An apparatus comprising a parallel plate waveguide (PPWG) comprising two plates separated by a distance that supports a multimode wave, and a transmitter configured to emit a wave having a frequency from about one hundred Gigahertz (GHz) to about ten terahertz (THz) and to couple to one mode of the PPWG. Also disclosed is an apparatus comprising two plates substantially parallel to one another and separated by at least about five millimeters (mm), and an antenna coupled to the two plates and configured to transmit or receive a wave having a frequency from about one hundred GHz to about ten THz. Disclosed is a method comprising polarizing an electromagnetic beam in the first transverse electric (TE1) mode with respect to a PPWG comprising two plates, adjusting the diameter of the electromagnetic beam based on the separation between the plates, and sending the electromagnetic beam into the PPWG.