A device for filtering electrical high frequency signals comprises a substrate carrying mechanical waves. At least one first transmitting transducer translating an electrical signal into mechanical waves in mounted in the substrate. A smooth interface layer having a frequency dependent reflection and transmission behaviour by means of amplitude or direction or phase is provided on the substrate. At least one second receiving transducer translating the mechanical waves into electrical signals is mounted either on the same side of the substrate as one first transmitting transducer and/or one second receiving transducer is mounted on the side opposite to the smooth acoustic interface layer. The smooth acoustic interface has a gradually varying acoustic impedance representing a filter for induced mechanical waves.