Research On Microwave Photonic Technology Based Broadband RF Channelization

With the dramatic increase of information and the growing bandwidth requirements of detection and alertness in military and civilian communications,the real-time capture of broadband signals has become a core enabling technology for many applications.The receiver requires high resolution,wide bandwidth,large dynamic range to deal with the high-density and complex signal environments.Combining the advantages of low-loss broadband photonics and microwave with fine narrowband control,the microwave photonics overcomes the electronic bottleneck of ultra-wideband analog processing and opens up a whole new solution for microwave signal generation,transmission and processing.Radio frequency photonic channelization is an effective way to realize accurate sensing and receiving of large instantaneous bandwidth signals.However,channelized technologies currently faces many technical challenges.Firstly,a narrowband optical filter with an ideal rectangular window function is needed to achieve channel division.Secondly,it is difficult to achieve high frequency resolution by spectral separation using dispersive devices.Thirdly,existing solutions are costly and complicated to operate.In view of the above technical challenges,this paper has carried out innovative research as below:1.Aiming at challenges such as the difficulty of simultaneous acquisition of fine optical spectrum control,high perceiving precision,and real-time detection,a RF channelization based on dual coherent optical frequency combs(OFC)is proposed.The mixing of two combs can achieve down-conversion of RF signals and the parallel channelization can be realized by a commercial wavelength de-multiplexer.This process not only avoids the participation of fine optical filtering,but also eliminates the need for fine alignment between the light source and the filter.In the experiment,a channelized receiver prototype with 20 GHz instantaneous receiving range is built with1 GHz channel bandwidth.The frequency response is an ideal rectangular window shape.For the nonlinear distortion of the modulator,a suppression algorithm based on post-digital compensation is proposed.The third-order intermodulation distortion(IMD3)is greatly suppressed and the dynamic range is increased by 20 dB.The ability to handle strong and weak signals of the system is greatly enhanced.2.Aiming at the disadvantages of the existing technologies such as complicated operation and high cost,a channelized receiver based on chirped pulse and inphase/quadrature(I/Q)demodulation is proposed.The mixing of the chirped pulse and its own delay produces an adjustable RF local oscillator(LO).By increasing the number of delayed chirped pulses,the coexistence of multiple LOs can be realized,which can be used for down-conversion in RF channelized reception.This paper proposes two kinds of channelization schemes.One is based on a mode-locked laser and a dispersive fiber,which achieves a channel bandwidth of 100 MHz and covers spectral range from DC to 20 GHz.The other is based on Talbot effect,using frequency-shifted feedback lasers to generate discrete chirped pulses.This scheme realizes 5 channels division within 500MHz receiving bandwidth,each channel has good receiving performance.These schemes can realize channel division just through optical couplers,providing a simple and efficient reception method for broadband RF signals.3.Aiming at the low frequency resolution of some schemes using dispersion devices for spectrum separation,a spectrum real-time detection mechanism based on optical Fourier transform and I/Q under-sampling is proposed.By time stretching,modulating,and time compressing the pulse,the frequency information of the modulated signal is mapped onto the time domain of the output signal.By subjecting I/Q under-sampling to the Fourier transform pulse,the wideband radio frequency signal is down-converted into the first Nyquist bandwidth.Meanwhile,this technology also has a filtering function,which greatly reduces the noise superposition caused by spectrum shifting in the sampling process and avoids the use of additional band-pass filters.In the experiment,accurate detection of spectrum in the range of 3.8GHz-15.8GHz was achieved and the frequency resolution is in the range of 100KHz.A filtering function with 15dB bandwidth of 6GHz was realized.This technique provides a new idea for channelization and also has important significance for under-sampling.