Abstract: Apparatus and related methods for an easily manufactured evanescent mode band reject filter that provides high performance with minimal dependence on critical dimensions. According to one embodiment, the present invention provides a band reject filter including a waveguide having an input, an output, a first wall between the input and the output, and a second wall opposite the first wall. The first wall is part of a substantially solid first block, and the second wall is part of a substantially solid second block. The waveguide is capable of transmitting an electromagnetic radiation signal from the input to the output, where the signal is at an operating frequency above a waveguide cutoff frequency. The band reject filter also includes at least one cavity coupled directly to the first wall of the waveguide, where the cavity is a substantially cylindrical cavity formed in the first block.