Surface-acoustic-wave duplexer with improved isolation

1. Field of the Invention A duplexer has four surface-acoustic-wave resonators, forming two filters, integrated on a piezoelectric substrate. The surface-acoustic-wave resonators are laid out so that the two resonators with intermediate resonance frequencies are separated from each other by one or both of the resonators with the highest and lowest resonance frequencies, thereby improving isolation between the two filters. In one configuration the two filters are ladder filters, and the resonators are laid out in a row in which the series-arm resonator of the receiving filter is followed by the shunt-arm resonator of the receiving filter, then the series-arm resonator of the transmitting filter, then the shunt-arm resonator of the transmitting filter. The two filters may also be separated by a groove in the substrate.