Research On The Generation Of Linearly Frequency Modulated Waveform Based On Microwave Frequency Multiplication

Linearly frequency modulated(LFM)waveform is a common signal in modern radar system.More and more researchers begin to search for the generation method of broadband LFM waveform.The traditional method of LFM waveform based on electronic technology has low frequency and low bandwidth due to the limited sampling rate.The LFM microwave signal generated by photonic technology can break through the above limitations and provide a new direction for solving the electronic bottleneck problem.Using microwave photon technology to generate LFM waveform has the advantages of wide band width,low phase noise,easy tuning and anti-electromagnetic interference.The research direction of this paper is to use microwave photon frequency doubling technology to generate LFM waveforms,and to use low carrier frequency and small bandwidth LFM waveform to produce high frequency signal with superior performance.The main research content is as follows:(1)This paper expounds the research significance and mathematical characteristics of LFM waveforms,introduces several methods of generating LFM waveforms and the research status of LFM waveform generation by research institutions at home and abroad.(2)This paper introduces the electro-optical modulator,one of the key components in the generation of microwave photonic LFM,especially the principle of modulation,the four commonly used modulators dual-driver Mach-Zehnder modulator(DDMZM),intensity modulator(IM),dual-parallel Mach-Zehnder modulator(DPMZM),dual-polarization binary phase-shift keying(DP-BPSK)modulator are theoretically deduced and analyzed,and the principle of photodetector and frequency doubling performance index are introduced.At present,four research schemes for generating octave microwave signals are briefly described.(3)Based on DP-BPSK modulator,this paper proposes a DP-BPSK based quad-octave and octave research scheme,both of which do not use electrical or optical filters and phase shifters.Through the simulation analysis,with a good radio spurious suppression ratio,the central frequency of 18 GHz,bandwidth of 4GHz and the central frequency of 36 GHz,bandwidth of 8GHz linearly frequency modulated waveform is generated.The results show that tuning performance of the proposed scheme is preferable.(4)Based on DPMZM,and puts forward two kinds of frequency doubling research plan,respectively is produced based on DPMZM fourfold frequency and microwave signal based on cascade DPMZM produce eight times frequency microwave signals,two research methods the same configuration,all is child modulator working point in minimum transmission,the main modulator working point in orthogonal bias,the tie-in way currently available commercial offset points controller,simple operation,high stability.The simulation results show that the LFM waveforms with center frequency 18 GHz,bandwidth 4GHz,center frequency 36 GHz and bandwidth 8GHz are generated,moreover,an experimental link was built to verify the feasibility of the quadrupling frequency scheme.The experimental results showed that after DPMZM was driven by 3GHz electrical signal,12 GHz electrical signal was output and quad-frequency was realized.