Single-phase Unidirectional Transducers for Low-loss Surface Acoustic Wave Devices

Abstract

<p>There has been an upsurge in interest recently in lower loss surface acoustic wave (SAW) devices for new signaI processing applications. In this thesis, a new generation of unidirectional transducers (UDTs) for the realization of low-loss SAW devices has been studied in which unidirectionaIity is effected by exploiting coherent internal reflections within a transducer. These single-phase UDTs (SPUDTs) offer many advantages and attractions that are unavaiIable in many previous UDT designs. CoupIed-mode theory is extensively used to analyze and characterize these structures. A general theory is proposed which will guide design and construction of all SPUDT devices. This includes specifications of the optimum conditions for achieving maximum directivity. An accurate and detailed model is also developed for SPUDTs with inter-IDT reflectors. The model accounts for all major electrode interaction effects and involves the cascade of transfer matrices of reflectors, transmission lines and transducers to realize the overall response. Experimental verifications have consistently shown that this model is very accurate in the analysis of SPUDTs.</p> <p>Based on a better understanding of the SPUDT concept, several new SPUDT designs have been developed. Special efforts are expended towards acquiring key properties never before obtained with SPUDTs, such as improved sidelobe suppression, wider bandwidths and higher operating frequencies. In these respects, the new designs represent a significant improvement over the earlier SPUDT designs. The final part of the thesis describes the theory and operation of a novel SPUDT-based multimode oscillator for frequency agile radar. An innovative injection-locking scheme involving FM chirp-mixing is also disclosed. Preliminary tests have indicated very encouraging results including low phase noise levels (120 dBc/Hz @ 10 kHz), wide tuning bandwidth (50%) and fast switching speeds (< 2 us).</p>