Generation Of High Speed Chirp Signal And Its Linearity Deviation Test And Evaluation

As one of the most commonly used non-stationary signals in the radar field,the linear frequency modulation signal has the advantages of large detection range,high measurement resolution,and insensitivity to Doppler shift when realizing pulse compression.In recent years,with the complexity of radar detection target characteristics and detection environment,higher requirements have been put forward for the working frequency band,working bandwidth and other indicators of radar signals.How to generate linear frequency modulation signal with large time bandwidth product,high frequency band and low linear deviation has become a research hotspot in the field of broadband RF signal generation.This paper focuses on the generation of linear frequency modulation signal and its linear deviation test and evaluation,reviews its research background and research status,and summarizes the advantages and disadvantages of various schemes.On this basis,this paper summarizes the mathematical models and evaluation indicators of linear frequency modulation signal.It introduces two linear frequency modulation signal generation systems based on radio frequency technology and microwave photonic technology,analyzes their structures and principles,and conducts experimental verification.Finally,A linear deviation testing scheme for linear frequency modulation signal based on optical domain mixing and phase discrimination is designed to achieve accurate real-time linear deviation testing,and theoretical analysis and experimental verification are conducted.The main work of this paper is summarized as follows:(1)This paper studies a linear frequency modulation signal generation scheme based on voltage controlled oscillator and phase-locked loop,which controls the phase-locked loop to output the local frequency signal,mixes with the output signal of voltage controlled oscillator to generate the linear frequency modulation signal,and cooperates with the front stage numerical control circuit to achieve a wide range of tunable bandwidth,center frequency and frequency modulation period;A signal generation system is set up in the experiment,and the phase noise of the output single frequency signal is-98 dBc/Hz@100 kHz.When sweeping,it can generate a linear frequency modulation signal with a center frequency of 2.5 GHz,a sweep bandwidth of 3 GHz,a frequency modulation period of 50 kHz,and a power flatness of less than 4dB within the output frequency band.The corresponding time bandwidth product is up to 60000 and the pulse compression performance is excellent.With the addition of the Hann window,the pulse stamping reduction ratio is 31250 and the first side lobe suppression ratio is 31.5 dB.After static open-loop correction,the linearity reaches 0.16%;The influence of nonlinearity of linear frequency modulation signal on pulse compression performance is analyzed.Simulation shows that the bigger the signal linear deviation is,the worse the pulse compression performance is.(2)This paper also studies the linear frequency modulation signal generation technology based on the fourier domain mode locking optoelectronic oscillator.The linear frequency modulation signal is generated based on the optoelectronic oscillator,the fourier domain mode locking technology,and the fast frequency modulation microwave photonic filter;A linear frequency modulation signal generation system is built in the experiment,and the phase noise of the output single frequency signal is-125 dBc/Hz@10 kHz.When sweeping,it can generate a linear frequency modulation signal with a center frequency of 4.6 GHz,a sweep bandwidth of 2.8 GHz,a frequency modulation period of 63.33 kHz,and a linearity of 0.86%.The corresponding time bandwidth product is up to 44212.After adding the Hann window,it can achieve a pulse compression ratio of 19253 and a first side lobe suppression ratio of 25.0 dB.(3)At last,this paper proposes a linear deviation test scheme of linear frequency modulation signal based on mixing frequency and phase detection method,establishes the test model,derives its test principle in the optical domain,analyzes the influence of differential delay,delay error and signal noise on the test method,and compares it with the instantaneous frequency measurement method,proving the necessity of accurate delay difference control in the optical domain;A test system is built to test the linear frequency modulation signals generated by the above two schemes,and the results are compared with those of static method and instantaneous frequency measurement method.The linearity deviation is less than 0.03%;The linear frequency modulation signals with different bandwidths generated by arbitrary waveform generator are tested and the consistency of the results is discussed,which proves the effectiveness of the test scheme.