An approach to accurate measurements of the electrical characteristics of SAW RF filters using neutral test environments

The paper discusses and classifies typical measurement setups used for the precise electrical characterization of surface acoustic wave (SAW) radio frequency (RF) components, such as, e.g., SAW filters and duplexers, in the context of nowadays demand for increased accuracy of measured filter data. The measurement setups are divided into test environments and application environments. By means of a couple of case studies the paper exemplifies the impact of printed circuit boards (PCBs) on the measured electrical filter characteristics. The effects observed are investigated by measurements and simulation. Simulation models established and analyzed take both relevant electromagnetic and acoustic effects into account. Comparisons of measurements and simulations indicate excellent agreement. The paper points out the necessity for measurement setups that provide a neutral environment to the filter. Here, the notion neutral environment implies minimal reflections, minimal feed-through or cross-talk, and minimal losses. It concludes with the proposal of a neutral environment, which has been successfully implemented in a couple of use cases. Performing the measurement using a neutral environment allows the determination of the filter characteristics without effects caused by the PCB, which is considered an essential prerequisite for an engineering approach to a modular design of a complex system, such as, e.g., the RF section of a mobile terminal.