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 re alisation of a low-side/back-lobe antenna provided that the spurious d iffraction of the dominant TM surface wave is properly blocked. The ra diation pattern of the antenna is similar to that of a monopole on an artificially soft (corrugated) disc. The accuracy of FDTD prediction i s tested by comparisons with far-field measurements and a moment-metho d analysis.