Quasi-Optical Spatial Power Combining Millimeter Wave High Power Traveling Wave Tubes

A quasi optical spatial power combining traveling wave tube has been successfully developed and used to increase the output power from solid state devices (as the driver). We report here the development of novel quasi optical spatial power combining for vacuum electronic devices and, more specifically, for traveling wave tubes (TWTs) to increase output power at millimeter waves (MMW) and higher frequencies. A quasi optical spatial power combining array of five complete plus two half slow wave structures (SWSs) was developed at W-band (center frequency 95 GHz) to achieve a combined output power of over 1000 Watts. These SWSs are arranged into a linear array. A sheet beam electron gun and a single stage collector were designed and implemented to mate to the SWSs for this W-band high power TWT. The SWSs were designed to be highly integrated and built as a single piece via microfabrication processes. Even with the relatively large size of the sheet beam electron gun and collector that was used for this initial study, the overall size of the W-band high power TWT is relatively small since the same vacuum envelope and electron beam focus optics are shared. With the present sheet beam electron gun design, the small signal bandwidth is 0.7 GHz. The bandwidth can be improved by using an electron gun with seven multiple electron beams to drive the seven slow wave structures. Design and fabrication of this W-band high power TWT will be presented to demonstrate the feasibility of the quasi optical spatial power combining millimeter wave high power traveling wave tubes. Higher output power can be achieved by employing a larger array.