Analysis of surface-wave excitation and radiation mechanisms of a monopole on a circular grounded dielectric slab with critical thickness

The properties of a monopole antenna on a circular, dielectric-loaded ground plane are analysed by using the finite-difference time-domain (FDTD) technique. The thickness of the dielectric slab has been chosen to maximise the decay of the space-wave contribution at grazing, thus reducing the space-wave diffraction at the truncation. This permits realisation of a low-side/back-lobe antenna provided that the spurious diffraction of the dominant TM surface wave is properly blocked. The radiation pattern of the antenna is similar to that of a monopole on an artificially soft (corrugated) disc. The accuracy of the FDTD prediction is tested by comparisons with far-field measurements and a moment-method analysis