Theoretical and experimental results of unidirectional interdigital transducers using grating SAW substrates and zero TCF ladder type filters at 2 GHz range

Surface acoustic wave (SAW) filters employing unidirectional interdigital transducers (UDT) show low loss properties. We propose a new single phase unidirectional transducer (UDT) with about λ/4 electrode width for the best transducer efficiency. The new UDTs are obtained by IDT on a very thin dielectric grating or a very thin dielectric grating with λ/8 shifts. Good UDT properties are obtained for very thin SiO₂ grating thickness (about 0.03 μm at 2 GHz with Al electrode thickness of 0.07 μm). We describe the experimental results of wide band and very low loss filters with under 1 dB insertion loss in the 2 GHz range. We also show ladder type SAW resonator filters using high coupling SiO₂/5°Y-X LiNbO₃ with zero temperature coefficients of frequency (TCF). The experimental results show under 1.6 dB insertion loss with a wide band and zero TCF in the 2 GHz range. Finally, we show the narrower band width of ladder type filters using the new configuration of IDTs and reflectors on high coupling substrates.