Wideband Reconfigurable Crossed-Dipole Antenna With Quad-Polarization Diversity

A design for antennas with quad-polarization diversity is described. The antenna structure is mainly composed of a reconfigurable crossed-dipole fed with coaxial baluns and a switchable feeding network. By controlling the states of p-i-n diodes embedded in the balun feeds, the crossed dipole can generate vertical and horizontal polarization radiations, and the phase of each polarization mode can be switched between 0 degrees and 180 degrees. As for the feeding network, it has four output ports and only two output ports are set to be active to excite the crossed dipole at a time. By integrating the crossed dipole with the feeding network, the resultant antenna can provide four polarization modes, including +/- 45 degrees linear polarizations (LPs) and dual-orthogonal circular polarizations (CPs). Moreover, the overlapped operation bandwidth of the four polarization modes is more than 35%, and within the bandwidth, the cross polarization level of the LP modes is less than -20 dB and the axial ratio of the CP modes is smaller than 3 dB. Good impedance matching is also achieved for each polarization mode.