The SAW is an elastic wave generated and propagated on the surface of piezoelectric substrates, and its amplitude decreases rapidly with the depth of the substrates. The basic structure of SAW filter is to fabricate two acoustic and electrical transducers, the interdigital transducer and IDT, on the polished surface of substrate material with piezoelectric characteristics, which are used as transmitting transducer and receiving transducer respectively.
The main characteristics of SAW filter are: High flexibility in design, analog/digital compatibility, group delay time deviation and good frequency selectivity (optional frequency range 10MHz~3GHz), small input and output impedance error, low transmission loss, anti-electromagnetic interference (EMI) performance, high reliability, small size and light weight of the fabricated device.
Its volume and weight are about 1/40 and 1/30 of the ceramic dielectric filter respectively, and it can realize a variety of complex functions. The characteristics and advantages of SAW filter are adapted to the requirements of modern communication system equipment and the portable telephone, such as lightweight, short, high frequency, digitization, high performance, high reliability and so on.
Its shortcomings are: The required substrate materials are expensive, and the substrate orientation, cutting, grinding, polishing and manufacturing process requirements are high.
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