Field solution for dielectric and ring loaded annular slot array antennas
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An analytical method based on the boundary value method is presented, which gives the field solution for annular slot array antennas fed by a radial waveguide or cavity, and loaded by dielectric layers and array of conducting rings. The appropriate Green's functions for different regions of the antenna due to magnetic and electric current rings are obtained. Then, the induced magnetic current over the slots and electric current on the conducting rings are expanded into a Fourier series with unknown coefficients. The final formulation is achieved by employing the Green's functions and applying the boundary conditions. The result is a linear system of equations. The unknown coefficients of Fourier series are obtained by solving this system of equations. Then, the electric field just above the last layer is found and the induced magnetic current is written in terms of the electric field. The far field formulation is derived using this magnetic current. The method is confirmed through comparison of its results with those of available numerical methods and good agreement is obtained. In comparison to these numerical methods, the proposed method is more efficient in computation time and memory requirement. The formulation is used to study the effects of dielectric loading and conducting ring loading. It is shown that both methods can improve the annular slot array antenna performance. The benefits and problems associated with each configuration are discussed and the effects of various parameters are investigated. Finite structures are also investigated, where open cavities with and without chokes and dielectric cover are used to shape the radiation patterns and improve the performance.