Approach to axial ratio improvement for circularly polarised microstrip patch antennas excited via two inputs

摘要

A novel approach to enhance a quality of circular polarisation of microstrip patch antennas is presented. It is applicable to microstrip antennas with square as well as circular patches which are excited through two inputs with a 90° phase shift. In this approach, an analytical model based on a superposition of the antenna far fields is used. This model leads to the closed-form formulas for correcting the axial ratio at the operating frequency by a proper amplitude and phase excitation of the patch antenna. The formulas use the simulated far fields of the patch antenna with only one input being active while the other one connected to the absorbing load. It is shown by numerical examples that this approach is particularly suitable for microstrip patch antennas excited with the through-substrate probes of coaxial connectors. Furthermore, it is illustrated by numerical examples that the excitation with a proper amplitude and 90° phase shift may be sufficient – from practical point of view – to ensure a high-quality circular polarisation. The proposed correction procedure enhances both the right- and the left-hand polarisations of the microstrip patch antenna of interest.