Element pattern approach to design of dielectric windows for conformal phased arrays

The realized element gain E- and H-plane patterns for two-dimensional circular cylindrical arrays with a concentric dielectric sleeve are subjected to a modal analysis. Numerical results demonstrate that an improper design of a dielectric window for a conformal phased array may easily result in element patterns that are not acceptable owing to undesirable blindspot dips and excessive ripple. These features derive from guided wave effects, and they may be even more troublesome in curved than in planar geometry. A procedure is outlined for obtaining a systematic design of dielectric windows; it provides for well-behaved forward region element patterns in each polarization. The procedure includes the dimensioning of window thickness for a maximal rate of radial decay of surface wave followed by the inclusion of a sufficiently large gap to decouple the surface wave from the array face. The numerical results indicate that for an appropriately dimensioned dielectric window a sufficiently large, curvature-dependent but practical air gap should reduce the forward region guided wave effects to a tolerable level simultaneously in both polarizations.