I. Introduction
Circular polarizations (CP) have been considered to use for high-speed wireless local area networks (LANs) because it is useful to mitigate the detrimental fading by multipath effects. However, in the case of wireless LANs, the path of the wave may be obstructed under certain conditions. This leads to the situation in which, for example, it is necessary to observe a reflected wave from a building or wall. In this case, the rotating direction is reversed and the axial ratio is varied depending on the angle of incidence and the material parameters of the wall. In various stages including this situation, it is also important to switch the polarization between LHCP and RHCP for polarization diversity. Moreover, continuous axial ratio variation may also useful to minimize polarization mismuch and power loss. A patch antenna which can switch LHCP and RHCP using diodes has recently been proposed [1]. However, the axial ratio control is still needed in addition to the switching.