A wide-band balanced SAW filter with longitudinal multi-mode resonator

This paper describes a new balanced SAW filter with wide fractional bandwidth over 5% in 1.8 GHz range. The developed SAW filter is utilizing 5IDT longitudinally coupled multi-mode resonator structure with inverted output IDTs. In order to obtain wide bandwidth, mode coupling conditions were studied. Fabricated SAW filter has been realized with 100 MHz bandwidth and low insertion loss of 2 dB successfully. The package size of the filter is very small such as 2.5/spl times/2.0/spl times/1.0 mm/sup 3/ with flip-chip bonding technology. This SAW filter enables one to eliminate balun coil, which contributes to reduce mobile portable phone size.