Circularly-Polarized Patch Antennas With Enhanced Bandwidth Based on Capacitively Coupled Orthogonal Patch Radiators

Circularly-polarized (CP) patch antennas with enhanced bandwidth based on capacitively coupled orthogonal patch radiators are proposed. Several patch radiators are alternately arranged one by one along the ${x}$ - and ${y}$ -direction, producing orthogonal currents and far fields. The adjacent patch radiators are coupled to each other and the coupling structure not only contributes to power distribution but also introduces 90° phase shift for circularly-polarized radiation. There is no need for an additional feeding circuit in the design. The far-field components are mapped to the excitation voltage of the equivalent circuit model and a quantitative design method based on the equivalent circuit model is proposed. The theoretical axial ratio response can be predicted and analyzed. Wideband CP patch antennas with 3 and 4 coupled radiators under a profile of $0.035{\lambda }_{0}$ are designed, fabricated, and measured as examples. Full-wave simulation results agree well with the theoretical ones. Multiple minima in the axial ratio response are produced to form wide bandwidth. The measured overlap bandwidths of reflection coefficient, realized gain, and axial ratio for these two antennas are 4.9% and 6.3%, respectively.