Axial ratio improvement of circular polarized dielectric resonator antennas with dual-point feeds

A novel approach to improve axial ratio (AR) of circular polarized (CP) dielectric resonator antennas (DRA) excited with dual-point feeds is presented. It is applicable to DRAs with different cross sections (e.g., square, circular) which are excited though two inputs having a 90-degree angular separation. The approach comprises two major stages. First, a complex excitation at the inputs of a DRA of interest, resulting in the AR of the value of one in the broadside radiation direction at the operation frequency, is determined. This excitation is calculated using the proposed closed-form formulas processing the simulated far-fields of the DRA excited with only one input. Furthermore, it is shown that a certain rigorously computed excitation of unequal amplitudes and 90-degree phase shift may be sufficient - from practical point of view - to ensure high-quality CP far-field for a DRA of interest. Second, the computed excitations serve as design requirements for branch-line couplers feeding the DRA. Numerical examples illustrate our approach.