Microwave Listener-based Signal Processing Research

This thesis is based on the project of implementing a microwave interception system, with the purpose of taking research on the anti-noise performance. Though the former microwave interception system can accomplish the undamped high sensitivity telemetry to medium vibration caused by acoustic excitation, and implement the reduction of speech signal, it doesn't have the capability of anti-disturbance and can't be utilized in actual combat.An improved scheme of microwave interception system is presented in this thesis. On the basis of the mathematical proof that the echo signal can be demodulated, both the original signal and the echo signal are kept in synchronization in frequency domain by means of controlling a servo system, and I/Q orthogonal signals are acquired. Then the cancellation signal is generated by modulating the attenuated original signal, and the scheme of carrier wave cancellation is transferred from single frequency to frequency modulation. Additionally, the relationship between the frequency difference and the range is taken into account, and the problem of anti-disturbance in one dimensional range is solved. A number of simulative experiments, with HFSS to different parameters of matching Magic-T, are carried out in this thesis, and the optimum size of the single-arm dimension of carrier wave canceller is obtained, which is 80x40x40mm. The size of the inner set metal coupon is 20x20x2mm, and that of the inner set metal bar isφ= 0.5 mm and h = 55 mm, additionally all the material is ideal conductor. The cancellation degree of this new carrier wave canceller is -14～-48 dB. In addition, the technique of noise suppression is proposed based on the analysis to noise source, and in particular the wavelet threshold de-noising method is elected. Based on the results of some simulative experiments, which are carried out with different threshold rules to the same speech signal, the wavelet base of "db5" and the threshold rule of penalty are adopted in this system. A series of threshold de-noising experiments aimed at the actual signals of the microwave interception system are carried out and the results prove to be effective.