Radiation of coupled-waveguide antennas

An investigation has been carried out on the two radiated beam patterns of a coupled-waveguide antenna. In general, the shapes of the two beams differ because of propagation asymmetry about the coupling plane. Using the analysis of the coupled-mode theory, it has been shown that, for antennas where very little of the input energy is radiated, the two beams can be made almost similar by appropriate reduction of the phase velocity of the nonradiating waveguide. The same principle, when applied to an efficient antenna, causes deterioration of the sidelobe levels, although the peaks of the two beams can still be maintained equal. For the efficient antenna, the problem of beam-port coupling is also considered with respect to uniform and cosine plus pedestal radiating aperture distributions.