Radiation Pattern Improvement of Cross-Band Dipoles Using Inductive-Loading Mode-Suppression Method

A ground-backed two-dipole antenna system is analyzed. The two antennas operate at different frequency bands. For the higher-band antenna (HBA), the radiation patterns are significantly distorted by the strong mutual coupling between two antennas. A method of mode suppression by inductive loading is proposed to improve the distorted radiation patterns of the HBA based on the characteristic-mode analysis (CMA). Modal significances and characteristic currents calculated by CMA help to identify the modes contributing to the pattern distortion and determine the loading locations on the lower band antenna. With the unwanted modes suppressed, the original 3 dB angular coverage range in H-plane is fully restored, and the boresight gain in E-plane is compensated by 1 dB. The results are experimentally validated.