Research On Multi-format Chirp Signal Generation Technology Based On Microwave Photonics

With its excellent all-day,all-weather,long-range detection and sensing capabilities,radar is widely used in the military,national economy and social development.In order to adapt to the increasingly complex electromagnetic environment and diverse working scenarios,modern radar systems are developing towards having large bandwidth,high carrier frequency,multi-function,multi-band and can be integrated.The frequency,time width,bandwidth and waveform of radar signal have a direct impact on the performance of radar system.Chirp waveform is widely studied and used as a large time bandwidth product(TB WP)radar waveform with large time width and bandwidth,which can effectively improve radar detection performance.However,traditional electronic radar systems are limited by the operating frequency and operating bandwidth of electronic components,which cannot meet the development needs of modern radar systems.Microwave photonics technology,as an emerging crossover technology integrating microwave technology and photonics technology,makes full use of the inherent advantages of photonics technology such as ultrawideband,low transmission loss,small phase noise and antielectromagnetic interference to realize the generation,processing,transmission and application of microwave millimeter wave signals,thus providing new ideas for the development of future radar technology.Signal source is one of the core components of radar system,and with the help of photonic technology can overcome the rate bottleneck of electronic devices to generate high-frequency and broadband chirp signals to further enhance the performance of radar system.In this paper,the key technology of chirp signal generation in microwave photonic radar is investigated for the future development of high carrier frequency,multi-band,multi-functional and miniaturized radar systems,and three chirp signal photonic generation schemes are proposed and the feasibility of the proposed schemes is verified by simulation system.The research work completed for the paper is as follows:1.A dual chirp signal generation scheme with flexible and adjustable multiplication factor is proposed,and the pulse compression capability and target detection capability of the generated signal are evaluated.The scheme utilizes the cascaded structure configuration of dual parallel MachZendel modulator(DPMZM)and polarization modulator(PoIM)to generate ±4th,±5th,and ±6th order optical sidebands with adjustable multiplication factors(8 times,10 times,and 12 times)by reasonably setting the amplitude and phase difference of the radio frequency(RF)drive signal and the DC bias point of the DPMZM,without using optical filters.The high frequency dual chirp signal with adjustable multiplication factors(8 times,10 times,12 times)is generated by balanced detection.The simulation generates dual chirp signals with center frequencies of 80 GHz,100 GHz and 120 GHz,and the bandwidth of each dual chirp signal is 22 GHz,which is four times the bandwidth of the baseband parabolic drive signal.The simulation results show that the generated dual-chirped waveforms not only have high pulse compression ratio(PCR),but also have "pinned" fuzzy functions,demonstrating the good pulse compression ability and distance-Doppler resolution of the generated signals.2.A complementary linearly chirped signal generation scheme with different TBWP dual-band is proposed.The scheme recombines a 5-tooth flat optical frequency comb(OFC)generated by a Mach-Zendel modulator(MZM)with a phase-chirped optical wave with different characteristics generated by a phase modulator(PM)driven by a baseband parabolic signal or a single chirp signal,which is subsequently recombined by a 2×2 optical coupler(OC)and injects it into a balance detector(BPD)for optical conversion,finally generating two different TBWP dual band complementary linearly chirped signals with two different TBWPs.In the case of parabolic-driven PM,the center frequency-bandwidth of the simulated generated signals are 20 GHz-7.6 GHz and 40 GHz-7.6 GHz,respectively,with a TBWP of 1556;when PM is driven by a single chirp signal,the generated signal has a bandwidth of 4 GHz and the same center frequency as that of parabolic-driven PM;the complementary linearly chirped signal generated by parabolic-driven PM has an autocorrelation of The self-correlation of the complementary linear chirp signal generated by the parabolic-driven PM has a larger PCR;and the signal generated by the baseband single-chirp driven PM shows a higher peak-to-partials ratio(PSR).3.The RF signal drives one arm of the DDMZMl and one arm of the DDMZM2 with a phase difference of 90°,while the other two arms of the DDMZM are driven by a baseband single chirp signal with an adjustable phase shift 6.The resulting modulated lightwave is photoelectrically converted to generate a multi-band,multi-format switchable chirp signal.The generated modulated lightwave is photoelectrically converted to generate a multiband switchable chirp signal in multiple formats.The chirp format and the number of frequency bands can be switched flexibly by configuring the phase difference θ for dual-band dual chirp signals and two tri-band chirp signals only.The simulation results show that the center frequencies of the generated dual-band dual-chirp signals are 10 GHz and 30 GHz,and the bandwidth of each band is 3.2 GHz;the center frequencybandwidth of both tri-band chirp signals are 10 GHz-1.6 GHz,20 GHz-6.4 GHz,and 30 GHz-1.6 GHz;compared with the bandwidth of the baseband single-chirp drive signal,the center frequency at compared with the bandwidth of the baseband single-chirp drives signal,a double-chirp signal with four times the bandwidth is generated at the center frequency of 20 GHz;the autocorrelation function shows that the generated waveforms all have good pulse compression capability.