Single-fed microstrip patch antenna with switchable polarization

A single-fed reconfigurable microstrip antenna that can provide various polarization diversities is presented in this paper. The antenna is excited by a microstrip feed line through aperture coupling. When two PIN diodes are used to respectively reconfigure the coupling slot and the open stub of the feed line, the polarization of the microstrip antenna can be switched between vertical and horizontal polarizations. For the reconfigurable antenna with the linear polarization diversity, it can be converted to a circularly-polarized antenna with switchable polarization sense by introducing a perturbation segment. Moreover, an antenna with the quadri-polarization diversity, including dual orthogonal linear polarizations and two circular polarizations, is also developed from the structure of the switchable circular polarization microstrip antenna, and only three diodes are required. Details of the antenna design are shown, and the measured results for the constructed prototype are also exhibited and discussed.