A device and method is provided that includes a window for coupling a signal between cavities of a device or between cavities of different devices. A wall or microstructure is formed on a surface and defines a cavity. The window is formed in the wall and comprises at least a portion of the wall and is electrically conductive. The cavity can be sized to resonate at various frequencies within the terahertz portion of the electromagnetic spectrum and generate an electromagnetic wave to carry the signal. The window allows surface currents to flow without disruption on the inside surface of the cavity.