Radiation characteristics of annular-slot arrays fed by radial waveguides

The paper establishes a method which gives the field solution for an annular slot array fed by a radial waveguide. It is shown that in order to obtain a solution, the aperture electric field is expanded into a finite series of suitable basis functions with unknown coefficients, the number of which is directly related to the electrical dimensions of the slots. The complex constants are then obtained by employing the appropriate Green's functions and an application of the boundary equation over the aperture. It is demonstrated that in general, higher order modes of the radial waveguide region excited by the slot discontinuities may have a significant effect on the solution. Finally, the possible application of the method for the design of arrays with directive beams is also discussed.