Wide bandwidth NSPUDT coupled resonator filter design

The results of a wide bandwidth natural single phase unidirectional transducer (NSPUDT) quartz coupled resonator filter design effort are discussed. The resulting 850-MHz filter yields a symmetric frequency response, a bandwidth in excess of 0.4%, an ultimate rejection in excess of 50 dB and a turnover temperature of 5°C which can be selectively placed between -25°C and 75°C depending on the rotated Y-cut angle of the quartz substrate. The transducers utilize asymmetric crystal orientations to achieve the unidirectionality with a simple single-level uniform two-electrodes-per-wavelength fabrication. Both theoretical model predictions and experimental results, along with a discussion of the effects of package parasitics, and measured turnover temperature data for several rotated Y-cut angles, are presented. Design considerations and several methods for increasing filter performance are discussed