The C1 configuration results in (a) and (b) show the power ratio (PR) as a function of the outer radius b; (c) and (d) show the electric field magnitude resulting in the peak PR values in (a) and (b), respectively; (e) and (f) show the associated directivities, while (g) and (h) show the associated power spectrums. The left column, i.e., (a), (c), (e) and (g), corresponds to the case with no PEC shell. The right column corresponds to the case with the PEC shell having an aperture extent of 2θ = 90°. Figure 2d, f and h corresponds to the second peak PR value attained for b = 8.543 mm.