Low noise amplifier gain fluctuation measurement system and method

Abstract

The present application provides a low noise amplifier gain fluctuation measurement system, which includes a phase modulator configured to up-convert the above-mentioned amplified microwave signal carrying the low-frequency component from the microwave domain to the optical domain based on the measurement optical carrier provided by the seed laser, and output the measurement optical signal after up-conversion; an optical filter configured to allow the first-order single sideband of the measurement optical signal of a specific angular frequency to pass; and down-convert the filtered measurement optical signal, perform analog-to-digital conversion and collect the difference frequency measurement signal output generated by the down-conversion, and process the difference frequency measurement signal output data obtained by the collection, so as to obtain the data detection, collection, and processing module of the fluctuation of the gain fluctuation of the low noise amplifier in time and / or frequency. The present application also discloses a corresponding method. The system or method of the present application can overcome the electromagnetic interference problem by up-converting the microwave signal to the optical domain.

Description

Technical Field

[0001] The present application relates to a measuring device and a measuring method for gain fluctuation of a low noise amplifier in the field of microwave signal processing. Background Art

[0002] The microwave signal received by the microwave photon receiver antenna is very weak, and a low noise amplifier (LNA) is needed to amplify the low power signal in order to achieve optimal modulation. The amplified signal is up-converted to the optical domain by a phase modulator, where the amplitude, angular frequency and phase information of the microwave signal are retained in the upper sideband of the modulated signal. Using optical devices such as lenses, optical filters, and photodetectors to transmit, process, and regulate information can overcome many bottlenecks in traditional electronic technology, such as electromagnetic interference. As an important component of the front end of the RF receiver, the gain fluctuation of LNA has a great influence on the receiver sensitivity, especially when the received signal is a broadband signal. Broadband spectral signal observation requires LNA to have high stability, but the gain profile of most LNAs is not flat and has certain fluctuations. Understanding the LNA gain fluctuation and compensating it in time is very critical to improving the performance of microwave optical links. In addition, understanding the gain fluctuation of LNA helps to reduce the noise factor of the receiver, thereby improving the sensitivity and stability of the receiver. Photons are electrically neutral particles and are naturally immune to complex electromagnetic environments, which facilitates the extraction of information in the optical domain.

[0003] Broadband signals require LNA gain to have high stability, and the flatter the gain profile, the better. When the LNA gain fluctuation is relatively stable, higher requirements are placed on measurement accuracy. The traditional LNA gain fluctuation measurement method is implemented in the electrical domain, and the strong electromagnetic interference leads to low measurement accuracy, which cannot meet the needs of broadband signals. The traditional measurement method requires calibration of the measurement system, and the device structure is complex and inefficient. Summary of the invention

[0004] The purpose of this application is to propose a measurement system and method for low noise amplifier gain fluctuation, to achieve accurate extraction of first-order sidebands in the optical domain, and to improve the accuracy of fluctuation measurement.

[0005] To this end, some embodiments of the present application provide a low noise amplifier gain fluctuation measurement system, characterized in that: it includes a measurement link, the measurement link includes: a signal source, which is configured to generate and provide a microwave signal, the microwave signal has an angular frequency ω RF A low noise amplifier configured to suppress the noise in the microwave signal and amplify the microwave signal, and introduce a low frequency component with a bandwidth of Δω into the microwave signal, wherein the angular frequency of the low frequency component is ω G; a phase modulator configured to up-convert the amplified microwave signal carrying the low-frequency component from the microwave domain to the optical domain based on the measurement optical carrier provided by the seed laser, and output the measurement optical signal after up-conversion; a seed laser configured to generate the optical carrier fed to the phase modulator, wherein the angular frequency of the measurement optical carrier is ω opt ; An optical filter configured to allow an angular frequency of ω opt +ω RF -ω G ,ω opt +ω RF , and ω opt +ω RF +ω G The first-order single sideband of the measurement optical signal passes through; and a data detection, acquisition, and processing module, which includes a photoelectric detector, an acquisition card, and a host computer, wherein the photoelectric detector is configured to down-convert the filtered measurement optical signal, and the acquisition card is configured to generate an angular frequency of ω for the down-conversion G The difference frequency measurement signal output is converted into analog-to-digital and collected, and the host computer is configured to process the collected difference frequency measurement signal data to obtain the fluctuation of the gain fluctuation of the low noise amplifier in time and / or frequency.

[0006] In some embodiments, the low noise amplifier gain fluctuation measurement system further includes a reference link, wherein the reference link includes directly leading the microwave signal generated and provided by the signal source to the phase modulator to up-convert the microwave signal from the microwave domain to the optical domain based on the reference optical carrier provided by the seed laser, and outputting the reference optical signal after up-conversion, wherein the angular frequency of the reference optical carrier is ω opt ; The reference optical signal is filtered by the optical filter to allow the angular frequency to be ω opt +ω RF The first-order single sideband of the reference optical signal passes through; the filtered reference optical signal is photoelectrically detected by the photodetector, the signal output generated by the photodetection is analog-to-digital converted and collected by the acquisition card to obtain reference noise signal data, and the reference noise signal data obtained by the collection and the difference frequency measurement signal data fed into the host computer are processed by the host computer, wherein the processing includes: subtracting the difference frequency measurement signal data and the reference noise signal data of the measurement link in the time domain to obtain a difference, and then Fourier transforming the difference to obtain the change of the low noise amplifier gain fluctuation in the frequency domain.

[0007] In some embodiments, the data detection, collection, and processing module further includes an oscilloscope that satisfies low-frequency signal sampling, and the LNA gain fluctuation variation over time, ie, the time spectrum, is obtained through the oscilloscope.

[0008] Some embodiments of the present application provide a method for measuring gain fluctuation of a low noise amplifier, which comprises the steps of: generating and providing a microwave signal, wherein the microwave signal has an angular frequency ω RF ; Use the low noise amplifier to suppress the noise in the microwave signal and amplify the microwave signal, and introduce a low frequency component with a bandwidth of Δω into the microwave signal, wherein the angular frequency of the low frequency component is ω G ; The above-mentioned amplified microwave signal carrying the low-frequency component is up-converted from the microwave domain to the optical domain based on the measurement optical carrier, and the measurement optical signal is output after up-conversion; the angular frequency of the measurement optical carrier is ω opt ; Filter the measured light signal to allow the angular frequency to be ω opt +ω RF -ω G ,ω opt +ω RF , and ω opt +ω RF +ω G The first-order single sideband of the measurement optical signal passes through; down-converting the filtered measurement optical signal, and the angular frequency generated by the down-conversion is ω G The difference frequency measurement signal output is converted into analog-to-digital and collected, and the difference frequency measurement signal data obtained by the collection is processed to obtain the fluctuation of the gain fluctuation of the low noise amplifier in time and / or frequency.

[0009] In some embodiments, the low noise amplifier gain fluctuation measurement method further comprises directly up-converting the microwave signal from the microwave domain to the optical domain based on the reference optical carrier, and outputting the reference optical signal after up-conversion, wherein the angular frequency of the reference optical carrier is ω opt ; Filter the reference optical signal to allow the angular frequency to be ω opt +ω RF The first-order single sideband of the reference optical signal passes through; the filtered reference optical signal is photoelectrically detected, the signal output in the photoelectric detection is analog-to-digital converted and collected to obtain reference noise signal data, and the reference noise signal data and the difference frequency measurement signal data fed into the host computer at the same time are processed, wherein the processing includes: subtracting the difference frequency measurement signal data and the reference noise signal data in the time domain to obtain a difference, and then Fourier transforming the difference to obtain the low noise amplifier gain fluctuation in the frequency domain.

[0010] The technical solution of the present invention, which converts microwave signals to the optical domain, can overcome the problem of electromagnetic interference and improve the measurement accuracy. In addition, the device is composed of microwave photonic equipment commonly used in laboratories, and the measurement method is simple, efficient and easy to operate. After understanding the fluctuation of the gain of the low-noise amplifier, timely compensation can reduce the noise coefficient of the entire link, improve the performance of the microwave link, and improve the sensitivity and stability of the receiver. Moreover, understanding the fluctuation of the gain of the low-noise amplifier also has a certain reference significance for improving the performance of the low-noise amplifier. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 is a schematic diagram of the principle of a system for measuring gain fluctuation of a low noise amplifier according to an embodiment of the present application;

[0012] Figure 2A is a schematic diagram of a time spectrum of a microwave signal of a measurement system for gain fluctuation of a low noise amplifier according to an embodiment of the present application;

[0013] Figure 2B is a schematic diagram of a spectrum of a microwave signal of a system for measuring gain fluctuation of a low noise amplifier according to an embodiment of the present application;

[0014] Figure 3A is a schematic diagram of a time spectrum of an LNA output signal of a low noise amplifier gain fluctuation measurement system according to an embodiment of the present application;

[0015] Figure 3B is a schematic diagram of the spectrum of an LNA output signal of a low noise amplifier gain fluctuation measurement system according to an embodiment of the present application;

[0016] Figure 4 is a schematic diagram of a modulator output signal of a system for measuring gain fluctuation of a low noise amplifier according to an embodiment of the present application;

[0017] Figure 5 is a schematic diagram of an optical filter output signal of a system for measuring gain fluctuation of a low noise amplifier according to an embodiment of the present application;

[0018] Figure 6 It is a schematic diagram of a data detection, acquisition and processing module of a measurement system for gain fluctuation of a low noise amplifier according to an embodiment of the present application;

[0019] Figure 7 is a schematic diagram of a photodetector output signal of a low noise amplifier gain fluctuation measurement system according to an embodiment of the present application;

[0020] Fig. 8A is a schematic diagram of the time spectrum of the output signal of the measurement link A of the measurement system for the gain fluctuation of the low noise amplifier according to the embodiment of the present application;

[0021] Figure 8B is a schematic diagram of the frequency spectrum of an output signal of a measurement link A of a measurement system for measuring gain fluctuation of a low noise amplifier according to an embodiment of the present application;

[0022] Fig. 9A 4 is a schematic diagram of the time spectrum of the denoising result of the measurement system of the gain fluctuation of the low noise amplifier according to the embodiment of the present application.

[0023] Fig. 9B 4 is a schematic diagram of a spectrum of a denoising result of a measurement system for a low noise amplifier gain fluctuation according to an embodiment of the present application. DETAILED DESCRIPTION

[0024] The embodiments of the present application will be described below with reference to the accompanying drawings.

[0025] The specific structural and functional details disclosed herein are merely representative and are for the purpose of describing exemplary embodiments of the present application. However, the present application can be implemented in many alternative forms and should not be interpreted as being limited to only the embodiments set forth herein.

[0026] It should be understood that, although the terms "first", "second", etc. may be used herein to describe various units, these units should not be limited by these terms. These terms are used only to distinguish one unit from another unit. For example, without departing from the scope of the exemplary embodiments, the first unit may be referred to as the second unit, and similarly the second unit may be referred to as the first unit. The term "and / or" used herein includes any and all combinations of one or more of the listed associated items.

[0027] The terms used herein are only for describing specific embodiments and are not intended to limit exemplary embodiments. Unless the context clearly indicates otherwise, the singular forms "one", "one" and "item" used herein are also intended to include plural numbers. It should also be understood that the terms "include" and / or "comprise" used herein specify the existence of stated features, integers, steps, operations, units and / or components, without excluding the existence or addition of one or more other features, integers, steps, operations, units, components and / or combinations thereof.

[0028] It should also be noted that, in some alternative implementations, the functions / actions mentioned may occur in a different order than that indicated in the accompanying drawings. For example, depending on the functions / actions involved, two figures shown in succession may actually be performed substantially simultaneously or may sometimes be performed in the reverse order.

[0029] Some embodiments of the present application provide a low noise amplifier gain fluctuation measurement system. The system schematic diagram is as follows: Figure 1As shown: it includes a signal source 1, a low noise amplifier (LNA) module 2, a phase modulator 3, a seed laser DFB 4, an optical filter 5 and a data detection, acquisition and processing module 6; wherein the data detection, acquisition and processing module 6 includes a photodetector 7, an acquisition card 8 and a host computer 9. The signal source 1 is configured to generate and provide a microwave signal having an angular frequency ω RF , LNA2 is configured to suppress the noise in the microwave signal and amplify the microwave signal; however, due to the fluctuation of the gain of the low noise amplifier, it will introduce a low-frequency component with a bandwidth of Δω into the microwave signal, and the angular frequency of the low-frequency component is ω G The phase modulator 3 is configured to up-convert the amplified microwave signal carrying the low-frequency component from the microwave domain to the optical domain based on the optical carrier provided by the seed laser, and output the optical signal after up-conversion; the seed laser 4 is configured to generate the optical carrier fed to the phase modulator 3, wherein the angular frequency of the optical carrier is ω opt ; The optical filter 5 is configured to allow an angular frequency of ω opt +ω RF -ω G ,ω opt +

[0030] ω RF , and ω opt +ω RF +ω G The first-order single sideband of the microwave signal passes; the data detection, collection, and processing module 6 is configured to have a diagonal frequency of ω G The low-frequency component signal is analog-to-digital converted and collected, and the analog-to-digital converted data is processed to obtain the fluctuation of the gain fluctuation of LNA2 in time and / or frequency.

[0031] The signal source 1 is configured to generate a microwave signal, and the expression of the microwave signal is: Amplitude A = 1, angular frequency ω RF =2πf RF , f RF =35GHz, the phase is The time spectrum and frequency spectrum diagram of the microwave signal are shown in Figure 2A , Figure 2B shown.

[0032] LNA2 is configured to suppress the noise in the microwave signal and amplify the microwave signal. However, due to the fluctuation of LNA gain, it will introduce a low-frequency component with a bandwidth of ΔA into the microwave signal. In order to explain the problem clearly, the frequency f fluctuating from 0 to 3 GHz is used here. G , the angular frequency is ω G , amplitude B = 0.2, phase Represents the low-frequency component. The LNA output signal at a certain moment contains a frequency of ω RF -ω G ,ω RF ,ω RF +ω G Component, here, ω G In this embodiment, the LNA gain is 20 dB, and the output of the double-sided spectrum of the amplified microwave signal carrying the low-frequency component in the time domain and frequency domain is as shown in the schematic diagram. Figure 3A , Figure 3B As shown:

[0033] The phase modulator 3 is configured to up-convert the amplified microwave signal carrying the low-frequency component from the microwave domain to the optical domain, and the optical field E of the optical signal output after up-conversion USB for:

[0034]

[0035] Where j is the imaginary unit, m is the modulation coefficient of the modulator, E opt is the input optical carrier amplitude, E RF+G is the amplitude of the amplified microwave signal in the microwave domain, ω opt is the optical carrier angular frequency, ω RF+G is the angular frequency of the amplified microwave signal in the microwave domain, is the optical carrier phase, is the phase of the amplified microwave signal. After modulation, the amplified microwave signal amplitude E is retained in the first-order sideband RF+G , angular frequency ω RF+G and Phase The optical carrier and first-order sideband signal output by the modulator are shown in the figure below. Figure 4 As shown, the second-order and higher-order sideband powers are low and are therefore neglected here.

[0036] The seed laser 4 is configured to generate an optical carrier signal with a wavelength of 1550nm fed to the phase modulator 3. The line width and relative intensity noise (RIN) of the seed laser 4 have a great influence on the performance of the entire link. Based on the link operating wavelength and the laser volume, the selectable lasers are distributed feedback lasers (DFB lasers) and external cavity lasers. The DFB laser grows a Bragg grating with a periodic structure in the active region to achieve optical feedback. Compared with the Fabry-Perot laser (FP laser), it has better wavelength selectivity and is easy to achieve dynamic single longitudinal mode narrow linewidth output. The external cavity laser uses an ordinary laser gain chip "external" fiber grating or diffraction grating as a wavelength selection unit, repeatedly resonates to form a laser, and further compresses the line width. From the perspective of link sensitivity and linear dynamic range, a DFB laser can be selected as the seed laser of the link.

[0037] The optical filter 5 is configured to allow an angular frequency of ω opt +ω RF -ω G ,ω opt +ω RF , and ω opt +ω RF +ω G The first-order single sideband of the microwave signal passes through. In order to accurately extract the above-mentioned first-order single sideband, the optical filter generally requires: the cutoff frequency meets the bandwidth requirements of the low-frequency component, the flatness in the band is low, the insertion loss is small, and the side mode suppression ratio is appropriate. The schematic diagram of the filtered output signal of the optical filter 5 is shown in Figure 5 shown.

[0038] The data detection, acquisition and processing module 6 is used for signal photoelectric conversion, analog-to-digital conversion and data acquisition and processing. Figure 6 The optical signal includes a photodetector 7, an acquisition card 8 and a host computer 9. The photodetector 7 is configured to down-convert the filtered output signal output by the optical filter to the microwave domain. The two frequency components in the filtered optical signal beat each other, and the high-frequency component obtained by the sum frequency cannot be detected by the detector. The difference frequency signal output schematic diagram is shown in FIG. Figure 7 As shown, it can be collected. The acquisition card 8 is configured to have a diagonal frequency of ω G The difference frequency signal is collected and converted into analog-to-digital format. Here, the angular frequency is 2ω G The component of is weak and can be actively filtered out by the photoelectric detector. The data processing software in the host computer 9 is configured to process the above angular frequency ω G The signal is converted into digital form and the collected data is processed to obtain the fluctuation of LNA gain fluctuation in time and frequency, that is, the double-sided spectrum of time spectrum and frequency spectrum. Fig. 8A , the schematic diagram of the spectrum is as follows Figure 8Bshown.

[0039] Depend on Fig. 8A , Figure 8B It can be seen that each instrument in the link of the system will introduce system noise into the signal. If the system noise is too large, the low-frequency component is likely to be submerged in the system noise. In order to remove the interference of system noise such as thermal noise generated by thermal motion of resistor elements in the link, shot noise caused by photodetector 7, and relative intensity noise generated by output power fluctuation of laser DFB4, a reference link B can be added to the link. Thus, the total link of the system is composed of two paths, in which the signal source 1, LNA2, phase modulator 3, seed laser DFB4, optical filter 5, data detection, acquisition, and processing module 6 constitute measurement link A. Signal source 1, phase modulator 3, seed laser DFB4, optical filter 5, data detection, acquisition, and processing module 6 constitute reference link B. Among them, the microwave signal in the reference link is the same microwave signal as that in the measurement link, and its processing in the phase modulator 3, seed laser DFB4, optical filter 5, data detection, acquisition, and processing module 6 is the same except that it will not be amplified by LNA but directly modulated into an optical signal, and other processing parameters are the same.

[0040] Thus, in the measurement link A, the signal source 1 generates and provides a microwave signal, wherein the microwave signal has an angular frequency ω RF ; A low noise amplifier 2 is configured to suppress the noise in the microwave signal and amplify the microwave signal, and introduce a low frequency component with a bandwidth of Δω into the microwave signal, wherein the angular frequency of the low frequency component is ω G The phase modulator 3 is configured to up-convert the amplified microwave signal carrying the low-frequency component from the microwave domain to the optical domain based on the measurement optical carrier provided by the seed laser, and output the measurement optical signal after up-conversion; the seed laser 4 is configured to generate the optical carrier fed to the phase modulator 3, wherein the angular frequency of the measurement optical carrier is The optical filter 5 is configured to allow an angular frequency of ω opt +ω RF -ω G ,ω opt +ω RF , and ω opt +ω RF +ω G The first-order single sideband of the measurement optical signal passes; the photodetector 7 is configured to down-convert the filtered measurement optical signal, and the acquisition card 8 is configured to generate an angular frequency of ω for the down-conversion GThe difference frequency measurement signal output is converted into analog-to-digital and collected, and the host computer 9 is configured to process the collected difference frequency measurement signal output data, so as to obtain the fluctuation of the gain fluctuation of the low noise amplifier 2 in time and / or frequency.

[0041] In reference link B, the microwave signal generated and provided by the signal source 1 is directly introduced to the phase modulator 3 to up-convert the microwave signal from the microwave domain to the optical domain based on the reference optical carrier provided by the seed laser and the same as the measurement optical carrier, and output a reference optical signal after up-conversion, wherein the angular frequency of the reference optical carrier is The reference optical signal is filtered by the optical filter 5 to allow an angular frequency of ω opt +ω RF The first-order single sideband of the reference optical signal passes through; the filtered reference optical signal is photoelectrically detected by the photodetector 7, the signal output generated by the photodetection is analog-to-digital converted and collected by the acquisition card 8 to obtain reference noise signal data, and the reference noise signal data obtained by the collection and the difference frequency measurement signal data of the measurement link A fed into the host computer at the same time are processed by the host computer 9, wherein the processing includes: subtracting the difference frequency measurement signal data of the measurement link A and the reference noise signal data in the time domain to obtain the difference between the two, and then performing Fourier transform on the difference to obtain the change of the gain fluctuation of the low noise amplifier 2 in the frequency domain.

[0042] It should be understood that in reference link B, when the filtered reference optical signal passes through the photodetector, the optical signal cannot be responded to by the photodetector, there is no beat frequency process, and therefore no difference frequency microwave signal is output, and its output signal is the noise of reference link B.

[0043] The above processing can remove the noise introduced by the device or apparatus other than LNA in the above measurement link A. The schematic diagrams of the denoising results of the LNA gain fluctuation in the time domain and the frequency domain are shown as follows: Fig. 9A , Fig. 9B As shown. Among them, Fig. 9A is the variation of LNA gain fluctuation over time, that is, the time spectrum. Fig. 9B It is the variation of LNA gain fluctuation in frequency (double-sided spectrum), that is, the spectrum.

[0044] In other embodiments of the present application, under the condition that the measurement accuracy requirements are met, the data detection, acquisition, and processing module 6 can replace the acquisition card 8 with an oscilloscope that meets the low-frequency signal sampling requirements or serve as an addition to the acquisition card. The oscilloscope can be used to obtain the change of LNA gain fluctuation over time, that is, the time spectrum.

[0045] The technical solution of the present invention can overcome the electromagnetic interference problem and improve the measurement accuracy by up-converting the microwave signal to the optical domain; mastering the fluctuation of LNA gain and making timely compensation can reduce the noise coefficient of the entire link, improve the performance of the microwave link, and improve the sensitivity and stability of the receiver. Understanding the fluctuation of LNA gain has a certain reference significance for improving LNA performance.

[0046] The above descriptions are only preferred specific embodiments of the present invention, which are all different implementations based on the overall concept of the present invention, and the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A low noise amplifier gain fluctuation measurement system, characterized in that: The method comprises a measurement link, wherein the measurement link comprises: A signal source (1) is configured to generate and provide a microwave signal having an angular frequency ; A low noise amplifier (2) is configured to suppress noise in the microwave signal and amplify the microwave signal, and introduce a bandwidth of The angular frequency of the low-frequency component is ; A phase modulator (3) is configured to up-convert the amplified microwave signal carrying the low-frequency component from the microwave domain to the optical domain based on the measurement optical carrier provided by the seed laser, and output the measurement optical signal after up-conversion; A seed laser (4) is configured to generate the optical carrier fed to the phase modulator (3), wherein the angular frequency of the measurement optical carrier is ; The optical filter (5) is configured to allow an angular frequency of , ,as well as A first-order single sideband of the measurement optical signal passes; and a data detection, acquisition, and processing module (6), comprising a photoelectric detector (7), an acquisition card (8), and a host computer (9), wherein the photoelectric detector (7) is configured to down-convert the filtered measurement light signal, and the acquisition card (8) is configured to convert the angular frequency generated by the down-conversion to The difference frequency measurement signal output is converted into analog-to-digital and collected, wherein the host computer (9) is configured to process the collected difference frequency measurement signal data to obtain the gain fluctuation of the low noise amplifier (2) in time and / or frequency.

2. The low noise amplifier gain fluctuation measurement system according to claim 1, characterized in that: The system also includes a reference link, wherein the reference link includes: directly leading the microwave signal generated and provided by the signal source to the phase modulator (3) to up-convert the microwave signal from the microwave domain to the optical domain based on the reference optical carrier provided by the seed laser, and outputting a reference optical signal after up-conversion, wherein the angular frequency of the reference optical carrier is equal to the angular frequency of the measurement optical carrier; filtering the reference optical signal by the optical filter (5) to allow the angular frequency to be The first-order single sideband of the reference optical signal passes through; the photoelectric detector (7) is used to perform photoelectric detection on the filtered reference optical signal, the acquisition card (8) performs analog-to-digital conversion on the output signal of the photoelectric detection and collects the data to obtain reference noise signal data, and the host computer (9) is used to process the reference noise signal data and the difference frequency measurement signal data simultaneously fed into the host computer, wherein the processing includes: The difference frequency measurement signal data and the reference noise signal data are subtracted in the time domain to obtain a difference between the two, and then the difference is Fourier transformed to obtain the gain fluctuation of the low noise amplifier (2) in the frequency domain.

3. The low noise amplifier gain fluctuation measurement system according to claim 1, characterized in that: The data detection, collection and processing module (6) also includes an oscilloscope that satisfies low-frequency signal sampling, and the LNA gain fluctuation variation over time, i.e., the time spectrum, is obtained through the oscilloscope.

4. A method for measuring gain fluctuation of a low noise amplifier, characterized in that: include Generate and provide a microwave signal having an angular frequency ; The low noise amplifier is used to suppress the noise in the microwave signal and amplify the microwave signal, and a bandwidth of The angular frequency of the low-frequency component is ; The amplified microwave signal carrying the low-frequency component is up-converted from the microwave domain to the optical domain based on the measurement optical carrier, and the measurement optical signal is output after up-conversion; the angular frequency of the measurement optical carrier is ; The measurement light signal is filtered to allow the angular frequency to be , ,as well as The first-order single sideband of the measured optical signal is passed; The filtered measurement optical signal is down-converted, and the angular frequency generated by the down-conversion is The difference frequency measurement signal output is analog-to-digital converted and collected to obtain difference frequency measurement signal output data, and the difference frequency measurement signal data is processed to obtain the gain fluctuation of the low noise amplifier in time and / or frequency.

5. The method for measuring gain fluctuation of a low noise amplifier according to claim 4, characterized in that: The method further comprises directly up-converting the microwave signal from the microwave domain to the optical domain based on a reference optical carrier, and outputting a reference optical signal after up-conversion, wherein the angular frequency of the reference optical carrier is equal to the angular frequency of the measurement optical carrier; filtering the reference optical signal to allow the angular frequency to be The first-order single sideband of the reference optical signal passes through; the filtered reference optical signal is photoelectrically detected, the reference noise signal output of the photoelectric detection is analog-to-digital converted and collected to obtain reference noise signal data, and the reference noise signal data obtained by the collection and the difference frequency measurement signal data fed into the host computer at the same time are processed, wherein the processing includes: The difference frequency measurement signal data and the reference noise signal data are subtracted in the time domain to obtain the difference between the two, and then the difference is Fourier transformed to obtain the low noise amplifier gain fluctuation in the frequency domain.

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