Abstract: A dual mode circular-type waveguide filter (10) has a cylindrical waveguide body (12) separated by septums (16, 18) into a plurality of resonant waveguide cavities (22, 24, 26). Mutually orthogonal electromagnetic fields (37, 81) in adjacent cavities (24, 26) are electromagnetically coupled with each other by an internal coupling element (60) which is mounted on one of the septums (18) and extends into the adjacent cavities. The coupling element comprises an elongate, conductive wire which includes a first portion (62) extending into one of the cavities and forming a magnetic loop, and a second portion (64) extending into the adjacent cavity and forming an electric probe. The coupling element provides an asymmetrical stopband pole (72a) in the frequency response (70) of the filter.