The Application Of The Electrically Small Antenna In Very Low Frequency Receiving System

The very low frequency signals throughout the world include artificial signals and natural signals.Artificial signals are mainly generated by ground-based low-frequency transmitting stations for communication and navigation;Natural signals are mainly produced by natural physical processes such as lightning,which can be used to monitor natural phenomena.The equipment used in VLF signal observation is called VLF receiving system,which is composed of receiver and antenna system,and it has the characteristics of low noise and high sensitivity.The traditional ground-based antenna system is large and bulky,which can't keep up with the times in many applications.There are higher requirements for antenna miniaturization and ease-erection when the system is used on aircraft and satellite.In this paper,we have done the miniaturization research on low-frequency wave antenna.There are three kinds of electrically small antenna:the small loop antenna,the magnet antenna and the electric field antenna.we analyzed their theory characteristics,and present the corresponding matching methods.Based on the analysis of measured data,we compared the advantages and characteristics of different types of electrically small antennas.First,we adopted the HZ-10 antenna produced by Rohde&Schwarz,and discussed the analog front-end design from both sensitivity and frequency response.The bandwidth is set to 5-50khz.Through theoretical analysis and verification,the transformer matching is coupled with the post-stage differential amplification.Then,the magnet antenna was studied,and the composition of the magnet antenna was introduced.We have compared the characteristics of nickel zinc iron oxide,manganese zinc iron oxide and permalloy,and permalloy was used as the magnetic core.Based on the empirical formula,the influence of the length-diameter ratio of the magnetic core was analyzed,and the influence of the size parameters on the induced voltage and SNR has been obtained by exploring the SNR theory of the hollow coil.We analyzed the resonant frequency based on the equivalent circuit model of the magnet antenna,and the solution of the frequency-response flattening was given.The process of manual winding of magnet antenna is improved by combining with the practice.Finally we studied the electric field antenna,and introduced the characteristics of the whip antenna,which is a kind of vertical polarization antenna.We identified the "antenna gain",which was the decision of electric field antenna performance parameters,by analyzing its equivalent circuit model when the amplifier was applied.Through the design of passive filter and amplifier module,the front-end matching design was completed and its noise characteristics have been analyzed.The amplitude information of VLF wave was extracted based on the VLF signal data which was observed by different types of antenna,and the performance of the antenna was investigated.The results show that the small loop antenna,as the reduced version of the AWESOME system antenn,has the lowest sensitivity in the three kinds of antenna.The magnet antenna is introduced on the basis of the small loop antenna,which has higher sensitivity in VLF frequency band.The electric field antenna has the best reception effect on the station signals,but the anti-jitter interference ability is weak.As a small portable device,the electric field antenna should be chosen.And if we want an airborne detector,it is best to choose the magnet antenna.