Research And Design Of Rf Tunable Filter

The current radar scout system has some problems for processing multiform signals,conrfonting the complex electromagnetic environment and various radar characteristic signals. The especial front-end in receiver can solve these problems,and this dissertation analyzes it. That is to say, a tunable filter which range of tunable centrofrequency is big substitutes for several normal filters. This front-end has the adaptive ability for the magnitude and frequency of input signals. It can prefilter for the input signals,eliminate the useless signals,and increase gain of small signals;decrease the gain of big signal. The dynamic range of receiver system is improved in this way.The tuanable bandpass filters presented here is an essential part of the RF frequency selection network. These filters enjoy such merits: narrow bandwidth, range of tunable centrofrequency is big, the high attenuation in the stopband ,its structure is compact and almost changeless bandwith and filter characteristics. During the course of the research, the focuses are put on the followings:1.Firstly,on the base of the theories of the network design and coupling-resonator filter design, we introduce the processes from the lowpass filter prototypes to the bandpass coupling-resonator filter, analyze the relation between the variable center frequency and the filter's parameters by consulting, design formulas are presented.2. About the tunable filier, the varactors in the resonator and design the resonator is analyzed detailedly in this paper. Depict the design idea of the tunable amplifier.3. The emphases of the work are to design the tunable filter, including getting the approximate equivalent model of combline filter, simulation process with the help of the ADS software, and test the filter. The first part is to obtain the exactor component on the base of the former analysis. For the big tuning range of this filter, this paper adapts a special method to simulate. The second part is to test and adjust filters.Finally, the possible causes of the problems is analysed and offer ideas to the later works.