Research On Compact Ultra-long Wave Receiver Front End Technology

Ultra-long wave communication refers to long-distance communication using electromagnetic wave with wavelength of 10km～100km.Ultra-long wave has the advantages of small attenuation,outstanding anti-interference ability and long transmission distance.It is mainly used in military communication,navigation positioning,geologic examination and time service.Therefore,ultra-long wave communication is of great significance to national security and ocean development.The antenna is the core part of the ultra-long wave receiver.Because the size of the antenna is associated with the wavelength,the majority of the antennas of the ultra-long wave receiver are bulky,which is not conducive to production and installation.In addition,the ultra-long wave receiving antenna is generally narrow in band width,low in gain,and there are many interference signals in the ultra-long wave band,resulting in weak received signal strength and slow information receiving rate.This paper mainly focuses on the problems of large size and low gain of ultra-long wave receiving antenna.The main contents are as follows:1.The traditional ultra-long wave receiving antenna is large in size.To solve this problem,a miniaturized ultra-long wave receiving magnetic antenna is fabricated using a magnetic core with high permeability.The magnetic antenna has the preponderances of good sensitivity,simple-fabrication,little size and high bandwidth.Starting with the theory of magnetic antenna and combining with the characteristics of magnetic materials,this paper studies the theory of receiving signal of magnetic antenna,constructs the equivalent circuit model of magnetic antenna,gives the transmission function under the circuit model of magnetic antenna,and expounds the manufacturing method and process of magnetic antenna.By analyzing and evaluating the magnetic antenna parameters,the winding method of the magnetic antenna coil and the number of winding turns are determined.The designed magnetic antenna has a working frequency of 10 k Hz～40k Hz,the adopted magnetic core specification is 17mm×17mm×250mm cuboid,and the antenna skeleton specification is 50 mm diameter and 100 mm length cylinder.2.The gain of the ultra-long wave receiving antenna is low.To solve this problem,the subsequent signal conditioning circuit of the magnetic antenna is designed in this paper.This circuit is composed of amplifier and filter,taking into account high gain and low noise.First,a two-stage cascaded LNA is designed and fabricated,with a total gain of60 d B.This paper designs passive LC bandpass filter with better rectangular coefficient and smaller in-band ripple.A low-noise test environment in accordance with TB / T86 d national standard was built using alloy materials,and the background noise of the designed signal processing circuit was tested.The measured results show that the background noise of the designed signal processing circuit is about 4.07 nv / Hz^1/2.3.Process and tune the designed magnetic antenna.The framework of the magnetic antenna is made by using 3D printing technology,and the magnetic antenna is made by series-wound multilayer enameled wire.The performance of magnetic antenna with and without magnetic core is compared and analyzed.Combining the magnetic antenna and signal conditioning circuit,the magnetic antenna is tested in the near field,and compared with the magnetic antenna designed in other literatures.The results show that the magnetic antenna designed in this paper can reduce the size by half with the same reception performance.