Comparison between arrays of rotating linearly polarized elements and circularly polarized elements

The gain and bandwidth characteristics of circularly polarized (CP) arrays comprising of rotated linearly polarized (LP) elements and hybrid-fed CP elements are presented. It is found that for small element spacing, the gain of the LP elements' array is comparable with that of the CP elements' array; however for large element spacing the former shows significantly lower gain than the latter. Furthermore, the bandwidth of a rotating LP elements' array is narrower than that of a CP elements' array. The bandwidth difference is explained invoking Floquet modal theory and the cavity model of a patch antenna. Variations of gain and bandwidth with element spacing are studied using a full wave analysis and the results for slot-fed and probe-fed patch arrays are shown. The advantages and disadvantages of rotating LP elements' arrays are discussed.