Folded waveguide resonator

A waveguide resonator comprising a number of side walls defining a cavity enclosed by said sidewalls defining the cavity; and two or more conductive plates extending into the cavity, each conductive plate having a first side and a second side opposite the first side, and wherein the conductive plates are adapted to cause a standing electromagnetic wave to fold around the conductive plates along at least a first and a second direction and to extend on both sides of each of the conductive plates; wherein the conductive plates are adapted to cause the standing electromagnetic wave to fold multiple times along at least the second direction.