A matching slot pair for a circularly-polarized slotted waveguide array

The analysis and the design of the matching slot pair for a circularly polarized slotted waveguide array are described. The position and the size of the slots are numerically optimized to suppress reflection and to realize a desired polarization in the tilted beam direction, which contributes to the improvement of the antenna efficiency. A boundary value problem is analyzed for the matching slot pair taking the wall thickness of a waveguide into account in order to evaluate the phase of aperture fields accurately. The position and the size of the slots are determined on the basis of this analysis. The design is verified by measuring the reflection coefficient, the radiation patterns, and the axial ratio of a model slot pair. It was verified experimentally that the return loss is below -15 dB over 0.1 GHz at the 4-GHz band and the 3-dB axial ratio bandwidth is about 5% in the titled beam direction.<
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