Design Of The High Frequency And Passband SAWF For Communication

With the development of communication,navigation,radar,mobile communication,programmed telephone and measured instrument devices, the high performance of SAWF is demanded. It includes low insert loss,high power durability,low shape factor,high stopband attenuation ,low passband fluctuation,low phase noise and so on. To improve perfomance of SAWF,the main content of study is as follows: 1) lower insert loss and higher power durability. One port SAW resanator was seen as a fundamental impedance element to replace each unity of a ladder-type circuit, and a ladder-type SAW filter was formed. In comparison with traditional transverse filter, this kind of filter has lower insert loss and higher power durability in the same conditions. 2) Improve of stopband attenuation and passband fluctuation. When unity filters are cascaded into a ladder-type filter, two kinds of circuits was obtained. One is T-type, the other is Π -type. In the Π -type circuit , the inter-stage impedance mismatching take palce. It would induce that transmisson characteristics become bad. By investigating reactance characteristics, we can use one resonator or more to reduce the inter-stage impedance mismatching. So in the ladder-type filter, one or more resonator was added can improve stopband attenuation and pass fulucuation of the filter. 3) Study on phase noise. The study on phase noise is very important in SAWF. Phase noise includes white noise ,flick noise and so on. They can deteriorate performance of the SAWF. In this paper we disscussed every source of phase noise. So we can avoid the factors which lead into phase noise in the corresponding procedures. A measurement procedure is developed specifically to characterize the phase noise of the SAWF. Effect of measurement on the phase noise is illustrated. Base on above study, a ladder-type SAWF was designed. The performace of SAWF is suited for the request and it is satisfied.