Rounded Corners in Microwave High-Power Filters and Other Components

Microwave high-power filters must be operated with internal air pressures of at least one atmosphere, or with a good vacuum. Pressures between these extremes result in reduced powerhandling ability. The breakdown processes for both high air pressure and vacuum are discussed, and it is made clear that any sharp corner on which the electric field would concentrate must be rounded if high-power operation is to be achieved. For good results in vacuum operation, the surfaces must be especially smooth and free of contamination, while in high-pressure operation, minor irregularities are less important. Various high-power filter configurations of importance are described, and the structural corners at which electric-field concentrations occur are pointed out. A number of simplified geometries are then shown that can represent the essential portions of the practical structures with sufficient accuracy for ordinary purposes. Formulas and graphs for these simplified geometries are presented that give the ratio of the maximum electric field strength on the boundary to a uniform reference field strength at a point sufficiently removed from the corner. In some cases, the boundary curve is an approximation to a circular arc, while in other cases a boundary shape is derived such that the electric field strength along the curve is constant. These constant-field-strength boundaries are optimum shapes from the standpoint of power-handling ability.