Diffraction by a multilayered dielectric-coated sphere with an azimuthal slot

The wall air-gap concept for low-loss lines and reactive-wall waveguides is employed in the exterior problem of a dielectric-coated sphere with an aximuthal slot. The results for the gain and radiation pattern for a specific case are based on a boundary-value solution, and are optimised numerically to establish the concept. It is shown that, for a spherical antenna of electrical radius k0a = 5, coated with a dielectric layer (of thickness and relative permittivity equal to 0.254¿ and 16, respectively), which encloses a wall airgap (of 0.00303¿ thickness), the increase in gain over the uncoated antenna is 5.17 dB, while the shift in the main lobe is 12.5°.