| With its excellent perception capability,radar plays an important role in many fields,such as in the military field,tracking and monitoring military targets,and air defense early warning;in the civilian field,it is used for medical imaging and autonomous driving of unmanned vehicles.With the increasingly complicated electromagnetic environment,in order to meet the needs of higher precision detection,future radar systems need to use multi-band,large-bandwidth radar waveforms.However,traditional electronic technology has its inherent bottleneck,which is restricted by factors such as electronic device operating bandwidth,operating frequency range,and system complexity.Technology of microwave photonics has the merits of high frequency band,large bandwidth,low loss,small volume,anti-electromagnetic interference and so on.It can effectively overcome the bottleneck of electronics,improve the working performance of radar system,and lay a solid foundation for promoting the development of radar technology in the future.In order to solve the limitations of traditional electrical and existing photonics technologies,two novel microwave photonic radar signal generation schemes are proposed in this paper: a photonic dual-band switchable dual-chirp signal generation scheme and a dual-chirp signal generation scheme based on pulse dispersion processing.Through the theoretical analysis of the above two schemes,as well as relevant simulation verification,combined with relevant experiments,the effectiveness of the two schemes is proved.The main contributions and innovations of this paper are as follows:1.Aiming at the demand of radar signal for multi-function radar and other systems,a scheme of photonic dual band switchable dual chirp signal generation based on dual drive dual parallel Mach Zehnder Modulator is proposed.It can not only generate dual band dual chirped signals at the same time,but also switch between single band dual chirped signals and dual band dual chirped signals.In this scheme,dual band dual chirp signal is successfully generated.The center frequency is 3 GHz and 5 GHz,and bandwidth is 1 GHz,it is easy to switch between two single frequency double chirped signals and one dual frequency double chirped signal by simply adjusting the bias voltage on the modulator.Through experimental demonstration,the integrated external modulator makes the whole system simple and stable in structure and easy to tune.2.Aiming at the demand of pulse compression radar for large-bandwidth radar waveform,a dual-chirped signal generation scheme based on pulse dispersion processing is proposed.By designing the frequency response of optical spectrum shaper,large-bandwidth dual-chirped microwave signal generation can be realized,with simple structure and strong tunability.In this scheme,the optical pulse is first shaped by a optical spectrum shaper,and the shaped optical pulse passes through a section of dispersion fiber.After frequency-to-time mapping,the pulse spectrum is mapped to the time-domain,and the double-chirp signal is obtained through the photodetector.In the experiment,dual chirp signals with duration of 10 ns and center frequency-bandwidth of 4.75GHz-2.3 GHz,3.8 GHz-3.4 GHz,7.6 GHz-4.5 GHz are generated.The feasibility of the scheme is proved by theoretical derivation,numerical simulation and relevant experimental results. |
