Mutual coupling reduction for integrated pin-made feed

The mutual coupling between two elementary sources exciting an integrated pin-made Fabry-Perot feed is analyzed. The integrated feed consists of one or two partially reflecting grids made by vertical metallic pins connecting the upper and lower metallic plates of a parallel plate waveguide. The two elementary sources are the inner conductor of a typical probe-like transition for parallel-plate waveguide structures. A mutual coupling reduction is observed for the two-grid case. In order to justify this effect, a dispersion analysis approach is used to express the field launched in the parallel plate waveguide by the integrated-feed in terms of a multi leaky-wave pole expansion. For the two-grid case, several leaky-wave poles are found, and it is shown that their interaction explains the observed mutual coupling reduction. The possibility to control and reduce the mutual coupling between closely-spaced feeds provided by the present integrated pin-made feed can be useful in compact planar antennas. Besides, the excitation of several leaky wave poles can be also used for shaping the field launched in the parallel plate waveguide.