Full-wave analysis of RF SAW filter packaging

As SAW filters move to higher frequencies and smaller sizes, the packaging structure has an increasing effect on the electrical performance of the device. In order to correctly design a SAW filter, the package performance must be considered concurrently in the design process. This paper describes several new methods for package simulation in which a full-wave electromagnetic (EM) simulator is used to create a package model. A ceramic chip and wire package is used to demonstrate the techniques. The package model is combined with a model of a SAW ladder filter at 1960 MHz and compared to measured data. The full-wave simulation is first performed on an empty package, with inductors used to represent bond wires. More accuracy can be achieved if simplified bond wires are included in the full-wave analysis, although computation time increases. A more accurate model of the bond wire shape increases simulation time, with no increase in accuracy. Our results demonstrate that full-wave analysis techniques are useful for predicting critical parameters such as the shape and rejection level of a SAW filter