阅读说明：本技术 微波信号时频特性测量方法及装置 (Microwave signal time-frequency characteristic measuring method and device ) 是由 朱丹 丁杰文 潘时龙 王梓豪 于 2021-09-23 设计创作，主要内容包括：本发明公开了一种微波信号时频特性测量方法,包括以下步骤：对重频为f-(MLL)的零啁啾光脉冲进行时域拉伸,生成啁啾光脉冲信号；将所述啁啾光脉冲信号分为N路并分别给予N个不同的延时,生成N路啁啾光脉冲延时信号,且τ-(i+1)-τ-(i)＝Δτ,NΔτ＝1/f-(MLL)；τ-(i)为第i路啁啾光脉冲延时信号的延时量,N为大于1的整数,i＝1,2,…,N-1；将微波信号分别调制于N路啁啾光脉冲延时信号,生成N路调制光脉冲信号；对N路调制光脉冲信号分别进行时域压缩,得到N路携带有微波信号频率信息的频时映射光信号；对N路频时映射光信号进行光电转换,并在数字域中提取得到微波信号的时频特性。本发明还公开了一种微波信号时频特性测量装置。本发明能够实现对高频大带宽微波信号的连续实时时频特性分析。(The invention discloses a microwave signal time-frequency characteristic measuring method, which comprises the following steps: for repetition frequency of f MLL Performing time domain stretching on the zero chirp optical pulse to generate a chirp optical pulse signal; dividing the chirp optical pulse signal into N paths and respectively giving N different delays to generate N paths of chirp optical pulse delay signals, wherein tau is i+1 ‑τ i ＝Δτ，NΔτ＝1/f MLL ；τ i The delay amount of the ith chirp optical pulse delay signal is N is an integer greater than 1, i is 1,2, …, N-1; respectively modulating the microwave signals to N paths of chirp optical pulse delay signals to generate N paths of modulation optical pulse signals; respectively performing time domain compression on the N paths of modulated optical pulse signals to obtain N paths of frequency-time mapping optical signals carrying microwave signal frequency information; and performing photoelectric conversion on the N paths of frequency-time mapping optical signals, and extracting the time-frequency characteristics of the microwave signals in a digital domain. The invention also discloses a microwave signal time-frequency characteristicAnd (4) a measuring device. The invention can realize continuous real-time-frequency characteristic analysis of the high-frequency large-bandwidth microwave signal.)

1. A microwave signal time-frequency characteristic measuring method is characterized by comprising the following steps:

for repetition frequency of f_MLLPulse width of T₀The zero chirp light pulse is subjected to time domain stretching to generate a pulse width T₁Chirped optical pulse signal of, T₁>T₀；

Dividing the chirp optical pulse signal into N paths and respectively giving N different delays to generate N paths of chirp optical pulse delay signals, wherein tau is_i+1-τ_i＝Δτ，NΔτ＝1/f_MLL(ii) a Wherein, tau_iFor the ith chirpThe delay amount of the optical pulse delay signal, wherein N is an integer greater than 1, i is 1,2, …, N-1;

respectively modulating microwave signals to the N paths of chirp optical pulse delay signals to generate N paths of modulation optical pulse signals;

respectively performing time domain compression on the N paths of modulated optical pulse signals to obtain N paths of frequency-time mapping optical signals carrying the frequency information of the microwave signals;

and performing photoelectric conversion on the N paths of frequency-time mapping optical signals, and extracting the time-frequency characteristics of the microwave signals in a digital domain.

2. The method for measuring microwave signal time-frequency characteristics according to claim 1, wherein the chirped fiber grating is used to perform time-domain stretching on the zero-chirp optical pulse, and the chirped fiber grating with opposite dispersion amount is used to perform time-domain compression on the modulated optical pulse signal.

3. The microwave signal time-frequency characteristic measuring method according to claim 1, wherein N different delays are respectively given to the N chirped optical pulse signals by using N electrically controlled delay lines with delay amounts increasing by an equal amount of Δ τ.

4. The method for measuring the time-frequency characteristics of microwave signals according to claim 1, wherein the specific method for extracting the time-frequency characteristics of the microwave signals in the digital domain is as follows:

receiving N paths of electric signals subjected to photoelectric conversion in parallel, performing analog-to-digital conversion respectively, aligning N paths of digital signals obtained through cyclic displacement, and performing differential operation on the ith path of digital signal and the (i + 1) th path of digital signal, wherein i is 1,2, … and N-1; equally dividing an optical pulse repetition frequency cycle into N unit time periods, wherein the length of each unit time period, namely the time domain resolution, is delta tau; when the amplitudes of the differential signals are less than or equal to 0, the frequency of the microwave signal in the ith unit time period is equal to the frequency directly calculated by the ith digital signal, and when the signals with the amplitudes greater than 0 exist in the differential signals, the frequency of the microwave signal in the ith unit time period is equal to the frequency calculated by the signals with the amplitudes greater than 0 in the differential signals.

5. A microwave signal time-frequency characteristic measuring device is characterized by comprising:

a time domain stretching module for stretching the repetition frequency of f_MLLPulse width of T₀The zero chirp light pulse is subjected to time domain stretching to generate a pulse width T₁Chirped optical pulse signal of, T₁>T₀；

A multi-path delay module for dividing the chirp optical pulse signal into N paths and respectively giving N different delays to generate N paths of chirp optical pulse delay signals, wherein tau is_i+1-τ_i＝Δτ，NΔτ＝1/f_MLL(ii) a Wherein, tau_iThe delay amount of the ith chirp optical pulse delay signal is N is an integer greater than 1, i is 1,2, …, N-1;

the electro-optical modulation module is used for modulating the microwave signals to the N paths of chirp optical pulse delay signals respectively to generate N paths of modulation optical pulse signals;

the time domain compression module is used for respectively performing time domain compression on the N paths of modulated optical pulse signals to obtain N paths of frequency-time mapping optical signals carrying the frequency information of the microwave signals;

and the signal processing module is used for carrying out photoelectric conversion on the N paths of frequency-time mapping optical signals and extracting the time-frequency characteristics of the microwave signals in a digital domain.

6. The microwave signal time-frequency characteristic measuring device according to claim 5, wherein the time domain stretching module is a chirped fiber grating, and the time domain compressing module is formed by N chirped fiber gratings having dispersion amounts opposite to those of the time domain stretching module in parallel.

7. The microwave signal time-frequency characteristic measuring device according to claim 5, wherein the multi-path delay module uses N electrically controlled delay lines whose delay amounts are increased by an equal amount of Δ τ to implement that N different delays are respectively given to the N chirped optical pulse signals.

8. The microwave signal time-frequency characteristic measuring device according to claim 5, wherein the signal processing module extracts the time-frequency characteristic of the microwave signal in a digital domain by using the following method:

receiving N paths of electric signals subjected to photoelectric conversion in parallel, performing analog-to-digital conversion respectively, aligning N paths of digital signals obtained through cyclic displacement, and performing differential operation on the ith path of digital signal and the (i + 1) th path of digital signal, wherein i is 1,2, … and N-1; equally dividing an optical pulse repetition frequency cycle into N unit time periods, wherein the length of each unit time period, namely the time domain resolution, is delta tau; when the amplitudes of the differential signals are less than or equal to 0, the frequency of the microwave signal in the ith unit time period is equal to the frequency directly calculated by the ith digital signal, and when the signals with the amplitudes greater than 0 exist in the differential signals, the frequency of the microwave signal in the ith unit time period is equal to the frequency calculated by the signals with the amplitudes greater than 0 in the differential signals.

Technical Field

The invention relates to a microwave signal time-frequency characteristic measuring method, in particular to a microwave signal time-frequency characteristic measuring method based on a microwave photon technology.

Background

The measurement of the time-frequency characteristics of microwave signals belongs to one of signal characteristic analysis methods, and the method mainly has the functions of performing combined analysis of time-domain and frequency-domain characteristics on received microwave signals to acquire information of the frequency distribution of the microwave signals along with time, and is one of key technologies of research and application in the fields of high-speed communication systems, radar electronic warfare systems, high-speed digital and analog signal analysis and the like.

The time-frequency analysis of microwave signals in a traditional electronic system is realized by mainly utilizing a digital signal processing method to convert analog microwave signals to be analyzed into digital signals through analog-to-digital conversion, and then calculating the time-frequency characteristics of the microwave signals on a digital domain through processing methods such as short-time Fourier transform, wavelet transform or Hilbert transform and the like. The method of calculating through the digital domain is only suitable for processing microwave signals with low frequency, narrow bandwidth and limited time length, and is difficult to carry out real-time-frequency characteristic analysis on the microwave signals due to the limitation of analog-digital/digital-analog conversion rate and the limitation of digital signal calculation and storage capacity when the method of calculating through the digital domain is faced with the microwave signals with high frequency, large bandwidth and long-time existence.

The microwave photon technology has the advantages of large bandwidth, capability of processing signals in parallel, electromagnetic interference resistance and the like, can solve the problems of an electronic system in analyzing the time-frequency characteristics of microwave signals, and common microwave signal time-frequency analysis methods based on the microwave photon technology are realized based on a frequency-time mapping principle. Microwave signal time-frequency analysis based on a single dispersive medium (see [ J).S.R.Konatham,and R.Maram,“Photonics-Based Real-Time 2D(Time-Frequency)Broadband Signal Analysis and Processing,”in 2019International Topical Meeting on Microwave Photonics(MWP),1-4(2019).]) As shown in fig. 1, the high-gravity generated by the mode-locked laserThe microwave signal time-frequency analysis method based on the microwave photon technology has the advantages of high time resolution, high time-frequency analysis speed and limited working frequency range and low frequency resolution of the system. Time-frequency analysis of Microwave signals Based on time-lens and dispersive media (see [ X.Xie, J.Li, F.yin, K.xu, and Y.Dai, "STFT Based on Bandwidth-Scaled Microwave Photonics," J.light.Technol.,39 (6)), 1680-.]) The basic principle of the method is as shown in fig. 2, a high-repetition-frequency optical frequency comb is generated by an optical frequency comb generation module, a radio-frequency signal to be detected is modulated to a positive side band and a negative side band of the optical frequency comb through an electro-optical modulator, different frequency bands of the side band signal of the optical frequency comb are filtered out by a Fabry-Perot cavity with Free spectrum intervals (FSR) different from that of the optical frequency comb, time sampling is completed by modulating a pulse envelope on the filtered optical signal, and finally frequency-time mapping is completed on the signal after time sampling by using a dispersion device to obtain time-frequency characteristics of the signal.

The two microwave signal time-frequency analysis methods based on the microwave photon technology both need an optical pulse signal with high repetition frequency as an original optical carrier signal, and the working frequency range of the system is limited by the repetition frequency of the optical pulse, which is generally less than 5GHz, so that real-time-frequency characteristic analysis is difficult to be performed on the microwave signal with high frequency and large bandwidth. Therefore, it is of great significance to provide a method and a device capable of performing real-time and continuous time-frequency characteristic analysis on high-frequency large-bandwidth microwave signals.

Disclosure of Invention

The technical problem to be solved by the invention is to overcome the defects of the prior art and provide a microwave signal time-frequency characteristic measuring method, which can realize real-time-frequency characteristic analysis of high-frequency large-bandwidth microwave signals and has the advantages of high time-frequency resolution and continuous time-frequency analysis capability.

The invention specifically adopts the following technical scheme to solve the technical problems:

a microwave signal time-frequency characteristic measuring method comprises the following steps:

for repetition frequency of f_MLLPulse width of T₀The zero chirp light pulse is subjected to time domain stretching to generate a pulse width T₁Chirped optical pulse signal of, T₁>T₀；

Dividing the chirp optical pulse signal into N paths and respectively giving N different delays to generate N paths of chirp optical pulse delay signals, wherein tau is_i+1-τ_i＝Δτ，NΔτ＝1/f_MLL(ii) a Wherein, tau_iThe delay amount of the ith chirp optical pulse delay signal is N is an integer greater than 1, i is 1,2, …, N-1;

respectively modulating microwave signals to the N paths of chirp optical pulse delay signals to generate N paths of modulation optical pulse signals;

respectively performing time domain compression on the N paths of modulated optical pulse signals to obtain N paths of frequency-time mapping optical signals carrying the frequency information of the microwave signals;

and performing photoelectric conversion on the N paths of frequency-time mapping optical signals, and extracting the time-frequency characteristics of the microwave signals in a digital domain.

Preferably, the zero-chirped optical pulse is time-domain stretched using a chirped fiber grating, and the modulated optical pulse signal is time-domain compressed using a chirped fiber grating with an opposite dispersion amount.

Preferably, N different delays are respectively given to the N chirped optical pulse signals by using N electrically controlled delay lines with delay amounts increasing by equal Δ τ.

Preferably, the specific method for extracting the time-frequency characteristic of the microwave signal in the digital domain is as follows:

receiving N paths of electric signals subjected to photoelectric conversion in parallel, performing analog-to-digital conversion respectively, aligning N paths of digital signals obtained through cyclic displacement, and performing differential operation on the ith path of digital signal and the (i + 1) th path of digital signal, wherein i is 1,2, … and N-1; equally dividing an optical pulse repetition frequency cycle into N unit time periods, wherein the length of each unit time period, namely the time domain resolution, is delta tau; when the amplitudes of the differential signals are less than or equal to 0, the frequency of the microwave signal in the ith unit time period is equal to the frequency directly calculated by the ith digital signal, and when the signals with the amplitudes greater than 0 exist in the differential signals, the frequency of the microwave signal in the ith unit time period is equal to the frequency calculated by the signals with the amplitudes greater than 0 in the differential signals.

Based on the same inventive concept, the following technical scheme can be obtained:

a microwave signal time-frequency characteristic measuring device comprises:

a time domain stretching module for stretching the repetition frequency of f_MLLPulse width of T₀The zero chirp light pulse is subjected to time domain stretching to generate a pulse width T₁Chirped optical pulse signal of, T₁>T₀；

A multi-path delay module for dividing the chirp optical pulse signal into N paths and respectively giving N different delays to generate N paths of chirp optical pulse delay signals, wherein tau is_i+1-τ_i＝Δτ，NΔτ＝1/f_MLL(ii) a Wherein, tau_iThe delay amount of the ith chirp optical pulse delay signal is N is an integer greater than 1, i is 1,2, …, N-1;

the electro-optical modulation module is used for modulating the microwave signals to the N paths of chirp optical pulse delay signals respectively to generate N paths of modulation optical pulse signals;

the time domain compression module is used for respectively performing time domain compression on the N paths of modulated optical pulse signals to obtain N paths of frequency-time mapping optical signals carrying the frequency information of the microwave signals;

and the signal processing module is used for carrying out photoelectric conversion on the N paths of frequency-time mapping optical signals and extracting the time-frequency characteristics of the microwave signals in a digital domain.

Preferably, the time domain stretching module is a chirped fiber grating, and the time domain compressing module is formed by N chirped fiber gratings with dispersion amounts opposite to those of the time domain stretching module in parallel.

Preferably, the multi-path delay module uses N electrically controlled delay lines with delay amounts increasing by an equal amount of Δ τ to implement that N different delays are respectively given to the N chirped optical pulse signals.

Preferably, the signal processing module extracts the time-frequency characteristics of the microwave signal in the digital domain by using the following method:

receiving N paths of electric signals subjected to photoelectric conversion in parallel, performing analog-to-digital conversion respectively, aligning N paths of digital signals obtained through cyclic displacement, and performing differential operation on the ith path of digital signal and the (i + 1) th path of digital signal, wherein i is 1,2, … and N-1; equally dividing an optical pulse repetition frequency cycle into N unit time periods, wherein the length of each unit time period, namely the time domain resolution, is delta tau; when the amplitudes of the differential signals are less than or equal to 0, the frequency of the microwave signal in the ith unit time period is equal to the frequency directly calculated by the ith digital signal, and when the signals with the amplitudes greater than 0 exist in the differential signals, the frequency of the microwave signal in the ith unit time period is equal to the frequency calculated by the signals with the amplitudes greater than 0 in the differential signals.

Compared with the prior art, the technical scheme of the invention has the following beneficial effects:

(1) according to the invention, the frequency information of the microwave signal to be detected is converted to the time domain signal by using the frequency-time mapping method based on the microwave photons, and the frequency information of the microwave signal to be detected can be obtained by measuring the time domain of the frequency-time mapping signal on the analog domain, so that complex digital domain operation is not needed, and the real-time performance of system time-frequency characteristic analysis is improved.

(2) The invention can use the optical pulse signal with low repetition frequency as the optical carrier, increases the time modulation window of the microwave signal to be measured, improves the working frequency range and the frequency resolution of the time-frequency characteristic measuring system, and solves the problem that the working frequency range of the existing microwave photon-based time-frequency characteristic analyzing method is limited.

(3) The invention utilizes the method of optical domain multi-path equal difference time delay and digital domain difference operation, and can improve the time resolution of the time-frequency characteristic measurement system under the condition of ensuring that the frequency resolution of the system is not changed.

(4) The invention can flexibly adjust the time-frequency joint resolution by controlling the delay difference of each level of optical link and the dispersion amount of the dispersion module, and has strong reconfigurability.

Drawings

FIG. 1 is a schematic diagram of a microwave signal time-frequency analysis system based on a single dispersive medium;

FIG. 2 is a schematic diagram of a microwave signal time-frequency analysis system based on a time lens and a dispersion medium;

fig. 3 is a schematic structural principle diagram of a microwave signal real-time-frequency analysis apparatus according to an embodiment of the present invention.

Detailed Description

Aiming at the defects in the prior art, the solution idea of the invention is to modulate a microwave signal onto an optical carrier based on a microwave photon technology, map frequency information of the microwave signal to a time domain through frequency-time mapping in the optical domain, directly measure the time domain signal in a time dimension to obtain the time-frequency characteristic of the microwave signal, avoid complex digital operation and improve the real-time performance of time-frequency characteristic analysis of high-frequency, large-bandwidth and long-period signals; meanwhile, the method of time delay control and parallel measurement is adopted, so that the microwave signal time-frequency analysis method has higher time domain resolution capability and larger working frequency range under the condition of ensuring high frequency resolution, and solves the problems that the working frequency range of the existing microwave signal time-frequency analysis method based on microwave photons is limited and the high time-frequency resolution is difficult to meet at the same time.

The microwave signal time-frequency characteristic measuring method comprises the following steps:

for repetition frequency of f_MLLPulse width of T₀The zero chirp light pulse is subjected to time domain stretching to generate a pulse width T₁Chirped optical pulse signal of, T₁>T₀；

Dividing the chirp optical pulse signal into N paths and respectively giving N different delays to generate N paths of chirp optical pulse delay signals, wherein tau is_i+1-τ_i＝Δτ，NΔτ＝1/f_MLL(ii) a Wherein, tau_iFor the ith chirp light pulseThe delay amount of the delay signal, N is an integer greater than 1, i is 1,2, …, N-1;

respectively modulating microwave signals to the N paths of chirp optical pulse delay signals to generate N paths of modulation optical pulse signals;

respectively performing time domain compression on the N paths of modulated optical pulse signals to obtain N paths of frequency-time mapping optical signals carrying the frequency information of the microwave signals;

and performing photoelectric conversion on the N paths of frequency-time mapping optical signals, and extracting the time-frequency characteristics of the microwave signals in a digital domain.

The microwave signal time frequency characteristic measuring device of the invention comprises:

a time domain stretching module for stretching the repetition frequency of f_MLLPulse width of T₀The zero chirp light pulse is subjected to time domain stretching to generate a pulse width T₁Chirped optical pulse signal of, T₁>T₀；

A multi-path delay module for dividing the chirp optical pulse signal into N paths and respectively giving N different delays to generate N paths of chirp optical pulse delay signals, wherein tau is_i+1-τ_i＝Δτ，NΔτ＝1/f_MLL(ii) a Wherein, tau_iThe delay amount of the ith chirp optical pulse delay signal is N is an integer greater than 1, i is 1,2, …, N-1;

the electro-optical modulation module is used for modulating the microwave signals to the N paths of chirp optical pulse delay signals respectively to generate N paths of modulation optical pulse signals;

the time domain compression module is used for respectively performing time domain compression on the N paths of modulated optical pulse signals to obtain N paths of frequency-time mapping optical signals carrying the frequency information of the microwave signals;

and the signal processing module is used for carrying out photoelectric conversion on the N paths of frequency-time mapping optical signals and extracting the time-frequency characteristics of the microwave signals in a digital domain.

For the public understanding, the technical scheme of the invention is explained in detail by a specific embodiment:

fig. 3 shows a basic structure of an embodiment of the microwave signal real-time-frequency characteristic measuring apparatus according to the present invention.

As shown in fig. 3, the microwave signal time-frequency characteristic measuring apparatus of this embodiment includes: 1 light pulse generator and 1 dispersion amount of beta₂The chirped fiber grating, 1 × N optical coupler, N electrically controlled optical delay lines, N electro-optical modulators, and N dispersion values of-beta₂The system comprises the chirped fiber grating, 1N photoelectric conversion arrays with input and output, and 1 analog-to-digital conversion and digital signal processing module.

Wherein the optical pulse generator and the dispersion amount are beta₂The chirped fiber grating forms a time domain stretching module, and is used for generating a zero chirped light pulse signal and performing time domain stretching, and the obtained chirped light pulse signal is used as an optical carrier.

The 1 XN optical coupler and the N electric control optical delay lines form a programmable multi-path delay module which is used for dividing the chirp optical pulse signal into N chirp optical pulse signals with incremental delay delta tau, wherein N is an integer larger than 1.

And the N electro-optical modulators form an electro-optical modulation module and are used for modulating the received microwave signals to be detected to the N paths of chirped optical pulse signals with the incremental delay delta tau to obtain N paths of modulated optical signals with microwave signals at different moments.

N dispersion amounts are-beta₂The chirped fiber bragg gratings form a time domain compression module, and the time domain compression module is used for performing time domain compression on the N paths of modulated optical signals to obtain N paths of frequency-time mapping optical signals carrying microwave signal frequency information.

The N input and N output photoelectric conversion arrays form a photoelectric conversion module, and are used for respectively carrying out photoelectric conversion on the obtained N paths of frequency-time mapping optical signals to obtain N paths of frequency-time mapping electric signals.

The analog-to-digital conversion and digital signal processing module is used for performing analog-to-digital conversion on the N paths of frequency-time mapping electric signals to obtain N paths of array signals, and then performing digital signal processing on the N paths of digital signals to extract the time-frequency characteristics of the microwave signals.

The optical pulse generator generates a zero-chirp optical pulse as an optical carrier signal, and assuming that the envelope of the optical pulse signal is gaussian, the mathematical expression is as follows:

wherein, T₀The zero-chirp optical pulse signal is dispersed by an amount of beta at full width at half maximum (defined as 1/e of the peak intensity) of the pulse₂The chirped fiber grating with the length z is subjected to time domain stretching, and the obtained time domain stretched optical pulse signal can be represented as:

wherein the length of the dispersion is definedA_zAnd theta_zRespectively, an amplitude term and a phase term which are independent of time, and the zero chirp optical pulse signal has a dispersion amount of beta as can be seen from formula (2)₂After the chirped fiber grating with the length z, the envelope of the output optical signal is still Gaussian, but the pulse width of the optical signal is T₀Spread out to T₁＝T₀(1+(z/L_D)²)^1/2And a phase term which is secondarily related to the time variable is also introduced, so that the output signal is a chirp optical pulse signal.

The time domain stretching optical pulse signal is divided into N paths by a 1 XN optical coupler, the N paths of optical signals are parallelly introduced into N electric control optical delay lines for equal-difference delay, taking the ith path of signal as an example, the delay amount introduced by the ith electric control optical delay line is tau_iThe delay amount of two adjacent paths of electric control optical delay lines meets the relation tau_i+1-τ_i＝Δτ，NΔτ＝1/f_MLLI is 1,2, …, N-1. Then the ith delayed time domain stretched optical pulse signal can be expressed as:

U_i(z,t-τ_i)＝|U_i(z,t-τ_i)|exp[jφ_i(z,t-τ_i)] (3)

the envelopes of two adjacent delayed time domain stretched optical pulse signals can be regarded as a gaussian time window with an initial time interval of delta tau on the time domain, which indicates that microwave signals in corresponding time windows of the different delayed time domain stretched optical pulse signals are selected to be modulated onto an optical carrier, the electro-optical modulator works in a carrier suppression state, and similarly, taking the ith path as an example, the ith path of modulated optical signal can be expressed as:

the dispersion of N-path modulated optical signals is-beta₂The N chirped fiber gratings with the length of z are subjected to time domain compression to obtain a frequency-time mapping optical signal carrying microwave signal frequency information, and taking the ith path as an example, the mathematical expression may be:

wherein A is_z,iAnd theta_z,iRespectively, an amplitude term and a phase term which are independent of time, and the frequency-time mapping optical signal is seen to be two signals with the distance of 2 beta₂zω_RF,iThe pulse time interval and the dispersion coefficient after frequency-time mapping are positively correlated with the frequency of the modulated radio frequency signal, and when the dispersion amount and the length of the chirped fiber grating are known, the frequency information of the microwave signal can be obtained by measuring the pulse time interval of the frequency-time mapping signal on the time domain. The N paths of frequency-time mapping optical signals are subjected to square-law envelope detection by the photoelectric detection array to obtain frequency-time mapping electrical signals, and taking the ith path as an example, the frequency-time mapping electrical signals can be represented as:

finally, the N channels of frequency-time mapping electrical signals are converted into digital signals through an analog-to-digital converter, and then the N channels of digital signals are respectively subjected to cyclic displacement with different lengths through a digital signal processor, so as to compensate the above-mentioned equal difference delay introduced in the optical link, taking the ith channel of digital signals as an example, the process can be expressed as follows:

after the cyclic shift, the difference operation is carried out on the ith digital signal and the (i + 1) th digital signal, i is 1,2, …, N-1, the nth digital signal and the next optical pulse repetition frequency period (1/f)_MLL) The 1 st path of digital signal is subjected to difference operation, namely N times of difference operation is carried out in one optical pulse repetition frequency period, and frequency information in a time period with the width of delta tau in one optical pulse repetition frequency period can be obtained by each time of calculation according to the sequence of the difference operation, because the N delta tau is 1/f_MLLTherefore, the microwave signal time-frequency characteristic of the time length of one optical pulse repetition frequency cycle can be obtained through N times of differential operation, the time domain resolution is delta tau, and the frequency domain resolution is 1/T₁The method for extracting the frequency characteristic after the difference operation is as follows: when the amplitudes of the differential signals are less than or equal to 0, obtaining frequency information in a corresponding time length by measuring the pulse spacing in the ith digital signal; when the differential signal has a signal with the amplitude larger than 0, frequency information in the corresponding time length is obtained by measuring the pulse interval with the amplitude larger than 0 in the differential signal, and the time information and the corresponding frequency information are combined to obtain the time-frequency characteristic. By circulating the above processes, the real-time-frequency characteristic analysis of the microwave signal can be completed.