| Doppler microwave radar works by principle of microwave doppler.In order to realize the intellectualization of household equipments and improve life quality of people,this paper combines doppler microwave radar with posture detection,also studies key circuits of microwave radar.The radar has function of basic human postures detection with installed in indoor.Fan-shaped beam antenna,integrated mixer of hardware,body signal detection circuit and logical realization of function of software are included in this paper.The radar has advantages include low cost,simple structure,flexible installation,and can greatly reduce the complexity of the algorithm.Firstly,Antenna increases a arc structure on both widths direction,which can increase current density of width direction with working frequency of 5.8GHz.It leads to the change of radiation characteristics of antenna in this way.With taking improved antenna as a element of antenna,this paper studies influence of number,spacing and size of array element for key performance of sector beam antenna by High Frequency Structure Simulator.Finally a three-element sector beam antenna with small antenna volume is designed.The maximum gain on radiation direction of the antenna is 9.2d B,and half-power beam width of E-plane and H-plane are 112 ° and 31 ° respectively.It also has a good fan-shaped beam detection function.Then,A microstrip balanced mixer integrating functions of transmitting,receiving,mixing,phase shifting and filtering is designed by studying working mechanism of schottky diode with a nonlinear device commonly,and working principle of microstrip balanced mixer.S-parameters and smith circle of mixer are extracted by means of harmonic balance method and joint simulation of momentum and schematic by Advanced Design System.Simulation results show that the value of ports VSWR of integrated mixer is 1.1 and 1.2 respectively at working frequency,that proves input and output ports have achieved good impedance matching,and the isolation of ports between LO and IF has reached 52 d B,which can better realize function of RF reception.Finally,signal detection circuits are designed and simulated by Multisim.Human tiny signals which include moving signal,micro action signal and respiratory signal with frequency between 250 m Hz～500m Hz are detected.Detection of basic human postures such as standing,sitting,lying,falling asleep,sleeping and waking up is finally realized logically with relevant microwave radar hardware design and working mode setting.Paper provides some ideas for development of indoor microwave radar and smart home industry in the future,and also provides a certain reference for design of other related circuits. |
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