by a feed probe, as shown in Figure 1. This antenna managed to provide efficient radiation in the direction normal to its ground plane and suitable for millimeter-wave (mm-wave) applications. The most crucial parameters in antenna are radiation pattern, beam efficiency, directivity, gain, bandwidth, and input impedance. Polarization is also one of the important parameters. Polarization in a given direction is the polarization of an electromagnetic wave transmitted by the antenna. The polarization is stated as the polarization in the direction of maximum gain if the direction is unfixed. According to [16], different polarizations result from different parts of the pattern because the polarization of the emitted energy differs with the radiation from the center of the antenna. Polarization is classified as linear, circular, and elliptical, as shown in Figure 2. These polarizations, depending on the amplitude and phase, shift between two waves. In general, polarization is described by an ellipse. Linear polarization is obtained when the ellipse becomes a straight line; whereas, circular polarization is obtained when the ellipse becomes a circle. Linear polarization (\(T\)\(\rightarrow\)\(\infty\) or \(T=0\)) is realized when the field is corresponded to a direction in time. Linear polarization is obtained if the field vector has one component or two orthogonal linear components with a 180\({}^{\circ}\) phase shift [16]. Linear polarization is also associated with an antenna system that is working with vertical and horizontal polarizations. The radiation pattern of an antenna is referred to as vertically polarized if the electric field vector is oscillating in the vertical direction. Conversely, the electric field will oscillate in the horizontal direction for horizontal polarization. For a linearly polarized (LP) wave, \(Ex\) and \(Ey\) are in phase with each other; whereas, circular polarization (\(T=1\)) occurs when the two orthogonal polarized components (\(x\)-direction and \(y\)-direction) have the same magnitude (\(Ex=Ey\)) and a 90\({}^{\circ}\) time-phase difference [18]. LP DRAs have been broadly explored and are still receiving considerable interest at present. However, the application of the LP antenna is only capable to detect signals in one direction and will face a polarization mismatch loss when the signal is curving from different angles [19]. Therefore, a circularly polarized (CP) antenna is preferable for various  
Figure 1: Cylindrical DRA: (**a**) full geometry; (**b**) feed configuration [15]. Figure 2: Types of polarization [17]. applications because it can receive a component of the signal persistently due to the angular variation, regardless of receiver orientation, thus making the CP antenna capable to transmit and receive signals in all planes so that the strength of the signals is not lost and transferred to another plane and is still used [20]. As a result, the gain and performances of the system can increase and the multipath effect can improve [21; 22]. Moreover, CP antennas have received considerable attention due to their advantages such as immunity to multi-fading, better weather penetration, and more mobility than LP antennas. For CP antennas, the operating bandwidth is determined as a frequency band in which the bandwidth where the reflection coefficient \(S_{11}<-10\) dB and that where axial ratio AR \(\leq\) 3 dB overlap [23]. Various DRAs with circular polarization have been designed by exploiting different dielectric resonator (DR) geometries and feeding configurations. Feeding configuration is also important to vary the resonant frequency and the quality (Q) factor. The usual designs of the feeding configurations can be separated into two types which are single feed and dual or multiple feeds. Generally, the CP fields of a DRA can be excited by a single feed, such as by using a slot-coupling feed [24], coaxial probe feed [25], or microstrip-line feed [26].