Research On The Acquisition Of Time-frequency Parameters Based On Microwave Photonics

Microwave time-frequency parameter acquisition is widely used in electronic warfare and plays an important role in modern warfare.Limited by the “electronic bottleneck”,conventional electrical-based methods cannot meet the measurement requirements of high frequency,large bandwidth,and high real-time nature,simultaneously.In recent years,photonics-assisted microwave time-frequency parameter acquisition has received much attention because of its unique advantages,such as high frequency,large bandwidth,and anti electromagnetic interference,and has provided many competitive solutions.However,there are still some problems and shortcomings in the existing photonics-based methods: 1)Most of the methods are only used for one-dimensional frequency parameter acquisition for stationary signals,while there is still little research on microwave pulse measurement and two-dimensional timefrequency parameter acquisition;2)Existing photonics-assisted two-dimensional timefrequency parameter acquisition schemes heavily rely on large dispersion and are limited by dispersion;3)How to improve the accuracy and resolution of filter-and FTTM-based time and frequency parameter acquisition methods in fast scanning measurement scenarios is rarely studied;4)The system complexity and cost of existing photonics-assisted DFS measurement systems still need to be further reduced.Based on the above requirements and problems,this dissertation conducts the following research:1.Aiming at the problem that the existing photonics-assisted time-frequency analysis methods are highly dependent on large dispersion and limited by dispersion,and to reduce the requirements of ADC and sampling rate for the DSP-based timefrequency analysis methods when processing high-frequency and large-bandwidth signals,the SBS-based two-dimensional time-frequency analysis methods are proposed.In the analog domain,the non-stationarys SUT is segmented,and the frequency information within multiple short-time windows after segmentation is extracted and time sequenced using the SBS-based FTTM.Thus,the optical analog time-frequency analysis methods are achieved.Experiments have verified that the analysis bandwidth of the analog STFT method is up to 12 GHz,and the dynamic frequency resolution is better than 60 MHz.To reduce the costs and facilitate engineering implementation,an all-optical analog STFT method without any high-frequency electronic devices and equipment was proposed.Based on the above,to achieve multi-resolution timefrequency analysis,an SBS-based analog wavelet-like transform is further proposed.SBS-based FTTM is implemented using nonlinear frequency-sweep signals with timevarying chirp rates.Experiments have verified the multi-resolution time-frequency analysis function.2.Aiming at the problem of limited performance of the filter-and FTTM-based time-frequency parameter acquisition systems in fast scanning measurement scenarios,a method was proposed to improve the accuracy and resolution of such systems in fast scanning measurement scenarios by broadening the filter bandwidth.Simulation and experimental results show that when the sweep rate is very fast,the pulse width of the low-speed electrical pulse generated by the FTTM process is mainly determined by the impulse response of the filter.Therefore,appropriately increasing the filter bandwidth can significantly reduce the pulse width,thereby improving the accuracy and frequency resolution.In the experiment,the frequency-sweep pump wave is used to broaden the SBS gain bandwidth.The effectiveness of this method is verified using SBS-baed STFT,wavelet-like transform,and MFM systems,respectively.The experimental results show that under similar fast scanning rates,the measurement accuracy of the MFM system has been improved by more than 10 times compared to the reported works,and the frequency resolution of STFT has also been much improved.3.Aiming at the measurement requirements of microwave pulses,a microwave pulse measurement method based on pulse replication was proposed.After the microwave pulse is converted to the optical domain by electro-optic conversion,it is replicated using an active fiber loop,and then its carrier frequency is measured using SBS-based FTTM.This not only improves the detection probability of the pulse to be measured within a single period,but also improves the measurement accuracy of its carrier frequency.The unknown pulses with PRIs of 20 μs and pulse widths of 0.65,0.85,1.00,and 1.20 μs are chosen to demonstrate the pulse replication,respectively.Under a certain frequency sweep chirp rate of 0.978 GHz/μs,the measurement errors are below ±12 and ±5 MHz by using one pair of pulses and multiple pairs of pulses,respectively.4.Aiming at the application requirements of high frequency and large bandwidth single-frequency continuous-wave radar,two microwave DFS measurement schemes based on optical mixing are proposed.Firstly,a microwave DFS measurement method based on cascaded electro-optical modulation and optical mixing is proposed.By introducing a fixed low-frequency reference,the value and direction of the DFS can be simultaneously obtained only by comparing the frequency of the reference and that of the generated low-frequency electrical signal.Experiments have verified that DFS measurement accuracy is better than ±0.05 Hz for microwave signals from 7 to 16 GHz.To improve the measurement sensitivity,another microwave DFS measurement scheme based on dual polarization binary phase shift keying modulator and optical single sideband mixing is further proposed.Due to the parallel optical mixing,the system can measure weak echo signals with power as low as -40 dBm.