High efficiency SAW transducers with low internal reflections and their application in high performance broadband SAW filters

The insertion loss of a broadband, transversal SAW filter is highly dependent on the electrical Q-value of transducers. On a material with a low piezoelectric coupling coefficient, the Q-value can be quite high even for a filter with a moderate fractional bandwidth. The main reason for the high Q-value of the transducers is the small number of fingers their main lobes. In the present paper we propose a transducer which utilize the high piezoelectric coupling efficiency of λ/4 wide fingers in such a way that both a low Q-value and low SAW reflections are achieved. Simulations and measurements of high performance broadband SAW filters with these transducers are compared, both at the fundamental and the third-harmonic frequency, and the changes in Q-values are analyzed