A multipaction-proof waveguide filter includes a main cavity and a number of corrugations extending from the main cavity. The main cavity includes corrugation interconnect regions between the plurality of corrugations. The corrugation interconnect regions include sloped surfaces, and the corrugations include flared nonparallel sidewalk. Due to the introduced sloped surfaces and flares, an increased Q is achieved, improved roll off is observed and multipaction risks are mitigated.