BALANCED LOW-LOSS SAW RING AND THREE-TRANSDUCER FILTERS WITH IMPEDANCE CONVERSION

摘要

This paper presents the balanced low-loss SAW filters with impedance conversion from 50–75Ω to 150–250Ω in a wide fractional bandwidth of 1.5–7%. The ring SAW filter on 128°YX LiNbO_3 and wideband three-transducer SAW filters with unidirectional IDTs on U-shaped MSCs on 128°YX, 64°YX, 41°YX LiNbO_3 are used for this purpose. The optimization of the SAW filters is provided with computer simulation using the equivalent circuit model. The 45–52 MHz samples of the balanced SAW filters have shown an insertion loss of around 2 dB, stopband attenuation of 30–50 dB. Two cascaded filters provided an insertion loss of around 3 dB and stopband attenuation of 60–100 dB.