Study On Realization And Application Of Reconfigurable Filters

In recent years, the wireless communication systems are required to work at multi-frequency and multi-standards which has results in ever more complicated systems. Microwave reconfigurable components have the potential to reduce the complicity of the system. As one of the most important components of the reconfigurable systems, the reconfigurable filter can be used in channel selection and image reject. The target of this thesis is to develop the technology to realize the reconfigurable filters, and design reconfigurable filters with different functions, wide tuning range and low insertion loss. Those filters may be used in the next generation reconfigurable wireless communication systems. Moreover, the application of reconfigurable filters is also investigated in this thesis which can expand the application range of the reconfigurable filters.The contributions of this work have been summarized as follows:1. The characteristics of four different varactor-loaded microstrip tunable resonators are studied. The corresponding design formulas are given. A center frequency reconfigurable filter with a wide tuning range is designed. A method to use the most popular coupling matrix design the center frequency reconfigurable filter is proposed. The coupling coefficient is analyzed by the even-mode method, and a center frequency tunable filter with constant bandwidth is proposed. Based on the source-load coupling theory, transmission zeros are introduced on both sides of the passband. A center frequency reconfigurable filter with high selectivity is proposed. By cascading the center frequency filter and the dipole antenna, a working frequency tunable antenna with unchanged radiation pattern is proposed. The two port filter coupling theory is extended to three port power divider design. This theory is combined with tunable resonator theory to design the working frequency tunable power divider.2. A varactor-loaded center frequency and bandwidth reconfigurable substrate integrated waveguide filter is proposed. The equivalent circuit of this filter is investigated. The characteristics of the tunable resonator has been analyzed. The method of tuning the coupling coefficient between two adjacent resonators has also been analyzed. The filter is implemented and the experiment results have proved the validity of the design concept. PIN diode-load center frequency and bandwidth switchable substrate integrated filters are proposed. The principles including how to tune the resonant frequency of the resonator, and how to tune the external quality factor as well as coupling coefficient are analyzed.3. The method of how to use the generalized Chebyshev function to synthesize filter is discussed. Tunable high pass filter and low pass filter are realized. Another compact coupling microstrip tunable low pass filter has been proposed. The network cascading theory is analyzed and used in the connection of formerly high pass filter and low pass filter. Then, a center frequency and bandwidth reconfigurable filter is formed. The experiment results are very good. The application of wide bandwidth reconfigurable filter in phase shifter is discussed.4. Based on the source-load coupling theory, a selectivity tunable filter is designed. The tunable resonator is used as a bandstop structure, and a reconfigurable filter with wide tuning range of transmission zeros are designed. Based on the dual-mode resonator theory, the PIN diode is used to design the transmission zero switchable filter.