High-power wide-band microwave windows

Summary form only given. Extensive efforts have been directed in recent years toward the development of microwave tubes with higher output power and, at the same time, with wider bandwidth. These tubes require new types of vacuum windows because the conventional windows are not adequate in their power handling capability and/or bandwidth. In order to meet these requirements, a group of waveguide windows have been developed recently. They are unique in configuration, simple to design and have a number of advantages over windows of conventional designs. Waveguide windows are generally designed by filling the waveguide cross-section with a dielectric material. Due to its higher value of dielectric constant, the waveguide containing window material has a lower cut-off frequency than that of other waveguide sections. This creates mode problems which will limit the useful bandwidth of these conventional windows. If the size of a waveguide with dielectric material is reduced in such a way that the cut-off frequency of this section is equal to that of other waveguide sections, the window can be used for a wider bandwidth. According to this design principle, a number of waveguide windows have been developed, in all of which the width dimensions are reduced from that of the adjoining waveguide, depending on the dielectric constant of the window material. These windows can be designed for rectangular waveguides or ridged waveguides or a combination of both types. If they are used with rectangular waveguide, the full waveguide bandwidth can be utilized through the windows. When they are used with ridged waveguide, their useful bandwidth is as wide as an octave. The measured VSWR is less than 1,3:1 over this entire frequency range. These window designs can be scaled to most frequency ranges of interest without difficulties. With proper cooling around the dielectric 589 material, their power handling capability is expected to exceed that of any conventional windows. The basic de- ign, development effort and test results of these windows will be described. Theoretical investigations aided by digital computers and experimental results to overcome the mode problems will be discussed also. These windows have been used successfully in a number of wide-band traveling wave tubes with the highest output power currently under development.