Research On Modulation Method And Three--dimentional Receiving Technology Of Super-low Frequency Mechanical Antenna

The propagation attenuation of super-low frequency(SLF,30-300Hz)signals in seawater,rock formations,special buildings an d other media is far less than that of high frequency signals,so it owns the significant applicational value in submarine communication,mine rescue and military affairs.However,the common SLF electric antennas are of high size huge,power consumption and with troubles of high construction and using costs.It brings limitation of mobility and portability of SLF wireless communication systems.In this paper,a kind of mechanical antenn a and its signal m odulation method based on magnetic dipole rotates to radiate SLF signal are designed,and they are verified by experiments.The main work is as follows:(1)The electromagnetic field generated by static,time-varying and rotating magnetic dipoles is derived.The near-field distribution of rotating permanent magnets is simulated,which verifies the feasibility of transmitting SLF signals by rotating permanent magnets.(2)A kind of polarization modulation method based on external modulator and the demodulation method based on three-dimensional vectors reception are proposed.The process that modulation,demodulation,reception an d transmittion of signal is analyzed by simulation,and the compensation method based on Euler angle rotation matrix is adopted to solve the problems that the data received at some special position s is un able to be demodulated.T he feasibility of the polarization modulation method is verified by building a complete mechanical antenna system for experimental test.(3)The amplitude modulation method based on "open-close" modulator is designed.Not only the signals received at any position in space and at an y attitude of the receiving end can be effectively demodulated,but also the demodulation process is simplified and the reliability of demodulation results are improved by using this modulation method.Finally,the superiority of the amplitude modulation method is verified by experiments.(4)The hardware of signal acquisition and digital processing is developed.The multi-channel inconsistency of acquisition module is corrected by module fractional-phase-delay,and the variational amplitude of received signal is automatically adjusted by module automatic-gain-control,which ensures the stability of demodulation process.