A Quad-Polarization Reconfigurable Antenna With Suppressed Cross Polarization Based on Characteristic Mode Theory

Based on characteristic mode theory (CMT), a quad-polarization reconfigurable antenna with suppressed cross polarization is proposed in this article. The proposed antenna is composed of the radiator, excitation units, and feeding network. A square conductive slab (SCS) is used as the main radiator, which is designed elaborately by characteristic mode analysis (CMA). Different modes of the radiator are stimulated selectively by four groups of balanced inductive exciters (BIEs) to realize horizontal polarization (HP), vertical polarization (VP), left-hand circular polarization (LHCP), and right-hand circular polarization (RHCP). Two p-i-n diodes are embedded into the feeding network to switch the excitation states of the four groups of BIEs, thereby achieving quad-polarization reconfiguration. More importantly, a novel method exploiting the CMA is adopted for achieving low cross polarization. By means of introducing the orthogonal mode, the cross-polarization component of the fundamental mode can be canceled out by the co-polarization component of the orthogonal mode, which greatly reduces the cross polarization from -10 to -40 dB in the two principal planes. The measurement results demonstrate that the quad-polarization agility and a cross-polarization level around -30 dB under all polarization states are achieved simultaneously, verifying the functionality and reliability of the proposed method.