Research On Generation Technology Of Chirp Signal With Large TBWP Based On Microwave Photonics

With the complexity and diversification of radar system operating environment and the gradual requirements for battlefield perception,people have put forward higher requirements for radar resolution.Because the traditional single-carrier rectangular pulse signal cannot provide a wide temporal duration and a large bandwidth at the same time,the linear frequency-modulated signal with pulse compression performance is widely used in modern radar systems.Therefore,microwave photonics technology has gradually become the research hotspot of modem radar systems.In the meanwhile,the millimeter wave signal generated by microwave photonics technology has overcome the disadvantages which made by traditional electrical methods.This paper focuses on the research of LFM signal generation based on microwave photonics technology and proposes two methods of LFM signal generation with large time-bandwidth product.The main researching work and innovations completed are as follows:1.Aiming at the demand of modern radar systems for large time-bandwidth product LFM signal,a photonic generation method based on cascaded DPMZM and PolM is proposed.In order to enlarge the TBWP,parabolic waveform is split in time domain and phase-encoded with binary sequence to increase the bandwidth and temporal duration of the generated signal simultaneously.A simulation based on Optisystem and Matlab is built and simulation results show that LFM microwave waveform with caiTier frequency of 40 GHz,bandwidth of 12.5 GHz,time duration of 819.2 ns and TBWP of 10,240 is generated,which verifies the feasibility of the proposed method.Compared with the existing methods,the proposed method features independent tunability of temporal duration and bandwidth.2.Aiming at the demand of modern radar systems for ultra-wideband LFM signal.A photonic generation method based on a frequency-sweeping laser combining a PolM and PolDM is proposed.A simulation based on Optisystem and Matlab is built and simulation results show that an ultra-wideband LFM signal with center frequency of 77 GHz,bandwidth of 5 GHz and TBWP of 2500 is generated,at same time,an ultra-wideband LFM pulse with center frequency of 77 GHz,bandwidth of 5 GHz and TBWP of 1250 is generated,which verifies the feasibility of the proposed method.Compared with the existing methods,the Sagnac loop is replaced by a PolDM for time delay in proposed method,making the structure easier to control.By changing the code of the optical switch,the proposed method can not only generate ultra-wideband LFM signal but also ultra-wideband LFM pulse with up chirp or down chirp,which has good reconfigurability.