Wide-band low-loss SAW filters for IF applications

摘要

While demand for RF filters used in portable phones is surely increasing, wideband IF filters are needed because of the demand for the transmission of higher bit rates. For the wide-band IF filters, small amplitude ripples and group delay ripples in the pass band, steep cut-off and low insertion loss are required. This paper relates to a wideband surface acoustic wave (SAW) filter with slanted finger interdigital transducers (SFITs) that is widely used in the intermediate frequency stages for wireless applications. The SAW filter with SFITs is suitably used as a mid- or wideband band-pass filter. In addition, the SAW filter using slanted finger unidirectional transducers (SFUDTs) can provide low-loss and flat pass-band characteristics. In this paper, the maximum intrinsic fractional bandwidth of the SFIT filter is discussed and several SAW filters with SFITs or SFUDTs on different substrates for wireless LAN and wideband CDMA applications are presented.