A wide-range tunable/switchable low-loss SAW filter

This paper presents a wide-range tunable/switchable low-loss SAW filter with a fractional tuning band of over 90%. A 3-D carrying construction with a bank of channel SAW filters is used. In this construction the channel SAW filters in the separate packages are located in an imaginary cylinder in the radial planes passing through a symmetry axis of this “cylinder”. Bandpass tuning (switching) is performed by switching the channel SAW filter by means of RF switches. This filter contained 24 channels. Each channel contained a three-transducer low-loss SAW filter using unidirectional IDTs on U-shaped multistrip couplers (MSCs) on 64° YX LiNbO₃ with a 1-dB fractional bandwidth of 3.8%. An optimization of the tunable SAW filter was carried out using a computer simulation on the basis of the equivalent circuit model. The tunable SAW filter covered a frequency range from 68.4 to 182 MHz with an amplitude ripple of 1 dB, insertion loss about 3 dB, stopband attenuation about 40 dB. The filter required no matching elements and had sizes of 55×15 mm