Coupled waveguide excitation of traveling wave antennas

The analogy of coupled waveguides to a pair of coupled transmission lines is employed to obtain a design procedure for the establishment (approximately) of a certain class of traveling wave field distributions over an aperture in a conducting plane. The aperture is the opening to free space in the broad wall of a rectangular waveguide (dielectric loaded). This waveguide is coupled to a second waveguide through a series of slots or holes. The coupled waveguides permit the simultaneous excitation of two modes whose propagation constants can be designed to have a convenient difference. The major features in the radiation patterns can be predicted by the superposition of the patterns of two line sources which are equivalent to the traveling wave field distributions of the two modes. Advantage is taken of the degree of adjustment possible in the propagation constants of these modes to obtain a variety of radiation patterns. In particular, it is found that directive radiation patterns with low side lobes (lower than those of a uniform distribution) can be synthesized.