The application of sequentially rotated feeding to dual polarisation antennas can lead not only to the well known improvements in crosspolarisation and input VSWR, but also to significantly better polarisation isolation. There are, however, many such antenna configurations that can be envisaged, and this paper clarifies the design and performance by application of firstorder analytical methods. Improved crosspolarisation suppression and polarisation isolation result for dual linear arrays, and, for dual circular antennas, crosspolarisation and input VSWR are improved. Investigation of several configurations indicates that isolation improvement cannot be achieved in the dual circular case except when the array is operated with a squinted beam. Measured results are presented that demonstrate this advance, and, together with computed results, indicate that the combination of sequential rotation and squinted beam produces dual circularly polarised arrays with many desirable performance features.