Impedance measurement system and antenna tuning device including the thereof

Abstract

This application relates to an impedance measurement system, comprising: a power supply circuit; a power-on control circuit configured to directly perform power-on or power-off operations on the power supply circuit; a trigger control circuit configured to determine whether to prepare the impedance measurement system for power-on based on the output of the impedance measurement system; a current sampling comparison circuit configured to sample the current and compare the sampled data with a reference current; and a voltage sampling comparison circuit configured to sample the voltage and compare the sampled data with a reference voltage. The impedance measurement system further comprises: a filter connected to the power supply circuit, the current sampling comparison circuit, and the voltage sampling comparison circuit, configured to filter out radio frequency noise to reduce radio frequency interference. An antenna tuning device including the impedance measurement system is also provided.

Description

Technical Field

[0001] This application relates to the field of aircraft communication system integration, and in particular to the optimized design of impedance measurement systems and corresponding antenna tuning devices for shortwave communication systems. Background Technology

[0002] Shortwave communication is a long-distance communication technology that enables communication between any two locations on Earth and can cover a wide geographical area. Therefore, in radio communication, shortwave communication is widely used in fields such as overseas radio communication, marine radio communication, aviation radio communication, and military radio communication.

[0003] The shortwave communication system of spacecraft typically operates in the frequency band of 2.0000MHz-29.9999MHz. Since signal transmission relies on ionospheric reflection, and the input impedance of the antenna changes in real time over a very large range (hundreds to thousands of ohms), the proper functioning of the antenna tuning equipment is crucial. However, during actual flight, faults such as disconnection or jamming of the antenna tuning equipment's power supply circuit can occur, rendering the high-frequency system unusable and resulting in a "HF 1 / 2TRANSMIT" CAS message, limiting long-distance communication for the flight crew. This is one issue. The shortwave communication equipment includes a high-frequency transceiver (installed in the electrical and electronic equipment bay), an antenna tuning device (located at the bottom of the vertical tail leading edge bay), and a high-frequency antenna (conformal to the vertical tail). Because the antenna tuning device is installed at a high position, repair and maintenance are difficult after a fault occurs; therefore, non-technical faults should be avoided as much as possible. This is another issue. Furthermore, the high-frequency communication system is a crucial system in ETOPS (Extremely High-Frequency Telecommunication Systems). It requires no relay stations, possesses strong resilience and security, and has a high survivability rate in special environments. Therefore, it is necessary to improve the performance of shortwave communication under long-distance conditions.

[0004] Specifically, existing shortwave communication technologies have the following problems:

[0005] Existing shortwave communication systems for civil aircraft consist of a transceiver, an antenna tuning device, and an antenna. The antenna tuning device is added because shortwave communication systems operate at low frequencies. Without it, the shortwave antenna would need to be several meters to tens of meters long to receive signals, which clearly does not meet the design and installation requirements of civil aircraft. Therefore, the antenna tuning device plays a crucial role, and its performance directly affects the communication effectiveness of the entire system.

[0006] Existing antenna tuning devices consist of five parts: a chassis assembly, an RF impedance matching network, an impedance measurement sensor circuit, a control circuit, and a power supply circuit. The impedance measurement sensor circuit monitors all information related to impedance matching, detecting the resistance, phase, and VSWR of the entire system, making it crucial to the antenna tuning device design. However, current antenna tuners use a single cable for power supply and communication, and the RF power signal during transmission can affect the impedance measurement sensor circuit, easily causing internal relays to disconnect, resulting in a power outage of the antenna tuning device. This renders the shortwave communication system unusable, displaying a "HF TRANSMIT" CAS message, increasing the operational burden on the crew. Therefore, it is necessary to adopt a simpler method to avoid these problems and improve the user experience of the shortwave communication system.

[0007] For example, patent document (CN217981646U) discloses an impedance detection circuit for an airborne antenna. This circuit includes an airborne antenna, an isolation module, a radio frequency signal transmitter, an inductor, a capacitor, a DC coupler analog switch, a voltage divider module, and a voltage sampling module. It uses the principle of resistor voltage divider to convert the impedance value of the airborne antenna into a voltage value, achieving rapid and accurate detection of the airborne antenna's impedance. However, the above solution cannot eliminate the influence of the radio frequency power signal on the impedance measurement sensor circuit during transmission.

[0008] The paper "A Novel Design and Implementation of Shortwave Vector Impedance Detection" proposes a novel design and implementation method for shortwave vector impedance detection. This novel design primarily modifies the data processing algorithm, directly processing the sampled data to reduce calculations involving down-conversion and Hilbert transform, making the algorithm simpler and more efficient. Its starting point is the detection principle, and the solution mainly addresses the issue from an algorithmic perspective, without improving the hardware circuitry of the device. More specifically, the impedance detection circuit comprises multiple modules; this paper improves the algorithm for the entire circuit without optimizing the hardware design of any specific module.

[0009] Therefore, there is a need for an optimized solution to prevent false triggering of the flip-flops inside the circuitry of the antenna tuning device. Summary of the Invention

[0010] This application presents an optimized design scheme for an impedance measurement system with a filter and a corresponding antenna tuning device. The aim of this application is to prevent false triggering of internal triggers by incorporating a filter circuit into the impedance measurement system of the antenna tuning device, thereby avoiding power outages in the antenna tuning device, reducing the failure rate of the shortwave communication system, reducing crew alarms during flight, and ensuring the reliability of the shortwave communication system in long-distance communication environments.

[0011] According to a first aspect of this application, an impedance measurement system is provided, comprising:

[0012] Power supply circuit;

[0013] A power-on control circuit is configured to directly perform power-on or power-off operations on the power supply circuit.

[0014] A trigger control circuit is configured to determine whether to prepare the impedance measurement system for power-on based on the output of the impedance measurement system.

[0015] A current sampling comparator circuit is configured to sample the current and compare the sampled data with a reference current.

[0016] A voltage sampling comparator circuit is configured to sample the voltage and compare the sampled data with a reference voltage;

[0017] The impedance measurement system also includes:

[0018] The filter connected to the power supply circuit, the current sampling comparison circuit, and the voltage sampling comparison circuit is configured to filter out radio frequency noise to reduce radio frequency interference.

[0019] According to a second aspect of this application, an antenna tuning device is provided, the antenna tuning device including the impedance measurement system as described in the first aspect.

[0020] This overview is provided to introduce, in a simplified form, some of the concepts further described in the detailed description below. This overview is not intended to identify key or essential features of the claimed subject matter, nor is it intended to limit the scope of the claimed subject matter. Attached Figure Description

[0021] To describe how the above and other advantages and features of the invention are obtained, a more detailed description of the invention, which has been briefly described above, will be presented with reference to specific embodiments of the invention shown in the accompanying drawings. It will be understood that these drawings depict only exemplary embodiments of the invention and are therefore not intended to limit its scope. The invention will be described and explained using the drawings and with the aid of additional features and details, in which:

[0022] Figure 1 A schematic structural diagram of an antenna tuning device is shown.

[0023] Figure 2 A schematic structural diagram of an impedance measurement system with an added filter according to an embodiment of this application is shown, in which the filter is loaded.

[0024] Figure 3A schematic structural diagram of a filter loaded into an impedance measurement system according to an embodiment of this application is shown.

[0025] Figure 4 A schematic structural diagram of an optimized impedance measurement system according to an embodiment of this application is shown. Detailed Implementation

[0026] To overcome the problems mentioned in the prior art, the solution of this application improves the architecture of the impedance measurement system in the antenna tuning system from the perspective of the usage environment (the usage environment of this solution is mainly the airborne environment), and solves the problem of accidental power failure of the antenna tuning subsystem.

[0027] Specifically, this application proposes a design scheme for an impedance measurement system with added filter circuit. By adding filter circuit design to the impedance measurement system of the antenna tuning device, the false triggering of the internal trigger (e.g., JK trigger) is prevented, thereby avoiding the power failure of the antenna tuning device caused by it.

[0028] The following detailed description of the scheme of this application is provided in conjunction with the accompanying drawings.

[0029] first, Figure 1 A schematic structural diagram of an antenna tuning device is shown.

[0030] Depend on Figure 1 It can be seen that the antenna tuning device mainly consists of an impedance measurement parameter detection system (hereinafter referred to as the "impedance measurement system"), a control circuit (including a microprocessor) and an RF impedance matching network.

[0031] An impedance measurement system (or "impedance measurement circuit") is configured to test the impedance of the antenna and transmit the detection results to the control circuit.

[0032] The control circuit is configured to control the values ​​of the components in the RF impedance matching network to achieve impedance matching with the detected impedance.

[0033] The radio frequency impedance matching network is configured to adjust itself to match the impedance detected by the impedance measurement system according to control commands from the control circuit.

[0034] All state parameters of the antenna are provided by the corresponding detection system. In addition, the impedance measurement system also provides a self-test function for the tuning equipment. This self-test function is a common feature of impedance measurement systems, therefore, it will not be discussed in detail.

[0035] As mentioned earlier, in the prior art, the transmission of radio frequency power signals can affect the circuitry of the impedance measurement system, easily causing the internal relays to disconnect and de-energizing the antenna tuning device. To address this problem, this application specifically designs an impedance measurement system with an added filter.

[0036] In other words, in order to overcome the problems of traditional impedance measurement systems, such as the tendency of triggers to be falsely triggered, this application provides a design that prevents the antenna tuning device from being powered off by adding a filter.

[0037] Specifically, in Figure 2 The diagram shows a schematic structural diagram of an impedance measurement system with an added filter according to an embodiment of this application.

[0038] In general, the main function of the impedance measurement system is to detect impedance by sampling current and voltage and comparing the sampled data with a reference circuit. Subsequently, the trigger control circuit determines whether to continue powering on the impedance measurement system based on the comparison result.

[0039] Specifically, module 1 is power supply circuit 1, which in the example is given as a 28V DC power supply, consisting of... Figure 1 The power supply is supplied to other circuit modules of the antenna tuning device. It should be understood that the power supply circuit can be adjusted according to specific application scenarios and is not limited to this example.

[0040] Module 2 is the power-on control circuit 2, which is configured to directly perform power-on or power-off operations on the power supply circuit (28V DC power supply in this example).

[0041] Module 3 is a trigger control circuit 3, configured to determine whether to power on the impedance measurement system based on its output. Module 3 differs from Module 2 in that it adds a logic processing circuit that receives the output logic information from the impedance measurement system.

[0042] A current sampling and comparison circuit is configured to sample the current and compare the sampled data with a reference current, comprising a (first) current sampling module and a current comparison module.

[0043] A voltage sampling and comparison circuit is configured to sample voltage and compare the sampled data with a reference voltage, comprising a (first) voltage sampling module and a (first) voltage comparison module.

[0044] Module 4 is a newly proposed filter 4 loaded within the impedance measurement system. As shown in the figure, the filter is connected to the power supply circuit, the current sampling comparison circuit, and the voltage sampling comparison circuit, and is mainly configured to filter out radio frequency noise to reduce radio frequency interference.

[0045] Specifically, the filter consists of a first filter connected to a power supply circuit, a current sampling comparison circuit, and a voltage sampling comparison circuit, and a second filter connected to the first filter and the current sampling comparison circuit.

[0046] The first filter is a low-pass inductor / capacitor filter, mainly used to filter out reactive parameters in the circuit, so that the current sampling comparator circuit and voltage sampling comparator circuit are as pure as possible, for example, to adjust the power factor and consistent RF input and leakage, but the RF network is not affected.

[0047] The second filter is used to filter out radio frequency noise and reduce radio frequency interference.

[0048] exist Figure 3 The diagram further illustrates a specific example circuit structure of the added filter.

[0049] As shown in the figure, the circuit of the filter may include a first filter with a low-pass inductor / capacitor and a second filter consisting of a diode, a first resistor R1, a first inductor L1, a capacitor C1 and a varistor.

[0050] Where iS is the signal source current, which is the original power supply signal from the impedance measurement system; iL is the current generated by radio frequency interference caused by frequently turning off the power supply of the antenna tuning device or frequently switching the tuning frequency; iC is the current generated by the active filter; and iN is the current finally input to the comparison module.

[0051] Figure 3 The first resistor, first inductor, and capacitor in the circuit form a classic architecture for an analog bandpass filter circuit. By detecting the harmonic current in the power supply current, the varistor in the second filter can be dynamically adjusted to efficiently solve radio frequency interference, i.e., filter out iL, so that the current through the first inductor L1 in the transmit mode is maintained at a normal level, thereby avoiding false triggering of the trigger and avoiding power outages during tuning.

[0052] By introducing the filter structure described above, the current sampling comparison circuit and the voltage sampling comparison circuit that pass through the first filter are as pure as possible, and at the same time, radio frequency interference can be efficiently resolved by dynamically adjusting the varistor in the second filter.

[0053] In a preferred embodiment, in addition to adding a filter, the impedance measurement circuit can be further improved by modifying the current sampling circuit, voltage sampling circuit, and other circuit components, making the detection results of the impedance measurement system more accurate. The improved circuit structure is as follows: Figure 4 As shown.

[0054] Figure 4A schematic structural diagram of an optimized impedance measurement system according to an embodiment of this application is shown, in which not only is a filter loaded, but other parts of the circuit are also improved.

[0055] Specifically, as shown in the figure, the improved impedance measurement system mainly adds the following components compared to the traditional solution: a first switch K1, a second switch K2, a third switch K3, a filter, a voltage reference 2, a second voltage comparison module N2, a third voltage comparison module N3, a second resistor R2, a second inductor L, and a trigger N5. For clarity, the newly added components are... Figure 4 The improvements are highlighted in red. The improvements mainly include the following aspects:

[0056] 1. Compared with traditional impedance measurement systems, the current sampling and comparison circuit has been improved, resulting in smaller current comparison errors. In the newly improved circuit, the current sampling and comparison circuit includes a first current sampling module, a second inductor L, a second current sampling module, and a current comparison module N4. The second inductor L can be designed as a variable inductor. After the first current sampling module completes its initial current sampling, the current passes through the second inductor, causing an increase in the current difference. Subsequently, the second current sampling module samples the current again. Finally, the current comparison module compares the initially sampled current with the resampled current. This processing makes the current differentiation more obvious, resulting in more accurate output values.

[0057] 2. Compared with the traditional impedance measurement system, the voltage sampling and comparison circuit has been improved by adding two voltage sampling and comparison circuits, resulting in a smaller voltage comparison error. Specifically, firstly, based on the original first voltage comparison circuit consisting of a first voltage reference module and a first voltage comparison module N1, a second voltage comparison circuit consisting of a second voltage reference module, a second voltage comparison module N2, and a second resistor R2 connected in series has been added; and a third voltage comparison circuit consisting of a third voltage comparison module N3 connected to the first voltage comparison module N1 and the second voltage comparison module N2 has been added.

[0058] The third voltage comparison module N3 compares the comparison result from the first voltage comparison circuit with the comparison result from the second voltage comparison circuit again to ensure the accuracy of the output result.

[0059] In this way, the newly added circuits enable the comparison of two voltages simultaneously after receiving the frequency command that needs to be tuned, instead of comparing only one voltage. The third voltage comparison module N3 circuit, namely voltage comparison module N2 and voltage comparison module N3, plays a "calibration" role.

[0060] 3. Compared with the traditional impedance measurement circuit, the new circuit incorporates a filter design; see details below. Figure 2 and 3 This filter further prevents interference from radio frequency signals generated during flight due to frequent frequency switching and use of high-frequency systems to the impedance measurement system.

[0061] 4. A new first switch K1 has been added, which can simultaneously control the signals of the first voltage reference and the second voltage reference. It automatically closes when the system is in transmit mode, and its function is to simultaneously control the two voltage comparison circuits when it is closed.

[0062] A second switch K2 has been added to control the connection of the power circuit;

[0063] A third switch K3 has been added to control the current sampling comparison circuit, which automatically closes in maintenance or test mode.

[0064] Therefore, in summary, switches K, K2, and K3 automatically open and close based on whether the output of the current comparison result and the voltage comparison result triggers trigger N5.

[0065] A new trigger N5 is added, designed to compare the comparison results from the current sampling comparator circuit and the voltage sampling comparator circuit to determine which of the switches K1, K2, and K3 should be opened / closed in different modes. Specifically, trigger N5 is activated when the current sampling comparator circuit output is low and the voltage sampling comparator circuit output is high or there is no input; when both the current and voltage sampling comparator circuits output are high, trigger N5 remains in its original state.

[0066] In addition to the aspects mentioned above, the improved impedance measurement system also includes the following improved designs:

[0067] 5. In the initial state of the system, whether in the launch or maintenance / test state, the system will use the power supply circuit. Subsequently, different switches will be turned on and off depending on the different comparison results. That is: in maintenance or test mode, no tuning work is required, so the power supply circuit should be disconnected; in launch mode, tuning work is required, so the power supply circuit should be continuously used.

[0068] 6. Based on design experience and application scenarios, the voltage regulator connected to the +28V DC power supply via the second switch K2 stabilizes the voltage to -4dB, and can be stabilized to -6dB via the second resistor R2 connected in parallel.

[0069] Having understood the specific circuit structure of the optimized impedance measurement system of this application, the various operating modes and application examples of the optimized impedance measurement system are described below. Generally speaking, the operating modes include: maintenance mode, test mode, and transmission mode. Based on its operating state, there are the following three application examples:

[0070] a) When the system is in maintenance or test mode and tuning is not required, there will be no radio frequency interference. The third switch K3 automatically closes, and the power supply circuit supplies power to the impedance measurement system. For example, the transceiver can provide a 28V DC voltage to the impedance measurement system of the antenna tuning system. The voltage regulator contains a third resistor (not shown) connected in parallel, which stabilizes the voltage at -4dB. Since the system is in test mode and the transceiver's preset frequency is not available, the current will flow through the topmost path. Because the current through the second inductor L is small in test mode, the sampling current difference across the second inductor is also small. Therefore, the current comparison module N4 will output a low level, triggering flip-flop N5 to continue outputting a low level, disconnecting the 28V power supply circuit, and preventing tuning.

[0071] b) When the system is in transmit mode and there is no radio frequency interference, the first switch K1 automatically closes, and the power supply circuit supplies power to the impedance measurement system. For example, the transceiver can provide a 28V DC voltage to the impedance measurement system of the antenna tuning system. The voltage regulator contains a third resistor connected in parallel, and the two stabilize the voltage at -4dB. The transceiver sends the frequency to be tuned to the frequency divider, whose internal transformer provides a voltage signal proportional to the radio frequency signal of different frequencies, and transmits it to the radio frequency impedance matching network to set different reactance component values, thereby achieving tuning at different frequencies. At the same time, since the circuit uses a second resistor R2 in parallel, two voltage references are generated at this frequency: voltage reference 1 and voltage reference 2. At this time, the input voltage signal is within the range of the two voltage references, and the first voltage comparison module N1 outputs a high level, the second voltage comparison module N2 outputs a high level, and the third voltage comparison module N3 outputs a high level. In the transmitting state, the current through the second inductor L is large, which increases the sampling voltage difference across the second inductor L. This causes the current comparison module N4 to output a high level. At this time, the trigger N5 outputs a high level, making its output high. Therefore, the JK trigger N5 cannot be triggered, and the trigger output remains in its original state, i.e., the output is high. This causes the first switch K1 and the second switch K2 to remain closed, continuously providing the power supply current for the power circuit to perform the tuning operation.

[0072] c) When the system is in transmit mode and radio frequency interference is present, the first switch K1 automatically closes, and the power supply circuit supplies power to the impedance measurement system. For example, the transceiver can provide a 28V DC voltage to the impedance measurement system of the antenna tuning system. The operating states of the first voltage comparison module N1, the second voltage comparison module N2, and the third voltage comparison module N3 are the same as in application example b, i.e., the first voltage comparison module N1 outputs a high level, the second voltage comparison module N2 outputs a high level, and the third voltage comparison module N3 outputs a high level. However, radio frequency interference will cause the current through the second inductor L to be smaller in the transmit state, which leads to the same scenario as in application example a), i.e., triggering the flip-flop N5 to output a low level, disconnecting the power supply circuit. At this time, the filter will filter out the radio frequency noise, reduce the radio frequency interference, and allow the impedance measurement system to work normally, maintaining the scenario in application example b).

[0073] In summary, this application presents an impedance measurement system with a filter, and an optimized design of an antenna tuning device including the impedance measurement system. Compared with the prior art, this application has the following advantages: by adding a filter circuit design to the impedance measurement circuit of the antenna tuning device, false triggering of the JK flip-flop inside the circuit is prevented, thereby avoiding power failure of the antenna tuning device, greatly reducing the failure rate of the high-frequency communication system during long-distance communication, and effectively ensuring the availability of the shortwave system in a long-distance communication environment.

[0074] While different embodiments have been described above, it should be understood that they are merely examples and not limitations. Those skilled in the art will appreciate that various modifications in form and detail may be made without departing from the spirit and scope of the invention as defined in the appended claims. Therefore, the breadth and scope of the invention disclosed herein should not be limited by the exemplary embodiments disclosed above, but should be defined solely by the appended claims and their equivalents.

Claims

1. An impedance measurement system for a shortwave communication system, comprising: Power supply circuit; A power-on control circuit is configured to directly perform power-on or power-off operations on the power supply circuit. A trigger control circuit is configured to determine whether to continue powering on the impedance measurement system based on the output of the impedance measurement system. A current sampling comparator circuit is configured to sample the current and compare the sampled data with a reference current. A voltage sampling comparator circuit is configured to sample the voltage and compare the sampled data with a reference voltage; The impedance measurement system is characterized in that it further includes: The filter connected to the power supply circuit, the current sampling comparison circuit, and the voltage sampling comparison circuit is configured to filter out radio frequency noise to reduce radio frequency interference. The filter includes: A first filter connected to the power supply circuit, the current sampling comparison circuit, and the voltage sampling comparison circuit is configured to filter out reactive parameters in the circuit. The second filter, connected to the first filter and the current sampling comparison circuit, is configured to filter out radio frequency noise and reduce radio frequency interference.

2. The impedance measurement system as described in claim 1, characterized in that, The first filter is a low-pass inductor / capacitor filter, while the second filter consists of a diode, a first resistor, a first inductor, a capacitor, and a varistor.

3. The impedance measurement system as described in claim 1, characterized in that, The current sampling and comparison circuit includes a first current sampling module, a second inductor, a second current sampling module, and a current comparison module; In this process, after the first current sampling module completes the initial current sampling, the current passes through the second inductor, causing the sampling current difference at the two ends of the second inductor to increase. Subsequently, the second current sampling module samples the current again. Finally, the current comparison module compares the initially sampled current with the resampled current.

4. The impedance measurement system as described in claim 3, characterized in that, The voltage sampling comparison circuit includes: A first voltage comparison circuit consisting of a first voltage reference module and a first voltage comparison module; A second voltage comparison circuit consisting of a second voltage reference module, a second voltage comparison module, and a second resistor connected in series; and A third voltage comparison circuit is composed of a third voltage comparison module connected to the first voltage comparison module and the second voltage comparison module; The third voltage comparison module compares the comparison result from the first voltage comparison circuit with the comparison result from the second voltage comparison circuit again to ensure the accuracy of the output result.

5. The impedance measurement system as described in claim 4, characterized in that, The impedance measurement system also includes: A first switch is configured to simultaneously control two signals supplied to the first voltage reference module and the second voltage reference module, wherein the first switch automatically closes when the system is in transmit mode to simultaneously control the first voltage comparison circuit and the second voltage comparison circuit. The second switch is configured to control the connection of the power circuit; A third switch is configured to control the current sampling comparison circuit, wherein the third switch is automatically closed when the system is in maintenance or test mode. A trigger is configured to compare the comparison result from the current sampling comparison circuit with the comparison result from the voltage sampling comparison circuit to distinguish which of the first, second, and third switches should be opened or closed in different modes; Specifically, the trigger is activated when the current sampling comparison circuit outputs a low level and the voltage sampling comparison circuit outputs a high level or there is no input; the trigger remains in its original state when the current sampling comparison circuit outputs a high level and the voltage sampling comparison circuit outputs a high level.

6. The impedance measurement system as described in claim 5, characterized in that, The impedance measurement system further includes a voltage regulator connected to the power supply voltage via the second switch, the voltage regulator stabilizing the voltage to -4dB and stabilizing the voltage to -6dB via a second resistor connected in parallel.

7. The impedance measurement system as described in claim 6, characterized in that, The impedance measurement system includes the following three operating modes: maintenance mode, test mode, and transmission mode; In the initial system state, regardless of whether it is in launch, maintenance, or test mode, the system will use the power supply circuit; subsequently, different switches will be turned on or off based on different comparison results. In the maintenance or test mode, tuning is not required and the power supply circuit is disconnected; however, in the transmission mode, tuning is required and the power supply circuit is continuously used for power supply.

8. The impedance measurement system as described in claim 6, characterized in that, The impedance measurement system includes the following three application examples: a) In the maintenance mode or the test mode, no tuning is required and there is no radio frequency interference. The third switch closes automatically, and the power supply circuit supplies power to the impedance measurement system. The voltage regulator contains a third resistor connected in parallel, and the two stabilize the voltage at -4dB. Since the maintenance or test mode is in effect, there is no transceiver preset frequency, and the current through the second inductor is small, resulting in a small sampling current difference across the two ends of the second inductor. Therefore, the current comparison module outputs a low level, which triggers the trigger to continue outputting a low level, disconnecting the power supply circuit and preventing tuning from being performed. (b) In the transmission mode and without radio frequency interference, the first switch automatically closes, and the power supply circuit supplies power to the impedance measurement system. The voltage regulator contains a third resistor connected in parallel, and the two stabilize the voltage at -4dB. Since the second resistor is used in parallel, the frequency generates two voltage references: a first voltage reference and a second voltage reference. At this time, the input voltage signal is within the range of these two voltage references. Therefore, the first voltage comparison module outputs a high level, the second voltage comparison module outputs a high level, and the third voltage comparison module also outputs a high level. Since the current through the second inductor is large in the transmission mode, the sampling current difference at the two ends of the second inductor is also large, which causes the current comparison module to output a high level. At this time, the trigger outputs a high level, so the trigger cannot be triggered, and the trigger output maintains its original state, that is, the output is a high level. This keeps the first switch and the second switch closed, continuously providing power current for performing the tuning operation. c) In the transmission mode and when radio frequency interference is present, the first switch automatically closes, the power supply circuit supplies power to the impedance measurement system, the first voltage comparison module outputs a high level, the second voltage comparison module outputs a high level, and the third voltage comparison module also outputs a high level; however, the radio frequency interference causes the current through the second inductor to be smaller in the transmission state, which triggers the trigger to output a low level, disconnecting the power supply circuit. At this time, the filter filters out radio frequency noise, reduces radio frequency interference, and enables the impedance measurement system to work normally.

9. The impedance measurement system as described in claim 3, characterized in that, The second inductor is a variable inductor.

10. An antenna tuning device, characterized in that, The antenna tuning device includes an impedance measurement system as described in any one of claims 1-9.

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