This paper presents the axial ratio beamwidth results obtained by different sequentially rotated microstrip patch antenna sub-array configurations. Simplified formulae of electrical radiation pattern allow a direct polarization estimation. To validate these formulae, a comparison with a rigorous calculation code using the Finite Difference Time Domain method (F.D.T.D.), through same cases simulated, gives good agreement. Finally, excitation errors introduced in simple analytical expressions are taken into account for two particular sub-arrays.