An acoustically coupled thin-film BAW filter, comprising: - a piezoelectric layer, - an input-port, - first electrodes on the piezoelectric layer and connected to the input-port for changing an electrical signal into an acoustic wave, - an output-port, - second electrodes on the piezoelectric layer and connected to the an output-port for changing an acoustic signal into electrical signal, - wherein the first and second electrodes (5, 6) are positioned such that acoustic coupling is achieved, the first and second electrodes (5, 6) defining an electrode region and an outside region such that the electrode region has the first or second electrode on top of it and the outside region has no electrode on top of it, - wherein the first and second electrodes have an interdigital electrode structure such that the first electrodes alternate with the second electrodes, - wherein the filter is capable of operating in a first order thickness-extensional TE1 mode, and - wherein a mass loading by the first and second electrodes, determined by the thickness of the electrodes and material density, is such that a k ∥ =0 frequency of the outside region's TS2 mode is between 93% and 99.9%, in particular between 95% and 99%, more particularly between 97% and 98%, of the electrode region's TE1 cutoff frequency, wherein the k ∥ =0 frequency is a frequency at which a lateral wave number k ∥ of a corresponding vibration mode equals 0, CHARACTERIZED in that - the number of electrodes N, electrode width W and gap width G between electrodes are designed such that N ∗ W+N ∗ G=λeven/2, where λeven is a desired wavelength of the lateral acoustic wave at the even mode resonance frequency, and such that the highest-order mode trapped in the structure is the desired odd mode resonance. - a piezoelectric layer, - an input-port, - first electrodes on the piezoelectric layer and connected to the input-port for changing an electrical signal into an acoustic wave, - an output-port, - second electrodes on the piezoelectric layer and connected to the an output-port for changing an acoustic signal into electrical signal, - wherein the first and second electrodes (5, 6) are positioned such that acoustic coupling is achieved, the first and second electrodes (5, 6) defining an electrode region and an outside region such that the electrode region has the first or second electrode on top of it and the outside region has no electrode on top of it, - wherein the first and second electrodes have an interdigital electrode structure such that the first electrodes alternate with the second electrodes, - wherein the filter is capable of operating in a first order thickness-extensional TE1 mode, and - wherein a mass loading by the first and second electrodes, determined by the thickness of the electrodes and material density, is such that a k ∥ =0 frequency of the outside region's TS2 mode is between 93% and 99.9%, in particular between 95% and 99%, more particularly between 97% and 98%, of the electrode region's TE1 cutoff frequency, wherein the k ∥ =0 frequency is a frequency at which a lateral wave number k ∥ of a corresponding vibration mode equals 0, CHARACTERIZED in that - the number of electrodes N, electrode width W and gap width G between electrodes are designed such that N ∗ W+N ∗ G=λeven/2, where λeven is a desired wavelength of the lateral acoustic wave at the even mode resonance frequency, and such that the highest-order mode trapped in the structure is the desired odd mode resonance.