Patent ID: 7973604

Claim:
A tunable filter device comprising: a distributed wide-band amplifier having at least two amplifying elements, an input transmission line connected to the input of the filter device and connecting inputs of the at least two amplifying elements, an output transmission line connected to the output of the filter device and connecting outputs of the at least two amplifying elements, and a frequency characteristics with a low cut-off frequency and a high cut-off frequency, wherein the high cut-off frequency is defined by the cut-off frequency of the input and output transmission lines together with decoupling capacitors of the at least two amplifying elements, wherein the low cut-off frequency is defined by direct current blocking capacitors of the distributed wide-band amplifier, wherein the value of the coupling capacitors and the direct current blocking capacitors are arranged to be changeable by respective external control signals, and wherein value of the direct current blocking capacitors is changeable by means of additional capacitors switchably arranged to be coupleable in parallel to the DC blocking capacitors in accordance to the external control signal.