This paper presents the effect of the interaction between the switch and the antenna parameters on the cross-polarization of a dual polarization switching antenna. It is shown that the isolated antenna cross-polarization combines with the isolation of the switch giving place to a degradation of the polarization purity of the combined dual polarization switching antenna. Analytical expressions for the combination of the switch isolation and the antenna cross-polarization in the switched antenna element are given. Simulations and pattern measurements are presented. © 2007 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2007.