A tunable filter having at least two tunable resonators (30, 40), a first resonator of the at least two tunable resonators comprising at least one inductance or transmission line, said inductance or transmission line having a first end (31 A) connected to the ground M and a second end (31 B) coupled to a second resonator of the at least two tunable resonators via a coupling impedance, and several switched capacitors having several value capacitators that vary depending on the position on the length of the inductance or the transmission line of which • said inductance or transmission line has several access points or connection points distributed along said inductance or transmission line allowing to connect or not connect a switched capacitor whose value is defined as a function of its position on the inductance or transmission line, • the switched capacitators are distributed along the inductance or transmission line in the following way: the capacitators of high weight, corresponding to the low tune frequencies, hence to an equally high inductance value seen at the second end (31 B) of said inductance or transmission line, are disposed further away from the ground than the capacitators of low weights, corresponding to the high frequencies that are disposed close to the ground towards the first end (31 A) of the inductance or the transmission line, • the values of the capacitors and their positions on the inductance or the transmission line are defined so that the impedance of the resonator is kept constant throughout the tuning band of the tunable filter, and the impedance of the resonator L equi C equi is kept constant at the tunable resonance frequency 1 2 π 1 L equi ∗ C equi L equi being the value of the equivalent inductance seen at the second end of said inductance or transmission line, C equi being the capacitator corresponding to all the switched capacitators, for a given configuration of the resonator. • said inductance or transmission line has several access points or connection points distributed along said inductance or transmission line allowing to connect or not connect a switched capacitor whose value is defined as a function of its position on the inductance or transmission line, • the switched capacitators are distributed along the inductance or transmission line in the following way: the capacitators of high weight, corresponding to the low tune frequencies, hence to an equally high inductance value seen at the second end (31 B) of said inductance or transmission line, are disposed further away from the ground than the capacitators of low weights, corresponding to the high frequencies that are disposed close to the ground towards the first end (31 A) of the inductance or the transmission line, • the values of the capacitors and their positions on the inductance or the transmission line are defined so that the impedance of the resonator is kept constant throughout the tuning band of the tunable filter, and the impedance of the resonator L equi C equi is kept constant at the tunable resonance frequency 1 2 π 1 L equi ∗ C equi L equi being the value of the equivalent inductance seen at the second end of said inductance or transmission line, C equi being the capacitator corresponding to all the switched capacitators, for a given configuration of the resonator.