Novel feed circuit for radial-line waveguide

Proposes a novel feed circuit for a radial-line waveguide. The conventional feed circuits for the radial waveguide are a circular waveguide and a center fed probe. The former is convenient for exciting several modes simultaneously with complex feeding structure. The latter has a simple structure, however, radiation characteristics should be controlled by the arrangement of antenna elements, such as a slot, a helical antenna, and a patch antenna. The radial-line slot antenna for DBS reception has a center feed probe exciting an axial symmetrical outward traveling wave and a spiral slot broadside array arranged to radiate circular polarization. The spiral slot arrangement of this array reduces radiation efficiency for small-sized antennas, because it disturbs an axial symmetry of aperture distribution and increases termination losses at the end of radial waveguide. To change this spiral arrangement to a ring array, it is necessary to excite a rotating mode by the feed circuit. Therefore, the paper proposes a new concept for the feed of a radial-line waveguide using a cavity resonator as the feed circuit. The authors describe four feed circuits for the radial-line waveguide. They compare the characteristics of these feed circuits for frequency band width and excited field distributions calculated by the mode matching method. The excitation of the rotating mode in the radial line waveguide is also discussed for these circuits