Circularly polarized rectangular dielectric resonator antennas with branch-line coupler for wideband applications

In this paper, two circularly polarized rectangular dielectric resonator antennas (RDRAs) are proposed for wideband applications. One common method for achieving the orthogonal modes for circular polarization is used by coupler. In this configuration, a 45° rotated branch-line coupler which is located under the hollow RDRA with two tapered excitation strips are connected to sidewall of RDRA to excite two degenerate TE111 modes is used. For the second antenna, a pair of tapered stubs and metallic vias is added to structure to increase bandwidth, and antenna gain. These antennas exhibit better results in comparison with similar conventional DRA with similar feeding technique. The major differences of the proposed antenna compared to the prior arts were using a few simple techniques simultaneously to improve impedance and axial ratio (AR) bandwidths, gain, and cost of structure. These techniques consist of using wideband branch-line coupler, hollow RDRA, placing the coupler under DR with 45° rotation, tapered excitation strip, FR4 substrate, and tapered stubs and metal vias in the second antenna. Both simulated and measured results are presented. These first and the second antennas offer an impedance bandwidth (S11 < −10 dB) of 69.4% and 96.3%, and axial ratio bandwidth (AR < 3 dB) of 52.45% and 57%, respectively.