== Slot-Coupled Spherical DRA ==
Just like a rectangular DRA, a spherical DRA can also be excited through a coupling slot. Figure 20 shows the geometry of a slot-coupled spherical DRA. The feed mechanism of this DRA is very similar to that of the rectangular DRA of Figure 1310, consisting of a coupling slot in the metallic ground plane, which is fed by an underpassing microstrip line printed on a thin dielectric substrate on the other side of the ground plane. In Figure 20, the radius of the dielectric hemisphere is a = 12.5mm and its relative permittivity is ε<sub>r</sub> = 9.5, which are identical to the case of Figure 15. The slot dimensions are L = 13.5mm and w = 0.9mm. The substrate has a thickness d = 0.635mm and a relative permittivity ε<sub>r</sub> = 2.96. The microstrip feed line parameters are w<sub>f</sub> = 1.45mm and L<sub>s</sub> = 13.6mm. The feed line extends to the edge of the substrate, where it is excited using a microstrip port. The metallic ground dimensions are 100mm × 100mm.
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