A frequency scanning radiometer system based on digital frequency selection and radiation imaging method

Abstract

The present invention discloses a frequency-sweeping radiometer system and a radiation imaging method based on digital frequency selection, which belongs to the field of radiation imaging. The system includes: a frequency-sweeping antenna with a "frequency-direction" scanning characteristic for receiving radio frequency analog signals in a target scene; an analog receiver for processing the radio frequency analog signals so that they meet the input requirements of an analog-to-digital converter; an analog-to-digital converter for converting the radio frequency analog signals processed by the analog receiver into digital signals; and a system core board, whose input end is connected to the output end of the analog-to-digital converter, and whose output end includes multiple output channels, which are used to sample the digital signals, obtain multiple parallel signals, calculate the frequencies of the parallel signals, and map the parallel signals together with the frequency information to the corresponding output channels according to a preset channel mapping rule. The present invention can improve the real-time performance of the radiometer system detection signal and reduce system complexity and hardware cost.

Description

Technical Field

[0001] The present invention belongs to the field of radiation imaging, and more specifically, relates to a frequency-scanning radiometer system based on digital frequency selection and a radiation imaging method. Background Art

[0002] The radiometer uses the electromagnetic signals emitted or reflected by the target itself to detect the target scene. It has the advantages of good concealment, passive detection, all-day and all-weather detection.

[0003] The current mainstream radiometric imaging technologies include real-aperture single-point scanning imaging, focal plane imaging, and synthetic aperture imaging. Single-point scanning imaging usually uses a single radiometer combined with a mechanical turntable to collect scene data point by point, resulting in long imaging time and high equipment complexity. Focal plane imaging uses a radiometer array instead of a single radiometer for reception, and then combines it with a scanning servo to complete scene imaging. Compared with single-point scanning imaging, the radiometer imaging time is greatly shortened, but at the cost of increased hardware costs. The synthetic aperture microwave radiometer uses a sparse array of small-aperture antennas to simulate an equivalent large-aperture antenna through synthesis, thereby improving spatial resolution while effectively reducing the size and weight of the antenna. In addition, the synthetic aperture system does not require mechanical scanning and can achieve staring imaging of the entire field of view. However, the large number of array elements makes the system structure and signal processing very complex.

[0004] In some applications, it's desirable for a radiometer to quickly capture radiation intensity from different angles to determine the target's location. However, the mainstream single-point scanning mode suffers from low efficiency and long update cycles, while focal plane and aperture synthesis modes are complex and expensive. Reported frequency-scanning radiometer solutions use analog frequency division technology, which carries high hardware cost and complexity, making large-scale frequency division systems difficult to implement.

[0005] Therefore, improving the real-time performance of radiation imaging and meeting the requirements of low complexity and low cost are of great practical significance. Summary of the Invention

[0006] In response to the defects of the existing technology and the need for improvement, the present invention provides a frequency-scanning radiometer system and a radiation imaging method based on digital frequency selection, the purpose of which is to improve the real-time performance of the detection signal of the radiometer system and reduce the complexity and hardware cost of the radiometer system, so as to improve the real-time performance of radiation imaging and meet the low complexity and low cost requirements of radiation imaging.

[0007] To achieve the above object, according to one aspect of the present invention, a frequency scanning radiometer system based on digital frequency selection is provided, comprising: a frequency scanning antenna, an analog receiver, an analog-to-digital converter and a system core board;

[0008] The frequency scanning antenna has a "frequency-direction" scanning feature and is used to receive RF analog signals in the target scenario;

[0009] The analog receiver is used to process the RF analog signal so that it meets the input requirements of the analog-to-digital converter;

[0010] An analog-to-digital converter, whose input end is connected to the output end of the analog receiver, is used to convert the radio frequency analog signal processed by the analog receiver into a digital signal;

[0011] The system core board has an input end connected to the output end of the analog-to-digital converter, and its output end includes multiple output channels; the system core board is used to sample the digital signal, obtain multiple parallel signals, calculate the frequency of each parallel signal, and map each parallel signal together with the frequency information to the corresponding output channel according to the preset channel mapping rules.

[0012] Furthermore, the system core board includes a sampling module, a phase rotation module, a polyphase filtering module, a DFT module and a channel mapping module connected in sequence;

[0013] The sampling module is used to sample digital signals to obtain multi-channel parallel signals;

[0014] The phase rotation module is used to perform phase rotation operation on multiple parallel signals to make the multiple parallel signals orthogonal to each other;

[0015] The polyphase filtering module is used to perform polyphase filtering operations on each parallel signal after phase rotation;

[0016] The DFT block is used to perform discrete Fourier transform on each parallel signal after polyphase filtering to obtain the frequency of each parallel signal;

[0017] The channel mapping module is used to map each parallel signal together with the frequency information to the corresponding output channel according to the preset channel mapping rules.

[0018] Furthermore, the system core board is implemented by an FPGA processing platform.

[0019] Furthermore, the polyphase filtering module is a broadband digital down-conversion structure based on a polyphase structure, and in the broadband digital down-conversion structure, the decimation multiple is equal to the number of channels.

[0020] Furthermore, in the broadband digital down-conversion structure, the mixing operation unit is located after the decimator.

[0021] Furthermore, the system core board uses shift, table lookup and accumulation operations instead of multiplication and accumulation.

[0022] Furthermore, the phase rotation operation in the phase rotation module is implemented by a constant coefficient multiplier and an addition and subtraction operation unit, and the constant coefficient multiplier is implemented by shift addition and subtraction.

[0023] Furthermore, the frequency scanning antenna includes M antenna units, each antenna unit has a fixed scanning angle; the scanning areas of the M antenna units are independent and continuous;

[0024] Wherein, M is a positive integer greater than 1.

[0025] According to another aspect of the present invention, there is provided a radiation imaging method, comprising:

[0026] Receive the signals output by each output channel of the frequency scanning radiometer system and invert the frequency of the target radio frequency signal;

[0027] According to the correspondence between the direction and frequency of the frequency scanning antenna, the location of the target is determined and imaging is achieved;

[0028] Among them, the frequency-sweeping radiometer system is the above-mentioned frequency-sweeping radiometer system based on digital frequency selection provided by the present invention.

[0029] According to another aspect of the present invention, there is provided a radiation imaging system comprising:

[0030] A receiving module, used for receiving signals output by each output channel of the frequency scanning radiometer system based on digital frequency selection;

[0031] An inversion module is used to invert the frequency of the target radio frequency signal based on the signals output by each output channel of the frequency scanning radiometer system based on digital frequency selection;

[0032] and an imaging module, which is used to determine the location of the target and realize imaging based on the correspondence between the direction and frequency of the frequency scanning antenna;

[0033] Among them, the radiometer frequency scanning system is the above-mentioned frequency scanning radiometer system based on digital frequency selection provided by the present invention.

[0034] In general, the above technical solutions conceived by the present invention can achieve the following beneficial effects:

[0035] (1) The radiometer system provided by the present invention uses a frequency-sweeping antenna with a "frequency-direction" scanning characteristic to detect the radio frequency analog signal in the target scene, and uses a system core board to divide the corresponding digital signal into multiple parallel signals. After calculating the frequency information of each parallel signal, it is mapped to the corresponding output channel. Finally, the information output by each output channel contains frequency information, thereby determining the frequency of the target radio frequency analog signal, and then determining the direction of the target according to the "frequency-direction" scanning characteristic of the frequency-sweeping antenna, thereby realizing radiation imaging. The present invention combines a system core board with a digital frequency selection function with a frequency-sweeping antenna with a "frequency-direction" scanning characteristic. Only a frequency-sweeping antenna unit is required to achieve this. Compared with traditional real aperture radiometers, no mechanical scanning is required, which alleviates the contradiction between the key performance indicators of the real aperture radiometer system and the system volume, weight, and process difficulty. Compared with the synthetic aperture radiometer, only a few antenna units and receiver units are required, the cost is low, and the signal processing complexity is low, which greatly alleviates the contradiction between the key performance indicators of the system and the system complexity and signal processing complexity. In general, the present invention can improve the real-time performance of the detection signal of the radiometer system and reduce the complexity and hardware cost of the radiometer system, which is conducive to improving the real-time performance of radiation imaging and meeting the low complexity and low cost requirements of radiation imaging.

[0036] (2) The present invention implements the system core board based on the FPGA platform, which can fully utilize the parallel operation characteristics of FPGA, enhance the computing power of the system, improve the instantaneous bandwidth and dynamic range, and have good frequency performance.

[0037] (3) The present invention utilizes a broadband digital down-conversion structure based on a polyphase structure to implement a polyphase filtering module in a system core board. Furthermore, the broadband digital down-conversion structure based on the polyphase structure can effectively solve the problem of consistency between the operating rate of the down-conversion structure and the output rate of the analog-to-digital converter. In a further preferred embodiment, in the broadband digital down-conversion structure, the mixing operation unit is located after the decimator, achieving pre-decimation, thereby significantly reducing the computational complexity of the polyphase filtering.

[0038] (4) Multiplier resources in FPGA are relatively scarce. In the present invention, when the system core board adopts the FPGA platform to implement the system core board, shift, table lookup and accumulation operations are used instead of multiplication and accumulation, and constant coefficient multipliers are realized through shift addition and subtraction, which can effectively reduce the occupancy of multiplier resources and improve the performance of the overall system.

[0039] (5) The frequency-scanning antenna used in the present invention is specifically composed of a plurality of antenna units with fixed scanning angles. The scanning areas of these plurality of antenna units are independent and continuous, thereby being able to obtain a larger scanning range with fewer antenna units and ensuring that the frequency-scanning antenna has a good "frequency-direction" scanning characteristic, that is, there is a good correspondence between the frequency and azimuth of the signal received by the frequency-scanning antenna, thereby improving the quality of subsequent radiation imaging. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 A block diagram of a frequency-scanning radiometer system based on digital frequency selection provided by an embodiment of the present invention;

[0041] Figure 2 A schematic diagram of a frequency scanning antenna provided in an embodiment of the present invention;

[0042] Figure 3 The digital intermediate frequency spectrum sub-bandwidth division scheme provided in the implementation of the present invention;

[0043] Figure 4 A schematic diagram of the structure of a polyphase filter provided by an embodiment of the present invention;

[0044] Figure 5 The present invention is a schematic diagram of a broadband digital down-conversion structure based on a multi-phase structure. DETAILED DESCRIPTION

[0045] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely for the purpose of explaining the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0046] In the present invention, the terms "first", "second", etc. (if any) in the present invention and the drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence.

[0047] In order to ensure the real-time performance of radiation imaging while meeting the requirements of low complexity and low cost, the present invention provides a frequency-scanning radiometer system and radiation imaging method based on digital frequency selection. The overall concept is to utilize the "frequency-direction" scanning characteristics of the frequency-scanning antenna to construct a radiometer system based on digital frequency selection, which includes a frequency-scanning antenna, an analog receiver, an analog-to-digital converter, and a system core board; on this basis, through the relationship between "frequency", "direction", "brightness temperature" and "pixel", brightness temperature imaging of a certain range of scenes is achieved. Compared with traditional real aperture radiometers, this system does not require mechanical scanning, which alleviates the contradiction between the key performance indicators of the real aperture radiometer system and the system volume, weight, and process difficulty; compared with the synthetic aperture radiometer, it only requires a few frequency-scanning antennas and receiver units, and the signal processing complexity is low, which greatly alleviates the contradiction between the key performance indicators of the system and the system complexity and signal processing complexity.

[0048] The scene radiation signal is further received by a specially designed frequency scanning antenna, and after subsequent amplification, filtering, mixing and other processing by the analog receiver, an intermediate frequency signal suitable for processing by an analog-to-digital (AD) converter is output. The analog signal of the intermediate frequency output is converted into a digital signal through AD and sent to the system core board. After phase rotation, multi-phase filtering, DFT and channel mapping, broadband digital frequency selection is realized, and multiple digital signals with specific center frequencies and bandwidths are output according to requirements. The voltage value is output after integration and square.

[0049] The following are examples.

[0050] Example 1:

[0051] A frequency scanning radiometer system based on digital frequency selection, such as Figure 1 As shown, it includes: frequency scanning antenna, analog receiver, analog-to-digital converter and system core board;

[0052] The frequency scanning antenna has a "frequency-direction" scanning feature and is used to receive RF analog signals in the target scenario;

[0053] The analog receiver is used to process the RF analog signal so that it meets the input requirements of the analog-to-digital converter;

[0054] An analog-to-digital converter, whose input end is connected to the output end of the analog receiver, is used to convert the radio frequency analog signal processed by the analog receiver into a digital signal;

[0055] The system core board has an input end connected to the output end of the analog-to-digital converter, and its output end includes multiple output channels; the system core board is used to sample the digital signal, obtain multiple parallel signals, calculate the frequency of each parallel signal, and map each parallel signal together with the frequency information to the corresponding output channel according to the preset channel mapping rules.

[0056] The radiometer system provided in this embodiment uses a frequency-sweeping antenna with a "frequency-direction" scanning characteristic (that is, there is a corresponding relationship between the signal frequency and direction obtained by scanning) to detect the radio frequency analog signal in the target scene, and uses the system core board to divide the corresponding digital signal into multiple parallel signals. After calculating the frequency information of each parallel signal, it is mapped to the corresponding output channel. Finally, the information output by each output channel contains frequency information, thereby determining the frequency of the target radio frequency analog signal, and then according to the "frequency-direction" scanning characteristic of the frequency-sweeping antenna, the direction of the target can be determined to achieve radiation imaging.

[0057] The specific implementation of each part in the embodiment of the present invention is described in detail below.

[0058] like Figure 2 As shown, in this embodiment, the frequency scanning antenna includes M antenna units, each antenna unit has a fixed scanning angle; the scanning areas of the M antenna units are independent and continuous;

[0059] Wherein, M is a positive integer greater than 1.

[0060] θ and R represent the scanning angle and angular resolution of each antenna unit, respectively. Since the scanning areas of the M antenna units are not only independent but also continuous with each other without blind spots, each antenna unit can independently observe the target within the angle range of θ and obtain the corresponding beam. The M beams observed by the M antenna units form a complete sector. The observation angle of the entire frequency-scanning antenna, that is, the field of view, is F = θ·M.

[0061] The frequency scanning antenna implemented in this embodiment is a distributed antenna array. Through reasonable layout and coordinated work, the entire distributed antenna array can achieve a wider observation angle. In actual applications, the number of antenna units M and the scanning angle and angular resolution of each antenna unit can be set accordingly according to specific detection requirements.

[0062] It's easy to understand that during operation, precisely adjusting the receiving frequency of the frequency-sweeping antenna enables a sequential antenna pattern scan, including left-to-right and right-to-left movements. To ensure consistent and accurate imaging, the scanning timing of each antenna beam must be synchronized. This scanning method is clearly visible on the ground or scene. After completing a scanning cycle, the system fully covers the (-F / 2, F / 2)-degree imaging field of view.

[0063] like Figure 1As shown, in this embodiment, the analog receiver specifically includes a low-noise amplifier, a mixer and a low-pass filter connected in sequence, which amplify, mix and band-pass filter the RF analog signal obtained by scanning the frequency scanning antenna in sequence, and obtain an intermediate frequency signal after mixing. The intermediate frequency signal will be input into the subsequent analog-to-digital signal converter after band-pass filtering.

[0064] It should be noted that Figure 1 The analog receiver shown in is only an optional embodiment of the present invention and should not be understood as the only limitation of the present invention. In other embodiments of the present invention, other design solutions may also be adopted according to the conversion requirements of the subsequent analog-to-digital converter. For example, in Figure 3 In [1], another receiver component is proposed, which includes a frequency conversion channel, a local oscillator, a reference crystal oscillator, a mixer, a filter, a demodulator, and an amplifier. The received radio frequency (RF) signal is mixed with the local oscillator (LO) signal to generate an intermediate frequency (IF) signal. The appropriate frequency is selected to ensure the quality of the signal after conversion. The high-frequency components after mixing are removed, and the IF signal is retained. The receiver output signal is connected to a high-speed AD device and a system core board for digital frequency selection processing. This solution directly connects a bandpass filter with a bandwidth of B to the intermediate frequency output, and then connects it to an amplifier. A high-speed data collector is used to accurately capture and digitally process the noise signal within bandwidth B.

[0065] like Figure 1 As shown, in this embodiment, the analog-to-digital converter specifically uses a high-speed ADC to obtain a higher conversion rate. The digital signal obtained by conversion will be input into a subsequent system core board. Optionally, the signal transmission protocol between the high-speed ADC and the system core board is JESD204B.

[0066] like Figure 1 As shown, in this embodiment, the system core board includes a sampling module, a phase rotation module, a polyphase filtering module, a DFT module and a channel mapping module connected in sequence; wherein:

[0067] The sampling module is used to sample digital signals to obtain multi-channel parallel signals;

[0068] The phase rotation module is used to perform phase rotation operation on multiple parallel signals to make the multiple parallel signals orthogonal to each other;

[0069] The polyphase filtering module is used to perform polyphase filtering operations on each parallel signal after phase rotation;

[0070] The DFT block is used to perform discrete Fourier transform on each parallel signal after polyphase filtering to obtain the frequency of each parallel signal;

[0071] The channel mapping module is used to map each parallel signal together with the frequency information to the corresponding output channel according to the preset channel mapping rules.

[0072] The channel mapping rule describes the correspondence between signal frequencies and output channels. In practical applications, it is often determined based on the detected signal frequency range and the number of output channels. In this embodiment, the system core board calculates the frequency information of each parallel signal through uniform DFT, which serves as the basis for channel mapping, thereby achieving balanced channel characteristics.

[0073] During data processing, this embodiment successfully transforms digital signals from the time domain to the frequency domain by applying Fourier transform technology. This further refines spectral analysis and accurately distinguishes noise signals generated by different beams. This enables this embodiment to capture noise signals from all beams within the scanning angle θ of the frequency-scanning antenna, while also simplifying the hardware configuration by eliminating components such as filters and power splitters.

[0074] As an optional implementation, the system core board of this embodiment is implemented by an FPGA processing platform, which can take advantage of the parallel operation characteristics of FPGA, greatly improving the computing power and obtaining performance advantages such as wide instantaneous bandwidth, large dynamic range, and frequency selection. Figure 4 As shown, x(nT) is the high-speed data after sampling, which contains all the information in the target signal band, N is the number of sub-bands of the digital filter bank, D is the decimation interval, and h k (nT), (k=0,1,2…N-1) are N digital filters, and the filter bank composed of N digital filters outputs N baseband signals: y k (nT), (k = 0, 1, 2 ... N-1). The passband and stopband cutoff frequencies of the prototype filter are designed to have a passband ripple of 0.1 dB and a stopband ripple of 75 dB. The filter coefficient is 208 order and the coefficient of each branch is 13 order.

[0075] Considering the relative scarcity of multiplier resources in FPGAs, this embodiment further optimizes the implementation of each module in the system core board. Specifically, a distributed arithmetic (DA) algorithm replaces multiplication and accumulation with shifts, table lookups, and accumulation operations. This algorithm also utilizes a high-speed clock to achieve resource reuse and easily implements compact layout constraints to reduce routing delays within the module. This embodiment specifically utilizes a DA filter structure with a clock rate to data rate of 2:1.

[0076] Furthermore, after the number of channels is determined, the phase rotation operation is equivalent to a complex constant multiplier, which can be implemented by constant coefficient multiplication and addition and subtraction operations, where the constant coefficient multiplier is implemented through shift addition and subtraction. Taking the calculation of x multiplied by sin 9π / 16 as an example, sin 9π / 16 is quantized to 011111011(251) using 9-bit two's complement fixed-point code. Therefore, x×251=x×256-x×4-x. A two-stage pipeline structure is used to complete the constant coefficient multiplication operation using shift operations and subtractors.

[0077] Through the above alternative design, the occupation of the multiplier resource in the FPGA can be reduced and the performance of the overall system can be improved.

[0078] In this implementation, the digital frequency selection implemented by the system core board is a process of moving the evenly divided sub-bands to the baseband using a filter bank with a decimator. Figure 5 As shown, in this embodiment, the polyphase filtering module is a broadband digital down-conversion structure based on a polyphase structure. To address the issue of consistency between the down-conversion structure's operating rate and the A / D output rate, this embodiment further improves the broadband digital down-conversion structure. The basic idea is to divide the target bandwidth signal, and the corresponding down-conversion sequence in each sub-band has a period equal to the decimation ratio. To this end, this embodiment selects the maximum decimation multiple, that is, the decimation multiple is equal to the number of channels. This design strategy ensures that only one data enters the corresponding channel at any time, and the earliest data to enter the channel will be located on channel N-1 at the last valid clock point. Since in this embodiment, the corresponding down-conversion sequence in each sub-band has a period equal to the decimation ratio, the mixing operation can be moved to after decimation.

[0079] Assume that the received signal is sampled in a single channel with a sampling rate of f s , the bandwidth is f s / 2, the subband bandwidth is B, and the total number of subbands is D. The dotted line part in the figure is the signal spectrum, and k represents the subband number. The subband where the signal is located is determined in advance by frequency measurement, that is, the value of k is determined, and then Figure 5 The structure is used to down-convert the signal. In the implementation of digital frequency selection, an efficient broadband digital down-conversion structure based on a multi-phase structure is used to solve the consistency problem between the down-converter operating rate and the A / D output rate.

[0080] Figure 5 In the mixing coefficient (k represents Figure 5 The number of the kth channel in represents a complete cycle of the mixing sequence.

[0081] The polyphase filter provided in this embodiment uses an N-order FIR low-pass filter as its core, and its characteristics are determined by a specific response function h LP(n) Definition: When the decimation rate K is equal to D, the filter of each channel (kth) will output the corresponding processing result.

[0082]

[0083] Let x p (m) = x(mD-p), g p (m) = h LP (iK+p), p=k=0,1···K-1, L=N / K, then

[0084]

[0085] definition but

[0086]

[0087] Assume that the filter adopts an even arrangement, Substituting into the above formula, we get

[0088]

[0089] Combining the above expressions, we can deduce the structure of frequency-selective filtering. By using the pre-decimation strategy, the amount of filtering calculations is significantly reduced. p (m) as a low-pass prototype filter h LP The order of the polyphase component of (n) is reduced by 1 / D compared to the original filter. This optimization enables the IDFT to be efficiently executed with the help of the FFT algorithm, which not only reduces the system data rate but also enhances the real-time processing capability.

[0090] The improved polyphase filtering structure of this embodiment successfully reduces the front-end processing speed by introducing a pre-decimator, thereby reducing the resource consumption of the system core board. In addition, the improved filter has a steep transition band and a small adjacent channel overlap characteristic.

[0091] The frequency scanning radiometer system based on digital frequency selection provided in this embodiment can be applied to any frequency band such as microwave and millimeter waves.

[0092] It should be noted that FPGA is only an optional implementation of the system core board in the present invention and should not be understood as the only limitation of the present invention.

[0093] Example 2:

[0094] A radiation imaging method, comprising:

[0095] Receive the signals output by each output channel of the frequency scanning radiometer system and invert the frequency of the target radio frequency signal;

[0096] According to the correspondence between the direction and frequency of the frequency scanning antenna, the location of the target is determined and imaging is achieved;

[0097] The frequency-scanning radiometer system is the frequency-scanning radiometer system based on digital frequency selection provided in the first embodiment.

[0098] Example 3:

[0099] A radiation imaging system, comprising:

[0100] A receiving module, used for receiving signals output by each output channel of the frequency scanning radiometer system based on digital frequency selection;

[0101] An inversion module is used to invert the frequency of the target radio frequency signal based on the signals output by each output channel of the frequency scanning radiometer system based on digital frequency selection;

[0102] and an imaging module, which is used to determine the location of the target and realize imaging based on the correspondence between the direction and frequency of the frequency scanning antenna;

[0103] The radiometer frequency scanning system is the frequency scanning radiometer system based on digital frequency selection provided in the above-mentioned embodiment 1.

[0104] It will be easily understood by those skilled in the art that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A frequency scanning radiometer system based on digital frequency selection, characterized in that: include: Frequency scanning antenna, analog receiver, analog-to-digital converter and system core board; The frequency scanning antenna has a "frequency-direction" scanning characteristic and is used to receive radio frequency analog signals in the target scene; The analog receiver is used to process the radio frequency analog signal so that it meets the input requirements of the analog-to-digital converter; The analog-to-digital converter, whose input end is connected to the output end of the analog receiver, is used to convert the radio frequency analog signal processed by the analog receiver into a digital signal; The system core board has an input end connected to the output end of the analog-to-digital converter, and an output end thereof includes a plurality of output channels; The system core board is used to sample the digital signal, obtain multiple parallel signals, calculate the frequency of each parallel signal, and map each parallel signal together with the frequency information to the corresponding output channel according to a preset channel mapping rule.

2. The frequency-scanning radiometer system based on digital frequency selection according to claim 1, characterized in that: The system core board includes a sampling module, a phase rotation module, a polyphase filtering module, a DFT module and a channel mapping module connected in sequence; The sampling module is used to sample the digital signal to obtain multiple parallel signals; The phase rotation module is used to perform a phase rotation operation on the multiple parallel signals to make the multiple parallel signals orthogonal in pairs; The polyphase filtering module is used to perform polyphase filtering operations on each parallel signal after phase rotation; The DFT block is used to perform discrete Fourier transform on each parallel signal after polyphase filtering to obtain the frequency of each parallel signal; The channel mapping module is used to map each parallel signal together with frequency information to a corresponding output channel according to a preset channel mapping rule.

3. The frequency-scanning radiometer system based on digital frequency selection according to claim 2, characterized in that: The system core board is implemented by an FPGA processing platform.

4. The frequency-scanning radiometer system based on digital frequency selection according to claim 3, characterized in that: The polyphase filtering module is a broadband digital down-conversion structure based on a polyphase structure, and in the broadband digital down-conversion structure, the decimation multiple is equal to the number of channels.

5. The frequency-scanning radiometer system based on digital frequency selection according to claim 4, characterized in that: In the broadband digital down-conversion structure, the frequency mixing operation unit is located after the decimator.

6. The frequency-scanning radiometer system based on digital frequency selection according to any one of claims 3 to 5, characterized in that: The system core board adopts shift, table lookup and accumulation operations instead of multiplication and accumulation.

7. The frequency-scanning radiometer system based on digital frequency selection according to any one of claims 3 to 5, characterized in that: The phase rotation operation in the phase rotation module is implemented by a constant coefficient multiplier and an addition and subtraction operation unit, and the constant coefficient multiplier is implemented by shift addition and subtraction.

8. The frequency-scanning radiometer system based on digital frequency selection according to any one of claims 1 to 5, characterized in that: The frequency scanning antenna includes M antenna units, each antenna unit has a fixed scanning angle; the scanning areas of the M antenna units are independent and continuous; Wherein, N is a positive integer greater than 1.

9. A radiation imaging method, characterized in that: include: Receive the signals output by each output channel of the frequency scanning radiometer system and invert the frequency of the target radio frequency signal; Determine the location of the target based on the correspondence between the direction and frequency of the frequency scanning antenna to achieve imaging; Wherein, the frequency-sweeping radiometer system is the frequency-sweeping radiometer system based on digital frequency selection as described in any one of claims 1 to 8.

10. A radiation imaging system, characterized in that: include: A receiving module, configured to receive signals output by each output channel of the frequency-scanning radiometer system based on digital frequency selection; An inversion module, configured to invert the frequency of the target radio frequency signal based on the signals output by each output channel of the frequency scanning radiometer system based on digital frequency selection; and an imaging module, configured to determine the location of a target and achieve imaging based on the correspondence between the direction and frequency of the frequency scanning antenna; Wherein, the radiometer frequency scanning system is a frequency scanning radiometer system based on digital frequency selection as described in any one of claims 1 to 8.

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