GHz-range low-loss wideband SAW filters using new narrow-gap floating electrode type unidirectional transducers

GHz-range unidirectional SAW transducers are very important for high efficiency SAW devices, for example, low loss SAW filters and high efficiency convolvers. Also, low-loss filters using unidirectional transducers (UDT) with good phase characteristics are very important for linear group delay devices, especially in digital communication systems. The frequency ranges of mobile communication systems are now 1 GHz and extending to 2.4 GHz. In the near feature, SAW devices will require the frequency range around 10 GHz. In this paper, λ/4 electrode thickness difference type single phase unidirectional transducer (ETD-SPUDT) and new narrow-gap floating electrode type single phase unidirectional transducer (NG-FEUDT) with the electrode pattern width of about λ/4 are investigated. They are fabricated by cutting part of a meander-line electrode using the shadow of the resist pattern. The theoretical and experimental results show low-loss and large directivity. Low-loss filters on 128° Y-X LiNbO₃ are fabricated by optical photo-lithography techniques in 2 GHz-range and by electron beam exposure in 5 GHz and 10 GHz-range. The results show a 3.0 dB insertion loss at 2 GHz, a 4.1 dB loss at 5 GHz and a 9.4 dB loss at 10 GHz