A terahertz band airport runway foreign matter detection radar system and method

Abstract

This invention discloses a terahertz-band foreign object detection radar system and method for airport runways. The system includes: a transmitting module for generating and transmitting a 240 GHz frequency-modulated continuous wave detection signal; a receiving module for receiving the echo signal and down-converting it to an intermediate frequency signal; a turntable system for driving the transmitting and receiving modules to rotate synchronously for azimuth scanning; and a digital control and processing module for generating baseband waveforms, acquiring angle information and intermediate frequency signals, and performing data processing to detect and locate foreign objects. This invention utilizes the physical law that the radar cross-section of a target is inversely proportional to the fourth power of its wavelength, fundamentally enhancing the electromagnetic scattering response of small targets and achieving high-sensitivity detection of millimeter-sized metal debris and non-metallic foreign objects, providing a reliable technical solution for foreign object detection on airport runways.

Description

Technical Field

[0001] This invention relates to the field of radar detection and aviation safety technology, and in particular to a terahertz frequency band radar system and method for detecting foreign objects on airport runways. Background Technology

[0002] Foreign Object Debris (FOD) refers to objects that should not be present on the runway and may cause damage to aircraft, such as metal parts, gravel, and plastic products. FOD poses a serious threat to flight safety. Traditional manual inspection methods are inefficient, highly susceptible to weather and lighting conditions, and require runway closures, disrupting airport operations. Therefore, developing automated, all-weather FOD detection systems has become an inevitable trend.

[0003] Currently, automatic FOD (Foreign Object Debris) detection on airport runways primarily relies on radar technology. Among these, millimeter-wave frequency-modulated continuous wave radar operating in the W-band (approximately 94 GHz) is the mainstream solution. This technology utilizes electromagnetic waves with a wavelength of approximately 3.2 mm and has achieved effective detection of typical FOD. However, its detection capability is fundamentally limited by radar equations. The radar cross-section (RCS) of a target is a key factor determining echo power. For electrically small targets (located in the Rayleigh scattering region) whose size is much smaller than the wavelength, their RCS is inversely proportional to the fourth power of the wavelength, resulting in extremely weak echo signals. For example, the theoretical RCS of a 2 mm diameter metal sphere at 94 GHz is close to or lower than the system noise floor of a typical millimeter-wave radar, making reliable detection difficult. Existing millimeter-wave radar's detection capability for millimeter-sized and non-metallic foreign objects is approaching its physical limits.

[0004] In theory, increasing the operating frequency to the terahertz band (such as 240 GHz) can significantly enhance the radar cross-section of small targets by utilizing shorter wavelengths, thereby improving detection sensitivity. However, in the terahertz band, due to the physical limitations of semiconductor devices and packaging parasitic effects, the output power of a single solid-state power amplifier is limited, resulting in generally insufficient overall transmit power; at the same time, the noise figure of the receiver link also faces greater challenges at high frequencies. The dual constraints of transmit power and receiver sensitivity make it difficult to directly translate simply increasing the operating frequency into an engineering-usable improvement in detection performance.

[0005] Therefore, how to overcome the detection sensitivity bottleneck of existing millimeter-wave radar from a physical perspective, and build an engineered system with high-power transmission and low-noise reception in the terahertz band to achieve highly reliable detection of tiny foreign objects on the runway surface, is a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0006] To address the technical problems existing in the background art, this invention proposes a terahertz frequency band airport runway foreign object detection radar system and method.

[0007] This invention proposes a terahertz frequency band airport runway foreign object detection radar system, comprising: The transmitting module is used to generate and transmit a frequency-modulated continuous wave detection signal with a frequency of 240 GHz; The receiving module is used to receive the echo signal reflected after the detection signal encounters the target, and to downconvert the echo signal to an intermediate frequency signal; The turntable system, mechanically connected to the transmitting and receiving modules, is used to drive the transmitting and receiving modules to rotate synchronously to achieve azimuth scanning. The digital control and processing module is electrically connected to the transmitting module, receiving module, and turntable system, respectively. It is used to generate baseband frequency-modulated continuous wave waveforms to control the transmitting signal form of the transmitting module, synchronously acquire the angle information of the turntable system and the intermediate frequency signal output by the receiving module, and process the acquired data to detect and locate foreign objects.

[0008] Preferably, the transmitting module specifically includes: Frequency source 1 is used to generate a local oscillator signal with a frequency of 38.745 GHz; The frequency doubler, whose input is connected to the output of the point frequency source 1, is used to multiply the 38.745GHz local oscillator signal to 77.49GHz. The first attenuator is connected between the point frequency source 1 and the frequency doubler to reduce the input power of the frequency doubler; A low-pass filter, whose input is connected to the output of a digital control and processing module, is used to receive baseband frequency-modulated continuous wave waveforms and perform filtering processing. The mixer has its local oscillator port connected to the output of the frequency doubler, and its intermediate frequency port connected to the output of the low-pass filter. It is used to mix the 77.49 GHz signal with the filtered baseband signal to obtain a frequency-modulated continuous wave signal with a center frequency of 80 GHz. A bandpass filter, whose input is connected to the output of a mixer, is used to filter out spurious signals from the mixing products and output a clean 80GHz frequency modulated continuous wave signal. A power amplifier, whose input is connected to the output of a bandpass filter, is used to amplify the power of an 80 GHz frequency-modulated continuous wave signal. An isolator, whose input is connected to the output of a power amplifier, is used to suppress reverse echo energy; A passive frequency tripler, whose input is connected to the output of an isolator, is used to multiply the amplified 80GHz frequency-modulated continuous wave signal to 240GHz. The transmitting horn antenna is connected to the output of a passive tripler to radiate a 240 GHz frequency-modulated continuous wave detection signal.

[0009] Preferably, the receiving module specifically includes: Point frequency source 2 is used to generate a local oscillator signal with a frequency of 39.665 GHz; The frequency tripler, whose input is connected to the output of the frequency source 2, is used to multiply the 39.665GHz local oscillator signal to 120GHz. The second attenuator is connected between the point frequency source 2 and the tripler to reduce the input power of the tripler. A receiving horn antenna is used to receive echo signals; A low-noise amplifier, whose input is connected to the output of the receiving horn antenna, is used to amplify the echo signal with low noise. The second harmonic mixer has its RF port connected to the output of a low-noise amplifier and its local oscillator port connected to the output of a third frequency multiplier. It is used to perform second harmonic mixing between the amplified echo signal and the local oscillator signal to output an intermediate frequency signal.

[0010] Preferably, it further includes: The transmitting reflector is rigidly connected to the outside of the transmitting module and is used to focus the detection signal radiated by the transmitting horn antenna into a high-gain beam. The receiving reflector is rigidly connected to the outside of the receiving module and is used to collect and focus the echo signal to the receiving horn antenna.

[0011] Preferably, it further includes: The first five-degree-of-freedom fine-tuning mechanism is connected between the transmitting module and the transmitting horn antenna, and is used to adjust the spatial position and direction of the transmitting horn antenna; The second five-degree-of-freedom fine-tuning mechanism is connected between the receiving module and the receiving horn antenna, and is used to adjust the spatial position and direction of the receiving horn antenna.

[0012] Preferably, the digital control and processing module includes: A waveform generator is used to generate baseband frequency-modulated continuous wave waveforms. The data acquisition unit is used to synchronously acquire the angle information of the turntable system and the intermediate frequency signal output by the receiving module; The signal processing unit, connected to the data acquisition unit, is used to sequentially perform digital down-conversion, pulse compression, and constant false alarm rate detection on the acquired intermediate frequency signal to obtain target point data, which includes distance, angle, and signal strength. The imaging and positioning unit, connected to the signal processing unit and the data acquisition unit, is used to associate target point data with angle information, generate a two-dimensional image, and output the location of the foreign object.

[0013] This invention proposes a terahertz band foreign object detection method for airport runways, applicable to any of the terahertz band airport runway foreign object detection radar systems described above. The method includes the following steps: Generate baseband frequency-modulated continuous wave waveform; A frequency-modulated continuous wave detection signal with a frequency of 240 GHz is generated based on the baseband frequency-modulated continuous wave waveform and radiated onto the surface of the airport runway. Drive the transmitting and receiving modules to perform rotational scanning; It receives the echo signal reflected after the detection signal encounters a foreign object, and downconverts the echo signal into an intermediate frequency signal; Simultaneously acquire rotational scanning angle information and intermediate frequency signals; Digital downconversion, pulse compression, and constant false alarm rate detection are performed on the intermediate frequency signal to obtain target point data including distance, angle, and signal strength; The target point data is associated with the angle information to generate a two-dimensional image and output the location of the foreign object.

[0014] Preferably, the step of generating a frequency-modulated continuous wave detection signal with a frequency of 240 GHz specifically includes: The 38.745GHz frequency signal was doubled to 77.49GHz; The baseband frequency-modulated continuous wave waveform is low-pass filtered and then mixed with a 77.49 GHz signal to obtain a frequency-modulated continuous wave signal with a center frequency of 80 GHz. Bandpass filtering is applied to the mixed signal to remove spurious signals; The filtered 80GHz frequency-modulated continuous wave signal is amplified and isolated. The amplified 80GHz frequency-modulated continuous wave signal was tripled to 240GHz.

[0015] Preferably, the step of down-converting the echo signal to an intermediate frequency signal specifically includes: Triple the frequency of the 39.665GHz spot frequency signal to 120GHz; The received 240GHz echo signal is amplified with low noise. The amplified echo signal is mixed with the 120GHz local oscillator signal using second harmonic mixing to output an intermediate frequency signal.

[0016] Preferably, in the constant false alarm rate (CFAR) detection, the target radar cross-section is inversely proportional to the fourth power of the operating wavelength, as shown in the following formula: ; in, and For the same target at wavelength and The radar cross-section below.

[0017] This invention proposes a terahertz-band airport runway foreign object detection radar system and method. By increasing the operating frequency to the 240GHz terahertz band, and utilizing the physical law that the radar cross-section of a target in the Rayleigh scattering region is inversely proportional to the fourth power of the wavelength, the electromagnetic scattering echo intensity of tiny foreign objects is fundamentally enhanced at the physical level, improving the detection capability for millimeter-sized metal debris and non-metallic foreign objects. Simultaneously, this application employs a multi-stage frequency doubling and power amplification link architecture in the transmitting module. By progressively increasing the frequency through the frequency doubling link and combining it with power amplification and spurious filtering, the engineering challenge of limited output power of solid-state power amplifiers in the terahertz band is solved. In the receiving module, second harmonic mixing technology is used, reducing the requirement for the local oscillator signal frequency, and a coherent signal source is used to ensure the synchronization consistency of the system frequency and time, achieving high-sensitivity reception. The synergistic effect of the physical and system layers enables a significant improvement in the radar system's detection sensitivity for extremely small foreign objects, enhancing the system's robustness and reliability in complex environments. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the system architecture of a terahertz-band airport runway foreign object detection radar system proposed in this invention. Figure 2 This is a flowchart illustrating the workflow of a terahertz-band foreign object detection method for airport runways proposed in this invention. Detailed Implementation

[0019] Reference Figure 1 The present invention proposes a terahertz frequency band airport runway foreign object detection radar system, comprising: The transmitting module is used to generate and transmit a frequency-modulated continuous wave detection signal with a frequency of 240 GHz.

[0020] Specifically, such as Figure 1 As shown, a frequency multiplier chain scheme is adopted to reduce the requirements for high-frequency sources and improve system stability and feasibility.

[0021] In this embodiment, the transmitting module specifically includes: Frequency source 1 is used to generate a local oscillator signal with a frequency of 38.745 GHz; The frequency doubler, whose input is connected to the output of the point frequency source 1, is used to multiply the 38.745GHz local oscillator signal to 77.49GHz. The first attenuator is connected between the point frequency source 1 and the frequency doubler to reduce the input power of the frequency doubler; A low-pass filter, whose input is connected to the output of a digital control and processing module, is used to receive baseband frequency-modulated continuous wave waveforms and perform filtering processing. The mixer has its local oscillator port connected to the output of the frequency doubler, and its intermediate frequency port connected to the output of the low-pass filter. It is used to mix the 77.49 GHz signal with the filtered baseband signal to obtain a frequency-modulated continuous wave signal with a center frequency of 80 GHz. A bandpass filter, whose input is connected to the output of a mixer, is used to filter out spurious signals from the mixing products and output a clean 80GHz frequency modulated continuous wave signal. A power amplifier, whose input is connected to the output of a bandpass filter, is used to amplify the power of an 80 GHz frequency-modulated continuous wave signal. An isolator, whose input is connected to the output of a power amplifier, is used to suppress reverse echo energy; A passive frequency tripler, whose input is connected to the output of an isolator, is used to multiply the amplified 80GHz frequency-modulated continuous wave signal to 240GHz. The transmitting horn antenna is connected to the output of a passive tripler to radiate a 240 GHz frequency-modulated continuous wave detection signal.

[0022] Specifically, such as Figure 1 As shown, second harmonic mixing and quadrature demodulation techniques are used to reduce the requirements for the local oscillator signal frequency and obtain complete phase information.

[0023] In this embodiment, the receiving module specifically includes: Point frequency source 2 is used to generate a local oscillator signal with a frequency of 39.665 GHz; The frequency tripler, whose input is connected to the output of the frequency source 2, is used to multiply the 39.665GHz local oscillator signal to 120GHz. The second attenuator is connected between the point frequency source 2 and the tripler to reduce the input power of the tripler. A receiving horn antenna is used to receive echo signals; A low-noise amplifier, whose input is connected to the output of the receiving horn antenna, is used to amplify the echo signal with low noise. The second harmonic mixer has its RF port connected to the output of a low-noise amplifier and its local oscillator port connected to the output of a third frequency multiplier. It is used to perform second harmonic mixing between the amplified echo signal and the local oscillator signal to output an intermediate frequency signal.

[0024] Among them, point frequency source 1 transmits two 100-megabit coherent signals, which are supplied to point frequency source 2 and FPGA board respectively, to ensure that the entire system is synchronized in frequency and time.

[0025] The turntable system, mechanically connected to the transmitting and receiving modules, is used to drive the transmitting and receiving modules to rotate synchronously to achieve azimuth scanning.

[0026] Specifically, the turntable system includes a high-precision servo motor, a rotating shaft, and a control driver. The transmitting and receiving modules (usually integrated within a single radar head) are mechanically connected and mounted on the rotating shaft via a rigid bracket. Under the command of the digital control and processing module, the turntable system drives the radar head to perform uniform rotational scanning in the horizontal plane from 0° to 360° or within a specific sector (e.g., ±60°), achieving azimuth coverage of the airport runway. The encoder provides real-time feedback of the rotation angle information to the digital control and processing module, ensuring strict synchronization between the angle and the echo data.

[0027] The digital control and processing module is electrically connected to the transmitting module, receiving module, and turntable system, respectively. It is used to generate baseband frequency-modulated continuous wave waveforms to control the transmitting signal form of the transmitting module, synchronously acquire the angle information of the turntable system and the intermediate frequency signal output by the receiving module, and process the acquired data to detect and locate foreign objects.

[0028] Specifically, the digital control and processing module is responsible for the control, data acquisition, and real-time signal processing of the entire system. Its hardware core can be implemented based on FPGA (Field Programmable Gate Array) and DSP (Digital Signal Processor) or SoC (System-on-a-Chip) platforms such as Zynq.

[0029] In this embodiment, the digital control and processing module includes: A waveform generator is used to generate baseband frequency-modulated continuous wave waveforms.

[0030] Specifically, a digital baseband FMCW waveform is generated in an FPGA or DSP using direct digital frequency synthesis (DDS) technology, converted into an analog signal by a DAC, and then sent to the transmitter module. The waveform parameters (start frequency, bandwidth, and modulation period) are configurable by software.

[0031] The data acquisition unit is used to synchronously acquire the angle information of the turntable system and the intermediate frequency signal output by the receiving module.

[0032] Specifically, the data acquisition unit includes a high-speed analog-to-digital converter (ADC). It simultaneously acquires two key data points: 1) angle information from the encoder of the turntable system; and 2) the I and Q intermediate frequency signals from the receiving module. This synchronization ensures that each echo sampling point corresponds to a precise azimuth angle.

[0033] The signal processing unit, connected to the data acquisition unit, is used to sequentially perform digital down-conversion, pulse compression, and constant false alarm rate detection on the acquired intermediate frequency signal to obtain target point data, which includes distance, angle, and signal strength.

[0034] Specifically, the signal processing unit performs real-time processing on the acquired intermediate frequency signal, and the process includes: Digital downconversion (DDC): The intermediate frequency signal is shifted to the baseband through digital mixing and low-pass filtering, and filtering and extraction are completed to reduce the data rate.

[0035] Pulse compression: A Fast Fourier Transform (FFT) is performed on the baseband signal, and the frequency modulation characteristics of the FMCW signal are used to achieve matched filtering in the range dimension, compressing long-duration pulses into narrow pulses, thereby obtaining high range resolution. The range resolution ΔR = c / (2B), where c is the speed of light and B is the signal bandwidth. This application can easily achieve bandwidths of several GHz in the 240 GHz band, thus obtaining centimeter-level or even higher range resolution.

[0036] Constant False Alarm Rate (CFAR) Detection: On the range image after pulse compression, an algorithm such as Cell Average CFAR (CA-CFAR) is used to adaptively set the detection threshold to detect potential foreign object targets from background clutter (such as runway ground echoes, rain and snow clutter) and output their range and signal strength information.

[0037] The imaging and positioning unit, connected to the signal processing unit and the data acquisition unit, is used to associate target point data with angle information, generate a two-dimensional image, and output the location of the foreign object.

[0038] Specifically, the imaging and positioning unit correlates the target point data (distance, intensity) output by the signal processing unit with the angle information synchronously acquired by the data acquisition unit. For each detected point, its two-dimensional position in a polar or rectangular coordinate system centered on the radar can be calculated using simple geometric relationships (distance × sin(angle), distance × cos(angle)). By accumulating all points within one frame scan (one complete rotation), a two-dimensional radar image of the runway can be generated, and the position coordinates of the foreign object can be directly output.

[0039] In this embodiment, it also includes: The transmitting reflector, rigidly connected to the outside of the transmitting module, is used to focus the detection signal radiated by the transmitting horn antenna into a high-gain beam; The receiving reflector is rigidly connected to the outside of the receiving module and is used to collect and focus the echo signal to the receiving horn antenna.

[0040] Specifically, the transmitting or receiving reflector is rigidly connected to the outside of the radar head to further focus the radiated beam of the horn antenna, forming a higher gain and narrower beam, thereby improving the range and azimuth resolution.

[0041] In this embodiment, it also includes: The first five-degree-of-freedom fine-tuning mechanism is connected between the transmitting module and the transmitting horn antenna, and is used to adjust the spatial position and direction of the transmitting horn antenna; The second fifth degree of freedom fine-tuning mechanism is connected between the receiving module and the receiving horn antenna, and is used to adjust the spatial position and direction of the receiving horn antenna.

[0042] Specifically, the first or second five-degree-of-freedom fine-tuning mechanism is connected between the radar body and the horn antenna to finely adjust the spatial position and pointing of the antenna during installation and commissioning, ensuring precise alignment of the transmitted or received beams and optimal matching of the reflector focus.

[0043] It should be noted that both the first and second five-degree-of-freedom fine-tuning mechanisms are derived from the ZX axis of the fine-tuning module and... By adjusting the module combination, precise and independent adjustment of the feed source with five degrees of freedom is achieved, with low coupling between the degrees of freedom and a clear and efficient adjustment process.

[0044] This application organically integrates a high-power radio frequency front-end, a high-precision turntable scanning unit, and a digital signal processing unit through a modular three-layer architecture, forming a compact and stable terahertz band airport runway foreign object detection radar system. This provides a practical and feasible technical path for the engineering application of terahertz band radar in the field of aviation safety and is of great value to improving the operational safety level of airport runways.

[0045] Reference Figure 1 and Figure 2 This invention proposes a terahertz band foreign object detection method for airport runways, applicable to any of the aforementioned terahertz band airport runway foreign object detection radar systems. The method includes the following steps: S1 generates a baseband frequency-modulated continuous wave waveform.

[0046] In this embodiment, the digital baseband FMCW signal is generated by the waveform generator of the digital control and processing module.

[0047] S2. Generate a frequency-modulated continuous wave detection signal with a frequency of 240 GHz based on the baseband frequency-modulated continuous wave waveform and radiate it to the surface of the airport runway.

[0048] In this embodiment, the step of generating a frequency-modulated continuous wave detection signal with a frequency of 240 GHz specifically includes: Double the frequency of the 40GHz spot frequency signal to 80GHz; The baseband frequency-modulated continuous wave waveform is low-pass filtered and then mixed with an 80GHz signal to obtain an 80GHz frequency-modulated continuous wave signal. The 80GHz frequency modulated continuous wave signal is amplified and isolated. The amplified 80GHz frequency-modulated continuous wave signal was tripled to 240GHz.

[0049] S3 drives the transmitting and receiving modules to perform rotational scanning.

[0050] S4. Receive the echo signal reflected after the detection signal encounters a foreign object, and downconvert the echo signal to an intermediate frequency signal.

[0051] In this embodiment, the step of down-converting the echo signal to an intermediate frequency signal specifically includes: Triple the frequency of the 40GHz spot frequency signal to a 120GHz signal; The 120GHz signal is split into two quadrature local oscillator signals with equal amplitude and a 90-degree phase difference. The received 240GHz echo signal was amplified with low noise and then divided into two equal echo signals. The two echo signals are mixed with the two quadrature local oscillator signals using second harmonic mixing to output an intermediate frequency signal.

[0052] S5. Synchronously acquire the angle information and intermediate frequency signal of the rotational scan.

[0053] S6. Perform digital down-conversion, pulse compression, and constant false alarm rate detection on the intermediate frequency signal to obtain target point data including distance, angle, and signal strength.

[0054] Specifically, the intermediate frequency signal is sequentially subjected to digital down-conversion, pulse compression (range dimension FFT) and constant false alarm rate detection to extract target traces representing foreign objects from the clutter background and obtain their distance and signal strength.

[0055] In this embodiment, in constant false alarm rate (CFAR) detection, the target radar cross-section is inversely proportional to the fourth power of the operating wavelength, and the relationship is as follows: ; in, and For the same target at wavelength and The radar cross-section below.

[0056] S7. Associate the target point data with the angle information to generate a two-dimensional image and output the location of the foreign object.

[0057] Specifically, the distance information of each target point is combined with its corresponding scanning angle information, and the two-dimensional position (X,Y) of the foreign object on the runway plane is calculated through coordinate transformation, and a visual image or alarm coordinates are generated.

[0058] It should be noted that, according to the radar equations, the maximum effective range of a radar is... With the target's radar cross-section (RCS), The relationship is For electrically small targets located in the Rayleigh scattering region, their radar cross-section is inversely proportional to the fourth power of the operating wavelength, i.e. .

[0059] In this embodiment, the maximum effective range of the radar With the target radar cross-section The relationship between the system performance and the system performance can be expressed by a simplified equation: ; in, For transmission power, For antenna gain, The system noise figure is... Boltzmann's constant, For temperature, For bandwidth, This application aims to achieve the minimum detectable signal-to-noise ratio. The synergistic effect of reducing F is as follows: Physical layer: Significantly increase the radar cross-section of the target by utilizing high-frequency, short-wavelength radar. ; In this application, the operating frequency is increased from 94 GHz (wavelength) in the prior art. Upgraded to 240GHz (wavelength) ), wavelength shortening ratio is Therefore, for the same small target, its radar cross-section at 240 GHz... Relative to radar cross-section at 94GHz The theoretical boost factor is 43 times (approximately 16.3 dB).

[0060] This means that, without changing other system parameters, the echo signal power can theoretically be increased by up to 16.3 dB solely by increasing the frequency, which is equivalent to increasing the signal strength by tens of times, thereby greatly improving the initial signal-to-noise ratio of small targets.

[0061] System layer: Constructing a high-power transmit and low-noise receive link; High-power transmit link: This is achieved through a combination of high-efficiency frequency multiplication technology and a power amplifier. The transmit module of this invention employs a high-performance solid-state power amplifier, combined with a high-efficiency frequency multiplier optimized for 240GHz, to efficiently and with low loss multiply lower-frequency, higher-power signals to 240GHz, and further amplify them, thereby obtaining a high transmit power P_t that is competitive in the terahertz band.

[0062] Low-noise receiver link: The receiver module of this application adopts a two-stage low-noise amplifier optimized architecture consisting of an intermediate frequency amplifier and a low-noise amplifier. The first-stage amplifier adopts an extremely low-noise design, and its noise figure is very low. The second-stage amplifier directly determines the system noise floor; it provides the main gain. This is to suppress the influence of noise in subsequent circuits. The overall system noise figure F can be approximated as: ; Through careful design, Extremely low and It is high enough to minimize the total noise figure F of the system, thus achieving high-sensitivity reception.

[0063] In summary, this application achieves its goals through frequency enhancement. The synergistic effect of the gain (approximately 43 times) and the high-power transmission and low-noise reception at the system layer results in a significant improvement in the overall signal-to-noise ratio of the system, enabling stable detection of millimeter-sized metal and non-metal fragments that are difficult to detect with existing technologies.

[0064] In the above-mentioned constant false alarm rate detection steps, it is based on the aforementioned physical gain that weak target echoes can be reliably identified from the noise floor.

[0065] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A terahertz frequency band airport runway foreign object detection radar system, characterized in that, include: The transmitting module is used to generate and transmit a frequency-modulated continuous wave detection signal with a frequency of 240 GHz; The receiving module is used to receive the echo signal reflected after the detection signal encounters the target, and to downconvert the echo signal to an intermediate frequency signal; The turntable system, mechanically connected to the transmitting and receiving modules, is used to drive the transmitting and receiving modules to rotate synchronously to achieve azimuth scanning. The digital control and processing module is electrically connected to the transmitting module, receiving module, and turntable system, respectively. It is used to generate baseband frequency-modulated continuous wave waveforms to control the transmitting signal form of the transmitting module, synchronously acquire the angle information of the turntable system and the intermediate frequency signal output by the receiving module, and process the acquired data to detect and locate foreign objects.

2. The terahertz frequency band airport runway foreign object detection radar system according to claim 1, characterized in that, The transmitting module specifically includes: Frequency source 1 is used to generate a local oscillator signal with a frequency of 38.745 GHz; The frequency doubler, whose input is connected to the output of the point frequency source 1, is used to multiply the 38.745GHz local oscillator signal to 77.49GHz. The first attenuator is connected between the point frequency source 1 and the frequency doubler to reduce the input power of the frequency doubler; The low-pass filter, whose input is connected to the output of the digital control and processing module, is used to receive baseband frequency-modulated continuous wave waveforms and perform filtering processing. The mixer has its local oscillator port connected to the output of the frequency doubler, and its intermediate frequency port connected to the output of the low-pass filter. It is used to mix the 77.49 GHz signal with the filtered baseband signal to obtain a frequency-modulated continuous wave signal with a center frequency of 80 GHz. A bandpass filter, whose input is connected to the output of a mixer, is used to filter out spurious signals from the mixing products and output a clean 80GHz frequency modulated continuous wave signal. A power amplifier, whose input is connected to the output of a bandpass filter, is used to amplify the power of an 80 GHz frequency-modulated continuous wave signal. An isolator, whose input is connected to the output of a power amplifier, is used to suppress reverse echo energy; A passive frequency tripler, whose input is connected to the output of an isolator, is used to multiply the amplified 80GHz frequency-modulated continuous wave signal to 240GHz. The transmitting horn antenna is connected to the output of a passive tripler to radiate a 240 GHz frequency-modulated continuous wave detection signal.

3. The terahertz frequency band airport runway foreign object detection radar system according to claim 2, characterized in that, The receiving module specifically includes: Frequency source 2 is used to generate a local oscillator signal with a frequency of 39.665 GHz; The frequency tripler, whose input is connected to the output of the frequency source 2, is used to multiply the 39.665GHz local oscillator signal to 120GHz. The second attenuator is connected between the point frequency source 2 and the tripler to reduce the input power of the tripler. A receiving horn antenna is used to receive echo signals; A low-noise amplifier, whose input is connected to the output of the receiving horn antenna, is used to amplify the echo signal with low noise. The second harmonic mixer has its RF port connected to the output of a low-noise amplifier and its local oscillator port connected to the output of a third frequency multiplier. It is used to perform second harmonic mixing between the amplified echo signal and the local oscillator signal to output an intermediate frequency signal.

4. The terahertz band airport runway foreign object detection radar system according to claim 1, characterized in that, Also includes: The transmitting reflector is rigidly connected to the outside of the transmitting module and is used to focus the detection signal radiated by the transmitting horn antenna into a high-gain beam. The receiving reflector is rigidly connected to the outside of the receiving module and is used to collect and focus the echo signal to the receiving horn antenna.

5. The terahertz frequency band airport runway foreign object detection radar system according to claim 3, characterized in that, Also includes: The first five-degree-of-freedom fine-tuning mechanism is connected between the transmitting module and the transmitting horn antenna, and is used to adjust the spatial position and direction of the transmitting horn antenna; The second five-degree-of-freedom fine-tuning mechanism is connected between the receiving module and the receiving horn antenna, and is used to adjust the spatial position and direction of the receiving horn antenna.

6. The terahertz band airport runway foreign object detection radar system according to claim 1, characterized in that, The digital control and processing module includes: A waveform generator is used to generate baseband frequency-modulated continuous wave waveforms. The data acquisition unit is used to synchronously acquire the angle information of the turntable system and the intermediate frequency signal output by the receiving module; The signal processing unit, connected to the data acquisition unit, is used to sequentially perform digital down-conversion, pulse compression, and constant false alarm rate detection on the acquired intermediate frequency signal to obtain target point data, which includes distance, angle, and signal strength. The imaging and positioning unit, connected to the signal processing unit and the data acquisition unit, is used to associate target point data with angle information, generate a two-dimensional image, and output the location of the foreign object.

7. A method for detecting foreign objects on airport runways in the terahertz frequency band, characterized in that, The method, applied to the terahertz frequency band foreign object detection radar system as described in any one of claims 1-6, comprises the following steps: Generate baseband frequency-modulated continuous wave waveform; A frequency-modulated continuous wave detection signal with a frequency of 240 GHz is generated based on the baseband frequency-modulated continuous wave waveform and radiated onto the surface of the airport runway. Drive the transmitting and receiving modules to perform rotational scanning; It receives the echo signal reflected after the detection signal encounters a foreign object, and downconverts the echo signal into an intermediate frequency signal; Simultaneously acquire rotational scanning angle information and intermediate frequency signals; Digital downconversion, pulse compression, and constant false alarm rate detection are performed on the intermediate frequency signal to obtain target point data including distance, angle, and signal strength; The target point data is associated with the angle information to generate a two-dimensional image and output the location of the foreign object.

8. The terahertz frequency band foreign object detection method for airport runways according to claim 7, characterized in that, The steps for generating a frequency-modulated continuous wave detection signal with a frequency of 240 GHz specifically include: The 38.745GHz frequency signal was doubled to 77.49GHz; The baseband frequency-modulated continuous wave waveform is low-pass filtered and then mixed with a 77.49 GHz signal to obtain a frequency-modulated continuous wave signal with a center frequency of 80 GHz. Bandpass filtering is applied to the mixed signal to remove spurious signals; The filtered 80GHz frequency-modulated continuous wave signal is amplified and isolated. The amplified 80GHz frequency-modulated continuous wave signal was tripled to 240GHz.

9. The method for detecting foreign objects on airport runways in the terahertz frequency band according to claim 7, characterized in that, The step of down-converting the echo signal to an intermediate frequency signal specifically includes: Triple the frequency of the 39.665GHz spot frequency signal to 120GHz; The received 240GHz echo signal is amplified with low noise. The amplified echo signal is mixed with the 120GHz local oscillator signal using second harmonic mixing to output an intermediate frequency signal.

10. The method for detecting foreign objects on airport runways in the terahertz frequency band according to claim 7, characterized in that, In the constant false alarm rate (CFAR) detection, the target radar cross-section is inversely proportional to the fourth power of the operating wavelength, and the relationship is as follows: ； in, and For the same target at wavelength and The radar cross-section below.

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