The measured performance of a millimeter wave beam splitter [in gyrotrons]

An essential component of any high power transmission system is a directional coupler that provides a sample of the forward and reflected power when this power is being delivered to the intended load. In the case of millimeter power delivered through a highly oversized corrugated waveguide, there is the much more complex issue of mode purity. The authors use a true beam splitter that provides a sample of the fields in the entire cross section of the waveguide. Our proposed means of overcoming the heat removal problem is to make the mirror an edge cooled CVD diamond disk having a very thin copper coating on the high power side of the mirror. A two dimensional array of holes is etched through the copper. An image of the incident wave free of aliasing is launched on the opposite side of the copper film. This process is easily scaled to frequencies greater than 170 GHz.