Research On Photonics-based Genration And Receiving Processing Of Radar Signals Based On Phase-locked Dual Optical Frequency Combs

Information superiority is the winning key in the information war.Electronic warfare(EW)is the main form and means of obtaining the information superiority.Due to the widespread applications and significant effects of radars in the modern military operations,the electronic countermeasures for the radars have become an important part of modern electronic warfare.The electronic countermeasures for the radars consists of two aspects.On the one hand,it is necessary to improve the anti-interference and low interception capability of the radar,that is,the radars are required to prevent enemy interception and carry out the effective and fast detection in the case of complex electromagnetic environment and enemy interference.On the other hand,it is necessary to enhance the ability to detect and intercept enemy radar signals,that is,the self-reconnaissance equipments are required to have broadband,highly sensitive receiving and processing capabilities,which are capable of intercepting enemy radar signals in complex environments with high power noise interference and multiple electromagnetic signals.Radar waveform design is the main means to improve the radar anti-interception and antiinterference ability.By increasing the radar signal bandwidth,reducing the signal peak power,processing the parameter agility and power management,using the complex modulation format,ultra-low sidelobe and other measures,the probability of interception and interference of the radars is greatly reduced,which can improve the detection efficiency in the working distance.Thus the goal is achieved,which is the radar can detect the enemy while the enemy cannot.In many electronic signal receiving technologies,such as superheterodyne receivers,channelized receivers,crystal video receivers,and instantaneous frequency measurement receivers,the channelized receiving technology is the current comprehensive performance of the best electronic reconnaissance receiving technology.Due to adopt a parallel receiving processing method by the frequency domain channel division,the channelized receiving technology not only has ultra-high intercept probability and the ability to simultaneously receive signals in the time domain,but also has relative superiority in receiving bandwidth and sensitivity.However,the traditional microwave technologies have restricted the high frequency broadband development of the radars in terms of frequency,bandwidth and noise.New technical methods are necessary to support the generation and reception of high frequency and wideband radar signals to meet the development needs of radar countermeasures.The signal generation methods based on microwave photonics have the capability of higher frequency and wider bandwidth and flexible tuning capability,which can effectively solve the technical problems in high frequency and wideband radar signal generation and reception processing.The applications of microwave photonics technology in radar have become the focus of related fields.However,the existing techniques of the microwave photonic radar signal generation and reception processing still have many basic problems to be solved,such as signal linearity,coherence,reconfigurability and noise performance.Based on the basic theory of radar and the future development needs of radar,this paper focuses on the basic theories and key technologies of high-frequency and wide-band radar signal generation and reception processing based on microwave photonics.The linearity,coherence and reconfigurability of the photonics-based radar signal generation are effectively resolved,and the problem of optical channelization receiving processing based on microwave photonic technology is alse solved,which promote the applications of microwave photonics in radar countermeasures.The main contents and innovations of the thesis are incarnated in the following aspects:1.Generation of cascaded optical modulation optical frequency comb with the photoelectric delay matching and its phase locking methodThe techolongy by beating with the dual optical frequency combs(OFCs)can realize the functions of frequency multiplication,frequency conversion and parameter reconstruction of microwave signals,which has wide applications in photonics-based signal generation and reception processing.The key of the techolongy is to generate the phase locked dual OFCs with flexible comb-tooth spacing.The traditional OFC generation method based on the laser mode locking faces the problems of weak comb-tooth spacing tuning ability,complicated structure and difficulty in interlocking each other.In this paper,the OFC generation based on the cascaded optical modulators and phase locking method with photoelectric delay matching are proposed.The optical frequency delay matching method is used to solve the problem of optical frequency comb stability under wide tuning range.Two phase-locked loops(PLLs)are adopted to lock the center frequency and the repetition frequency of the two OFCs,respectively,which suppresses the damage problem of coherence between the combs after passing through different fiber links,and ensures the dual OFCs coherence.It lays the foundation for the subsequent microwave photonics technology based on beating phase-locked dual OFCs.2.The photonics-based frequency modulated continuous wave(FMCW)radar signal generation method based on phase-locked dual OFCsThe FMCW radars have a wide range of applications in target ranging and speed measurement.It is necessary to develop the FMCW radar signals with high carrier frequency,ultra-wide sweeping range,high linearity and low phase noise,which can improve the resolution of the radar and other performances.Because of the frequency and bandwidth limitations of electronic devices,traditional microwave technologies are difficult to meet the needs of modern radars.In this paper,a photonics-based parameter-reconfigurable FMCW radar signal generation method based on phase-locked dual OFCs is proposed,which realizes the generation of FMCW radar signals with the bandwidth of 10 GHz,the sweep time of 30 ms,and the center frequencies of 10 GHz and 242 GHz,respectively.The chirped linearity of the generated FMCW radar signals are 116.117 kHz and 125.461 kHz,respectively.The generation makes a breakthrough in carrier frequency,bandwidth,time width,chirped linearity,phase noise and reconfigurability of FMCW radar signals,which can meet the development needs of continuous wave radar well.3.The photonics-based linear frequency modulation(LFM)pulse radar signal generation method based on phase-locked dual OFCsIn the coherent pulsed radar,it is necessary to ensure that each radar transmitting pulse has the same initial phase(ie,inter-pulse coherence).So the received signal-to-noise ratio can be improved with coherent accumulation of multiple echo signals.While the Doppler shift is extracted by the phase information of the target echo signal,and the speed of the target is obtained.Aiming at the shortcomings of current optical pulse radar method in modulation bandwidth,time bandwidth product,pulse width,pulse-to-pulse coherence and reconfigurability,this paper proposes a LFM pulse radar signal generation method based on phase-locked dual OFCs.Thanks to the phase synchronization characteristic between the phase-locked dual OFCs,the pulse radar signals with pulse-to-pulse coherence are generated by beating the different comb teeth from dual OFCs.The Ka-band LFM pulse signals with 6 GHz bandwidth are realized,and the coherent radar experimental test system is alsp established.The coherent accumulation,pulse compression and distance resolution test of the echo pulses are completed,and the availability of this method in high frequency broadband coherent radar is verified.4.The all-optical channelization receiving technology based on dual OFCsHigh-bandwidth,high-sensitivity,and large dynamic reception are the main development goals of radar signal reception and processing,and the channelized reception has the best overall performance.However,due to the limitations of analog-to-digital converter(ADC)technology,traditional channelized reception techniques face bandwidth bottlenecks.In this paper,an all-optical channelized receiving method based on phase-locked dual OFCs is proposed.Splitting of signal frequency bands is achieved by beating of phase-locked dual OFCs with different comb-tooth spacing.The parallel down-conversion and demodulation of the signals are performed by orthogonal photoelectric mixing,thereby realizing channelized reception processing with a bandwidth of 20 GHz and a channel width of 500 MHz.The proposed method can greatly improves the bandwidth of channelized reception and meet the development needs of modern electronic reconnaissance.