Research On Nonlinear Problems In Continu-Ous-wave Wireless Measurement Systems

Nonlinear problems are critical issues in the design of a continuous-wave (CW) wireless mea-surement system. In this dissertation, the source of the nonlinear problems, their impact on the system performance, and corresponding elimination methods have been studied.From a system point of view, it is observed that there is an inherent conflict between the system requirement for linearity and the nonlinear system composition. To solve this problem, it is highly desired to precisely model the nonlinear subsystem through theoretical or experimental analysis, and then construct an inverse subsystem to eliminate the nonlinear issues.However, it should be aware that the non-ideal issues in the system implementation, such as the quadrature channel imbalance, DC-offsets in the baseband signals, and the phase wrapping caused by codomain restriction of the arctangent functions, will do harm to the construction of the inverse subsystem, and introduce additional nonlinear components. Their bad effects have been eliminated or compensated with appropriate methods, with the aid of these methods, an instruments-based CW radar system has been constructed.Then, three promising applications of the CW wireless measurement systems have been in-troduced. In the case of noncontact displacement and vibration detection, it is shown that not only the frequency and velocity, but also the amplitude of vibration can be measured. In addition, the linear CW measurement system is also capable of tracking the displacement trajectory. In an ab-initio investigation of1-D microwave imaging of human cardiac motion, the detected time domain trajectory of cardiac motion fits the theoretical pattern in medical textbooks. A polynomial fitting technique has been proposed to eliminate the respiration motion. And the measurement results from different orientations have been reported. Last but not least, an example of CW measurement system used in near-field analog quantities monitoring has been reported. Not only the data trans-mission through impedance modulation, but also the power transfer via magnetic resonance can be achieved by this system. Be aware that the nonlinear problems will no doubt do harm to the measurement results. In order to extend the application of the CW wireless measurement system, it is essential to maintain its linearity.