A new ceramic waveguide window for use on X-band valves

During the development of all-ceramic klystron valves, the conventional resonant window, incorporating a thin ceramic disc sealed to a metal diaphragm, was found to have several disadvantages. A new window was therefore developed which simplifies the input and output structures of microwave valves. The new window consists basically of a length of circular waveguide filled with alumina-type ceramic, transmitting only the TE11 mode. At one end the ceramic protrudes into the valve resonant cavity sufficiently to give the correct coupling. At the other end there is a short transition from ceramic-filled circular waveguide to air-filled rectangular waveguide 16. The valve vacuum is maintained by a gold-brazed molybdenum-manganese seal between the ceramic and the copper ferrule which together make up the circular waveguide section. A flange is soldered or clamped to the end of the ferrule after valve processing, for connection between the valve and the external waveguide system. The window has been satisfactorily applied to the type SZ20 klystron and tests have shown that it is also capable of passing 1600 watts c.w. power. This corresponds to a power density in the ceramic of about 16 kW/in2.