Waveguide devices and methods for radio-frequency applications. In some embodiments, a radio-frequency waveguide can include a dielectric block having a first edge that joins a mounting surface and a first adjacent surface. The waveguide can further include a conductive coating that substantially covers the dielectric block, and defining a wrap-around opening that exposes the dielectric block along the first edge. The wrap-around opening can include a strip on the first adjacent surface along the first edge and a strip on the mounting surface along the first edge, such that the first edge of the dielectric block is continuously exposed within the wrap-around opening.