I. Introduction
Dielectric resonator antennas (DRAs) were first proposed about two decades ago [1]. Due to their attractive characteristics, DRAs received much attention as antenna elements. DRAs can be designed by different shapes (rectangular, cylindrical, hemispherical, etc.) of dielectric materials having a wide range of dielectric constant. Due to lack of metallic loss, they have high radiation efficiency and high power-handling capability. Also, different feeding mechanisms can be used for the excitation of DRAs, including the excitation by slots, probes, microstrip lines, dielectric image guides, and coplanar lines [2]–[3]. In addition, various antenna characteristics can be easily controlled, such as input impedance, bandwidth, and radiation pattern, through different choices for the antenna parameters and feed mechanism. Recently, extensive research has been done to achieve DRA bandwidth enhancement by embedded DRAs, stacked DRAs, or with special shaping of the DRAs [4]. All these features make wideband DRAs advantageous as antenna elements for array applications.