Abstract: Quasi-optical stripline devices for forming and controlling a beam of radio waves are described. The devices include a strip transmission line having a pair of mutually parallel flat outer conductors and a flat center conductor with a dielectric between them. The center conductor has a narrow channel region, a wide expansion region and a tapered region smoothly connecting the regions. A beam of radio waves propagates freely in the expansion region and can be controlled in a quasi-optical manner by the pattern of the center conductor. The quasi-optical nature facilitates easy visualization of the devices for easy design and manufacture.