A solution to reducing insertion loss and achieving high sidelobe rejection for wavelet transform and reconstruction processor using SAW devices

摘要

An arbitrary wavelet transform and reconstruction processor is composed of multiple single-scale wavelet transform devices (SSWTDs) with different scales. For improving the performance of the processor using surface acoustic wave (SAW) devices, this research investigates how to reduce the insertion loss (IL) and achieve a high sidelobe rejection. To reduce the triple transit echo (TTE) and to achieve a high signal-noise ratio (SNR), the structure of the SSWTD consists of two electrode-widths-controlled (EWC) single phase unidirectional transducers (SPUDTs). In the propagation process of the SAW, the unidirectional characteristic of the new structure reduces the bidirectional loss of the entire device. In addition, to enlarge the fractional bandwidth and the sidelobe rejection, the internal structure of the SSWTD uses an input apodized transducer according to the envelope of the Morlet wavelet function as well as an output withdrawal weighting transducer. In this paper, we present a SSWTD for scale 2~(-2) as an example to illustrate the design method and experimental results. The new device is fabricated on 128° rotated YX-cut lithium niobate (Y128°X-LiN-bO_3) with the electromechanical coupling coefficient k~2=5.5% and the SAW velocity 3992 m/s. We get the experimental frequency response with the center frequency 68.14 MHz, the minimum IL -9.96 dB, the fractional bandwidth 3.3%, the maximum passband ripples 0.4 dB and the sidelobe rejection greater than 40 dB. The proposed method and structure can be extended to an arbitrary SSWTD. The experimental results confirm that the performance of the wavelet transform and reconstruction processor can be improved by the proposed solution.