Design of low–loss saw filters employing distributed acoustic reflection transducers

Abstract

AbstractAs a means to reduce the loss in an SAW filter, the IDT (interdigital transducer) called the internal reflection‐type transducer has been studied extensively recently. This IDT is believed to be useful as a filter for video and broadband data transmission since it is simple in structure and has low loss over a broadband while its fabrication process and external circuit are simple. So far, the filter constructed with this IDT has had a large ripple in the passband due to a large spurious reflection. To alleviate this problem, a new distributed acoustic reflection transducer is proposed as an internal reflection type IDT in which suppression of the unwanted spurious reflection is possible over a broad frequency range. Next, the operation mechanism of this IDT is investigated and a first‐order design method is presented. It is pointed out that a low‐loss filter with an insertion loss less than 10 dB and spurious reflection suppressed by more than 45 dB can be realized with this IDT over a broad frequency range.