Characteristic Mode Inspired Single-Plate Unidirectional Antenna Using Complementary Characteristic Radiation

Based on characteristic mode theory (CMT), a novel single-plate complementary antenna with a unidirectional radiation pattern is proposed in this communication. The proposed antenna is composed of an isosceles right triangular conductive slab (IRTCS), three inductive coupling elements (ICEs), and a feeding network. By exciting two complementary current modes of IRTCS simultaneously, the radiation of IRTCS can be tailored. More specifically, ICEs can stimulate the electric dipole and magnetic dipole current modes of IRTCS concurrently through appropriate excitation, thereby realizing an endfire radiation pattern by combining the two complementary characteristic fields with suitable modal weighting coefficients (MWC). For proof of concept, a prototype is fabricated, and the measured results demonstrate that a good unidirectional radiation pattern is achieved with a front-to-back ratio (FBR) larger than 20 dB, which verifies the feasibility and reliability of the proposed method. Compared with the conventional complementary antennas or Huygens source antennas which need two different radiating sources to realize the electric and magnetic dipole radiations individually, the proposed method reuses the radiating aperture and achieves the unidirectional radiation by a single radiating aperture.