Contents I. Introduction
In THE past two decades, the dielectric resonator antenna (DRA) has received tremendous attention due to a number of attractive features such as its small size, light weight, low loss, wide bandwidth, and ease of excitation [1]–[4]. The shape of the DRA can be hemispherical, cylindrical, or rectangular. Among these shapes, the rectangular one has the largest number of design parameters (width, length, and height), facilitating the antenna design. Okaya and Barash [5] divided the modes of the rectangular DRA into two categories, namely the and modes. The fundamental mode has been investigated by different researchers extensively [6]–[9]. It produces a radiation pattern which is similar to that of a magnetic dipole, with the strongest radiation found in the boresight (broadside) direction. It is known that the fundamental omnidirectional modes of the hemispherical and cylindrical DRAs are the [10] and [11], [12] modes, respectively, with their mode indices referring to field variations along the spherical/cylindrical coordinate variables. Both of the modes are excited by a centrally fed probe and radiate like an electric monopole. However, little or no information of the analogous mode was found for the rectangular DRA. In this paper, a rectangular DRA with a square cross section is operated in the mode for the first time. It was found that its radiation pattern is omnidirectional in the horizontal plane as similar to that of an electric monopole.
