Diversity and directivity mode-switchable planar antenna by stacking and unfolding four antenna elements

Abstract

A novel diversity and directivity mode-switchable planar antenna is presented. The antenna structure consists of four circular antenna elements. In the diversity mode, the four elements are unfolded on a plane for polarization diversity. Because of the orthogonal arrangement of the four elements, good diversity performance can be achieved. The antenna function is changed to directivity mode when the four elements are folded and stacked. Each element works as a reflector, a driver, and a director, as seen in the Yagi-Uda antenna principle, indicating that the antenna represents high directivity. A bent feed line and two methods of feeding are used to improve the directivity, for which a 4.5-dB greater peak gain is achieved than with the diversity mode. At 2.4 GHz, the antenna simulation results are consistent with the measurement results, and the performance is successfully proven.