Low-loss NSPUDT SAW filters with inclined reflectors on quartz

This paper presents the low-loss natural single phase unidirectional transducer (NSPUDT) SAW filters, which use SAW propagation direction reversal without the reversal of NSPUDT directivity. In this design the input and output NSPUDTs are placed in parallel acoustic tracks. SAW transmission between these tracks and propagation direction reversal are provided by a double reflection from the inclined reflectors. An asymmetric quartz crystal orientation was chosen where conventional IDTs with the lambda/4 electrodes have SAW unidirectional radiation (lambda is the SAW wavelength on the central frequency of the filter). The 56 MHz and 172 MHz experimental filters with the LC-matching showed an insertion loss of 8-10 dB and low ripple within the passband.