SURFACE ACOUSTIC WAVE FILTER Russian patent published in 2008 - IPC H03H9/64 

FIELD: physics; electricity.

SUBSTANCE: surface acoustic wave filter consists of a piezoelectric acoustic line, on the working surface of which there is, in one acoustic channel, a central interdigital transducer - sectional, connected to the input terminal, and two identical lateral interdigital transducers, arranged symmetrically relative the centre and connected to the output terminal. The filter is characterised by that, the electrodes of the central and lateral interdigital transducers with width of λ/4, where λ is the wave length, and height 0.12÷0.15 mcm, are "buried" in the groove of the acoustic line, made with depth of 0.1÷0.12 mcm. The lateral interdigital transducers are uniform, and the central interdigital transducer is made in form of a set of 1+2N sections - middle, and 2N lateral, and symmetrical to it. The length M_o of the middle section and the length M_n of each lateral section in wave length λ, are chosen from the relationship: Σ2M_n≤M_o, where: f_o - is the central frequency of the amplitude-frequency response; Δf' - is the given passband of the filter; the number n, determining the phase of each lateral section relative the middle section in the central interdigital transducer, is chosen from the expression: n≥2M_o. The expression from which the envelope curve of the amplitude-frequency response of the central interdigital transducer is determined is given.

EFFECT: improved filter selectivity and reduced distortions of the amplitude-frequency response without increase in losses.

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