Compact Circularly Polarized Dielectric Resonator Antenna Excited by an Underlaid Quadrature Coupler

Today, the demand for wireless communications is growing faster than ever, as RF/microwave technology has undoubtedly become a part of our daily lives. In wireless communications, the antenna plays a very important role because it directly affects the transmission and reception. Recently, the dielectric resonator antenna (DRA) has been studied extensively due to the inherent merits of its low loss, small size, low cost, and ease of excitation.Initially, studies of the DRA have mainly concentrated on linear polarization. In some applications, such as satellite communications, circular polarization (CP) is more welcome because the polarization of a signal may be changed during its propagation. As a result, the CP DRA has attracted extensive attention over the last decade. A common problem of the CP DRA is that it has either a narrow bandwidth or a large feeding network. In this project, a compact wideband CP DRA excited by an underlaid quadrature coupler is proposed for the first time. A preliminary study shows that the new structure can give a wide CP (axial-ratio) bandwidth of 15.2%, which is ~ 4-5 times wider than those of existing compact DRA designs. By switching the source to the correct port of the quadrature coupler, the CP DRA can generate either left-hand or right-hand CP fields, giving a switchable CP DRA. The proposed structure can also be utilized to design compact polarization diversity CP DRAs. Diversity antennas are extensively used in personal communications because they can be used to alleviate the fading and multi-reflection problems.An external resistor is usually needed for the isolation port of a quadrature coupler. In this project, a new dualfunction DRA that simultaneously serves as a CP antenna and a match load for the quadrature coupler will also be investigated. This dualfunction structure desirably avoids the need for the external resistor.The problems will be theoretically modeled, along with comprehensive measurements. Design curves will be generated, and the results will facilitate engineers to design the compact CP DRAs and their arrays easily and quickly.