Abstract: A ladder filter comprising a plurality of bulk acoustic wave resonators, the resonators comprising a plurality of series resonators series resonators in series between an input terminal and an output terminal of the filter, and one or more shunt resonators each connected between a junction between two series resonators and a common terminal, the series resonators comprising an input series resonator connected to the input terminal and an output series resonator connected to the output terminal, and wherein the shunt resonators are designed to satisfy: a unity aspect ratio and wherein the series resonators are designed to satisfy an aspect ratio different from unity. The aspect ratio is defined as the ratio of length to width of the resonator.

Abstract: A bulk acoustic wave resonator comprising a substrate (5), a Bragg reflector (4), a top (1) and a bottom (3) electrode and a piezoelectric layer (2) with means for suppression of the pass-band ripples in a bulk acoustic wave filter. The means for absorbing or scattering the spurious modes are a roughened rear side of the substrate (6), an absorbing layer (5) disposed on the rear side of the substrate (6) and/or an absorbing layer (5) disposed on the front side of the substrate.

Abstract: A filter structure, comprising a first signal line, a second signal line, a third signal line and a fourth signal line, said first and third signal lines defining an input port and said second and fourth signal lines defining an output port of a section of said filter structure, said section being defined by a first bulk acoustic wave resonator (A) which is connected between said first signal line and said second signal line, a second bulk acoustic wave resonator (G) which is connected between said third signal line and said fourth signal line, a third bulk acoustic wave resonator (C) which is connected between said first signal line and said fourth signal line, and a fourth bulk acoustic wave resonator (E) which is connected between said second signal line and said third signal line; is characterized in that a frequency pulling factor defined d of at least one of said acoustic wave resonators is non-zero, said frequency pulling factor d being defined by for first and second bulk acoustic wave resonators havi

Abstract: A bulk wave resonator comprising: a substrate (1); a layer (3) of piezoelectric material deposited on the substrate; a first electrode (2) and a second electrode (4) which are arranged on opposite surfaces of the layer (3) of piezoelectric material, the overlapping area of the first electrode (2) and second electrode (4) defining the resonance range of the bulk wave resonator, characterized in that the overlapping area in an intersecting plane parallel to at least one of the electrodes (2, 4) has an aspect ratio in the range from 1 (b/a) 100, where a is the length and b the width of the bulk wave resonator. The invention also relates to a bulk wave filter comprising such bulk wave resonators.