Key Technologies Of RF MEMS Switches For Millimeter-wave Reconfigurable Antennas

RF MEMS(Radio Frequency Micro-Electromechanical Systems)is one of the important application fields of MEMS technology.RF MEMS switches are used for signal processing in RF and microwave frequency circuits,and are important components of wireless communication systems.RF MEMS switches have the advantages of miniaturization,low insertion loss,high isolation,good linearity,easy integration,etc.,and are important basic technologies for realizing reconfigurable antennas.Based on MEMS switches,reconfigurable antennas combine the advantages of low loss and high isolation of MEMS switches with the performance adjustability and controllability of reconfigurable antennas,which have important significance for the design of high-performance 5G communication systems.This dissertation focuses on the urgent demand for high-performance MEMS switches and reconfigurable antennas based on MEMS switches for communication microsystems,and conducts in-depth research on the difficult problems such as "high capacitance ratio MEMS switch design for Ka-band reconfigurable antennas",“circuit model establishment and parameter calculation of coplanar waveguide asymmetric defect ground structure",and "radiation direction solution of reconfigurable antennas based on MEMS switches" The main research results and innovations of this dissertation are as follows.First,for the problem of low capacitance ratio of the on/off state of the capacitive MEMS switch,the factors that restrict the capacitance ratio of the MEMS switch are studied,and a MEMS switch high capacitance ratio performance analysis model based on a capacitive-resistive dynamic adjustable structure is proposed.A "Ji" shaped bending folding beam sandwich structure high capacitance ratio MEMS switch based on MIM(Metal-Isolator-Metal,MIM)floating electrode layer is designed,which effectively alleviates the dielectric charging effect of the switch and improves the capacitance ratio of the switch.The measured results show that compared with the capacitance ratio of about 100 of the fixed beam MEMS switch based on the traditional single variable capacitor model,the capacitance ratio of the switch designed in this dissertation is increased to 246.3.Second,for the problem of calculating the structural parameters of the asymmetric defect ground structure in the coplanar waveguide of the MEMS switch design,a distributed capacitance model of the asymmetric defect ground structure is established,and a method for calculating the equivalent capacitance and characteristic impedance of the asymmetric defect ground structure based on the first kind of elliptic integral is proposed.On this basis,a MEMS single-pole double-throw switch combining defect ground and common ground structure is designed,which effectively reduces the on-state capacitance of the switch and realizes the characteristic impedance matching of the switch working frequency band.The measured results show that the isolation degree of the MEMS singlepole double-throw switch is better than 25dB,compared with the MEMS single-pole double-throw switch without loading defect ground structure,the MEMS single-pole double-throw switch combining defect ground and common ground structure designed in this dissertation effectively reduces the insertion loss from 1dB to 0.5dB,improving the pass rate of RF signal.Third,for the problem of analyzing the spatial electromagnetic radiation mechanism of the multi-radiation patch antenna based on MEMS switch,a pattern reconfigurable antenna design method based on phase superposition effect and a pattern solution method based on spatial vector superposition method are proposed,and a pattern reconfigurable antenna based on MEMS switch is developed based on this theory.The measured results show that the antenna works at 35GHz,and the antenna pattern can be reconfigured with the main lobe direction being-7.9°,0° and 8°respectively,and the measured results are in good agreement with the theoretical calculation.Compared with the pattern reconfigurable antenna based on phase shift network,the antenna designed in this dissertation effectively reduces the antenna size by about 50%while achieving multiangle reconfiguration.Fourth,a pattern reconfigurable antenna array based on 3dB microstrip branch line coupler is designed,and MEMS single-pole doublethrow switch is used for signal path selection.The measured results show that the array pattern can achieve±16° reconfiguration,and the gain reaches 16.1dBi.