A Pattern/Polarization Diversity Antenna Based on Three-mode Composite Transmission Line

In this communication, a pattern and polarization diversity antenna is proposed for millimeter-wave application. The multi-mode transmission line is adopted to drive the three radiation mode, which means the three different radiation modes totally share the radiation aperture and excitation transmission line. The multi-mode composite transmission line confine the fields of all transmission modes in the same space, which greatly simplifies the complex feed network of conventional antennas with diversified radiation patterns. A prototype working at 28 GHz is designed with a overlapped bandwidth of 13.8%. Hollow beam radiation, vertically polarized end-fire radiation and horizontally polarized end-fire radiation are respectively excited by TEM-mode, TEl0-mode and a special folded TE2o-mode.