A multi-frequency band high spectral resolution ground-based microwave radiometer

Abstract

The application discloses a multi-frequency-band high-frequency-spectral-resolution ground-based microwave radiometer, which comprises a reflector antenna, a beam separator, a corrugated horn feed source, a broadband superheterodyne receiver, a variable local oscillator source, a middle-frequency filter and detector group, an AD acquisition module, a servo structure, a cold / hot calibration source, a temperature monitoring and constant-temperature control module and a control and signal processing module. The application adopts a quasi-optical feed network, realizes multi-frequency-band, same-visual-axis and simultaneous observation of target radiation signals, and improves the accuracy of atmospheric parameter inversion by using multi-frequency-band data fusion. Meanwhile, the application realizes rapid switching of a receiving radio frequency signal band by changing the frequency of the local oscillator source, simultaneously realizes high-frequency-spectral-resolution detection of signals in the radio frequency band range by using a narrow-band middle-frequency filter group and a detector group, and the system has the advantages of simple system structure and high frequency resolution.

Description

Technical Field

[0001] This invention relates to the field of microwave radiometer technology, and more specifically to a multi-band high spectral resolution ground-based radiometer. Background Technology

[0002] Atmospheric temperature and humidity are crucial meteorological parameters, and microwave radiometers are an important technological means for detecting them. Spaceborne microwave radiometers are widely used for climate / meteorological research and weather forecasting over large global areas. However, for short-term atmospheric parameter detection in localized areas, the accuracy is limited due to the temporal and spatial resolution limitations of spaceborne microwave radiometers, as well as the influence of the upper atmosphere. To address this issue, ground-based radiometers were developed.

[0003] For vertical detection of atmospheric temperature and humidity profiles, it is necessary to receive radiation signals from multiple frequency bands of the atmosphere. For example, the 20-30 GHz band (K-band) is used to detect the water molecule content in the atmosphere, thereby detecting atmospheric humidity; while the 50-60 GHz band (V-band) is used to detect atmospheric temperature. At the same time, within a certain detection frequency band, the more subdivided the detection channels, the higher its spectral resolution, thereby obtaining a finer distribution curve of atmospheric vertical parameters.

[0004] This invention discloses a multi-band high-frequency resolution ground-based microwave radiometer. Employing a quasi-optical network design, it ensures that the atmospheric detection paths across multiple frequency bands are identical. Compared to using multiple ground-based microwave radiometers with different frequency bands, it features simultaneous observation along the same line of sight, theoretically achieving higher accuracy in atmospheric parameter inversion. Furthermore, the system employs a superheterodyne structure, switching the radio frequency band by changing the local oscillator frequency and achieving frequency subdivision through intermediate frequency filtering. Compared to filtering and detection at the radio frequency level, this method offers advantages such as high frequency resolution and low cost. Summary of the Invention

[0005] The main technical problem solved by this invention is to overcome the problems of different atmospheric observation paths and insufficient frequency resolution in existing ground-based microwave radiometers for different frequency bands. A multi-band high-frequency resolution ground-based microwave radiometer is proposed, which uses a quasi-optical feeding network to achieve simultaneous observation of multiple frequency bands along the same line of sight; it uses a superheterodyne receiver structure to change the local oscillator to achieve video frequency switching, and uses an intermediate frequency filter detection method to achieve high frequency resolution.

[0006] To achieve the above-mentioned objectives, the present invention adopts the following technical solution: A multi-band high-spectral-resolution ground-based microwave radiometer consists of a reflector antenna, a beam splitter, a broadband corrugated horn feed, a broadband superheterodyne receiver, a variable local oscillator, an intermediate frequency filter and detector group, a servo structure, a cold / hot calibration source, a temperature monitoring and constant temperature control module, and an AD acquisition / control and signal processing module.

[0007] The reflector antenna is part of a parabolic sphere of revolution, with the focal point of the parabola coinciding with the phase center of the feed horn. A rotating shaft is mounted behind the reflector antenna, connected to a servo structure. The servo structure drives the parabolic antenna to rotate, allowing the parabola to sequentially observe atmospheric radiation brightness temperature and the brightness temperature of cold and hot calibration sources.

[0008] Beam splitters separate microwave radiation signals from multiple frequency bands simultaneously received by a reflector antenna based on frequency band or polarization. Frequency selective surfaces are used to separate two frequency bands that are far apart; they allow high-frequency radiation signals to pass through while completely reflecting lower-frequency radiation signals. Polarization splitters can be used to separate electromagnetic waves with two different polarizations.

[0009] A corrugated horn feed is used to receive microwave radiation signals after beam splitting. Corrugated horn feeds offer advantages such as wide bandwidth, stable phase center, and rotationally symmetrical radiation pattern, and are often used as the feed horn for broadband receivers.

[0010] Wideband superheterodyne receivers are characterized by low noise, high gain, and a wide RF frequency input range and a wide local oscillator frequency input range. By changing the local oscillator frequency, the receiving RF frequency can be switched, and the intermediate frequency output has sufficient bandwidth.

[0011] A variable local oscillator source is used to provide a local oscillator signal with a variable frequency to a broadband superheterodyne receiver, thereby enabling the reception of radiated signals in different frequency bands.

[0012] The intermediate frequency (IF) filter bank, located after the IF output of the superheterodyne receiver, is used to finely subdivide the IF signal within a fixed frequency range into several frequency bands, thereby achieving high-frequency resolution measurements. Each filter is followed by a detector to measure the power at that subdivided frequency.

[0013] The cold calibration source provides a cold reference for the radiometer's two-point calibration. It consists of an insulated container, liquid nitrogen-soaked absorbing material, and a wave-transparent material to prevent condensation, and is located directly below the parabolic antenna. The hot calibration source consists of a metal cone coated with absorbing material and a temperature sensor, and is located to the side of the parabolic antenna. As the parabolic antenna rotates one revolution driven by a servo structure, it sequentially observes the sky brightness temperature, the brightness temperature of the hot calibration source, and the brightness temperature of the cold calibration source. Through two-point calibration, the equivalent radiation brightness temperature of the weather can be obtained.

[0014] The AD acquisition module converts the analog voltage output from the detector array into a digital signal for storage and transmission; the control module implements the rotation control of the servo structure and angle information feedback, and the feedback angle information has a synchronous correspondence with the acquired voltage information. The signal processing module completes the calibration processing of the radiometer received signal and displays the sky brightness temperature.

[0015] The temperature monitoring and control module surrounds analog components such as the superheterodyne receiver, intermediate frequency filter / detector group, and AD acquisition module. Through a certain temperature control strategy, it keeps the temperature of the entire receiver link within a very small temperature fluctuation range, reduces the impact of ambient temperature changes on receiver gain, and improves the accuracy of radiometer measurements.

[0016] Compared with existing ground-based radiometers, the advantages of this invention are:

[0017] (1) By adopting the quasi-optical network design concept, atmospheric radiation signals of multiple different frequency bands are observed simultaneously and along the same line of sight, which theoretically improves the accuracy of atmospheric parameter inversion.

[0018] (2) By adopting a superheterodyne receiver structure, changing the local oscillator to switch the radio frequency, and subdividing the frequency through the intermediate frequency filter bank, low-cost, high-frequency resolution observation can be achieved. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the structure of a multi-band high spectral resolution ground-based microwave radiometer according to the present invention; Detailed Implementation

[0020] like Figure 1 As shown, the multi-band high spectral resolution ground-based microwave radiometer provided by the present invention includes: a reflector antenna 1, a beam splitter 2, a broadband corrugated horn feed 3, a broadband superheterodyne receiver 4, a variable local oscillator 5, an intermediate frequency filter and detector group 6, an AD acquisition module 7, a servo structure 8, a cold calibration source 9, a hot calibration source 10, a temperature monitoring and constant temperature control module 11, and a control processing module 12.

[0021] The reflector antenna 1 is part of a parabolic sphere of revolution, with the focal point of the parabolic sphere coinciding with the phase center of the broadband corrugated horn feed 3. A rotating shaft is mounted behind the reflector antenna, and this shaft is connected to a servo structure 8. The servo structure 8 drives the parabolic antenna to rotate, allowing the parabola to sequentially observe the atmospheric radiation brightness temperature, the radiation brightness temperature of the cold calibration source 9, and the radiation brightness temperature of the hot calibration source 10.

[0022] Beam splitter 2 separates microwave radiation signals from multiple frequency bands simultaneously received by reflector antenna 1 according to frequency band or polarization. Frequency selective surface is used to separate two frequency bands with a large frequency interval; the frequency selective surface allows high-frequency radiation signals to pass through, while lower-frequency radiation signals are completely reflected back. Polarization splitter can be used to separate electromagnetic waves with two different polarizations.

[0023] The broadband corrugated horn feed 3 is used to receive microwave radiation signals after beam splitting. The corrugated horn feed 3 has advantages such as wide bandwidth, stable phase center, and rotationally symmetrical radiation pattern, and is often used as the receiving antenna for broadband receivers.

[0024] The wideband superheterodyne receiver 4 is characterized by low noise, high gain, and a wide RF frequency input range and a wide local oscillator frequency input range. By changing the local oscillator frequency 5, the receiving RF frequency can be switched, and the intermediate frequency output has sufficient bandwidth.

[0025] The variable local oscillator source 5 is used to provide a variable frequency local oscillator signal to the broadband superheterodyne receiver, thereby enabling the reception of radiated signals in different frequency bands.

[0026] The intermediate frequency (IF) filter bank and detector bank are located after the IF output of the superheterodyne receiver. They are used to finely subdivide the IF signal within a fixed frequency range into several frequency bands, thereby achieving high-frequency resolution measurement. Each filter is followed by a detector to measure the power at that subdivided frequency.

[0027] The cold calibration source 9 provides a cold reference for the radiometer's two-point calibration. It consists of an insulated container, liquid nitrogen-soaked absorbing material, and a wave-transparent material to prevent condensation, and is located directly below the parabolic antenna. The hot calibration source 10 consists of a metal cone coated with absorbing material and a temperature sensor, and is located to the side of the parabolic antenna. When the reflector antenna 1 rotates one revolution under the drive of the servo structure 8, the antenna sequentially observes the sky's radiation brightness temperature, and the radiation brightness temperatures of the cold and hot calibration sources 9 and 10. Through two-point calibration, the equivalent radiation brightness temperature of the weather can be obtained.

[0028] The AD acquisition module 7 converts the analog voltage output from the detector group into a digital signal for storage and transmission to the control / processing module 12. The control / processing module 12 implements the rotation control of the servo structure 8 and provides angle information feedback, and the feedback angle information is synchronized with the acquired voltage information; the control / processing module 12 also performs calibration processing of the radiometer received signal and displays the sky brightness temperature.

[0029] The temperature monitoring / control module 11 surrounds analog components such as the superheterodyne receiver 4, variable frequency source 5, intermediate frequency filter / detector group 6, and AD acquisition module 7. Through a certain temperature control strategy, it controls the temperature of the entire receiver link within a very small temperature fluctuation range, reduces the impact of ambient temperature changes on receiver gain, and improves the accuracy of radiometer measurements.

[0030] Compared with existing ground-based radiometers, the advantages of this invention are:

[0031] (1) By adopting the quasi-optical network design concept, atmospheric radiation signals of multiple different frequency bands are observed simultaneously and along the same line of sight, which theoretically improves the accuracy of atmospheric parameter inversion.

[0032] (2) By adopting a superheterodyne receiver structure, changing the local oscillator to switch the radio frequency, and subdividing the frequency through the intermediate frequency filter bank, low-cost, high-frequency resolution observation can be achieved.

Claims

1. A multi-band high-spectral-resolution ground-based microwave radiometer, characterized in that: The multi-band high-spectral-resolution ground-based microwave radiometer includes: a reflector antenna, a beam splitter, a corrugated horn feed, a broadband superheterodyne receiver, a variable local oscillator, an intermediate frequency filter and detector group, an AD acquisition module, a servo structure, a cold / hot calibration source, a temperature monitoring and constant temperature control module, and a control and signal processing module. The reflector antenna is a rotating parabolic surface used for time-division receiving multi-band signals radiated from the atmosphere, cold calibration source, and hot calibration source. The reflector antenna is connected to a servo structure, which causes the reflector antenna to rotate. Within one revolution, the radiated signals from the sky, hot calibration source, and cold calibration source are observed sequentially. The reflector antenna focuses the target radiated signal onto the focal point of the reflector antenna. The beam splitter is located between the reflector surface and the focal point of the reflector antenna. It is used to separate multi-band signals. In the case of using a frequency selective surface to achieve beam splitting, high-frequency signals pass through the beam splitter and enter the high-frequency corrugated horn feed; low-frequency signals are reflected by the beam splitter and enter the low-frequency corrugated horn feed. The corrugated horn feed has the advantages of wide bandwidth, stable phase center, and rotational symmetry. Its phase center coincides with the focal point of the reflector antenna and is used to receive the radiated signal after passing through the beam splitter and transmit it to the superheterodyne receiver. Superheterodyne receivers are characterized by low noise and high gain, and have a wide range of RF frequency input and local oscillator frequency input. They downconvert wideband signals within a certain frequency band to a fixed intermediate frequency band by changing the local oscillator frequency several times. Under the control of the control and signal processing module, the output frequency of the variable local oscillator source can be changed in sequence to achieve the purpose of equivalent receiving radio frequency signal frequency switching. The intermediate frequency filter and detector group are used to subdivide the fixed intermediate frequency signal output by the superheterodyne receiver into multiple channels, and the detector performs power detection on each subdivided channel; The AD acquisition module is used to amplify and digitally acquire the output analog signal of the detector and transmit it to the control and signal processing module. The cold / hot calibration source provides a reference for the periodic two-point calibration of the ground-based radiometer. The cold calibration source consists of an insulated barrel and liquid nitrogen-immersed absorbing material, located directly below the reflector antenna, providing a cold calibration reference temperature of approximately 80K. The hot calibration source consists of a metal cone coated with a high-emissivity absorbing material. A high-precision temperature sensor is pre-installed on the back of the metal cone, and the temperature can be read through the control / data processing module. The temperature monitoring and control module surrounds analog components such as the superheterodyne receiver, intermediate frequency filter / detector group, and AD acquisition module. Through a certain temperature control strategy, it controls the temperature of the entire receiver link within a very small temperature fluctuation range, reduces the impact of ambient temperature changes on receiver gain, and improves the accuracy of radiometer measurements. The control and signal processing module performs system control and signal processing functions. The system control functions include controlling the servo structure used for the rotating transmitting antenna and reading its angle information; controlling the output frequency of the variable frequency source; reading the temperature of the thermal fixed source temperature sensor; setting and reading the parameters of the temperature detection and control module; and reading the data from the AD acquisition module. The signal processing module is used to separate the observation target and the observation frequency of the radiometer receiver signal, as well as to calibrate the measurement data of different frequencies.

2. The multi-band high-spectral-resolution ground-based microwave radiometer according to claim 1, characterized in that, The multi-band high-spectral-resolution ground-based microwave radiometer adopts a quasi-optical feed network, enabling multi-band, same-axis, and simultaneous observation of target radiation signals. It employs a broadband superheterodyne receiver structure, achieving rapid switching of the received radio frequency signal band by changing the local oscillator frequency. It also uses a narrowband intermediate frequency filter bank and a detector bank to simultaneously achieve high-spectral-resolution detection of signals within this radio frequency band, offering advantages such as simple system structure and high frequency resolution.

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