Analysis And Design Of High Performance Tunable Microstrip Filters

Nowadays,with the rapidly developing wireless communication technology,the tunable filter can make more efficient use of the limited spectrum resources to alleviate the increasing scarce spectrum resources,as a key component of the reconfigurable system.Therefore,tunable filters have been researched more and more extensively and deeply by domestic and foreign scholars in recent years.Because of the obvious advantages of tuning speed,tuning range,cost,size etc.,the research of tunable filters loaded with varactors has been becoming very popular.Based on the varactor,several tunable microstrip filters with high performance are designed in this paper,and the main research contents are as follows:1.The tunable filter based on folded open loop ring resonators:the folded open loop ring resonators are used to couple with the input/output feeding lines,which make the structures simpler and passbands independently tunable.The resonators are asymmetric,which make the fractional bandwidth keep constant during the tuning process.Besides,a capacitor and a resistor in series are attached at the center of the resonator to suppress the harmonics.2.The tunable filter based on the dual composite right/left-handed structure:High-performance and miniaturization have become one of the main research trends of tunable filters.Compared with the traditional resonators,the dual composite right/left-handed resonator is much smaller in size,therefore,it is more advantageous in miniaturized filter design.Two miniaturized tunable filters with an adjustable center frequency are realized by loading varactors at different positions of the resonators.Besides,an external quality factor tuning network is added between the port and the resonator,which could achieve a good matching performance during the tuning process.3.The filter with a controllable bandwidth based on the dual composite right/left-handed structure:A filter with a fixed frequency and tunable bandwidth is realized by adding a bandwidth control network between the dual composite right/left-handed resonators.Combined with the tunable filter based on the dual composite right/left-handed resonators,a miniaturized fully tunable filter with a simultaneously controlling bandwidth and center frequency is designed.