Design And Implementation Of Tunable RF Filters

As a key components of microwave reconfigurable communication systems,tunable RF filters have been a hot topic resent years. This thesis presents the theoretical analysis and design examples of tunable filters.First, this thesis analyzes the classic filter characteristic functions P(s), E(s)and H(s) to extract the coupling matrix. Then, a new design theory for tunable filters based on filter synthesis theory is proposed. It shows tunable filters can be realized base on untunable filters which loaded tuning elements.Based on this design theory, this thesis designed and fabricated several tunable filters, including a tunable microstrip filter and a tunable cavity filter which is quite rare in publicized papers.In this thesis, design and fabricate a dual-band dual-mode microstrip filter.Dual-band center frequency is 2.35 GHz / 3.35 GHz, respectively. Detailed analysis and calculation of the SLR design characteristics and design process constitute filter.The test results in line with expectations.On this basis, a novel varactor tunable dual-band bandpass filter using stub-loaded stepped-impedance resonators is proposed. Dual-band center frequencies are adjustable in 0.8 ~ 1.02 GHz and 2.02 ~ 2.48 GHz. the source-load coupling and T-shape stub-loaded lines are employed in this design. In the overall tuning range, the proposed filter is designed with 5-6 transmission zeros. This dual-band tunable filter has the advantages of high selectivity and less control voltages.The implementation of electrically tunable cavity filters is a difficulty in tunable filter design. This thesis presents a tunable cavity filter base on SIW technology.Both the theoretical analysis and the design process is presented. Fabricated results show that the control voltages loaded on the filter can control the center frequency and the External-Q. This design will help further promote of the electrically tunable cavity filters.