| With the booming development of vital sign monitoring technology,the Radio-Frequency biological radar system has become a research hotspot in this field due to its wide range of working conditions,strong penetrability and good directionality.At present,the research of biological radar mainly focuses on improving the performance of dual-antenna system architecture for single-direction detection.In order to simplify the radar architecture and expand the detection range,the system architecture of traditional detection radar has been improved and some key circuit and antenna used in the system are emphatically designed in this thesis.The main researches are summarized as follow.The basic theory of bio-radar and the detection principle of vital sign signal are analyzed.On this basis,the traditional single-direction,dual-antenna detection radar architecture is improved,and a single-antenna bio-radar architecture with active scanning capability within a certain spatial range is proposed.Then,the principle of some key circuit and antenna used in the system are analyzed emphatically and the design methods are explored.The frequency-scanning antenna is specifically researched.The topological structure of the frequency-scanning antenna is analyzed,and influence of the slow wave line on the frequency-scanning antenna is discussed.Two frequency-scanning antennas based on the structures of SIW and microstrip are designed respectively.Based on the electromagnetic wave propagation characteristics of the slow wave transmission line and combined with the structure of the SIW with radiation slits on the surface,a frequency-scanning antenna with a scanning angle of-50~0?50~0 in the frequency band5.65GHz-6.05GHz is designed,which basically meeting the requirements of wide-range scanning and low-level sidelobe.Based on the microstrip structure,the patch unit is fed in series by the microstrip slow wave line,and a frequency scanning antenna with wide-range scanning,good radiation performance,low-level sidelobe and convenient processing is designed.In the frequency band 5.2GHz-6.1GHz,the range of scanning angle is-38~0?38~0,which can ensure that the antenna can scan in both positive and negative directions.The gain of the antenna is stable,and the gain range is10.9d B-14.8d B.The radiation performance of the antenna meets the requirements of wide-range scanning and low-level sidelobe.The influence of ferrite on passive circulator performance is studied.Based on the gyromagnetic characteristics of ferrite under the action of magnetic field and combined with the topological structure of the stripline double Y-junction and the?/4 impedance transformation line,a circulator with high isolation,low loss,and good transmission performance in the frequency band 4.35GHz-6.5GHz is designed.The bandwidth of the circulator is about 2.15GHz,and the relative bandwidth reaches 39%.In order to facilitate circuit integration and simplify the processing difficulty,an active quasi-circulator with a simple structure and excellent performance is designed on the basis of the structure of the Wilkinson power divider and the unidirectional conductivity of the transistor.The isolation between the receiving and transmitting branches of the active quasi-circulator is realized by isolation resistor in the Wilkinson power divider,and the good transmission performance of each port is realized by the high and low impedance lines.Finally,in the frequency band 5GHz-6GHz,the designed active quasi-circulator has high isolation and good transmission performance. |
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