A description for the on-axis polarization of four-element sequential-rotation arrays with arbitrary radiators is presented, characterizing the contributions from the feed network and the antenna elements separately. This separation provides criteria for an optimization of the individual radiators including mutual coupling effects without an impact of the applied feed network on the optimization process. Moreover, severe specifications for the polarization purity of a four-element sequential-rotation array can be subdivided into separate, less severe requirements for the elements and the excitation-structure, using the description presented. Measurement methods for the determination of the identified characteristic parameters are discussed along with possible limiting factors of the theory. Experimental results are presented for a four-element array of helix antennas which shows the impact of mutual coupling on the element performance and illustrates the excellent polarization properties of the discussed array type for the entire mainbeam. The predicted figures for the cross-polarization of the array and the measurement results are in good agreement.
