Abstract: One embodiment of the present invention includes a waveguide. The waveguide comprises an elongated member having a conductive bottom surface and a hollow channel. The hollow channel is defined by a first conductive sidewall, a second conductive sidewall, and a conductive inner surface. The waveguide also comprises a plurality of conductive ridge portions projecting from the conductive inner surface and extending between the first conductive sidewall and the second conductive sidewall. The conductive ridge portions can partition the hollow channel into a plurality of hollow recesses. The waveguide further comprises a plurality of switches associated with each of at least one of the plurality of conductive ridge portions. At least one of the plurality of switches associated with a respective one of the plurality of conductive ridge portions can be activated to couple the respective one of the plurality of conductive ridge portions to the conductive bottom surface.