Patent ID: 7092685

Claim:
A method for tuning a radio filter, said filter being operable in a frequency range and comprising a filter input connection, a filter output connection and at least two resonator modules, each of said at least two resonator modules having a tuning mechanism, said filter being adapted to receive at least one filter input signal being within said frequency range, characterised in that the method is performed with a radio filter having at least two of said resonator modules coupled in cascade, whereof a first resonator module being connected to said filter input connection and a final resonator module being connected to said filter output connection, said method comprising the steps of: (a) mixing said filter input signal with a low frequency signal so as to generate a single side band signal, (b) mixing each resonator output signal with the single side band signal, said resonator output signal being offset in phase from said filter input signal each by a first set of relative phase differences dependent on a present tuning of each resonator module, each resonator output signal being one in a group consisting of: a signal originating from a resonator output signal present on a resonator output connection, and a signal probed within the resonator module, (c) mixing the single side band signal with a reference signal originating from the input signal on the input connection, (c1) wherein the mixing in step (b) and the mixing in step (c) is performed simultaneously for each resonator module, so as to obtain a set of phase references, (d) comparing, at a frequency range about that of the low-frequency signal, mixing products resulting from step (b) and (c), respectively, for each of said at least two resonator modules, so as to determine a second set of relative phase differences between the filter input and resonator output signals, and (e) operating, based on said second set of phase differences, the tuning mechanisms to tune each resonator module, so as to adjust said second set of phase differences to a set of predetermined values.