Research And Design Of Microstrip Tunable Filter

The problem of spectrum congestion is becoming more and more prominent with the rapid development of the modern wireless communication system. Spectrum technologies, such as spread spectrum, frequency hopping and the dynamic frequency allocation ect., have been widely used in order to improve the utilization of the spectrum resources. As a key component in these technologies, electronically tunable filter has attracted more and more attention. Furthermore, miniaturization, high performance, fast tuning speed, wide tuning range ect. are becoming the design requirements of the tunable filter.Firstly, the research significance and research status of the tunable filter are introduced in the paper, and the basic theory of filter design is illustrated. Finally, two different kinds of tunable filters are presented based on the tunable filter synthesis theory. The designed filters contain a lowpass filter, a tunable lowpass filter with ultra-wide stopband and a tunable bandpass filter with constant bandwidth.Both the lowpass filter and the tunable lowpass filter are designed based on the design goal of miniaturization and wide stopband. Firstly, the performance of stepped-impedance resonators, triangular patch resonators and butterfly resonators are researched, then, a compact microstrip lowpass filter with ultra-wide stopband is proposed by using resonator loading technology and slow wave design form. Furthermore, a miniaturized tunable lowpass filter with ultra-wide stopband is presented combining with the application requirements and research status of the tunable lowpass filter.The design methods of the tunable microstrip bandpass filter with constant absolute bandwidth are investigated and summarized, and the multi-mode tunable E-shape resonator is also analyzed by the even-odd method. Then a tunable filter with constant absolute bandwidth is presented based on the multi-mode tunable E-shape resonator. Furthermore, to solve some shortages and achieve better performance, another kind of tunable filter is designed by making some improvements on the tunable filter designed before. In the design process, the presented filter is simulated, fabricated, and measured. Good agreement between the simulated and measured results validated the design rationality.