Analysis and measurement of transducer end radiation in SAW filters on strongly coupling substrates

The authors present the analysis of spurious responses generated at the ends of surface-acoustic-wave interdigital transducers (IDTs). Utilizing the method of moments, the analysis is based on a Green´s function concept and a spectral-domain representation. The influence of end fingers as well as the influence of a grounded metal back plane on the charge distribution was simulated. Three effects are shown: the first is the charge accumulation of grounded guard fingers located close to the IDT end, resulting in unwanted end radiation: the second is acoustic end reflections in split-finger IDTs, occurring at the transition from the periodic finger structure to the free substrate; and the third is the finger charge induced by the metallic ground plane when the transducer is driven unbalanced to ground. Computer simulations based on the proposed method agree well with measurements