GHz-range low-loss wide band filters using new electrode thickness difference type of unidirectional transducers

Submicron fabrication techniques are very important for higher frequency-range SAW devices. The frequency ranges of mobile communication systems are now at 1 GHz and extending to 2.3 GHz. 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. In this paper, a new electrode thickness difference type of single phase unidirectional transducer (ETD-SPUDT) with an electrode pattern width of λ/4 is investigated. The ETD-SPUDT with a narrow gap electrode is fabricated by removing part of a meander-line electrode by using the shadow of the resist pattern. The theoretical and experimental results show the low loss and large directivity. The low loss filter on 128° Y-X LiNbO₃ is fabricated by optical photolithography techniques in the 1~2 GHz range and by electron beam exposure in the 5 GHz range. The results show 2.2 dB insertion loss at 1 GHz, 3.0 dB at 2 GHz and 4.1 dB at 5 GHz