Pattern synthesis approach for circularly polarised four-dimensional antenna arrays

A novel pattern synthesis approach for circularly polarised (CP) four-dimensional (4D) antenna arrays with microstrip patch elements is presented. Sequential rotation method is used to reduce the cross-polarisation component of the CP antenna array and good circular polarisation purity is achieved. Moreover, the time modulation technique of 4D antenna arrays is adopted for the realisation of low sidelobe levels (SLLs), thus forming a CP 4D antenna array. The differential evolution (DE) algorithm is used to optimise the time sequences, and hence low SLLs and sideband levels (SBLs) are obtained. To achieve low SLLs and low SBLs simultaneously, both of the static amplitude excitations and time sequences are optimised by the DE algorithm. Simulation results show that the CP 4D patch arrays can be used to achieve lower SLLs, while the dynamic-range ratios of the amplitude excitations can be very small or even uniform.