Research On The Tunable Dual-Band RF Filters

With the rapid development of wireless communication, spectrum resources become moreand more limited, cognitive radio emerged as a hot research topic because it can effectivelyimprove the utilization ratio of spectrum resources. As an effective method to achieve cognitiveradio systems, multi-band and multi-mode devices are taking more and more attention, becausethey have the ability to support different communication standards with a single device so as tomeet the requirements of broadband coverage.Tunable filters are the basic component of cognitive radio, a single tunable filter can replace afilter group. Compared with the traditional multi-band communication system which uses a filtergroup consisting of multiple single-band filters, the size, power consumption and costs of tunablefilter have clear advantages. Tunable dual-band filters can be used simultaneously in two differentcognitive radios, so they have great research value.In this thesis, researches on the single-band and dual-band tunable filters are performedbased on the theory of uniform impedance resonator and variable impedance resonator. The majorwork can be categorized as follows:1. A hairpin bandpass filter has been designed and implemented, measured results havedemonstrated the designed filter is suited for WCDMA system.2. A3rdorder combline tunable filter has been designed by co-simulation with Schematic andMomentum of ADS, measured results have demonstrated the effectiveness of the design principle.3. A new deformed combline tunable filter, of which center frequency and bandwidth can betuned simultaneously, has been proposed and implemented, measured results matched to thesimulated results.4. Based on principle of independent electrical coupling and magnetic coupling, an open-looptunable filter with constant absolute bandwidth has been designed, simulated results havedemonstrated the effectiveness of the design principle.5. A simple tunable dual-band filter has been designed and simulated.6. A new tunable dual-band filter structure with constant absolute bandwidth has beenproposed and implemented. The measured results were good match to the simulated results.