Saw ladder filter with inter-stage matching saw resonator

A resonator-type SAW filter having a plurality of SAW resonators with respective interdigital transducers formed on a single piezoelectric substrate, said SAW resonators being coupled in a ladder network configuration having at least one .pi.-type section with a first ladder stage and a second ladder stage, said .pi.-type section being formed by a series-arm SAW resonator and two shunt-arm SAW reasontors, said sereis-arm SAW ersonator having a first resonant frequency and a first antiresonant frequency, the interdigital transducer in said series-arm SAW resonator having a first electrode finger pitch, said .pi.-type section also comprising:

• an inter-stage matching SAW resonator coupled in series with said series-arm SAW resonator, said inter-stage matching SAW resonator having a second resonant frequency and a second antiresonant frequency, said inter-stage matching SAW resonator having an interdigital transducer with a second electrode finger itch, said second electrode finger pitch being more narrow than said first electrode finger pitch, said second resonant frequency being higher than said first resonant frequency by a first amount, and second antiresonant frequency being higher than said first antiresonant frequency by a second amount substantially equal to said first amount, said inter-stage matching SAW resonator reducing impedance mismatching between the first ladder stage and the second ladder stage of said .pi.-type section.