Frequency sweep radiometer system based on digital frequency selection and radiation imaging method

Abstract

The invention discloses a frequency scanning radiometer system based on digital frequency selection and a radiation imaging method, and belongs to the field of radiation imaging, and the system comprises a frequency scanning antenna which has a frequency-direction scanning characteristic and is used for receiving a radio frequency analog signal in a target scene; the analog receiver is used for processing the radio frequency analog signal to enable the radio frequency analog signal to meet the input requirement of the analog-to-digital converter; the analog-to-digital converter is used for converting the radio frequency analog signal processed by the analog receiver into a digital signal; the input end of the system core board is connected with the output end of the analog-to-digital converter, the output end of the system core board comprises a plurality of output channels, and the system core board is used for sampling the digital signals to obtain multiple paths of parallel signals, calculating the frequency of each path of parallel signals and outputting the frequency of each path of parallel signals; and according to a preset channel mapping rule, each path of parallel signal and the frequency information are mapped to a corresponding output channel. According to the invention, the real-time performance of the radiometer system for detecting signals can be improved, and the system complexity and the hardware cost can be reduced.

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.

[0003] The current mainstream radiation imaging technologies mainly 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 the scene point by point, which takes a long time to image and has high equipment complexity. Focal plane imaging uses a radiometer array to receive instead of a single radiometer, and then combines 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 small-aperture antenna array to simulate an equivalent large-aperture antenna through synthesis, thereby improving the spatial resolution and effectively reducing the size and weight of the antenna. In addition, the synthetic aperture system does not require mechanical scanning and can achieve stare imaging of the entire field of view. However, the large number of array elements makes the system structure and signal processing very complicated.

[0004] In some applications, it is hoped that the radiometer can quickly capture the radiation intensity of scenes in different directions to determine the location of the target. However, the mainstream single-point scanning mode has low efficiency and a long information update cycle, while the focal plane and comprehensive aperture mode systems are highly complex and costly. The frequency scanning radiometer solutions that have been reported use analog frequency division technology, which has high hardware cost and complexity, making it difficult to implement a large-scale frequency division system.

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

[0006] In view of the defects of the prior art 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] Further, the system core board includes a sampling module, a phase rotation module, a polyphase filtering module, a DFT module and a channel mapping module which are connected in sequence;

[0013] The sampling module is used to sample the digital signal to obtain multiple parallel signals;

[0014] The phase rotation module is used to perform phase rotation operation on the multi-channel parallel signals so that the multi-channel parallel signals are 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 rule.

[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, in which 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 extractor.

[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 to achieve imaging;

[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, used for inverting the frequency of the target radio frequency signal according to the signal 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 according to 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 the system core board to divide the corresponding digital signal into multiple parallel signals, calculates the frequency information of each parallel signal, and maps it 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 cooperates with the system core board with a digital frequency selection function and the frequency-sweeping antenna with a "frequency-direction" scanning characteristic, and only needs a frequency-sweeping antenna unit to achieve it. Compared with the traditional real aperture radiometer, 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 comprehensive aperture radiometer, only a few antenna units and receiver units are needed, 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 beneficial 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, and the broadband digital down-conversion structure based on a polyphase structure can effectively solve the problem of consistency between the working 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 extractor, and pre-extraction is achieved, thereby significantly reducing the amount of calculation of polyphase filtering.

[0038] (4) Multiplier resources in FPGA are relatively scarce. In the present invention, when the system core board is implemented on an FPGA platform, shift, table lookup and accumulation operations are used instead of multiplication and accumulation, and a constant coefficient multiplier is implemented 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 the 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 better "frequency-direction" scanning characteristic, that is, there is a good correspondence between the signal frequency and azimuth 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 A 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 provided by the private company. DETAILED DESCRIPTION

[0045] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain 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 can 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 accompanying drawings are used to distinguish similar objects but not necessarily to describe a specific order or sequence.

[0047] In order to ensure the real-time performance of radiation imaging and meet 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 the traditional real aperture radiometer, 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, only a few frequency-scanning antennas and receiver units are required, 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 achieved, and digital signals with multiple specific center frequencies and bandwidths are output as required, and the voltage value is output after integration and square.

[0049] The following are examples.

[0050] Embodiment 1:

[0051] A frequency scanning radiometer system based on digital frequency selection, such as Figure 1 As shown, it includes: a frequency scanning antenna, an analog receiver, an analog-to-digital converter and a 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 scanning 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 RF analog signal in the target scene, and uses the system core board to divide the corresponding digital signal into multiple parallel signals, calculates the frequency information of each parallel signal, and maps it to the corresponding output channel. Finally, the information output by each output channel contains frequency information, thereby determining the frequency of the target RF analog signal, and then determining the direction of the target according to the "frequency-direction" scanning characteristic of the frequency scanning antenna, thereby realizing radiation imaging.

[0057] The specific implementation methods of each part in the embodiments of the present invention are 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 to 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 practical applications, the number of antenna units M and the scanning angle and angular resolution of each antenna unit can be set according to specific detection requirements.

[0062] It is easy to understand that when working, by accurately adjusting the receiving frequency of the frequency-scanning antenna, an orderly antenna pattern scan can be achieved, including movement from left to right or from right to left. To ensure the continuity and accuracy of imaging, the scanning timing of each antenna beam needs to be synchronized. This scanning method is clearly visible on the ground or scene. After completing a scanning cycle, the system can fully cover the imaging field of view range of (-F / 2, F / 2) degrees.

[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 implementation 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 analog-to-digital converter connected subsequently. For example, in Figure 3 In the paper, 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. Select a suitable frequency to ensure the quality of the signal after conversion. Remove the high-frequency components after mixing, retain the IF signal, and connect the receiver output signal to the high-speed AD device and the 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 an amplifier, and uses a high-speed collector 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 converted digital signal 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 the digital signal to obtain multiple parallel signals;

[0068] The phase rotation module is used to perform phase rotation operation on the multi-channel parallel signals so that the multi-channel parallel signals are 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 rule.

[0072] The channel mapping rule describes the correspondence between the signal frequency and the output channel. In practical applications, it is often determined according to 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 as the basis for channel mapping, and can obtain balanced channel characteristics.

[0073] In the data processing stage, this embodiment successfully transforms the digital signal from the time domain to the frequency domain by applying Fourier transform technology, further refining the spectrum analysis, and accurately distinguishing the noise signals generated by different beams. This enables this embodiment to have the ability to capture all beam noise signals within the scanning angle θ of the frequency scanning antenna, and is more streamlined in hardware composition, reducing components such as filters and power dividers.

[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 runtime, greatly improve the computing power, and obtain performance advantages such as wide instantaneous bandwidth, large dynamic range, and frequency selection. The multi-phase filter structure is as follows 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 subbands in 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. The passband ripple is 0.1dB and the stopband ripple is 75dB. The filter coefficient is 208 order and the coefficient of each branch is 13 order.

[0075] Considering the relatively scarce multiplier resources in FPGA, this embodiment further optimizes the implementation of each module in the system core board. Specifically, a distributed arithmetic (DA) is used to replace multiplication and accumulation through shift, table lookup and accumulation operations. High-speed clocks can also be used to achieve resource reuse and compact layout constraints are easily implemented to reduce wiring delays within the module. This embodiment specifically uses a DA filter structure with a clock rate and 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, wherein the constant coefficient multiplier is implemented by 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) according to the 9-bit binary complement fixed-point code, then x×251=x×256-x×4-x, and the constant coefficient multiplication operation is completed by using a two-stage pipeline structure 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. In order to deal with the consistency problem between the working rate of the down-conversion structure 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 is equal to the decimation ratio due to the period. 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 each moment, and the earliest data entering the channel will be located on the N-1 channel at the last valid clock point. Since in this embodiment, the corresponding down-conversion sequence in each sub-band is equal to the decimation ratio due to the period, 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 , bandwidth is f s / 2, the subband bandwidth is B, and the total number of subbands is D. The dotted line 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, a high-efficiency 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 the 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 (the 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 has been 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 with 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 multi-phase filter structure of this embodiment successfully reduces the front-end processing speed by introducing a front-end extractor, thereby reducing the resource consumption of the system core board, and the improved filter has a steep transition band and a smaller 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 wave.

[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] Embodiment 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 to achieve imaging;

[0097] The frequency-sweeping radiometer system is the frequency-sweeping radiometer system based on digital frequency selection provided in the above-mentioned embodiment 1.

[0098] Embodiment 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, used for inverting the frequency of the target radio frequency signal according to the signal 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 according to 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 only 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 protection scope 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 the radio frequency analog signal in the target scene; The analog receiver is used to process the radio frequency analog signal so that it meets the input requirement 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 a 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 phase rotation operation on the multiple parallel signals so that the multiple parallel signals are orthogonal in pairs; The multiphase filtering module is used to perform multiphase 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 the 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 as claimed in 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 as claimed in 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 as claimed in claim 4, characterized in that: In the broadband digital down-conversion structure, the mixing operation unit is located after the extractor.

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; According to the correspondence between the direction and frequency of the frequency scanning antenna, the position of the target is determined to achieve imaging; Wherein, the frequency-sweeping radiometer system is a 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, used for receiving signals output by each output channel of the frequency scanning radiometer system based on digital frequency selection; An inversion module, used for inverting the frequency of the target radio frequency signal according to the signal output by each output channel of the frequency scanning radiometer system based on digital frequency selection; and an imaging module, used to determine the location of the target and realize imaging according to the corresponding relationship 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.

Images