A SAW contiguous filter bank with an m derived ladder

Abstract

An m-derived ladder for combining SAW (surface acoustic wave) filters in a contiguous filter bank is proposed. The series element in each m-derived ladder section is composed of a parallel resonant circuit. The input transducer of a SAW filter is used as the shunt element in each section. A pole of attenuation is produced at the resonant frequency of the series element. Thus, the third-harmonic spurious response of the SAW filter is greatly suppressed by setting the pole of attenuation in the vicinity of the third harmonic. A ten-channel version of the filter bank was constructed, operating in the frequency range from 110 to 200 MHz. The insertion loss was 10+or-1.7 dB, which was as low as that of a constant k ladder filter bank, and the attenuation was greater than 42 dB in the third harmonics from 330 to 600 MHz.<>