An adaptive filter comprising: a tunable filter having an input node and an output node, the tunable filter being selectively tunable to define a pass band associated with a first signal band and a reject band associated with a second signal band, wherein the tunable filter is configured to pass signals having frequencies within the first signal band between the input node and the output node, and wherein the tunable filter is configured to block signals having frequencies within the second signal band; and wherein the tunable filter comprises: a coupling impedance element, the coupling impedance element comprising a first inductive element and a first tunable capacitor connected in either a series arrangement or a parallel arrangement between the input node and the output node; a first shunt impedance element connected between the input node and a ground; and a second shunt impedance element connected between the output node and the ground; and wherein the adaptive filter is characterised in that the coupling impedance element is selectively tunable both to a first mode at which a coupling impedance of the tunable filter is tuned such that the pass band has a minimum pass band insertion loss at frequencies that are less than frequencies within the reject band and alternatively to a second mode at which the coupling impedance of the tunable filter is tuned such that the pass band has a minimum pass band insertion loss at frequencies that are greater than frequencies within the reject band. a tunable filter having an input node and an output node, the tunable filter being selectively tunable to define a pass band associated with a first signal band and a reject band associated with a second signal band, wherein the tunable filter is configured to pass signals having frequencies within the first signal band between the input node and the output node, and wherein the tunable filter is configured to block signals having frequencies within the second signal band; and wherein the tunable filter comprises: a coupling impedance element, the coupling impedance element comprising a first inductive element and a first tunable capacitor connected in either a series arrangement or a parallel arrangement between the input node and the output node; a first shunt impedance element connected between the input node and a ground; and a second shunt impedance element connected between the output node and the ground; and a coupling impedance element, the coupling impedance element comprising a first inductive element and a first tunable capacitor connected in either a series arrangement or a parallel arrangement between the input node and the output node; a first shunt impedance element connected between the input node and a ground; and a second shunt impedance element connected between the output node and the ground; and wherein the adaptive filter is characterised in that the coupling impedance element is selectively tunable both to a first mode at which a coupling impedance of the tunable filter is tuned such that the pass band has a minimum pass band insertion loss at frequencies that are less than frequencies within the reject band and alternatively to a second mode at which the coupling impedance of the tunable filter is tuned such that the pass band has a minimum pass band insertion loss at frequencies that are greater than frequencies within the reject band.