Temperature compensated high power bandpass filter

Abstract

A bandpass filter makes use of at least one waveguide cavity that is thermally compensated to minimize drift of a resonant frequency of the cavity with thermal expansion of cavity components. The compensation relies on deformation of the shape of at least one cavity surface in response to thermally induced dimensional changes of the cavity. A control rod is used to limit the movement of a point on the deformed surface, while the rest of the surface moves with the thermal expansion. The control rod is made of a material having a coefficient of thermal expansion that is significantly different than that of other filter components. The rod may also be arranged to span more thermally expandable material than defines the filter such that, as the filter expands, the point of deflection is moved toward the interior of the filter beyond its original position. In an alternative embodiment, an end plate of each cavity is secured to the rest of the cavity along its periphery, and has a convex shape facing away from an interior of the cavity. As the cavity expands radially, it forces the convexity of the end plate inward, compensating for the expansion in other cavity dimensions.