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Study On Key Technologies Of Microwave Photonic Signal Generation And Receiving For Wideband Radars

Posted on:2018-05-31Degree:DoctorType:Dissertation
Country:ChinaCandidate:Y X XuFull Text:PDF
GTID:1318330518971011Subject:Physical Electronics
Abstract/Summary:PDF Full Text Request
In modern pulse compression radar system,it's required to generate and process wideband signals with large time-bandwidth product,in order to achieve high detection resolution.But the performance of traditional radar systems is limited by the bandwidth of electronic devices,which is the so-called "electronic bottleneck".In this context,it's an attractive idea to use the photonic technology in the generation and receiving of radar signals due to the advantages of low loss,large bandwidth and immunity to electromagnetic interference offered by photonics.In this dissertation,several key technologies of wideband signal generation and receiving in the RF front end of the photonic radar are studied.For photonic radar signal generation,we investigate the generation of linearly chirped,phase-coded and dual-chirp signals.The system condition in linearly chirped signal generation system based on frequency-to-time mapping are discussed,and several schemes for the generation of wideband signals are proposed.For radar signal receiving,we propose and discuss the undesired frequency chirping effect in the photonic time-stretch ADCs for the first time.The time-frequency uncertainty effect in the photonic ADCs based on spectral encoding is also put forward and discussed,for the first time to our knowledge.The major innovations and contributions of this dissertation are as follows.(1)The photonic linearly chirped signal generation system based on frequency-to-time mapping is investigated.A new condition which is much relaxed than the "far-field condition" is proposed and is verified by simulations and experiments.According to the analysis,the limitation of signal's time-bandwidth product is significantly increased under the new condition,which can help improve the range resolution of radar system.Thus,the proposed new condition is believed to be helpful in the design of the photonic generation system for linearly chirped signal.(2)To eliminate the range measurement ambiguity induced by the range-Doppler coupling effect,we propose a novel scheme for the photonic generation of wideband dual-chirp signals.The system design is verified by simulations and experiments.The proposed scheme is based on the structure of cascaded modulators.With this scheme,the dual-chirp signal with quadruple time-bandwidth product can be generated with the input of a linearly chirped signal.Thus,the range resolution of the radar systems can be improved and the range-Doppler coupling effect is cancelled out.(3)Regarding the photonic time stretch systems,the undesired frequency chirping in the output signal is presented for the first time to our knowledge,and is then verified by simulations.The exact expression of the frequency chirping is obtained based on a precise derivation of the ADC's analytical model.Finally,a method to eliminate the undesired frequency chirping is proposed.(4)The photonic analog-to-digital conversion system based on fiber nonlinearity and spectral encoding is investigated.A system condition for achieving acceptable performance is proposed according to the time-frequency uncertainty principle.The theoretical results are verified by numerical simulations and a proof-of-concept experiment.It's the first time that the influence of time-frequency uncertainty in this system is discussed.The criterion to achieve acceptable performance is obtained based on the analysis of ADC's effective number of bits.We believe that the presented result is important to the design of spectral-encoding based photonic ADCsIn conclusion,photonic wideband signal generation and analog-to-digital conversion techinques for wideband radars are studied in this dissertation.Owing to the advantages of large bandwidth and immunity to electromagnetic interference offered by photonics,the presented results are believed to be valuable in the research of the photonic radar technique and the performance improvement of wideband radars.
Keywords/Search Tags:Microwave photonics, microwave signal generation, radar signal processing, photonic analog to digital conversion
PDF Full Text Request
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