1. A filter network comprising an input for receiving a signal to be filtered, an output for providing a filtered signal,
a plurality of circuit branches providing a single circuit path for carrying said signal between the input and the output,
each circuit branch comprising one or more filter elements, and at least one resonant circuit associated with a switch device,
the switch device being operable between an on state, in which said at least one resonant circuit is connected to said circuit
path thereby affecting how said single circuit path filters the signal, and an off state in which said at least one resonant
circuit is substantially isolated from said circuit path thereby not substantially affecting how said single circuit path
filters the signal; and a switch control input for receiving a signal for operating the switch device between the on and off
states.
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