A circuit for filtering a radio frequency signal at a given frequency comprises an input terminal, a filter device, and an active AC shunt circuit having first and second input terminals and an output terminal, where the first input terminal of the active AC shunt circuit is connected to the input terminal. The filter device is connected between the input terminal and the second input terminal of the active AC shunt circuit, and is provided for attenuating the radio frequency signal at the given frequency to the second input terminal of the active AC shunt circuit. The active AC shunt circuit is provided for shunting a signal at a frequency other than the given frequency as contained in the radio frequency signal to ground, and for outputting the radio frequency signal as filtered at its output terminal.