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WIDEBAND TWO-MODE LEAKY SURFACE ACOUSTIC WAVE FILTER WITH NON-EQUIDISTANT ELECTRODES OF TRANSDUCERS AND REFLECTING GRATINGS
Victor S. Orlov, Moscow Technical University of Communication and Informatics, Moscow, Russia, filtrov-pav@yandex.ru
Abstract
Asymmetric magnitude response with flat high frequency slop and «shoulder» with level -(10-15) dB appears by traditional section of two mode filters because of leaky surface acoustic wave (SAW) internal reflection from transducers electrodes. Additionally, gaps between input and output transducers represent like acoustical heterogeneities for leaky SAW. As result , ripples of magnitude response in pass band are increased and additional losses appear because of transformation of leaky SAWs in balk acoustic waves ( BAW). Structure of ultra-high frequency (UHF) two cascade leaky SAW filter is described , which allows to degrease an influence of indicated effects significantly. At frequency 1310 MHz such structure allows to achieve wide pass band width about BW3=8,7%, close to as much as possible, realize high selectivity 52-56 dB near pass band and no less 43-48 dB in wide frequency range before 3.0 GHz. «Shoulder» suppression before 52-54 dB at high frequency slop is obtained it two wais. First , via application of reflection gratings between transducers like additional acoustical frequency selective elements. Second, via modulation of pitches of groups electrodes in transducers and reflecting gratings with next optimization these pitches. Parallel connection of sells in each cascade is used for insertion loss decreasing. In contrast to analogues, standard technology , wafer and electrode materials are used. As result, described structure may be used like basic structure for leaky filters.
Keywords: leaky surface acoustic wave, two mode filter, sell, cascade, interdigital transducers, reflecting grating, insertion loss, selectivity.
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Information about author:
Victor S. Orlov, Moscow Technical University of Communication and Informatics, Moscow, Russia