In order to demonstrate the radiation performance of the fabricated antenna, its radiation patterns
are also measured. The measured and simulated radiation patterns in E-plane (xoy-plane) and H-plane
(yoz -plane) at 4, 8, 12 and 16 GHz are depicted in Figures 8 and 9, respectively. It is observed from
the plots that the measurement results are in good agreement with the simulation results. As one can
see from the plots, the radiation patterns of the designed dipole antenna exhibit bidirectional radiation
characteristics in the xoy-plane and omnidirectional radiation characteristics in the yoz -plane at 4 and
8 GHz, which are comparable to that of a conventional dipole antenna. The main deviation from the
radiation patterns of a conventional dipole antenna is the asymmetry of antenna structure. At 12 and
16 GHz, the radiation patterns of the designed antenna exhibit endfire radiation characteristics. This
is because the radiation patterns of the proposed antenna are mainly affected by the balun and the
beveled tapered slot at the high frequencies. The balun reduce the back radiation and the tapered slot
increases the directivity of the antenna in the high frequency band. Anyhow, the main lobes of the
radiation patterns are approximately fixed toward the endfire direction (y-axis direction) within the
operating frequency bandwidth. Stable radiation patterns are still observed.