The Theory And Applications Of Microwave Strong Nonlinearity On High Temperature Superconducting Film

Microwave nonlinearity is an intrinsic property of high temperaturesuperconductor(HTS).The investigation of microwave nonlinearity of HTS thin filmbenefits not only the theory of superconductivity but the applications of microwavedevices.And the sources of microwave nonlinearity are studied intensively,because it isthe most important mechanism for understanding microwave nonlinearity.Recentreports show that current driven nonlinearity is the main source of microwavenonlinearity at low field,and traditional views hold that the heat effect plays a key roleat high field.At the same time,one can confirm that microwave magnetic field plays arole as nonlinear sources,but what and how it plays is not clear at present.Thefollowing work on field induced microwave nonlinearity is included in this dissertation:The bridged resonator is studied intensively to measure the microwave nonlinearityThis resonator is developed by inserting one short narrow strip line(bridge) in uniformhalf wavelength resonator,and its electrical parameters are related to the physicalparameters of the bridge analytically.At the same time,microwave current is uniformlyconcentrated in the bridge,and the strength of on bridge microwave current isanalytically related to electrical parameters.By using this resonator as probe,microwave nonlinearity at high field can be measured at low externally appliedmicrowave power.Microwave nonlinearity of HTS film is measured from low field(tested average microwave magnetic field strength is 7Oe) to high field,till the bridgeshows high loss for microwave field(tested average microwave magnetic field strengthis 190Oe).Tested results show that microwave nonlinearity varies dramatically whenapplied microwave magnetic field is at 40Oe,160Oe and 190Oe.By these results wecan con finn that microwave nonlinearity relates to DC lower critical field at mediumand high field.DC biased nonlinearity is tested to verify this field depended nonlinearity.During the measurement procedure,some power depended hystereses like phenomenaare observed on HTS thin film at microwave frequency.Two simple models areproposed to understand the experimental results.One models the high loss property oflocal HTS film in high microwave field from the view of time domain.The other models the competition procedure between Meissner state and vortex state in distributedfield,and this model explains the dynamical interplay procedure between loss andcurrent.By the two models,the field induced microwave nonlinearity is proposed as themain nonlinearity source at medium and high field.At the same time,combined withthe surface barrier and grain boundary analyses,high frequency hysteresis is explained.Some new microwave devices are proposed for applications.The design procedures ofmicrowave filters with limited amplitude and HTS switchers with ultra-broad band areproposed.