Research And Realize Of Wide Pass Band Low Loss Saw Filter

The design of slant low-loss SAW filters mainly consists of slanted IDT analysis,SPUDT IDT analysis and capacitor weight analysis. These techniques have fulfilled thecurrent demands for low-loss, small-size and wide-bandwidth SAW filters. At the timewhen the concept of third-generation mobile communication came out, none of theSAW filter manufacturers in china had the expertise in design and process of slantlow-loss SAW filters, especially in accuracy analysis. The main reason was that they didnot have an accurate physical model. From2004, our institute has started the researchon design methods, accurate modeling and process technology of slant low-loss SAWfilters. Today, we have made more progress in implementation of our own design andsucceeded in mass production of this kind of SAW Filters by local manufacturers.Accurate physical model used in the design and manufacture of SAW filters is thekey to the simulation and provides important guidance to the production process. Forthe design of broadband low-loss SAW filters, the core issue in the theoretical design isto build an accurate physical model. In this paper, we adopt the approximation theory toestablish the initial weighted structure (i.e., the actual physical structure). We build ourmodel with this structure, and then employ the COM model or FEM/BEM model toanalyze the periodic transducer structure and optimize the entire transducer unit. Theoptimized geometry will be used to improve the performance of the filters. We focus onCOM model and FEM/BEM model to reach our analysis method, which is the keytechnique of SAW filter design. We integrate the Plessky periodic Green’s function,harmonic wave guide theory by Y. Zhang and Hashimoto discrete Green’s function,while borrows ideas from Ventura’s improvement in the calculation of periodic Green’sfunction, as well as from Yongan Shui’s numerical method that realizes accurate andhigh-speed numerical calculation of SAW propagation characteristics with metal gridarrays. As a result, we have developed a new analysis method that is suitable tomodeling and design of broadband low-loss SAW filters for practical application, interms of accuracy and calculation speed.For the production process of broadband low-loss SAW filters, in addition tocompleting the research on the production process, we have designed experiments and verified the reliability of the filters. We have studied the property and reliability of thebroadband low-loss SAW filters under impact of different processing techniques,including using SMT pastes with different properties and groove-opening in the back ofthe piezoelectric crystal. And we have tested the effectiveness and feasibility of theprocess techniques through actual manufacture.Via research in design and process, we have worked out a rather completedescription of the design modeling and product process methods and demonstrated theeffectiveness and feasibility of our methods by testing applications of actual products.