Dielectric-rod antennas, also known as Polyrod antennas, are regarded as a type of surface-wave antenna. While a wide range of configurations are possible for dielectric-rod antennas, in most cases they have a tapered rod of circular or rectangular cross section. In these antennas, the feeding waveguide couples part of the input power into a surface wave which travels along the dielectric rod with minimal reflection. The surface wave then continuously radiates as it travels along, gradually transforming from a strongly bounded wave to a free-space wave.
Reduced side lobe levels are attainable through proper design, however this also results in reduced gain. By adding a horn launcher (or a short flared section at the waveguide termination) a further reduction of the side lobe level may be achieved....Typical pattern performance of the circular tapered polyrod with horn launcher. Typical S11 performance of the circular tapered polyrod with horn launcher.