A multi-channel unmanned aerial vehicle long-range detection system

Abstract

The present application relates to the technical field of remote identification of unmanned aerial vehicle, and particularly relates to a multi-channel unmanned aerial vehicle long-distance detection system, which is provided with multiple radio frequency receiving units, each of which is connected with a receiving antenna, a double-frequency band-pass filter, a program-controlled low-noise amplifier, an impedance matching network and a radio frequency demodulation module in turn in series, so as to reduce the cascade noise coefficient of the receiving link, improve the receiving sensitivity and the detection distance; a serial port multiplexing unit connects the data output ends of the multiple radio frequency demodulation modules to the same universal asynchronous receive-transmit transmission interface of the main control unit, so as to save the interface resources of the main control unit; the multiple universal input-output control pins are connected to the power supply circuits of the low-noise amplifiers respectively, and according to the comparison result of the signal strength indication information and the preset near-distance threshold value, the power supply on-off of each low-noise amplifier is independently controlled, so as to realize the far-near field adaptive gain control.

Description

Technical Field

[0001] This invention relates to the field of remote identification technology for unmanned aerial vehicles (UAVs), and in particular to a multi-channel long-range detection system for UAVs. Background Technology

[0002] Drone remote identification technology is a key means in the field of low-altitude security. Ground detection equipment achieves real-time detection and tracking by receiving identification signals broadcast by drones. Currently, mainstream drone remote identification and detection receivers on the market generally adopt a minimum system board architecture with a single Wi-Fi / Bluetooth SoC chip (such as the ESP32 series). The radio frequency signal enters directly into the chip without any external filtering or low-noise amplification processing.

[0003] Such solutions generally suffer from insufficient detection range in practical applications. Actual measurements show that their effective detection radius is only about 300m, which is insufficient to meet the actual needs of airports, border areas, and large-scale events requiring kilometer-level coverage. According to the wireless communication receiver sensitivity formula, the receiver sensitivity directly depends on the cascaded noise figure. Because the chip's own receiver noise figure is as high as 6dB to 8dB, and there is no pre-amplifier after the antenna to suppress subsequent noise, the overall sensitivity is only about -86dBm. Based on calculations using the free-space path loss formula, under the typical condition of a UAV transmit power of +17dBm, 300m is already the theoretical limit.

[0004] In other words, within a limited detection range, the device needs to cover as much airspace as possible to capture targets, but the single-channel architecture also has limitations in terms of airspace coverage. A single radio frequency channel can only connect to one antenna; when using a directional antenna, the effective coverage angle is limited, and when using an omnidirectional antenna, the long-distance gain is insufficient—both cannot be achieved simultaneously. To achieve large-area coverage, multiple devices must be deployed in a network, but there are challenges in data synchronization and collaborative processing among multiple devices, significantly increasing system complexity and cost. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a multi-channel long-range detection system for unmanned aerial vehicles (UAVs) that can improve the detection range of remote identification signals of UAVs and achieve large-scale horizontal airspace coverage.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: A multi-channel UAV long-range detection system includes a main control unit, a serial port multiplexing unit, and multiple independent radio frequency receiving units; Each of the radio frequency receiving units is connected in series with a receiving antenna, a dual-band pass filter, a programmable low-noise amplifier, an impedance matching network, and a radio frequency demodulation module. The radio frequency demodulation module is configured to receive and demodulate remote identification protocol data packets broadcast by the UAV. The data output terminals of multiple radio frequency demodulation modules are all connected to the same general asynchronous transceiver interface of the main control unit through a serial port multiplexing unit. The main control unit is provided with multiple general-purpose input / output control pins. Each general-purpose input / output control pin is connected to the power supply circuit of the programmable low-noise amplifier in the corresponding radio frequency receiving unit, so as to control the on / off state of each programmable low-noise amplifier. The main control unit controls the switching on and off of each programmable low-noise amplifier based on the received signal strength indication information; when the signal strength indication information is higher than a preset proximity threshold, the power supply to the corresponding programmable low-noise amplifier is cut off; when the signal strength indication information is lower than the preset proximity threshold, the power supply to the corresponding programmable low-noise amplifier is turned on.

[0007] The beneficial effects of this invention are as follows: This invention employs multiple independent radio frequency (RF) receiving units. Each RF receiving unit is sequentially connected in series with a receiving antenna, a dual-band pass filter, a programmable low-noise amplifier, an impedance matching network, and an RF demodulation module. This effectively reduces the cascade noise figure of the receiving link, significantly improving receiving sensitivity and detection range. Simultaneously, each RF receiving unit can be connected to antennas pointing in different horizontal directions, and the effective coverage sectors of each antenna are interlocked, enabling a single device to achieve wide-area horizontal airspace coverage. A serial port multiplexing unit connects the data outputs of multiple RF demodulation modules to a single universal asynchronous transceiver interface of the main control unit, enabling… Multiple channels share a single hardware serial port, effectively saving interface resources of the main control unit and reducing system complexity. The main control unit's multiple general-purpose input / output control pins are connected to the power supply circuits of the low-noise amplifiers in each RF receiving unit. Based on the comparison between the signal strength indication information and the preset near-field threshold, the power supply of each low-noise amplifier is independently controlled. When the signal strength is higher than the near-field threshold, the power supply is cut off to avoid saturation distortion caused by strong signals. When the signal strength is lower than the near-field threshold, the power supply is turned on to ensure the amplification gain of weak signals at long distances. This achieves near-field and far-field adaptive gain control, enabling the system to maintain excellent receiving performance across the entire distance range. Attached Figure Description

[0008] Figure 1 This is a connection block diagram of the multi-channel UAV long-range detection system of the present invention; Figure 2 This is a block diagram of the overall hardware architecture of the present invention; Figure 3This is a detailed block diagram of the single-channel radio frequency link of the present invention; Figure 4 This is a detailed hardware wiring diagram of the serial port multiplexing unit of the present invention; Label Explanation: 1. Main control unit; 2. Serial port multiplexing unit; 3. RF receiving unit; 4. Receiving antenna; 5. Dual-bandpass filter; 6. Programmable low-noise amplifier; 7. Impedance matching network; 8. RF demodulation module; 9. Dual-channel communication unit; 10. Local storage unit; 11. Power supply unit. Detailed Implementation

[0009] To explain in detail the technical content, objectives, and effects of the present invention, the following description is provided in conjunction with the embodiments and accompanying drawings.

[0010] Please refer to Figure 1 A multi-channel UAV long-range detection system includes a main control unit 1, a serial port multiplexing unit 2, and multiple independent radio frequency receiving units 3; Each of the radio frequency receiving units 3 is connected in series with a receiving antenna 4, a dual-band pass filter 5, a programmable low-noise amplifier 6, an impedance matching network 7, and a radio frequency demodulation module 8. The radio frequency demodulation module 8 is configured to receive and demodulate remote identification protocol data packets broadcast by the UAV. The data output terminals of the multiple radio frequency demodulation modules 8 are all connected to the same universal asynchronous transceiver interface of the main control unit 1 through a serial port multiplexing unit 2. The main control unit 1 is provided with multiple general-purpose input / output control pins. Each general-purpose input / output control pin is connected to the power supply circuit of the programmable low-noise amplifier 6 in the corresponding radio frequency receiving unit 3, so as to control the on / off state of each programmable low-noise amplifier 6 respectively. The main control unit 1 controls the on / off state of each programmable low-noise amplifier 6 according to the received signal strength indication information; when the signal strength indication information is higher than a preset proximity threshold, the power supply of the corresponding programmable low-noise amplifier 6 is cut off; when the signal strength indication information is lower than the preset proximity threshold, the power supply of the corresponding programmable low-noise amplifier 6 is turned on.

[0011] As can be seen from the above description, the beneficial effects of the present invention are as follows: This invention employs multiple independent radio frequency (RF) receiving units 3, each of which is sequentially connected in series with a receiving antenna 4, a dual-band pass filter 5, a programmable low-noise amplifier 6, an impedance matching network 7, and an RF demodulation module 8. This effectively reduces the cascade noise figure of the receiving link, significantly improving receiving sensitivity and detection range. Simultaneously, each RF receiving unit 3 can be connected to antennas pointing in different horizontal directions, and the effective coverage sectors of each antenna are interlocked, enabling a single device to achieve wide-area horizontal airspace coverage. A serial port multiplexing unit 2 connects the data outputs of multiple RF demodulation modules 8 to the same universal asynchronous transceiver unit 1. The interface allows multiple channels to share a single set of hardware serial port resources, effectively saving interface resources of the main control unit 1 and reducing system complexity. The multiple general-purpose input / output control pins of the main control unit 1 are connected to the power supply circuits of the low-noise amplifiers in each RF receiving unit 3. Based on the comparison between the signal strength indication information and the preset near-field threshold, the power supply of each low-noise amplifier is controlled independently. When the signal strength is higher than the near-field threshold, the power supply is cut off to avoid saturation distortion caused by strong signals. When the signal strength is lower than the near-field threshold, the power supply is turned on to ensure the amplification gain of weak signals at long distances. This realizes near-field adaptive gain control, enabling the system to maintain excellent receiving performance across the entire distance range.

[0012] Furthermore, the dual-bandpass filter 5 is a surface acoustic wave (SAW) filter, and the operating frequency band of the SAW filter includes 2.402 GHz to 2.484 GHz and 5.725 GHz to 5.850 GHz. The out-of-band suppression index of the SAW filter outside the passband is greater than or equal to 45 dB.

[0013] As described above, by employing a surface acoustic wave filter and setting the operating frequency bands to 2.402GHz~2.484GHz and 5.725GHz~5.850GHz, the filter is precisely matched with the operating frequency band of the UAV remote identification protocol, ensuring low-loss passage of useful signals. By setting the out-of-band suppression index to no less than 45dB, various interference signals outside the passband are effectively attenuated, preventing strong interference from causing the low-noise amplifier to prematurely enter the saturation region, thereby ensuring the signal purity and reception reliability of the receiving link across the entire frequency range.

[0014] Furthermore, the noise figure of the programmable low-noise amplifier 6 under normal temperature conditions is less than or equal to 1.2dB, and the radio frequency signal gain range of the programmable low-noise amplifier 6 is 16dB~20dB.

[0015] As described above, by limiting the noise figure of the low-noise amplifier to no more than 1.2dB and the RF signal gain range to 16dB~20dB, the additional noise introduced by the low-noise amplifier itself is extremely low, and sufficient gain is provided to suppress the noise contribution of the subsequent circuits. The combination of the two results in a significant reduction in the cascaded noise figure of the entire receiving link, thereby effectively improving the receiving sensitivity and detection range of the system.

[0016] Furthermore, the power supply circuit of the programmable low-noise amplifier 6 is provided with a field-effect transistor, and the gate of the field-effect transistor is connected to the general-purpose input / output control pin of the main control unit 1.

[0017] As described above, by setting a field-effect transistor in the power supply circuit of the low-noise amplifier and directly connecting the general-purpose input / output control pin of the main control unit 1 to the gate of the field-effect transistor, fast on / off control of the power supply to the low-noise amplifier is achieved. This control method has a simple circuit structure, fast response speed, and the field-effect transistor consumes almost no static current in the off state, which is beneficial to reducing system power consumption.

[0018] Furthermore, the serial port multiplexing unit 2 is an analog switch chip, the model of which is CD4052, and the channel selection pin of the analog switch chip is connected one-to-one with the general-purpose input / output pin of the main control unit 1.

[0019] As described above, by using the CD4052 analog switch chip as the serial port multiplexing unit 2, this chip has a dual four-to-one structure. The two sets of switches are controlled by the same set of channel selection pins, which can synchronously complete the bidirectional switching of multiple signals. The channel selection pins are connected one-to-one with the general-purpose input and output pins of the main control unit 1. The main control unit 1 can complete the channel selection by simply outputting high and low levels. The control logic is simple and reliable, the switching speed is fast, and the electrical performance parameters such as on-resistance and crosstalk between channels are better than the requirements of serial communication, without affecting the communication quality.

[0020] Furthermore, the impedance matching network 7 is a π-type LC impedance matching network 7, which is connected between the RF output terminal of the programmable low-noise amplifier 6 and the RF input terminal of the RF demodulation module 8.

[0021] As described above, by setting a π-type LC impedance matching network 7 between the RF output terminal of the programmable low-noise amplifier 6 and the RF input terminal of the RF demodulation module 8, impedance matching between the two stages is achieved, so that the signal power amplified by the low-noise amplifier can be transmitted to the RF demodulation module 8 with minimal reflection loss, ensuring that the gain advantage of the low-noise amplifier is not offset by the reflection loss caused by impedance mismatch.

[0022] Furthermore, the insertion loss of the link after the impedance matching network 7 and the programmable low-noise amplifier 6 are cascaded is less than or equal to 0.8 dB.

[0023] As described above, by limiting the insertion loss of the link after cascading the impedance matching network 7 and the programmable low-noise amplifier 6 to no more than 0.8dB, the power loss of the RF signal along the entire transmission path is minimized, so that the amplification effect of the low-noise amplifier on weak signals can be effectively transmitted to the RF demodulation module 8, thus preserving the detection distance gain brought about by the improved sensitivity to the greatest extent.

[0024] Furthermore, the number of radio frequency receiving units 3 is four, and the four radio frequency receiving units 3 are arranged at 90° intervals in the horizontal direction.

[0025] As described above, by setting the number of radio frequency receiving units 3 to four and arranging the four radio frequency receiving units 3 at 90° intervals in the horizontal direction, the coverage sectors of the antennas connected to each unit are connected end to end in the horizontal direction, forming a complete 360° omnidirectional coverage area, thereby eliminating detection blind spots. A single device can complete all-round detection of UAV targets in the surrounding airspace.

[0026] For further details, please refer to Figure 1 It also includes a dual-channel communication unit 9, which is connected to the main control unit 1.

[0027] As described above, by setting up a dual-channel communication unit 9 connected to the main control unit 1, the system can simultaneously possess two heterogeneous communication links: Ethernet wired communication and cellular network wireless communication. When one link fails due to network failure, signal blind spot, or physical disconnection, the system can automatically switch to the other link to continue reporting the detection data, effectively ensuring the reliability and real-time performance of data transmission and avoiding data reporting interruptions caused by single link failures.

[0028] For further details, please refer to Figure 1 It also includes a local storage unit 10, which is connected to the main control unit 1.

[0029] As described above, by setting up a local storage unit 10 connected to the main control unit 1, the system can write the detection data into the local storage card in real time when both communication links are interrupted. After the communication links are restored, the system can automatically read the cached data and retransmit it to the backend server, thus achieving zero data loss during network outages, ensuring the integrity and traceability of the detection data, and meeting the requirements of security audit for data continuity.

[0030] In existing technologies, single-channel UAV remote identification and detection equipment is widely used in low-altitude security scenarios such as airports, borders, and large-scale events. These devices are typically deployed in open outdoor environments or urban building complexes, collecting remote identification signals broadcast by UAVs through a single radio frequency receiving channel. To improve detection range, low-noise amplifiers are usually introduced at the hardware front end to enhance the reception of weak signals. However, when the low-noise amplifier is always in a fixed gain state, if a strong signal is present at close range, the amplifier will enter the nonlinear saturation region, generating harmonic distortion and intermodulation distortion, causing the signal on that channel to be unable to be properly demodulated. As deployment environments become increasingly complex, this problem becomes more prominent, and single-channel equipment alone is insufficient to meet the practical needs of large-area airspace coverage.

[0031] To at least address the aforementioned problems, this invention provides a multi-channel UAV long-range detection system, comprising a main control unit 1, a serial port multiplexing unit 2, and multiple independent radio frequency (RF) receiving units 3. Each RF receiving unit 3 is sequentially connected in series with a receiving antenna 4, a dual-bandpass filter 5, a programmable low-noise amplifier 6, an impedance matching network 7, and an RF demodulation module 8, thereby reducing the cascade noise figure of the receiving link and improving receiving sensitivity and detection range. The serial port multiplexing unit 2 connects the data output terminals of multiple RF demodulation modules 8 to the same universal asynchronous transceiver interface of the main control unit 1, enabling multiple channels to share a set of hardware serial port resources. The multiple universal input / output control pins of the main control unit 1 are respectively connected to the power supply circuits of each low-noise amplifier. Based on the comparison result between the signal strength indication information and the preset near-range threshold, the power supply of each low-noise amplifier is independently controlled. When the signal strength is higher than the near-range threshold, the power supply is cut off to avoid saturation distortion; when the signal strength is lower than the near-range threshold, the power supply is turned on to ensure the amplification gain of weak signals at long distances. In this way, the detection range of remote identification signals of UAVs can be effectively increased to the kilometer level. A single device can have a wide horizontal airspace coverage capability. At the same time, it can realize adaptive gain control of near and far fields, so that the system can maintain excellent reception performance in the entire range. In addition, multiple radio frequency receiving units share a set of hardware serial port resources, which effectively reduces the system complexity.

[0032] Please refer to Figures 1 to 4 As shown, one embodiment of the present invention is as follows: Please refer to Figure 1 A multi-channel UAV long-range detection system includes a main control unit 1, a serial port multiplexing unit 2, a dual-channel communication unit 9, a local storage unit 10, multiple power supply units 11, and multiple independent radio frequency receiving units 3. The main control unit 1 is provided with multiple general-purpose input / output control pins. Each general-purpose input / output control pin is connected to the power supply circuit of the programmable low-noise amplifier 6 in the corresponding radio frequency receiving unit 3, so as to control the on / off state of each programmable low-noise amplifier 6 respectively. The main control unit 1 controls the on / off state of each programmable low-noise amplifier 6 according to the received signal strength indication information; when the signal strength indication information is higher than a preset proximity threshold, the power supply of the corresponding programmable low-noise amplifier 6 is cut off; when the signal strength indication information is lower than the preset proximity threshold, the power supply of the corresponding programmable low-noise amplifier 6 is turned on.

[0033] like Figure 2 As shown, in this embodiment, there are four radio frequency receiving units 3. The four radio frequency receiving units 3 are arranged at 90° intervals in the horizontal direction. Each channel covers a 90° sector, and the combination achieves full coverage of the horizontal 360° airspace.

[0034] like Figure 3 As shown, each of the radio frequency receiving units 3 is connected in series with a receiving antenna 4, a dual-band pass filter 5, a programmable low-noise amplifier 6, an impedance matching network 7, and a radio frequency demodulation module 8. The four radio frequency receiving units 3 employ identical hardware design and component selection. The specific implementation parameters are detailed below using channel 0 as an example: The receiving antenna 4 uses a 50Ω impedance-matched SMA-KE (external screw, internal hole) right-angle RF connector, which is mounted on the front panel of the device and supports external dipole, patch, or Yagi antennas with various gain and directivity specifications.

[0035] In this embodiment, the dual-band pass filter 5 is a surface acoustic wave (SAW) filter, employing a custom-designed dual-band narrowband SAW filter, packaged in a 1.4mm×1.1mm CSP package or a 3.0mm×3.0mm QFN package. Key performance indicators: operating frequency bands include 2.402GHz~2.484GHz and 5.725GHz~5.850GHz; first passband 2402MHz~2484MHz (insertion loss ≤1.8dB, in-band ripple ≤0.8dB); second passband 5725MHz~5850MHz (insertion loss ≤2.2dB, in-band ripple ≤1.0dB); notch rejection between the two passbands ≥35dB; out-of-band rejection ≥50dB for 3300MHz~3600MHz; and out-of-band rejection ≥45dB for 4800MHz~4900MHz. The out-of-band rejection index is greater than or equal to 45dB. Operating temperature range: -40℃ to +85℃; frequency temperature coefficient: ≤-35ppm / ℃.

[0036] In this embodiment, the programmable low-noise amplifier 6 uses a domestically produced alternative, such as model BGU8M1X or QPL9503, or a similar model. The measured electrical performance parameters at 2.45GHz are as follows: noise figure NF = 1.1dB (less than or equal to 1.2dB) at room temperature, gain G = 18.2dB (the RF signal gain range of the programmable low-noise amplifier 6 is 16dB~20dB), input return loss |S11| = -14dB, output return loss |S22| = -12dB, output power P1dB at the 1dB gain compression point = +16.5dBm, output power OIP3 at the third-order intermodulation cutoff point = +29dBm, and operating current 8mA (3.3V power supply). The RF input and output ports of the programmable low-noise amplifier 6 are internally matched to 50Ω, requiring only a DC blocking capacitor (a 100pF multilayer ceramic capacitor using C0G dielectric material) for external AC coupling.

[0037] According to Friis's cascade noise figure formula, the approximately 18 dB gain provided by the programmable low-noise amplifier 6 can reduce the noise contribution of subsequent stages (impedance matching network 7 and the internal RF front-end of the RF demodulation module 8) by approximately 63 times (10^(18 / 10)≈63). Therefore, the total cascade noise figure of the entire RF receiving link is mainly determined by the insertion loss of the surface acoustic wave filter and the noise figure of the programmable low-noise amplifier 6 itself. Its theoretical calculation value is: NF_total≈NF_SAW+(NF_LNA - 1) / G_SAW≈1.6dB (where NF_total is the total noise figure of the entire receiving link from the antenna port to the demodulation stage, NF_SAW is the noise figure of the surface acoustic wave filter itself, NF_LNA is the noise figure of the programmable low-noise amplifier 6 itself, and G_SAW is the gain of this filter stage). Compared to the approximately 7dB noise figure of the native bare board, the cascaded noise figure of this solution is reduced by approximately 5.4dB, corresponding to an increase in receiver sensitivity of approximately 5.4dB, from approximately -86dBm to approximately -91dBm. Based on calculations using the free space loss formula, under the conditions of 2.4GHz frequency band and transmit power +17dBm, the receiving distance can be extended from approximately 300m to approximately 1600m (theoretical value). Further optimization with high-gain antennas and other engineering techniques can further enhance the actual effective detection distance to the kilometer level.

[0038] To facilitate understanding of the technical effects of this invention, the complete RF link budget calculation process is provided below: Calculation conditions: The transmitter is an OpenDroneID Wi-Fi Beacon with a transmit power of +17dBm (50mWEIRP) and a transmit antenna gain of 0dBi (omnidirectional); the receiver operates at a frequency of 2437MHz (center frequency of the 2.4GHz band) and has a receive antenna gain of 3dBi; the signal bandwidth B = 20MHz; the minimum signal-to-noise ratio SNR_req for protocol demodulation is 8dB (802.11g OFDM mode).

[0039] Step 1: Calculate the noise floor. kTB = -174dBm / Hz + 10lg(20×10) 6 )≈-174+73= -101dBm (where KTB is the thermal noise power at the receiver input). Step 2: Calculate the cascade noise figure: NF_total=1.6dB; Step 3: Calculate receiver sensitivity: P_rx(min) = -101dBm + 1.6dB + 8dB ≈ -91.4dBm (where P_rx(min) is the minimum signal power that the receiver needs to receive at the antenna port to ensure that the protocol can demodulate, which is the receiver sensitivity). Step 4: Calculate the maximum allowable path loss: PL_max = P_tx + G_tx + G_rx - P_rx(min) = 17 + 0 + 3 - (-91.4) = 111.4 dB (where PL_max is the maximum allowable path loss, P_tx is the transmit power, G_tx is the transmit antenna gain, G_rx is the receive antenna gain, and P_rx(min) is the receive sensitivity). Step 5: Substitute the values ​​into the free space path loss formula to calculate the maximum distance: 111.4=32.45+20lg(2437)+20lg d→20lg d≈111.4-32.45-67.74= 11.21; lg d≈0.56→d≈3.63km; The theoretical calculations above show that, under ideal free-space propagation conditions, the maximum single-channel detection range of this invention can reach approximately 3.6 km. In practical engineering, considering actual propagation factors such as atmospheric attenuation, multipath fading, polarization mismatch, and antenna pattern nulls, a link margin of 3 dB to 6 dB is typically allowed, resulting in an actual effective detection range of approximately 1.5 km to 3 km. Compared to the native bare-board detection range of approximately 300 m, this invention achieves a 5 to 10-fold increase in detection range.

[0040] A P-channel enhancement-mode MOS field-effect transistor is connected in series in the power supply circuit of the programmable low-noise amplifier 6 as a power switch. The gate of this field-effect transistor is connected to the general-purpose input / output control pin of the main control unit 1. In this embodiment, the P-MOS switch is model SI2301, with the following main parameters: drain-source breakdown voltage V_DS = -20V, on-resistance R_DS(on) = 0.13Ω when V_GS = -4.5V, gate-source threshold voltage V_GS(th) = -0.9V, and total gate charge Qg = 4.5nC. Figure 3 As shown by the dashed line, the gate is connected in series with a 10kΩ current-limiting resistor and then to the PB0-PB3 general-purpose input / output control pins of the main control unit 1. A 100kΩ pull-down resistor is connected in parallel between the gate and source. When the general-purpose input / output control pin of the main control unit 1 outputs 0V, the gate-source voltage of the P-MOS switch is negative and its absolute value is greater than the turn-on threshold voltage. The P-MOS switch is turned on, and the programmable low-noise amplifier 6 receives power and enters normal operation. When the general-purpose input / output control pin outputs a high level (i.e., 3.3V), the gate-source voltage is approximately zero, the P-MOS switch is turned off, and the programmable low-noise amplifier 6 is powered off and enters bypass mode. The switching response time of this on / off control method is no more than 10μs, and the static power consumption is zero.

[0041] In this embodiment, the impedance matching network 7 is a π-type LC impedance matching network 7, connected between the RF output of the programmable low-noise amplifier 6 and the RF input of the RF demodulation module 8. The π-type LC adjustable impedance matching network 7 consists of a surface-mount inductor Ls1 (2.2nH, 0402 package, quality factor ≥50 at 2.4GHz), a surface-mount inductor Ls2 (1.5nH, 0402 package), and a surface-mount capacitor Cp (0.8pF, 0402 package, C0G material), forming a π-type topology. It is mounted approximately 2mm after the output DC blocking capacitor of the programmable low-noise amplifier 6 and before the RF input pin pads of the RF demodulation module 8. The overall insertion loss of the cascaded impedance matching network 7 and the programmable low-noise amplifier 6 is no higher than 0.8dB.

[0042] In this embodiment, the RF demodulation module 8 is an ESP32-C5 module, configured to receive and demodulate remote identification protocol data packets broadcast by the drone, supporting 2.4GHz and 5GHz dual-band Wi-Fi 6 and Bluetooth 5 protocol stacks. The firmware of the RF demodulation module 8 is based on ESP-IDF v5.2 or later SDK, configured in Wi-Fi sniffer mode, dual-band parallel listening, and includes a built-in OpenDroneID protocol parsing library.

[0043] like Figure 2 and Figure 4As shown in this embodiment, the serial port multiplexing unit 2 is an analog switch chip, specifically the CD4052 analog switch chip, which is a dual 4-to-1 CMOS analog switch chip (TSSOP-16 package) / multiplexer chip manufactured by Texas Instruments (TI). The channel selection pins of this chip are connected one-to-one with the general-purpose input / output pins of the main control unit 1. Internally, this chip contains two sets of 4-to-1 analog switches (X group and Y group) that are functionally completely independent but jointly controlled by the same set of address selection lines (A, B).

[0044] like Figure 4 As shown, the specific pin connections are as follows: The X0~X3 input terminals of the X group switches are respectively connected to the UART_TX output pins of the four ESP32-C5 modules, and the X_COM common terminal is connected to the RX pin (i.e., PA10) of the USART0 chip in the main control unit 1; the Y0~Y3 input terminals of the Y group switches are respectively connected to the UART_RX input pins of the four ESP32-C5 modules, and the Y_COM common terminal is connected to the TX pin (i.e., PA9) of the USART0 chip in the main control unit 1; the channel selection pins A and B are respectively connected to the two general-purpose input / output pins PA0 and PA1 of the main control unit 1; the INH pin is directly grounded, and the chip is always in the enabled state; the VDD pin is connected to a 3.3V power supply, and a decoupling capacitor is connected in parallel nearby; the VEE pin and VSS pin are grounded.

[0045] The CD4052 analog switch chip has a typical on-resistance of approximately 125Ω under 3.3V power supply conditions, inter-channel crosstalk of less than -40dB at a frequency of 1MHz, and a switching time of approximately 30ns. These electrical performance parameters are far superior to the signal integrity requirements of UART serial communication (typical baud rate of 115200bps) and will not introduce bit errors.

[0046] The data output terminals of multiple RF demodulation modules 8 are all connected to the same general asynchronous transceiver interface of the main control unit 1 through the serial port multiplexing unit 2. The combination logic of the two-bit binary address is as follows: when A=0 and B=0, channel 0 is selected; when A=1 and B=0, channel 1 is selected; when A=0 and B=1, channel 2 is selected; when A=1 and B=1, channel 3 is selected.

[0047] The polling cycle design needs to balance two conflicting requirements: a shorter polling cycle reduces data latency across channels and increases refresh rate; while a longer dwell time on a single channel ensures complete reception of a maximum-length Remote Identification Protocol (RIP) data frame. At a baud rate of 115200 bps, the serial transmission time for a maximum-length RIP data packet (approximately 512 bytes) is about 44 ms. Considering a certain margin, this embodiment sets the polling cycle to 60 ms, allocating a communication window of approximately 15 ms per channel.

[0048] The dual-channel communication unit 9 is connected to the main control unit 1.

[0049] The dual-channel communication unit 9 includes a wired Ethernet communication link and a wireless cellular communication link; In this embodiment, the wired Ethernet communication link uses the YT8512 chip from Yutai Microelectronics as the core to construct the RMII interface Ethernet PHY layer. The YT8512 chip is connected to the MAC built into the main control unit 1 via a 7-wire RMII bus. The clock output of the 25MHz active crystal oscillator is simultaneously connected to the XI pin of the YT8512 chip and the RMII_REF_CLK pin (PA1) of the main control unit 1. The MDI differential pairs (TXP / TXN, RXP / RXN) are connected to the RJ45 integrated socket through an H1102NL 1:1 network isolation transformer.

[0050] At the hardware level, by pulling the RX_DV pin up to 3.3V through a 10kΩ resistor and pulling the RXD3 pin down to GND through a 10kΩ resistor, the YT8512 chip enters the RMII2 interface mode by default after power-on.

[0051] In this embodiment, the wireless cellular communication link is based on a DX-CT511 module from China Mobile IoT Company. This module is based on the ASR1603 chip platform and supports LTE CAT1 cellular network access and GPS / BeiDou dual-mode satellite positioning. The DX-CT511 module is connected to the UART6 peripherals (i.e., PC6-TX and PC7-RX) of the main control unit 1 via a universal asynchronous transceiver interface.

[0052] The module is externally connected to a combined LTE main antenna (SMA interface) and a GNSS active ceramic antenna (SMA interface). It uses the AT command set for dialing, TCP / UDP data transmission and reception, and GNSS positioning information polling.

[0053] The local storage unit 10 is connected to the main control unit 1.

[0054] like Figure 2 As shown, in this embodiment, the local storage unit 10 uses a four-wire SDIO bus to connect to an external TF memory card. The SDIO peripheral of the main control unit 1 is configured as a 4-bit parallel data bus mode (D0~D3), occupying four I / O pins PC8~PC11, plus CLK (PC12) and CMD (PD2) to form a standard 6-wire SD interface.

[0055] The TF card slot uses a push-pull self-ejecting Micro SD Card Socket. The CD pin of the card slot is a normally open mechanical contact, which closes to GND when the card is inserted. The CD signal line is connected to the PE0 pin of the main control unit 1 (configured as an EXTI0 external interrupt input, triggered by a falling edge). After performing 50ms debounce processing in the interrupt service routine, the FatFS disk mount function is called.

[0056] The FatFS file system is configured in FAT32 format with a sector size of 512 bytes, and long filename support and the TRIM command are enabled. The directory structure for log storage is / LOG / YYYYMM / YYYYMMDD / , and a CSV file is generated every hour. Each line of the file contains fields such as timestamp, channel number, UAV UAS ID, latitude and longitude, altitude, speed, RSSI, and data source identifier.

[0057] In this embodiment, the multiple power supply units 11 adopt a power supply architecture with two-stage conversion and independent voltage regulation in different zones.

[0058] The first stage uses an SCT2630 wide input voltage buck converter to step down the 48V from a wide input voltage range of 12V to 24V or the output of a PoE powered module to a 3.8V intermediate DC bus voltage. The SCT2630 wide input voltage buck converter supports an input voltage range of 4.5V to 60V and a maximum output current of 3A.

[0059] The second stage uses a high-frequency synchronous buck converter (MP2225) to convert the 3.8V intermediate bus voltage into two independent output voltages: one 5V / 1A supplying the DX-CT511 LTE module; the other 3.3V / 2A supplying all digital and analog devices in the 3.3V voltage domain of the system.

[0060] In terms of power supply mode, the 802.3at compliant PoE receiving module extracts 48V DC power from the RJ45 network cable, and after full-bridge rectification and negotiation with the PD controller, outputs a stable 12V / 2A to the input terminal of the SCT2630 wide input voltage buck converter; an external 12V or 24V battery / switching power adapter is connected to the input terminal of the SCT2630 wide input voltage buck converter through a DC 5.5×2.1mm round power socket (with reverse connection protection diode); when PoE and DC are connected at the same time, the higher voltage is automatically selected for power supply through the dual Schottky diode OR-ing circuit, and the other is used as a hot backup.

[0061] like Figure 2As shown, the main control digital circuit area, the RF analog circuit area, and the communication module area are each powered by an independent low-dropout linear regulator. The power supply loop of the RF analog circuit area includes a ferrite bead isolation device and a π-type power filter network connected in series. An independent ultra-low noise LDO linear regulator is inserted between the 3.3V digital power bus and the RF analog power supply, and a π-type low-pass filter network consisting of a series ferrite bead and a parallel multilayer ceramic capacitor is arranged at both the input and output terminals of the LDO.

[0062] like Figure 2 As shown by the dashed line, in this embodiment, the main control unit 1 selects the serial ports of four ESP32-C5 modules through a time-division polling CD4052 analog switch chip. After receiving the demodulated data packets from each channel in each round, it extracts the signal strength indication information. The main control unit 1 determines the approximate distance of the current target through a pre-calibrated signal strength indication-distance mapping table. When the signal strength indication information of a certain channel is detected to be higher than the preset near-distance threshold (corresponding to a distance of approximately 500m), it immediately pulls up the level of the corresponding general-purpose input / output control pin to cut off the power supply to the programmable low-noise amplifier 6 of that channel, avoiding saturation distortion caused by strong signals. When the signal strength indication information falls back below the near-distance threshold, it pulls down the general-purpose input / output control pin to turn on the power supply to the programmable low-noise amplifier 6 of that channel, ensuring the amplification gain of weak signals at long distances. A threshold hysteresis of approximately 3dB is set by software to prevent the programmable low-noise amplifier 6 from frequently switching when the target repeatedly crosses the threshold.

[0063] In this embodiment, the main control unit 1 uses a microcontroller, model GD32F427VIT6, manufactured by GigaDevice, as the core control chip of the entire system. This chip is based on the ARM Cortex-M4 32-bit RISC core, with a maximum operating frequency of 200MHz. It has a built-in single-precision hardware floating-point unit and a complete DSP instruction set, and integrates 2MB of Flash program memory and 256KB of SRAM on-chip. In terms of peripheral resources, it integrates a 10 / 100Mbps Ethernet MAC controller (supporting RMII and MII interfaces), up to 8 universal asynchronous transceiver interfaces, 2 SDIO host controllers, and up to 82 general-purpose input / output control pins.

[0064] In this embodiment, the ARM Cortex-M4 core runs at 168MHz (this embodiment selects a conservative clock frequency to reduce power consumption and electromagnetic interference; 200MHz is the chip's nominal maximum frequency). The built-in 10 / 100M Ethernet MAC controller communicates with the external YT8512 physical layer chip via the RMII interface, occupying the following pins: RMII_REF_CLK (PA1), RMII_TX_EN (PG11), RMII_TXD0 (PG13), RMII_TXD1 (PG14), RMII_RX_DV (PA7), RMII_RXD0 (PC4), RMII_RXD1 (PC5), MDIO (PA2), and MDC (PC1). USART0 (PA9-TX, PA10-RX) is connected to four ESP32-C5 modules via CD4052 in a time-division multiplexing configuration, with a baud rate of 115200bps and 8N1 frame format. UART6 (PC6-TX, PC7-RX) connects to the LTE module of model DX-CT511 with a baud rate of 115200bps; SDIO peripherals (PC8-D0, PC9-D1, PC10-D2, PC11-D3, PC12-CLK, PD2-CMD) can be connected to TF memory cards; The two general-purpose input / output control pins PA0 and PA1 serve as channel selection address lines A and B for the CD4052 analog switch chip. The four general-purpose input / output control pins PB0 to PB3 respectively control the gates of the P-MOS switches in the power supply circuit of the four-way programmable low-noise amplifier 6; PA4 can be optionally connected to the INH pin of the CD4052 analog switch chip to quickly disable all analog switch channels in specific scenarios.

[0065] The software is built upon the FreeRTOS real-time operating system to construct a multi-task parallel processing framework. The main tasks include: serial port polling scheduling (60ms cycle), remote identification protocol data parsing, signal strength indication threshold determination and programmable low-noise amplifier control, Ethernet and cellular network dual-network transmission, TF card file system read / write, satellite positioning information update, and system health monitoring and watchdog timer. The tasks are decoupled and communicate with each other through message queues and semaphores to avoid data races and deadlocks.

[0066] Compared with the prior art, the present invention has the following significant advantages: (1) Significant improvement in detection distance: By setting up multiple independent radio frequency receiving units 3, each of which is connected in series with a receiving antenna 4, a dual-band pass filter 5, a programmable low-noise amplifier 6, an impedance matching network 7 and a radio frequency demodulation module 8, the cascade noise figure of the receiving link is significantly reduced from about 7dB to about 1.6dB, corresponding to an increase in receiving sensitivity of about 5.4dB. The effective detection distance of a single channel is significantly increased from about 300m to 1.5km to 3km in open environments (theoretically up to 3.6km) and no less than 1.5km in urban building-obstructed environments. The detection coverage area is increased by about 25 to 100 times. Multiple radio frequency receiving units 3 enable a single device to have horizontal large-area airspace coverage capability, so that the system can meet the engineering requirements of large-area application scenarios such as airport perimeter radius and long-distance linear coverage of border lines.

[0067] (2) Near-field adaptive gain control: The main control unit 1 utilizes its rich set of general-purpose input / output control pins to achieve independent power supply control for each of the four programmable low-noise amplifiers 6. Combined with software-level signal strength indication threshold determination (500m switching threshold plus 3dB hysteresis anti-jitter), a simple, zero-static-power, microsecond-level response near-field adaptive gain control strategy is achieved. This strategy effectively solves the inherent contradiction in the traditional fixed-gain programmable low-noise amplifier 6 scheme, where strong signals at close range cause saturation distortion and weak signals at long range cause insufficient amplification. This allows a single hardware configuration to simultaneously adapt to UAV target detection within a full range from tens of meters to several kilometers.

[0068] (3) Reliable communication at all times and zero data loss: The dual physical links of Ethernet and cellular network in the dual communication unit 9 are heterogeneously redundant, and the local storage unit 10 provides a three-level data protection system with large-capacity local circular storage. This fundamentally solves the problem of irrecoverable data loss caused by the interruption of a single communication link. During the network outage, all data is written to the local storage unit 10, and the data is automatically resumed after the network is restored, ensuring the eventual consistency of the backend cloud database and the integrity of security audit.

[0069] (4) Efficient reuse of hardware resources: The application of serial port multiplexing unit 2 expands the single set of hardware general asynchronous transceiver transmission interface of main control unit 1 into four independent logical channels through time division multiplexing. The polling period is 60ms. Under the premise of almost not increasing the processing burden of main control chip, the centralized access problem of multi-channel RF demodulation module 8 is solved, and the valuable hardware general asynchronous transceiver transmission interface resources of main control chip are saved for other functional expansion needs.

[0070] (5) Full-scene power supply compatibility: It supports dual-mode power supply of 12V to 24V wide voltage DC and Ethernet power supply. With the independent voltage regulation architecture of the partition and the dedicated low-noise power supply filtering network of the RF area, it can maintain stable RF receiving performance in harsh outdoor electromagnetic environments.

[0071] To objectively verify the technical effects of this invention, a systematic field comparison test was conducted in a science and technology park and its surrounding area in a certain city. The test conditions were uniformly as follows: The drone platform is equipped with the Pixhawk open-source flight controller and the OpenDroneID protocol stack. It broadcasts Wi-Fi Beacon signals through a module of model ESP32-C3, with a transmission power set to +17dBm (50mW EIRP). The transmitting antenna is a 2.4GHz rod-shaped omnidirectional antenna (gain of 2dBi) and the antenna is mounted at a height of 1.5m. The receiving end mounts the device of this invention and the original ESP32 bare board (without filter, without low noise amplifier, and the same antenna) side by side on a 2m high tripod, and records the detection data logs of the two devices simultaneously through a laptop computer.

[0072] Test environment A is an open environment, selected in a standard track and field stadium and surrounding open green space. The terrain is flat, the line of sight is unobstructed, and the background electromagnetic noise is typical of an urban scene. Test environment B is an urban occlusion environment, located on an internal road between high-rise office buildings, with surrounding buildings ranging from 60m to 150m in height. The drone's flight path crosses non-line-of-sight areas, resulting in a complex electromagnetic environment.

[0073] The results of the comparative tests are shown in Table 1: Table 1: Comparison of Test Results for Multiple Test Items

[0074] As shown in the table above, the system of this invention significantly outperforms existing native ESP32 bare-board solutions in all key performance indicators, especially in terms of detection distance, which is improved by approximately 9.9 times in open environments and 8.4 times in urban obstructed environments. In extreme tests simulating a complete interruption of the communication link (simultaneously disconnecting the Ethernet cable and removing the cellular SIM card), the system of this invention automatically transferred the detection data to the local storage unit 10. After communication was restored, the system completed the retransmission of all cached data within approximately 3 minutes, and the cloud database audit showed no data gaps. The device operated stably continuously for more than 720 hours (30 days) in the above test environment without any failures such as crashes, restarts, or data anomalies, and the system reliability was initially verified.

[0075] In summary, the multi-channel UAV long-range detection system provided by this invention, by setting up multiple independent radio frequency (RF) receiving units, each of which is sequentially connected in series with a receiving antenna, a dual-band pass filter, a programmable low-noise amplifier, an impedance matching network, and an RF demodulation module, effectively reduces the cascade noise figure of the receiving link and significantly improves receiving sensitivity and detection range. Simultaneously, each RF receiving unit can be connected to antennas pointing in different horizontal directions, and the effective coverage sectors of each antenna are interlocked, enabling a single device to achieve wide-range horizontal airspace coverage. A serial port multiplexing unit connects the data output terminals of multiple RF demodulation modules to a common port on the main control unit. The universal asynchronous transceiver interface allows multiple channels to share a single set of hardware serial port resources, effectively saving interface resources of the main control unit and reducing system complexity. The main control unit's multiple universal input / output control pins are connected to the power supply circuits of the low-noise amplifiers in each RF receiving unit. Based on the comparison between the signal strength indication information and a preset near-range threshold, the power supply to each low-noise amplifier is independently controlled. When the signal strength is higher than the near-range threshold, the power supply is cut off to avoid saturation distortion caused by strong signals; when it is lower than the near-range threshold, the power supply is turned on to ensure amplification gain for weak signals at long distances. This achieves near-field and far-field adaptive gain control, enabling the system to maintain excellent receiving performance across the entire distance range.

[0076] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent modifications made based on the content of the present invention specification and drawings, or direct or indirect applications in related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A multi-channel unmanned aerial vehicle (UAV) long-range detection system, characterized in that, It includes a main control unit, a serial port multiplexing unit, and multiple independent radio frequency receiving units; Each of the radio frequency receiving units is connected in series with a receiving antenna, a dual-band pass filter, a programmable low-noise amplifier, an impedance matching network, and a radio frequency demodulation module. The radio frequency demodulation module is configured to receive and demodulate remote identification protocol data packets broadcast by the UAV. The data output terminals of multiple radio frequency demodulation modules are all connected to the same general asynchronous transceiver interface of the main control unit through a serial port multiplexing unit. The main control unit is provided with multiple general-purpose input / output control pins. Each general-purpose input / output control pin is connected to the power supply circuit of the programmable low-noise amplifier in the corresponding radio frequency receiving unit, so as to control the on / off state of each programmable low-noise amplifier. The main control unit controls the switching on and off of each programmable low-noise amplifier based on the received signal strength indication information; when the signal strength indication information is higher than a preset proximity threshold, the power supply to the corresponding programmable low-noise amplifier is cut off; when the signal strength indication information is lower than the preset proximity threshold, the power supply to the corresponding programmable low-noise amplifier is turned on.

2. The multi-channel UAV long-range detection system according to claim 1, characterized in that, The dual-bandpass filter is a surface acoustic wave (SAW) filter. The operating frequency band of the SAW filter includes 2.402 GHz to 2.484 GHz and 5.725 GHz to 5.850 GHz. The out-of-band suppression index of the SAW filter outside the passband is greater than or equal to 45 dB.

3. The multi-channel UAV long-range detection system according to claim 1, characterized in that, The noise figure of the programmable low-noise amplifier is less than or equal to 1.2dB under normal temperature conditions, and the radio frequency signal gain range of the programmable low-noise amplifier is 16dB~20dB.

4. The multi-channel UAV long-range detection system according to claim 1, characterized in that, The power supply circuit of the programmable low-noise amplifier is equipped with a field-effect transistor, and the gate of the field-effect transistor is connected to the general-purpose input / output control pin of the main control unit.

5. The multi-channel UAV long-range detection system according to claim 1, characterized in that, The serial port multiplexing unit is an analog switch chip, model CD4052, and the channel selection pin of the analog switch chip is connected one-to-one with the general-purpose input / output pin of the main control unit.

6. The multi-channel UAV long-range detection system according to claim 1, characterized in that, The impedance matching network is a π-type LC impedance matching network, which is connected between the RF output of the programmable low-noise amplifier and the RF input of the RF demodulation module.

7. The multi-channel UAV long-range detection system according to claim 6, characterized in that, The insertion loss of the link after the impedance matching network and the programmable low-noise amplifier are cascaded is less than or equal to 0.8 dB.

8. The multi-channel UAV long-range detection system according to claim 1, characterized in that, The number of radio frequency receiving units is four, and the four radio frequency receiving units are arranged at 90° intervals in the horizontal direction.

9. The multi-channel UAV long-range detection system according to claim 1, characterized in that, It also includes a dual-channel communication unit, which is connected to the main control unit.

10. The multi-channel UAV long-range detection system according to claim 1, characterized in that, It also includes a local storage unit, which is connected to the main control unit.

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