An experimental and theoretical comparison for the insertion loss of paired IDTs for high frequency harmonics

Several theoretical models are known to describe the harmonic response of surface acoustic wave (SAW) interdigital transducers (IDTs) of different topologies. The experimental results for insertion loss for IDTs, obtained for several tens of frequency harmonics, are compared with theoretical predictions of the well-known model, based on the "quasi-static approximation". The paired transducer insertion loss of LiTaO₃ (Y-112⁰) and ST-X quartz were measured using a harmonic rich split finger IDT (metallization ratio is 0.6 and electrode thickness is 0.1μm, approximately) over a frequency range from 30 MHz to above 2.4 GHz (LiTaO₃) and to above 1.6 GHz (quartz). It is shown that the measured conversion loss of the IDT is in good agreement (about 1.5 dB) with theoretical results up to the 47th harmonic for LiTaO₃ and up to the 43rd harmonic for quartz.