Research On Photonic Microwave Spectral Analysis

As an important and enabling technology in microwave photonics, photonic technique for microwave spectral analysis has been widely used in national defense systems and attracted more and more interest in the past few years owing to the advantages of low weight, wide bandwidth, low loss and immunity to electromagnetic interference. In this thesis, according to the practical demand and development tendency, we propose two novel approaches to implement photonic microwave spectrum analysis based on the basic link.A photonic approach for instantaneous spectrum analysis of microwave signal based on phase modulation to intensity modulation is demonstrated, in which the phase-modulated optical signal is converted to intensity-modulated signals in two independent paths by using a dispersive medium and a frequency discriminator, respectively. Then the ratio of microwave power detected by photodiodes can be utilized to determine the microwave frequency. The stability of the system is improved due to the use of only one laser source and the bias-free phase modulator. Simulations and experiments are performed to verify the effectiveness and feasibility of the system. The error and the dynamic range of the scheme are also analyzed in terms of theory and numerical simulations.A photonic system for microwave spectral analysis based on Fourier cosine transform is presented. The spectral information is obtained by processing a microwave power versus second-order dispersion function with the mathematical treatments of Fourier cosine transform and variable replacement. The function is the product of the power spectrum of the signal with its spectrum to be analyzed and the power transfer function of the phase-modulated radio over dispersive link system. The capability to analyze microwave signals with multiple frequency components is the key feature of the proposed system. Computer simulations are implemented to prove the correctness and feasibility of the system. The sensitivity, the spectral resolution and the effective measurement bandwidth of the scheme are also quantitatively discussed.