2 GHz range low loss IIDT filters using narrow gap IDT structure and new cross-over techniques

GHz-range low-loss transducers and filters are required for communication systems, especially mobile telephone communication systems. Many types of low-loss transducers and filters with wide bandwidth utilizing high electro-mechanical coupling coefficient(K² ) materials such as LiNbO₃ and LiTaO₃ have been developed. In this paper, we describe SAW filters employing IIDT (Interdigitated Interdigital Transducers) so that the wide bandwidth and the lowest insertion loss can be obtained. The IIDT filters are fabricated on 128° Y-X LiNbO₃ by the anodic oxidation techniques with narrow gap IDTs. The electrode width is almost 1 μm for 2 GHz range. Multi-bonding techniques are required for ordinary IIDT filters to connect each group of bus-bars. We have developed a new cross-over connection without the need for multi-bonding. Calculation results, including the cross-over capacitance, show very low loss characteristics. The experimental results showed the insertion loss of 1.19 dB at 2 GHz with the matching condition