Design Of Small Loop Antenna And High-sensitivity Receiver

With the continuous development of information technology,the impact of the ionosphere on human life is becoming more and more significant,and the research on the ionosphere is becoming more and more refined,which also puts more new demands on ionospheric observation equipment.Aiming at the problems of the large size of the antenna and receiver sensitivity that need to be further improved in current digital ionosonde,this paper designs and implements a small loop antenna that can be used to receive ionosphericecho signals,and proposes a corresponding high-sensitivity receiver modular design scheme.The feature and generation mechanism of the F3 layer in low-latitude regions were analyzed and studied by using the observation data of ionosonde.First,this paper briefly introduces the basic composition of digital ionosonde and the need to improve the design.It focuses on the theoret ical analysis of the feasibility and scheme selection of small loop antenna and high-sensitivity receiver design.A small orthogonal active loop antenna for 1MHz~30MHz ionospheric echodetection is designed and implemented.It is mainly composed of four parts: a loop antenna and a preamplifier located outdoors,and a RF/DC separation module and a power supply module located indoors.The receiver performance test was performed using it and a ionosonde in Wuhan.The results show that compared with the traditional orthogonal folded dipo le antenna,the orthogonal active loop antenna has the same ability to receive the echo and multiple echoes of ionosphere,and can distinguish the O wave and X wave.It also has the advantages of high cost performance and simple erection.It provides a new solution for the flexible deployment of ionosonde.Then,the down-conversion module and RF pulse generation module of the receiver were improved,and the design of the high-sensitivity receiver was completed.In the down-conversion module,the design scheme of "high Q-value crystal filter+high intermediate frequency" is adopted to suppress the mirror interference and simplify the design of the filter circuit.In the RF pulse generation module,the design scheme of "FPGA + STM32 + DDS" is adopted to achieve precise timing control of the four signals and ensure the quality of the output high-frequency signals.The test results show that the newly developed receiver has achieved good results in mirror interference suppression,and the overall sensitivity of the receiver can reach-120 d Bm.Compared with the original receiver,the echotraces received are optimized in terms of cont inuity and tail height.Finally,this paper uses the observation data of the ionosonde to analyze the changing feature and generation mechanism of the F3 layer in low latitudes.The SAO so ftware was used to calibrate the 105120 ionograms to obtain important parameters such as fo F3,fo F2,h'F3,and h'F2.The statistical data were analyzed by Matlab to study the general feature,seasonal variation feature,daily variation feature,longitude and latitude dependence of the F3 layer under different so lar activity levels.It provides new data samples and perspectives for the research of the F3 layer in global low-latitude area.In summary,a small orthogonal active loop antenna is designed and implemented in this paper,and a modular design scheme of a high-sensitivity receiver is proposed.The feature of the F3 layer in low-lat itude region is analyzed and researched using the observation data of the ionosonde.The results show that the newly developed small orthogonal active loop antenna has the advantages of small size and good signal reception performance;the high-sensitivity receiver achieves the design goal of suppressing mirror interference and improving ionosonde's sensitivity;the study result of F3 layer are also representative and accurate.The work in this paper not only provides a solution for the flexible deployment of ionosonde,but also has important significance for the research of low-latitude ionosphere.