The Design And Application Of Radar Systems Based On Antenna Array

The earth's space environment,including the neutral and ionized state of the earth's upper atmosphere,the earth's external magnetic field and the impact of their solar radiation,which is closely related to human survival and activities.The space environment of the earth is related to the physics of thin gas,the electrical conductivity of the gas,the photochemical of the atmosphere,the particles of various energy and their electromagnetic radiation,and the behavior of the magnetized plasma.The research and application about the earth's space environment is of great significance for the high-frequency radio communication,space weather science,and national defense construction.To acknowledge the needs of both basic science and useful space weather operations,a ground-based program to monitor China's geospace environment is currently under way.Called the Meridian Space Weather Monitoring Project(or Chinese Meridian Project).The Meridian Project consists of a chain of 15 ground-based observatories located roughly along 120° E longitude and 30° N latitude.Each observatory is equipped with multiple instruments to measure key parameters such as the baseline and time-varying geomagnetic field,as well as the middle and upper atmosphere and ionosphere from about 20 to 1000 km.With the support of the Meridian Meridian Project,the Wuhan MST radar and the Hainan coherent scatter phased array radar are introduced in this thesis.Wuhan University began to develop ground-based ionospheric sounding systems for ionospheric research and HF radio propagation in 2001.The prototype of WIOBSS(Wuhan Ionospheric Oblique Backscattering Sounding System)was developed successfully in 2003.The previous WIOBSS systems are single channel systems.Based on WIOBSS,the Wuhan Ionospheric Oblique Backscattering Sounding System with the addition of an antenna array(WIOBSS-AA)was developed,which is the newest member of the WIOBSS family.An ultra-wide ionospheric monitoring experiment was carried out in 2015.The main work of this thesis consists of three parts:1.Simulation of the antenna array of the three radar systems.Antenna system is the core and soul of a radar.The antenna arrays of the WIOBSS?AA,the Wuhan MST radar,and the HCOPAR were designed and validated by the Computer Simulation Technology MICROWAVE STUDIO(CST MWS).The antennas in the WIOBSS-AA,the Wuhan MST radar,and the HCOPAR are the linear polarized log-periodic dipole antenna,the linear polarized three-element Yagi and the linear polarized five-element Yagi.The characteristics of the radiation pattern of the antenna arrays are analysed in the thesis.The WIOBSS-AA is a multi-channel radio system using phased-array antenna technology.This radio system applies an array composed of five log-periodic antennas to form five beams(The five beams pointed to 285°,300°,315°,330°,and 345° in a clockwise manner)that span an area to the northwest of the radar site.The Wuhan MST radar is a monostatic radar with an active phased antenna array consisting of 576 Yagi antennas and operated at 53.8 MHz.The 3-element Yagi antennae are arranged in a square grid of 96m side length to form the aperture of 9216m2.This antenna array arrangement forms the five symmetric radar beams of vertex,east,west,south,and north.The beam width is 3.2°,the maximum directive gain is 34.8dB,and the total transmitting peak power is?172 kW.The zenith angle of the oblique beams is adjustable between 0-20° with 1° step.The average power aperture product of the radars is 3.2×108 Wm2.The HCOPAR is operated with a peak power of 54 kW and uses the Barker codes for good sensitivity.Its antenna array is composed of 18x4 five-element Yagi antennas and used for both transmitting and receiving.The Yagi antennas are arranged in a rectangular grid of 100m long and 20m wide,covering an area of 2000 m2.This antenna arrangement forms seven radar beams from-22.5° to 22.5° in azimuth with the angle step of 7.5°.2.The hardware design and implementation of the three radar systems.The WIOBSS-AA is a multi-channel radio system which consists of three parts:the transmitting part,the receiving part and the synchronization module.The system operates in the HF band.The system parameters can be configured through software flexibly.The operating frequency of Wuhan MST radar is 53.8 MHz.The hardware frame of the MST radar is composed mainly of T/R module,receiver,digital signal processing system and terminal unit.The HCOPAR also operates in VHF band.It is an active phased array system which consists of 72 digital transceiver units.The digital transceiver unit is composed mainly of T/R module and digital cell.The HCOPAR uses a central control computer for commanding and data processing,employs the Ethernet for data exchanges between the central processor and the transceivers.3.The applications of the three radar systems.The WIOBSS-AA applies the backscatter technology to monitor the northwest ionosphere.In the ultra-wide ionospheric monitoring experiment,WIOBSS-AA periodically transmitted the phase-coded pulse train waveform and received the echoes during the pulse interval.The antenna array main beam direction was steered to obtain the oblique backscatter swept-frequency ionogram.Applications of the inversion algorithms to the backscatter ionograms in different directions can extract the useful information regarding the ionospheric electron density distribution along the propagation paths.The electron density map over a fan-shaped region can be obtained by applying a two-dimensional interpolation algorithm.The Wuhan MST radar applies multiantenna beams to measure the line-of-sight Doppler velocities in five directions sequentially within 5 min.The wind velocity can be estimated by the measured radial velocity of the five beams through the DBS technique,which is based on the motion of the fluctuations with the background wind.There are two basic observation modes of the HCOPAR,one is the fix-beam mode and the other is the fan-beam mode.In the fix-beam mode,only one beam(usually Beam 4)is selected to observe the irregularities continuously,the data with high time resolution can be obtained.In the fan-beam mode,the seven beams sequentially detect the ionosphere to obtain the zonally drifting features of the irregularities.4.The upgrade program of HCOPAR is put forward with the Chung-Li VHF radar's experience.The Chung-Li VHF radar consists of three identical antenna,transmitter and receiver modules.There are three antenna subarrays with 32(4 X 8)Yagi antenna elements arranged in an isosceles triangle.The spatial structure of field-aligned irregularitie can be reconstructed with interferometry technique using this non-coaxial antenna array.The experience of the Chung-Li VHF radar is introduced in this thesis.The upgrade program of HCOPAR is also put forward in the end of this thesis.