Coupled waveguide antennas

A structure consisting of two coupled waveguides is proposed as a leaky-wave antenna. The analysis of this device is based on coupled-mode theory. Previous coupled-mode treatments are extended, since radiative loss is not neglected and the asymmetry of the structure is taken into account. Two cases are considered: the coupling parameter constant with distancezalong the antenna and the coupling as a function ofz. In both, the radiative attenuation is maintained constant. It is found that the first case permits two "normal modes" to propagate and, if both modes are excited, the patterns may be superposed to produce desirable overall results. An example is given of an approximation to a pencil beam pattern. By means of the second method, essentially any of the common excitation functions may be produced. An example is given of an antenna to achieve a cosine-on-a-pedestal excitation. Experimental results are given and compared to theory. Suggestions are presented for further work.