8 Mm Radar Scatterometer Developed And Measurement Experiments

Characteristics of radar terrain retain have great value for airborne radar design, microwave remote sensing and radar altimeter design. Scattering coefficient measurements are the primary means to study the characteristics of radar terrain retain. And the development of the equipment of scattering coefficient measurement, scatterometer, is one of the key techniques of the measurement.Used for measuring the scattering coefficient of bare farmland at near-virtical incidence, a 8mm wave radar scatterometer is designed. It is a Linear Frequency Modulated Continuous Wave (LFMCW) system with a single antenna.Transmit signals is produced by the VCO, which is drived by the linear sweep voltage.And the recericer uses the architecture of zero-IF. IF signal of radar return is sampled by an A/D card after amplified and filtered. Then digital signal is stored in computer. Using the power spectum of IF signal, radar parameter and geometic information, scattering coefficient of the target could be calculated.The range resolution of LFMCW system could be decreased by nonlinerity in frequency sweep. This thesis analyses theoretically the effects of frequency nonlinearity on the range resolution of LFMCW system, and measures the FM nonlinearity of the system with the IF signal phase information of a point target. Finally the FM nonlinearity of LFMCW scantterometer is corrected from 2.3% to 0.4%, using a open-loop pre-distortion correction method. After FM nonlinearity correction, the range resolution is increased.Calibration is the main difference between scattermeter and conventional radar. Two calibration method, internal calibration and external calibration, are discussed. Then a standard metal ball with known RCS is used to calibrate the LFMCW scatterometer, using external calibation method. Distance information shoould be known as measuring the scattering coefficient, so rang measurement of scatterometer is also calibrated for accurate Ranging.Finally, a land-based scattering coeficient measurement platform is built and a scattering coeficient field measurement method is designed. Average scattering coeficient of bare farland is measured at near-vertical (0°-10°) incidence at Ka band, and the scattering coeficient data are also analyzed briefly.This developed 8mm wave LFMCW radar scatterometer provides a hardware foundation for measuring a variety of terrain at near-vertical incidence later. The measured scattering coefficient data, which is measured on different surface and frequency, could provide a reference for modeling of characteristics of scattering. Furthermore, the scattering model of land at near-vertical incidence could provide a theoretical basis for the design of radar altimeter.