A multiport distribution network is provided that supports N inputs and N outputs, where N>1, the multipart distribution network providing an independent distribution path extending from each input to each output, each path being formed from a sequence of at least two fundamental units. Each fundamental unit comprises a circuit formed of multiple resonator cavities and having n input ports for receiving respective input signals, and n output ports for outputting respective output signals, where n>1, and wherein the circuit is configured to: (i) at each input port, split an input signal received at that input port into n equal signal components and provide each of the n signal components to a respective output port of the circuit; and (ii) at each output port, combine the signal components received from the n input ports to form an output signal for that output port. The multipart distribution network is configured to apply the same filter transfer function along each independent distribution path.

Example directional couplers and devices including one or more directional couplers are disclosed. In an example, a directional coupler comprises a first electrically conductive portion and a second electrically conductive portion, a first ground plane electrical conductor disposed in a plane between the first electrically conductive portion and the second electrically conductive portion, and a second ground plane electrical conductor and a third ground plane electrical conductor disposed such that the first and second electrically conductive portions and the first ground plane electrical conductor are between the second and third ground plane electrical conductors. The first ground plane electrical conductor includes at least one hole directly between the first electrically conductive portion and the second electrically conductive portion.

A plasma generator by means of a resonant waveguide is disclosed. The plasma generator comprises: an annular or elliptical central waveguide that includes a plurality of slots on the inner side surface thereof; a first incident waveguide that is tangentially connected to the central waveguide to enable electromagnetic wave communication; an electromagnetic wave supply unit that transmits electromagnetic waves to the incident waveguide; and a plasma chamber that has an electromagnetic wave incident window which is positioned on an outlet side of the slots to seal the inside of the central waveguide, and through which electromagnetic waves introduced through the slots may be radiated to the outside.