF signal, and the third inductor L3 is an AC blocking inductor, which blocks the influence of the RF AC signal on the DC voltage.

[0038] In order to realize automatic adjustment of the DC voltage across the variable capacitor C2, an adjustable voltage module is provided in the antenna peripheral circuit, and the controller controls the connection of the adjustable voltage module, and the output end of the adjustable voltage module is connected to the adjustment voltage input end of the adjustable matching network module; the controller is used to control the output voltage of the adjustable voltage module according to the incident signal and the echo signal when the antenna impedance is mismatched. Preferably, the adjustable voltage module is composed of a boost chip NCP1406 and a rail-to-rail operational amplifier MAX44248, which are used to amplify the precision-adjustable voltage output by the microprocessor. The amplification factor is determined by the configuration of the operational amplifier peripheral circuit and is calculated based on the following formula:

[0039]

[0040] Among them, R f R1 is a feedback resistor connected between the output terminal and the inverting input terminal of the operational amplifier; R2 is an input resistor connected between the inverting input terminal of the operational amplifier and ground.

[0041] The above-mentioned adjustable matching network module changes the DC voltage across the variable capacitor, thereby changing the impedance of the entire antenna to meet the matching requirements. As another implementation, multiple groups of capacitors and inductors may be provided, and the number of capacitors and inductors connected to the matching network may be changed to change the parameters of the matching network, thereby changing the impedance of the entire antenna to meet the matching requirements.

[0042] Combine the following Figure 7 The working process of the hemispherical helical antenna system of the present invention for performing adaptive impedance matching according to environmental changes is described in detail.

[0043] Take the case where the antenna works in the 170MHz±0.1MHz frequency band as an example. When the antenna is working, it actively radiates electromagnetic wave signals outward. When the environment in which the antenna is located changes, it will cause the antenna impedance mismatch, resulting in changes in the incident signal power and the reflected signal power. The bidirectional coupler couples the changed signal power and transmits it to the environmental detection module. At this time, the environmental detection module cooperates with the controller to output a DC voltage with adjustable accuracy. The voltage is amplified by the adjustable voltage module and outputs a DC voltage of 0-26V in 50mV steps to the adjustable matching network module to adjust the input impedance of the antenna, and obtain 26 groups of voltage values ​​of the incident signal coupling power and the reflected signal coupling power, where the incident signal coupling power and the reflected signal coupling power are obtained by the environmental detection module. In the controller, the voltage values ​​of 26 groups of incident signal coupling power and reflected signal coupling power are subtracted to find the DC voltage value with the largest difference, return the optimal value and output the control signal when the difference between incident signal coupling power and reflected signal coupling power is the largest, control the adjustable voltage module to maintain the optimal voltage value, so that the antenna can maintain the optimal impedance matching under the current operating frequency of 170MHz±0.1MHz in the current environment. It has been proved through experiments that the antenna can maintain the optimal matching under the changes of air, soil and water, such as Figure 4 shown.

Claims

1. A hemispherical helical antenna, characterized in that: The antenna comprises an antenna body, which comprises a hemispherical shell, a metal guide rod and a metal wire. The metal wire is wound on the outer peripheral wall of the hemispherical shell in a spiral form from the top of the hemispherical shell to the opening, and the spacing between each two adjacent turns of the wound spiral line decreases from the winding starting point; the metal guide rod is located inside the hemispherical shell, and a hole is opened on the top of the hemispherical shell for the metal guide rod to pass through. One end of the metal guide rod is connected to one end of the metal wire located on the top of the hemispherical shell through the hole, and the other end of the metal guide rod is used as a signal input end, and the other end of the metal wire is suspended.

2. The hemispherical helical antenna according to claim 1, characterized in that: A spiral groove matched with the spiral line is provided on the outer peripheral wall of the hemispherical shell, and the metal wire is located in the spiral groove.

3. The hemispherical helical antenna according to claim 1, characterized in that: The helical form of the helix is ​​determined by the following formula: t∈(SR,2*n*π) Among them, x, y, z are the coordinates of each point of the helix, d is the radius of the hemispherical shell, n is the total number of turns of the helix, t is the helix angle, SR is the starting helix angle of the helix, and 2*n*π is the ending helix angle of the helix.

4. The hemispherical helical antenna according to claim 1, characterized in that: The antenna also includes an environment adaptive matching unit, which includes a bidirectional coupler, an adjustable matching network module, an environment detection module and a controller; the bidirectional coupler is respectively connected to the environment detection module and the adjustable matching network module, and is used to couple the incident signal to the environment detection module and the adjustable matching network module, and couple the echo signal reflected from the antenna to the environment detection module, and the environment detection module is used to detect whether the antenna working environment has changed according to the received incident signal and echo signal; the controller controls the connection between the environment detection module and the adjustable matching network module, and is used to feedback adjust the adjustable matching network module when the antenna impedance is mismatched, so as to achieve antenna impedance matching.

5. The hemispherical helical antenna according to claim 4, characterized in that: The adjustable matching network module includes an input terminal, a first series branch consisting of a first inductor and a second inductor, a second series branch consisting of a first capacitor and a variable capacitor, a third inductor and an output terminal. The two ends of the first series branch are respectively connected to the input terminal and the output terminal, one end of the second series branch close to the first capacitor is connected to the series point of the first inductor and the second inductor, the other end of the second series branch is grounded, one end of the third inductor is connected to the series point of the first capacitor and the variable capacitor, the other end of the third inductor is used as an adjustment voltage input terminal, the input terminal is used to access the radio frequency signal, and the output terminal is connected to the antenna body.

6. The hemispherical helical antenna according to claim 5, characterized in that: The antenna also includes an adjustable voltage module, the controller controls the connection to the adjustable voltage module, and the output end of the adjustable voltage module is connected to the adjustment voltage input end of the adjustable matching network module; the controller is used to control the output voltage of the adjustable voltage module according to the incident signal and the echo signal when the antenna impedance is mismatched.

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