Tunable Radio Frequency Filter And Matching Network

With the increasing number of communication systems and frequency bands,adjustable/reconfigurable RF devices are playing an increasingly important role by implementing adjustable circuit components in circuit topologies to form adjustable circuit parameters.The dynamic deployment of RF circuits reduces the size and complexity of circuits and is widely used in broadband receivers,multimode communication,multi-frequency communication and software radio.In the RF transceiver system,the filter acts as an important component in the frequency channel,which can filter out interference and noise outside the signal band.The antenna matching network connects the RF front end to the antenna and plays a vital role in the transmission and reception of electromagnetic signals.Studying tunable filters and tunable matching networks is of great significance in improving the broadband adaptability and robustness of RF systems and reducing the size of RF systems.First,a tunable LC bandpass filter with cross-coupling and bandwidth compensation is designed in this thesis.Electrical coupling is introduced between the source and load,and a magnetic-dominanted,electrical-assisted hybrid coupling is introduced between the tunable LC resonators,and finally LC cross-coupling is produced.Two transmission zeros are generated alongside the passband to improve frequency selectivity and out-of-band rejection.The LC-based magnetic-dominanted,electrical-assisted hybrid coupling is used to compensate for the bandwidth of the tunable bandpass filter.The designed circuit was simulated by ADS and SONNET softwares,and the test was finally completed.The test result was consistent with the simulation.The filter is tunable in the 70MHz to 270MHz frequency range with an absolute bandwidth of 20MHz to 55MHz,a relative bandwidth of 21%to 27%,and the insertion loss of less than 3dB at all center frequencies,while isolation is greater than 50dB.Secondly,a?-type tunable antenna matching network is designed in this thesis.Two adjustable components are added and SMV1212 series varactors are used to tune the matching network.The matching network of the design was verified by simulation,and the manufacturing and testing were completed to verify its adjustable performance.The the resonant frequency of the antenna and the matching network is from 630MHz to 1.04GHz,and the absolute bandwidth of S₁₁<-10dB is about 8MHz²0MHz.Morever,the tunable matching network can adjust the input impedance of the matching network when the external environment changes and optimize the reflection coefficient.The matching circuit has separate resonant frequency and impedance matching tunable capability.the antenna is matched and adjusted according to different impedances in the complex conditions.